AGRICULTURAL EXTENSION SERVICE Extension Folder 552-1980 UNIVERSITY OF MINNESOTA

STRAY VOLTAGE PROBLEMS <- WITH DAIRY COWS R. D. Appleman and H. A. Cloud Many dairymen are losing milk pro­ dairymen. The number of cows Even when the stray voltage duction and experiencing cow affected and the severity of the problem has been corrected, milk health problems at milking time due milk let-down problem appear to production may remain abnor­ to small currents of electricity pass­ be dependent on the level of mally low for awhile because of ing through the cows' bodies. This stray voltage present. The mech­ the associated problems. condition may be caused by low anism of how this occurs is not It must be remembered that voltages existing on the grounded understood. When milk out is other factors such as mistreatment, neutrals of the farm electrical sys­ uneven, more machine stripping milking machine problems, disease, tem. Stray voltages can result from is required and longer milking sanitation, and nutritional disorders several electrical sources, but the time becomes apparent. can create problems which manifest major problem appears to be volt­ 2. Cows extremely nervous while in themselves in the above seven ages existing on the grounded neu­ the parlor. This trait often is char­ symptoms. A careful analysis of all tral network. acterized by the cows dancing or possible causes is necessary if the The prevalence of this problem stepping around almost continu­ proper corrective procedure is to be in Minnesota remains uncertain, but ously while in the parlor stall. found. the authors have been directly in­ However, dairymen are re­ volved on more than 50 farms in a 2- minded that cows may become WHAT CAUSES STRAY year period. Some experts feel that nervous for other reasons, such VOLTAGE? 20 percent or more of all parlor barn as malfunctioning milking equip­ All modern dairy facilities de­ dairy farms may be affected. ment or rough handling by the pend on electrical energy supplied The loss in milk production and operator. over rural distribution networks. The dairy farm income-combined with 3. Cows reluctant to enter the par­ primary distribution system together the aggravation, time, and cost of lor. When cows are subjected to with the secondary farmstead wiring correcting the problem-may be stray voltages in the parlor stalls, and all electrical equipment and substantial. One farmer with an 80- they soon become reluctant to grounded components form a com­ cow herd suffered a 3,000-pound enter the parlor. In extreme plex network. All parts of this net­ drop in annual milk production per cases, nearly all cows have had work are interconnected through an cow for a 2-year period and spent to be driven into the parlor and electrically conductive system con­ more than $15,000 to replace com­ there was a tendency to "stam­ sisting of the primary and secondary ponents of the milking system in an pede" out of the parlor upon re­ neutrals and all grounded equip­ attempt to correct the problem. lease. But again, this symptom is ment and facilities. The grounded not specific since cows may be neutral system is connected to earth TERMINOLOGY trained to expect the parlor oper­ through "ground rods" driven into The problem has been identi­ ator to chase them into the milk­ the soil and through electrically fied by several different names. ing stalls. grounded equipment and facilities in Among dairymen, stray voltage or 4. Increased mastitis. When milk contact with the soil. tingle voltage is the most common. out is incomplete, more mastitis Figure 1 shows a portion of the The most correct terminology, and is likely to occur. All that is re­ grounded neutral system containing that used by most power company quired is the presence of infec­ examples of neutral conductors and representatives, is neutral-to­ tious bacteria. This, in turn, will grounding conductors. All neutrals ground or neutral-to-earth voltage. result in an increased somatic and all grounding conductors are at­ Another name sometimes used, but cell count. tached to the grounding block at the one that has an altogether different 5. Reduced feed intake in the par­ service entrance of the barn which, meaning among electrical engi­ lor. If cows detect stray voltage in turn, is connected to the service neers, is transient voltage. The term while eating from the grain feed­ entrance ground rod. The grounding neutral-to-earth (N-E) voltage will be ers, a reluctance to eat and block is connected to the secondary used here and refers to the voltage reduced feed intake is almost neutral leading to the transformer. existing between the neutral system certain to occur. The secondary neutral is electrically and zero-potential earth. bonded to the primary neutral at the 6. Reluctance to drink water. Stray transformer. voltages may reach the cows in Figure 1 shows only the neutral SYMPTOMS OF STRAY stall barns through the water VOLTAGE PROBLEMS and grounding circuits. The dashed­ supply or metal drinking cups. line and arrows indicate the primary Animal reactions will vary de­ Thus, cows soon be.come reluc­ and secondary high voltage con­ tant to drink. pending upon the severity of the nections. This circuitry will have no problem. If one or more of the follow­ 7. Lowered milk production. Each direct effect on the grounded neutral ing symptoms persists, stray volt­ of the symptoms described previ­ system unless there is a "ground ages may be contributing to the ously is associated with stress, fault" electrically connecting the problem: reduced nutrient intake, or dis­ high voltage conductors to the 1. Uneven milk out. This is the most ease. In any case, a drop in daily grounded network. However, as we common symptom expressed by milk production is to be expected. will see later, loads added to the

