Electric Wiring on Refrigeration Plants

This specification has been revised to include specific requirements for packaged units.

Object

The purpose of this standard is to specify the correct materials and methods to be used in the electrical wiring of refrigeration plants.

General

Wiring arrangements shall comply with the Electricity (Factories Act) Special Regulations 1908 and 1944 and with the latest edition of Institution of Electrical Engineers “Regulations for the Electrical Equipment of Buildings”. Where the customer has his own Electrical Specifications those shall be complied with unless they would result in bad practice under the special circumstances which sometimes occur in refrigeration. The electrical contractor shall notify Star Refrigeration, in writing, when any conflicts occur. Design and installation shall be in accordance with BS7671 – (latest edition)

Materials – Inside Low Temperature Areas

All power wiring within cold stores is to be carried out in butyl insulated cable adequately clipped. Conduit or cable trunking shall not be used within cold stores. Where wiring is to be brought through the insulated wall of the cold store, this is to be done within a PVC tube or tubes which are to be filled with silicone or granulated cork and Denso-paste on completion and testing of the installation. Ample clearance is to be left for the sealant. Beam clips may be used where appropriate. PVC insulated cables in conduit or trunking may be used. All conduit or trunking shall be galvanised. The fitting of junction boxes within the cold store shall be avoided unless special approval has been obtained from Star. Where this is unavoidable, the boxes shall be sealed to prevent moisture ingress.

Materials – Outside Low Temperature Areas

All field and plantroom wiring shall be steel wire armoured or enclosed in conduit or trunking. Steel wire armoured cable shall be fixed to an electrical tray or ladder rack unless it’s shorter than 2m. Use of flex outside containment shall be limited to a maximum length of 2m unless agreed otherwise.

Inverter Drives

Any motor fitted with an inverter shall be wired in a screened cable. Care should be taken to avoid inverter cables being run close to PLC and process signal cables and thermocouples.

Thermocouple and Transducer Wiring

The signal wiring for PLC thermocouples and transducers shall be run in a separate trunking. Where possible, the trunking should be placed at least 300mm from any mains cables which are running in parallel to the run of the signal wiring. Individual thermocouple or transducer cables may be run on cable tray provided: 1. they are run in screened cable. 2. they are run at least 150mm from the nearest mains or inverter cables.

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Motor Protection Thermistor

Where motors are fitted with thermistor protection and thermistor protection is required by the contract electrical specification, the thermistor wiring shall be run in a screened cable. This cable shall be run with other screened cables or run at a distance at least 150mm from the nearest mains cable.

Emergency Stops

Each emergency stop shall have a label fitted adjacent to it clearly identifying its associated equipment. Unless specified otherwise each package unit where the biggest motor is > 20kW shall have one emergency stop button.

Each emergency stop shall have a 40mm mushroom head and a shroud to prevent accidental activation. The emergency stop push button will be “turn to release” and will not have a key. The e-stop can be locked off if required by fitting a padlock through the shroud. The recommended emergency stop is manufactured by Telemecanique. Any deviation from this must be in writing from Star Refrigeration Ltd.

Each emergency stop shall have two sets of “normally closed” contacts that will be wired in series.

The complete emergency stop comprises of the following part numbers:

 Single hole 80 x 80 x 49mm depth zinc alloy push button enclosure with yellow lid and blue base - Part No: Telemecanique XAPJ1201

 Single hole 80 x 80 x 74.5mm depth zinc alloy push button enclosure with yellow lid and blue base - Part No: Telemecanique XAPJ1501

 Turn to reset latching 40mm diameter emergency stop pushbutton - Part No: Telemecanique ZB4BS54

 2 Normally closed contact block to fit ZB4BS54 - Part No: Telemecanique ZB4BZ104

 60mm Emergency stop label surround - Part No: Telemecanique BY9330

 Emergency stop pushbutton padlockable yellow shroud - Part No: Telemecanique BZ1605

Arrangements

Cold store cooler electric defrost heaters (coil block or drip tray) and drain line heaters shall not be fitted with local isolators unless specifically requested for that contract. Our assessment of this is that electrical panels can be isolated to allow heater fuses to be removed so local isolation is not required. Ensure warning labels are fitted to the cooler to say isolate elsewhere before removing cover.

The electrical wiring contractor shall consider the minimum heater cable size to the heaters inside the cooler and fit appropriately rated MCBs in a steel electrical enclosure (typically in the roof void) before the cooler.

Care should be taken that electric motors within cold stores are so mounted that drain holes, if any, are effective.

Remote motors (except compressor motors) on all air coolers, air-cooled condensers (unless stated otherwise e.g. on packaged water chillers) and evaporative condensers and fan peripheral heaters shall be wired through local isolators of a type designed to be disconnected on load. Suitable types are manufactured by Legrand, Rockwell and ABB. Irrespective of the load, isolators smaller than 10A shall not be used for this purpose. Such isolators for cold store fans shall be located within the cold space, adjacent to the motor. For fan peripheral heaters the local isolator will break both the phase and neutral connections. For the case of drain line heaters (where the starter panel can be temporarily isolated to allow disconnection of the heaters) local isolation is not required. Our assessment of this is that electrical panels can be temporarily isolated in the rare instance that a drain line heater has to be changed. There is no maintenance requirement for drain line heaters apart from checking that they are working.

Machinery rooms for ammonia shall be constructed in accordance with latest version of EN 378 -3 which requires that, “Walls, floors and ceilings shall be tightly sealed”. Electrical cables shall therefore be tightly sealed in ducting or conduit (by Star’s electrical sub-contractor unless agreed otherwise) so that vapour cannot pass along the cables in either direction.

Package Units – General, Indoor Equipment

Cables shall be:  Type YY or BS6500 for solenoids and switches.  Type SY cable for pumps up to 16A rating.  Belden 8760 or equivalent (screened) for analogue devices

Cable containment shall be:  galvanised conduit or trunking when Type YY or BS6500 is allowed.  galvanised cable tray.  flexible conduit up to 1000m long.  unistrut (with plastic end-caps)

Containment shall be securely fastened to the packaged unit frame and shall not be attached with beam clips, sticky-backs or similar. Use of flex outside containment shall be limited to a maximum length of 2m unless agreed otherwise.

Junction boxes shall:  be powder coated or galvanised pressed steel with the appropriate IP rating.  have individual clamp type terminal connections. Pinch screw terminals are not allowed.  have appropriate cable glands fitted in such a manner that the IP rating is not diminished.

Package Units – General, Outdoor Equipment

As above except:  consider plastic junction boxes.  all cable containment shall be free-draining.  all cable glands shall be on the underside of junction boxes unless agreed otherwise.

Package Units – Building Services

As above except:  all containment shall be stainless steel.  sticky-backs or similar shall not be used for cable support.  beam clips shall not be used.

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