2 Figure 1. The grounded neutral network on a single-phase distribution line

TRANSFORMER FARM SERVICE ENTRANCE ------PRIMARY "HOT" - -L~'HOT;;-- ---F-----~- - I SECONDARY NEUTRAL I PRIMARY NEUTRAL I I -~l I IL2 L 1 ,J- _'f_l ELECTRICAL BOND I • • I 240 VOLT BETWEEN PRIMARY 1 GROUND MOTOR AND SECONDARY BARN NEUTRAL SERVICE I ENTRANCE: NEUTRAL 120 VOLT MOTOR .----+--, I I ---~I------_J PRIMARY GROUNDING NEUTRAL NEUTRAL GROUND TERMINAL ROD AT TRANSFORMER BLOCK __ I __ I __I __ J 120 VOLT CIRCUITS

GROUNDED STANCHION PRIMARY NEUTRAL OR PARLOR PIPE GROUND RODS ALONG FARM r THE LINE SERVICE ENTRANCE GROUND

system create various effects on the Figure 2. A dairy cow subjected to a neutral-to-earth (N-E) voltaQe

grounded neutral network. SECONDARY NEUTRAL FROM Every part of the grounded THE TRANSFORMER neutral network including the con­ ductors, the connections, the earth, I -] and the contact between the ground I BA N I I SERVICE I rods and the earth, has some resist­ I ENTRANCE ance to the flow of electric current. l~+-~I ANY VOLTAGE ON THE GROUNDED GROUNDING NEUTRAL SYSTEM IS READ BY THE TERMINAL VOLTMETER AS A NEUTRAL- TO - Due to these resistances, whenever BLOCK-/ there is a current in the neutral sys­ EARTH VOLTAGE tem a voltage exists between it and

earth. These voltages are reflected VOLT METER to all parts of the interconnected net­ STANCHION PIPE OR work and, if they are sufficiently ANYTHING ELSE THAT 1 IS "'ELECTRICALLY- _ high, may be detected by an animal. GROUNDED ) 1 -' \ I / \ They exist as neutral-to-earth (N-E) \,' \ (,. )\.__;\ ""ISOLATED"" voltages and will cause a current ~) I / • l GROUND ROD flow through the body of an animal AS A REFERENCE- bridging the gap between the neu­ ''"' "--.. I tral network and the earth, as shown SERVICE ENTRANCE in figure 2. In this case, the cow's GROUND ROD back feet provide a connection to "true ground" through the wet con­ crete and the wet soil underneath. The front portion of her body is in COW IN CONTACT· ~CK FEET IN contact with the grounded neutral WITH GROUNDED GOOD CONTACT NEUTRAL NETWORK WITH EARTH -'TRUE"' system through the pipe, wet con- GROUND

3 crete, feeder, etc. She may be sub­ Figure 3. Location of an "isolated" ground rod used as a reference in neutral-to­ jected to the same N-E voltage read earth voltage measurements by the voltmeter in figure 2. This voltage causes a current to flow through her body and can result in "ISOLATED" GROUND ROD USED serious problems when it is high AS A REFERENCE FOR NEUTRAL­ enough to cause discomfort. TO- EARTH VOLTAGE READINGS AT LEAST 25 FEET FROM ANY Neutral-to-earth voltages re­ UNDERGROUND PIPES, ELECTRICAL EQUIPMENT, OR GROUND RODS. sult from the voltage differential cre­ ated by current flowing in any part of the neutral network. The voltage de­ I pends on the resistance of and the YOUNG I STOCK ---_lt._41:§:R \ current flowing in all parts of the in­ ----, terconnected neutral system. Many I factors affect this: \ METER POLE \ 1. loads on all parts of the distribu­ tion system 2. length and size of the primary neutral SERVICE ENTRANCE 3. grounding resistances on the pri­ mary neutral HOUSE 4. resistances of all connections on SHOP 8 the primary neutral MACHINE SHED 5. grounding resistances on the farm 6. length and size of all secondary neutrals 7. current in the secondary neu­ trals, as affected by balancing of line-to-neutral loads (120 volts) 8. resistance of connections on the secondary neutrals the intermittent "here today, gone of this "isolated" ground rod and 9. ground fault currents tomorrow" nature of the problem. voltmeter will be discussed in the The cause of excessive N-E section entitled "Standardized Mea­ The effect of these voltages on voltages often is very difficult to lo­ surements." In this position the volt­ dairy cattle is influenced greatly by cate. Its source may be on the farm, meter reads the maximum voltage other conditions. The current off the farm, or a combination of the to which a cow could be subjected if through a cow's body depends on two. The problem occurs whenever one contact point is touching the the voltage as well as the resistance the combination of neutral resist­ grounded neutral system and an­ of the current path through her body ances and currents creates a volt­ other is in good contact with the to "true" ground. This depends on: age large enough to cause the cattle earth. 1. resistance of the cow's body discomfort. This condition can exist Figure 4 illustrates how the N-E 2. resistance of her contact points because of the inherent characteris­ voltage on a farm can be affected by 3. the soil moisture conditions af­ tics of the electrical distribution sys­ the electrical load of other farms on fecting the "grounding" resist­ tem and is not necessarily the result the same distribution system. The ances of electrical faults or poor wiring. load on the neighboring farm is ac­ companied by a current in the pri­ 4. the soil-concrete contact The following examples show several N-E voltage conditions and mary neutral. The voltage required 5. conductivity of the concrete and will help develop a better under­ to move this current through the the soil standing of the problam. Figure 3 grounded neutral system is partially Soil moisture conditions affect shows the location of an "isolated" reflected onto the secondary neutral both the N-E voltage and the resist­ ground rod used as a reference on the farm system and exists as ance of the electrical path through when measuring N-E voltages. If N-E voltage. Experience indicates the cow's body to earth. As a result, one lead of a voltmeter is attached that farms near the end of the distri­ the problems and symptoms vary to the service entrance ground of bution line are more likely to suffer greatly with time and weather condi­ the barn, as shown in figure 2, and from N-E voltages. tions. The wide variability of all the the other lead is attached to the "iso­ Figure 5 illustrates how added factors which affect N-E voltage, as lated" ground rod, it will read the farm loads increase N-E voltage on well as the reaction of the cow to N-E voltage existing on the network the same farm. The added load is these voltages, partially explains at this location. The location and use accompanied by an increased cur-

4 Figure 4. Neutral-to-earth voltages on a farm due to other farm loads on the same line

TRANSFORMER --1 I SECONDARY NEUTRAL I ) PRIMARY NEUTRAL II L2 L1 ~ ~

PRIMARY i•-t ·, NEUTRAL GROUND L BARN I I VOLTMETER RODS ALONG THE 1 WILL RESPOND LINE Es~HWJ~e EI i I I' TO CHANGES I r----+--, I IN LINE LOAD I___ J

OTHER LOADS ON THE ARROWS INDICATE POSSIBLE * SAME DISTRIBUTION FLOW OF PRIMARY NEUTRAL SYSTEM -ANY LOAD IS CURRENT FROM OTHER ACCOMPANIED BY A FORMS DEPENDING ON CORRESPONDING PRIMARY RELATIVE RESISTANCES 6 L VOLT NEUTRAL CURRENT LOADS V METER t

TRANSFORMER TRANSFORMER SERVICE ENTRANCE GROUND GROUND GROUND ROD ROD ROD

"ISOLATED" REFERENCE GROUND ROD

Figure 5. Increase in neutral-to-earth voltage due to increasing loads on the same farm

TRANSFORMER

NEUTRAL

L2 ANY INCREASE_/----~ I IN FARM LOAD IS ACCOMPANIED BY -·h AN INCREASE IN PRIMARY NEUTRAL BARN I VOLTMETER WILL CURRENT RESPOND TO E1E.ffi',,(~~E I I CHANGES IN LINE LOAD I~--+-~ I L' __ J ANY INCREASE IN PRIMARY NEUTRAL CURRENT IS ACCOMPANIED BY AN INCREASE vi----;::::::tu.....a:::;------, IN N - E VOLTAGE AT THE BARN SERVICE ENTRANCE ~ V VOLT METER

SERVICE ENTRANCE GROUND ROD

5 Figure 6. Neutral-to-earth voltages created by the voltage drop in the secondary stall, metal grate, milk pipeline, con­ neutral to the barn crete floor on which the cow stands, and concrete parlor floor on which the operator stands. Although sci­ ---•-ij I --s~~DNDARY NEUTRAL entists still are uncertain which con­ B11 ~:::~=------, tact points are more important, the ~ Is-- milk pipeline may be extremely im­ portant since milk in the long milk hose, claw, and inflations will con­ L,1 ~ Lz duct currents from the pipeline to the inner tissue of the teat. ANY UNBALANCE CURRENT~ ~--! --r IN L 1 8 Lz CREATED BY 120 If the N-E voltage (AC) ex­ VOLT LOADS OR GROUND FAULT ~ VOLTMETER RESPONDS CURRENTS CREATES AN \ TO INCREASE IN ceeds 1.0 volt (using the test proce­ INCREASE IN N-E VOLTAGE AT \ SECONDARY NEUTRAL dure described later) a problem may THE BARN BECAUSE OF THE \~URRENT VOLTAGE DROP IN THE exist. Larger voltages will cause in­ SECONDARY NEUTRAL creasingly severe problems. When readings are obtained at midday,

VOLT while system loads are normally re­ METER duced, and the AC voltage is in the 0.5- to 0.9-volt range, the system SERVICE should be monitored at milking time ENTRANCE "ISOLATED" OR GROUND ROD -~ REFERENCE GROUND ROD -~-- when system loads usually are higher. Neutral-to-earth voltages of less than 0.5 volts generally are not considered cause for concern.

Cause for Concern- 1.0 or more AC volts Monitor and Watch- 0.5 to 1.0 volts rent in the primary neutral at the Ground fault currents in the transformer. The increased voltage barn will increase the N-E voltage as Consider to be Normal­ accompanying the increased cur­ a result of the increased load on the Less than 0.5 volts rent is reflected onto the farm neutral primary neutral and the increased system through the bond between current in the secondary neutral. the primary and secondary neutrals at the transformer. WHEN CAN STRAY HOW TO MEASURE STRAY VOLTAGE Figure 6 illustrates how the N-E VOLTAGE BE A PROBLEM? voltage at the barn can be affected On any electrical distribution Confusion exists because inap­ by the current in the secondary neu­ system it is necessary to have some propriate and poor quality voltmeters tral from the transformer. An in­ voltage existing between all electri­ sometimes are used to determine crease in unbalanced line-to-neutral cally grounded equipment and the whether a problem exists. The volt­ (120-volt) loads at the barn is ac­ earth. These N-E voltages exist on meter should: all grounded motor casings, water companied by an increase in neutral 1. be equipped with an AC voltage pipes, sinks, bulk tanks, stall and current. The increased voltage to scale having a full scale reading stanchion pipes, feeders, milking move this current through the neu­ of 2 to 5 volts, with the capability equipment, etc. Asdesr ·· .dearlier, tral is reflected onto the grounded of reading to the 0.1-volt level, as these voltages will force an electric neutral system at the barn service shown in figure ?a. entrance. Excessively high N-E volt­ current through any conductor, in­ ages at the barn can be created by cluding a cow's body, providing a 2. have a relatively high resistance large, unbalanced 120-volt loads pathway to earth. (above 5,000 ohms) and be bat­ and high neutral resistances caused Since all metal pipes and feed­ tery operated, so it does not re­ by poor connections, long second­ ers are connected to the neutral sys­ quire connection to electrical ary neutrals, or conductors that are tem, there are a number of possible service. too small. These create increased contact points between which these 3. not read DC voltage on the AC voltages on the secondary neutral at N-E voltages may cause a current scale. To test this capability, the barn and can cause an exces­ flow through the cow's body. Some connect the two voltmeter leads sive N-E voltage at the barn service of those contact points are the to each terminal of a conven­ entrance. feeder, waterer, stanchion, metal tional dry cell battery ( 1 ½ to 6 DC

6 Figure 7. Equipment for measuring stray voltages

7a. 7b. 7c. 7d.

AC 20V CAPACI TOR USED CHECKING THE TO BLO CK DC 0 METER FOR DC VO LTAGES ON READING ON THE AC SCALE 0 AC SCALE

350 - 500 OHM 5- 10 MICRO ­ RESISTOR IN PAR ALLEL WI TH METER FLASHLIGHT FARA D DI GITAL BATTERY CAPACITOR RESISTOR MULTIMETER

volts) , as shown in figure 7b. If a Most milking machine com­ grounded neutral system and an positive reading is obtained, in­ pany representatives, many power isolated or true ground (see figures stall a 5 or 10 micro-farad capaci­ company employees, some milking 2 and 3). tor "in series" with one of the equipment dealers, and some veter­ This voltage is measured rather leads from the voltmeter, as inarians and county extension than voltages within the milking par­ shown in figure 7c. agents have equipped themselves lor itself because generally this volt­ 4. be able to estimate the potency with suitable voltmeters and are pre­ age is the maximum expected of the voltage source and the re­ pared to lend assistance. Someone between any two locations in the sistance of the "isolated" ground familiar with electrical systems, wir­ milking parlor, unless an electrical rod. To accomplish this, a 250- to ing, and equipment should be con­ fault exists. If this voltage reaches a 350-ohm resistor must be avail­ sulted and, if possible, be present problem level, as discussed earlier, it able to parallel the input leads of when measurements are made. is possible it exists in the milking the voltmeter as shown in figure parlor or barn and may be difficult to 7d. STANDARDIZED locate. Several digital read-out AC volt­ MEASUREMENTS When measuring N-E volt­ meters have proven very satisfac­ To provide a common refer­ ages, the effect of the resistance of tory for detection of stray voltages. ence and to standardize measure­ the "isolated" ground rod can be The purchase price of these meters, ments, the authors recommend the determined by placing a 350- to which will not read DC on the AC use of a copper-clad ground rod lo­ 500-ohm resistor across the input scale, is approximately $80. An ex­ cated 25 feet or more from the barn terminals of the voltmeter (resistor ample of such a meter is Cata­ and isolated from any other compo­ in parallel with meter) as shown in log Number 22-198, available from nent such as water piping. The figure 7d. Normally there will be a Radio-Shack. Digital read-out me­ ground rod should be at least 4-feet slight reduction in voltage. This is ters allow a technician to observe deep and in moist soil. Connect one partially caused by the resistance of short period spike voltages consid­ insulated lead of the voltmeter to the the "isolated" ground rod . If there is erably higher than normal readings "isolated" ground rod and the other a large reduction in the voltmeter frequently observed on Minnesota insulated lead to the bare ground reading (more than 20 percent of the dairy farms. This occurs most fre­ wire leading from the barn entrance reading) the resistance of the "iso­ quently when a motor or other electri­ box to the ground rod at the barn lated" ground rod is too high. In this cal device is started. Its significance (service entrance grounding con­ case relocate the rod or reduce its and effect on the cow has not yet ductor). In this position the voltmeter resistance by saturating the sur­ been determined. will read the voltage between the rounding soil with water.

7 HOW TO DETERMINE THE to indicate a serious problem. How­ closed and the loads are oper­ SOURCE OF THE PROBLEM ever, any changes in readings taken ating. The increase in neutral­ during these times will help identify to-earth voltage as each load is It is necessary to follow a well­ the cause of a stray voltage problem added is due either to the in­ organized, step-by-step procedure if it exists. crease in primary N-E voltage to successfully analyze a stray volt­ as a result of the increased load age problem. Low level AC and DC 4. After connecting the voltmeter or to faulty equipment on that voltages can be read practically any as described in step 2, record circuit. place within the dairy facility. These the voltmeter reading. If any 240-volt load causes a may or may not be significant and 5. Record the voltmeter reading may or may not be related to the stray current flow in the secondary after opening the main discon­ neutral to the barn (as indicated voltage problem. The voltage levels nect at the barn service en­ will vary widely during the day, from by the clamp-on ammeter) it is a trance. Since the secondary result of ground faults in the day to day, or from season to season. neutral to the barn is not discon­ Proper interpretation of voltage equipment. Very slight changes nected, any N-E voltage is in neutral current may be de­ readings and changes in voltages being transmitted to the barn are necessary for successfully ana­ tected as a result of the in­ through the secondary neutral creased N-E voltage forcing lyzing a stray voltage problem. and originates someplace else. The following step-by-step pro­ some current through the elec­ 6. Leave the main disconnect cedure will help isolate the source of trical system grounds at the switch at the barn open. Record the problem: barn. These will be very small the N-E voltage at the barn after and are not an indication of 1. Identify and label all circuits opening each of the disconnect ground faults in the equipment. and loads in the barn service switches at the remaining ser­ 9. Record the voltmeter readings entrance panel, giving the vice entrances on the farm. loads and type of circuit; that is, as each 120-volt circuit is recon­ After each service entrance is nected and the loads turned on. line-to-line (240-volt) or line-to­ disconnected, the N-E voltage neutral (120-volt) loads. The secondary neutral current at the barn should drop slightly to the barn (read by the clamp­ 2. Connect one lead of the voltme­ if there are any loads operating on ammeter) and the N-E volt­ ter to the bare copper wire lead­ on that service entrance. If the age readings will increase and ing to the service entrance voltmeter reading at any step is decrease as the unbalanced ground rod at the barn. This relatively high (above 0.5 volts) load on the secondary neutral to wire connects the service en­ and drops to a much lower the barn changes. trance ground rod to the value ~ess than 0.2 volts) when grounding block in the service the service entrance is discon­ If the N-E voltage increases entrance panel. Connect the nected, the loads on that ser­ significantly (perhaps 0.3 volts other lead of the voltmeter to vice entrance should be or higher) with a maximum un­ the insulated wire leading to the checked out later. This drop in balanced load on the barn neu­ "isolated" ground rod de­ voltage could be caused by a tral, the voltage drop in the scribed in the previous section. faulty load on that service en­ neutral may be causing prob­ If the "isolated" ground rod is trance or it may be the result of lems. The problems may be a truly isolated and not influenced a heavy load on the entrance at high neutral resistance created by the voltage gradients in the the specific time. by poor connections or the re­ sistance of the wire itself. Im­ earth surrounding the electrical The voltage recorded at the system grounds, the voltmeter proving connections, better barn when all service entrances balancing of the line-to-line will now read the N-E voltage are open is due to N-E voltage existing at the barn. loads, and/or a larger neutral on the primary neutral created wire may help relieve the prob­ 3. A clamp-on ammeter on the by loads at other locations on lem. Making sure the current in secondary neutral to the barn the main distribution system. A the barn neutral is minimized will help identify electrical faults check should be made at this during milking (by selection of if they are contributing to the time by opening the main dis­ offsetting 120-volt loads) may problem. This can be done later connect to the farm. There help solve the problem. it subsequent voltage readings should be no change in the N-E indicate suspected faults. voltage at the barn. 10. Have someone watch the volt­ meter throughout the milking Steps 4 through 9 may take 7. Reconnect all service en­ time and periodically record the several hours and should be done trances on the farm and discon­ readings. Pay particular atten­ during periods of low electrical us­ nect each individual circuit in tion to major changes in fluctua­ age, possibly in mid-morning or mid­ the service entrance at the tions in the readings. These afternoon. Neutral-to-earth voltages barn. may occur rapidly and may last recorded during this time will be 8. Record the voltmeter reading only a short time. Close atten­ considerably lower than at high load when each 240-volt circuit in tion is necessary to observe periods and may not be high enough the barn service entrance is these changes.

8 If voltages above 1.0 volt are and secondary neutral systems The only way to detect these present during milking, some have not been truly isolated). N-E voltages is to measure the volt­ corrective action is necessary. age between the equipment or facili­ If the tests outlined in steps 4 Refer to the section "When Can ties and earth. A voltmeter reading through 11 show an N-E voltage It Be A Problem?" If voltages in between the equipment and the problem, the results should indicate the 0.5- to 1.0-volt range are floor may be adequate. However, whether the problem originates on present, the N-E voltage should the best measurement is between the farm, off the farm as a result of be continuously monitored and the equipment and the "isolated" an excessive primary N-E voltage some corrective measures may ground rod used as a reference for or a combination of the two. ' be necessary. If the symptoms measuring N-E voltages. persist and voltages above 0.5 If the voltage is an "induced" are not present, the N-E voltage STRAY VOLTAGES voltage, grounding the isolated should be monitored to see if it NOT RELATED TO equipment should solve the prob­ is periodic due to weather, soil N-E VOLTAGES lem. If the problem is faulty, non­ moisture conditions, or other grounded electrical equipment the systematic fluctuations. If these tests do not indicate a fault must be corrected and the problem originating from the N-E equipment properly grounded. If the N-E voltages obtained in voltage, further checks are neces­ steps 4 through 10 indicate the sary. Voltages can be induced on Voltages imposed on milk problem may be a result of high N-E isolated (non-grounded) conductors pipelines by electrical circuits con­ V?!tages on the primary neutral, ad­ located in the barn or milking parlor. trolling the operation of the milk d1tIo~~I testing is necessary. This pump, pulsator, or other electrical add1t1onal testing must be done in Two such cases have been components of the milking system cooperation with the power com­ do?ume~ted, both involving cow can cause problems. If the problem pany because it involves an altera­ trainers in stanchion barns. In one appears only when placing the milk­ tion in their system which only they case a voltage was induced on a ing equipment on the cow and dur­ non-grounded, stainless steel milk can do. ing milking, these control circuits pipeline running parallel to the cow should be checked to see that they 1 I . Repeat steps 4 through 1o in train~r. In the other case a voltage are properly installed and wired. cooperation with the power w~s induced on a water pipe paral­ company after their employ­ leling the cow trainer about 2 feet WHAT TO DO IF THE ees, under the direction of their away. The pipe was isolated from PROBLEM ORIGINATES supervisors and engineering the well and pump by a section of ON THE FARM consultants, have discon­ rubber garden hose. In each case a The results of the tests outlined nected the bond between the voltage of 2 to 4 volts was measured !n th~ previous sections should help primary neutral and the sec­ between the pipes and the floor or 1dent1fy the problem if it occurs on ondary neutral at the transfor­ other grounded surface. When a the farm. If these tests suggest mer. The disconnection of this 350-ohm resistor was inserted across the input terminals to the faulty equipment or large voltage bond_ is not possible with single drops on the secondary neutral, cor­ bushing transformers in com­ voltmeter the voltage dropped to near zero. This indicates the source rective action should be taken as mon use today and requires indicated. The following guidelines changing transformers. This is not capable of delivering signifi­ cant current. However, the current will help reduce the effect of prob­ step requires disconnecting lems created on the farm: the bond only; it is critical that flow when the cow made initial con­ the primary neutral and sec­ tact was enough to cause discom­ 1. Have a licensed electrician or a ondary neutral connections to fort. In the case of the water line, the representative of the power com­ the transformer remain intact cows were reluctant to contact the pany check the electrical system and are not disconnected. This waterers to drink. However, the to make sure all farmstead wiring farmer noted, if one cow was drink­ bond is shown schematically in meets the proper code require­ ing the others would drink with no figure 1 . After the bond between ments. apparent discomfort. the primary and secondary neu­ 2. Check to make sure all service trals has been disconnected Induced voltages of this type entrance grounds are adequate. there should be no change i~ may not be indicated by voltmeters 3. Establish and maintain good the N-E voltage at the barn with low input impedance. In both of neutral circuits and connections. when 240-volt loads are oper­ the above cases the voltages were Heavy use, high humidity, corro­ ated. If this voltage increases detected by meters with input impe­ sive silage acids, urine, and with these loads, there is either dances of 10 megohms. ma~ure make dairy farms poor an electrical fault in the equip­ Another potential problem volt­ environments for electrical wir­ ment or the voltage on the pri­ age source is leakage from improp­ ing and equipment. mary neutral is feeding back erly grounded, faulty electrical onto the secondary neutral equipment. In this case, a hazard­ 4. Look for faulty equipment that through the earth or some other ous condition exists to both humans may have leakage currents by electrical connection (primary and animals. measuring the current draw of

9 operating equipment and by Figure 8. Interconnection of the primary and secondary neutrals through a spark checking the currents in the gap with the secondary neutral grounded at the transformer (Section 97D, National Electrical Safety Code) ground and neutral wires. ------5. Make every effort to balance, as well as possible, the line-to-neu­ PRIMARY tral ( 120-volt) loads on the barn TANK NEUTRAL service entrance in operation during milking. LIGHTNING ARRESTOR 6. If the problem is created by 10 kV MAXIMUM VOLTAGE 0 excessive voltage drop in the 0 secondary neutral and better balancing of 120-volt loads is not feasible, install a larger diameter neutral wire to reduce its resist­ INSULATED PRIM~II~ SEPARATE ance. Another proposed solution GROUND is to separate the neutral -- -- (grounded conductor) from the grounding conductors at the barn service entrance and run a separate, insulated grounding conductor which is grounded only at the transformer. This 20 FT. MINIMUM modification must be checked out with the proper authorities. It is discussed in Section 250-21 of the National Electrical Code and Figure 9. Bonded wire mesh used to form an equi-potential plane may or may not be acceptable. 7. Ground all electrical equipment such as manure pumps, silo un­ loaders, water heaters, and pumps to the service entrance ground. Use large wire (number 9, 10, or 12). Insulation is not needed on these grounding wires. Spot weld or use pressure clamps rather than soldering or WIRE MESH wrapping connections. Improp­ IN FLOOR erly grounded equipment is ex­ tremely dangerous in milking parlor and dairy barn environ­ MILKING PARLOR ments. GROUND 8. Provide adequate power circuits. Too many service entries be­ come overloaded as more and larger equipment is installed. 9. If it is possible, consider convert­ be considered if the problem origi­ disconnected from the primary ing to three-phase service. nates off the farm: neutral at the transformer. This 1. The power company should thor­ procedure will provide relief if the oughly check the primary neutral problem voltage originates on the on the entire distribution system primary neutral. Operation under WHAT TO DO IF THE to be sure of proper grounding, these conditions must be under no high resistance connections, the direction of the power com­ PROBLEM ORIGINATES pany. Section 97D of the National OFF THE FARM and no large-fault loads on neighboring farms. Electrical Safety Code provides If the problem originates off the for this if interconnection is made farm it is a result of excessively high 2. The power company should through a proper spark gap and N-E voltage on the primary neutral. check the load balance on the the secondary neutral is properly In this case the solution must be a three-phase service serving the grounded (shown in figure 8). cooperative effort between the single-phase distribution line. However, some power compa­ power supplier and the dairy 3. Consult with the power company nies, because of company safety farmer. The following steps should about leaving the farm neutral policies, will choose not to op-

10 erate with non-interconnected way is to embed 1a-gauge cop­ sources, and appropriate corrective neutrals. per wire in slots cut in the floor action, combined with recom­ 4. In consultation with the power and grout them over. These must mended bonding procedures during company, install an isolation be bonded together and to all construction of new parlors provide transformer to serve the farm-a metal structures in the parlor. the most satisfactory approach for procedure used in hospitals, eliminating stray voltage problems. where the problem is fairly com­ SUMMARY mon. In doing this the dairyman THREE CASE HISTORIES assumes responsibility for main­ Many dairymen have been taining proper neutral grounding successful in eliminating stray volt­ Number 1 on the isolated system. Com­ age problems. Others have at least This dairyman had 80 cows plete isolation is required, and reduced the severity of their prob­ and had experienced a drop in milk tests should be run to document lems. Sometimes the response has production of nearly 3,000 pounds this by showing no increase in been a dramatic reduction in the in­ annually per cow for a 2-year period. N-E voltage at the barn when cidence of mastitis and number of After seeking advice from nutrition 240-volt loads are operated. cows culled, frequently followed by consultants, extension agents, vet­ 5. Provide an equi-potential plane an impressive increase in produc­ erinarians, and milking equipment as shown in figure 9. This proce­ tion. But remember that the causes dealers, and after spending more dure is practical in milking parlors of stray voltages often are difficult to than $15,000 in replacing compo­ but probably is impractical in stall­ locate. This can be very frustrating nent parts of his milking system, he barn facilities. If the entire milking since the condition may exist even became aware of the stray voltage parlor-including floor, stalls, with no electrical faults. In these problem. and feeders-is at the same po­ cases, it requires the cooperation of His case was a classical exam­ tential, there can be no electrical the power company because its so­ ple of low level voltages entering his shock (as in the "bird on a wire" lution may involve an alteration in parlor from off-farm sources through phenomenon). A 2-inch by 2- their system. the power company primary neutral inch, 9- or 10-gauge, galvanized, The response of dairy cattle to and his farm's secondary neutral welded wire mesh is imbedded in corrective measures will vary con­ electrical systems. Disconnecting the concrete floor over the entire siderably. An immediate, dramatic the farm secondary neutral from the milking parlor including cow stalls response is probable if a severe primary neutral at the transformer and operator pit. The wire mesh problem is completely solved. How­ and installing a lightning arrester should be covered with a layer of ever, a more gradual improvement (gapper) corrected this problem concrete not thicker than 2 is likely with some cows or some (see figure 8). The results of mea­ inches. Weld or clamp the mesh herds depending on severity of the surements taken at several cow at all possible locations to other problem, degree of solution, and in­ contact points before and after dis­ conductors such as stalls, floor dividual characteristics of the ani­ connection of this bond are shown in grates, and feeders. It is impor­ mals. The mammary glands of cows table 1. tant that the complete interior of affected by stray voltages may have Cows soon became calmer the milking parlor be electrically become infected with mastitis and, and milked out more completely and connected. Use stainless steel depending on severity, both produc­ easier within only a few days. The clamps when connecting to stain­ tion and milking characteristics occurrence of new mastitis infec- less steel milklines. lnsta//ation of could be permanently hampered. an equi-potential grounding mat Experience indicates some cows re­ is highly recommended in all new spond more rapidly than others. Also, there is some indication that milking parlors. This method Table 1. AC Voltage Readings With when installed correctly removes once some cows have been sub­ and Without Electrical the shock potential for the cow in jected to a severe case they may Bond at Transformer Con­ the parlor. It does not prevent a remain fearful of stray voltages and nected Between Primary exhibit some of the symptoms after and Secondary Neutrals differential voltage from occur­ (Case History Number 1) ring when the cow enters the par­ the solution has been implemented. lor from the holding corral, which Up to now, progress has been Voltage when: is not a part of the equi-potential hampered by the lack of cooperative Location bonded isolated interchange. Those involved with plane. In these cases, there may Walk-way behind be a reluctance for cows to enter livestock have not fully recognized COWS 0.8 0.28 the complexities of the electrical the milking parlor. Stall, at front feet 1.0 0.32 6. An equi-potential plane can be system. Similarly, power company engineers frequently have failed to Stanchion and approximated by placing a heavy feeder 1.2 0.35 recognize the sensitivity of dairy cat­ metal base over the concrete Stanchion spike, portion of the cow platform and tle to low level stray voltages. when water electrically bonding it to all metal Proper measurement tech­ heater kicked on 4.0 0.85 structures in the parlor. Another niques, identification of stray voltage

11 11UIIUiilil1W1l1f1Uii~if UIIH1~1 :, 3 1951 D01 921 061 J .. tions dropped noticeably. While Cow behavior response and $1,000. There is little doubt, how­ there was a 4- to 5-pound increase improved milk production were ap­ ever, that this investment saved him in daily milk production per cow parent within a few days. Still, his many problems and considerable fi­ within 10 days, several cows did not mastitis problem did not simply dis­ nancial loss. respond until they went through a appear. His mastitis infections, pri­ dry period and freshened again sev­ marily Streptococcus agalactea eral months later. and Staphylococcus aureus, did not disappear until he established a Number 2 sound mastitis prevention program This farmer found that his stray involving dry cow treatment and voltage problem originated on the culling of chronically infected cows. farm. This conclusion was drawn when the stray voltage measure-· Number 3 ments remained high after the bond This dairyman with 120 cows in between the power company pri­ a new, cold free-stall and parlor sys­ mary neutral and the farm second­ tem did not have a stray voltage ary neutral had been temporarily problem, even though the authors disconnected by power company detected 1.5 volts when a voltmeter representatives. was connected between the service With the assistance of his local entry ground wire and an isolated The authors of this publication are R. D. electrical contractor, several im­ reference ground. Appleman, extension dairyman, and H. A. provements in his electrical system The reason was apparent when Cloud, extension agricultural engineer. How­ were made: it was learned that this dairyman ever, this publication is the result of several years of experience and study related to stray 1. A fault in a submersible water had installed an equi-potential plane voltage problems with dairy herds in Minne­ pump motor was corrected. in his new milking parlor. He had sota. Numerous people have contributed, through their writings and personal contact. 2. The balance of the electrical load brought the potential of the parlor floor and all metallic structures to Some of these people are: Lloyd B. Craine, on his two 120-volt lines to the Department of Electrical Engineering and service entry of his barn was im­ the same levels by embedding a Grady F. Williams, Cooperative Extension proved. 2-inch by 2-inch, number 9, galva­ Service, Washington St'ate University; Leo nized, welded wire mesh about 2- Soderholm, USDA-SEA,AR, Ames, Iowa; 3. A larger-diameter secondary inches below the floor surface (see Fred J. Feistmann, Agricultural Engineer, neutral wire was installed be­ figure 9). British Columbia Department of Agriculture; tween the service entry and and William Fairbanks, Cooperative Exten­ It was necessary to provide a sion Service, University of California. transformer pole to reduce the gradual transition between the par­ The authors thank Vern Albertson, De­ secondary neutral resistance. lor floor and entrance areas to the partment of Electrical Engineering, and 4. The neutral system connections milking parlor by tapering the mesh Robert Gustafson, Department of Agricul­ tural Engineering, University of Minnesota, were repaired and replaced to depth. The added cost of making for their help in reviewing the manuscript as provide a better path for the neu­ this equi-potential plane in his new well as their consultation over the last several tral currents. parlor (in 1978) was approximately years.

The information given in this publication is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Minnesota Agricultural Extension Service is implied. Issued in furtherance of cooperative extension work in agriculture and home economics, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Norman A. Brown, Director of Agricultural Extension Service, University of Minnesota, ·St. Paul, Minnesota 55108. The University of Minnesota, including the Agricultural Extension Service, is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, creed, color, sex, national origin, or handicap. 20¢

This publication replaces Dairy Fact Sheet No. 21.