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BS 7671 Section 717 - Mobile or Transportable Units. Applicable to refrigeration trailers?

Daniel Hickson

Does a refrigeration trailer that is utilised to transport food goods between the clients depots and is then connected into the sites electrical supply through a trailer hook up connection unit to facilitate running of the refrigeration equipment classified as "Mobile or Transportable Unit" and therefore warrant the requirements of BS 7671 Section 717?  

The trailer will maintain the connection to the sites power supply for a few hours to facilitate loading/unloading. 

The regulations now adds further detail for PME installations, where it can only be permitted if one of the below applies: 

  

Would part (ii) be a satisfactory measure in the above scenario for a PME supply? 

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    Putting the regs aside for a moment, electrically this is similar to a caravan, albeit a very cold one, where no one sleeps (though some caravan holidays have felt like sleeping in an ice box, so maybe not so different) and normally for that PME would not be permitted. The risks are about the same as a car on charge, as the body of the vehicle - I presume - is at mains earth potential while connected to shore power, and folk do presumably touch the thing as part of normal operations of loading and unloading.

    This would normally be solved in the caravan case by wiring the 'shore power' sockets as TT. But that may mean the whole site has to be TT if you cannot get far enough away from bonded services and bits of the 'indoor' installation. (which is possible - farms with supplies of hundreds of amps are often TT, but it needs some more planning.)

    for small loads (trucks full of radio gear for example) a transformer is used, either in the truck or static, to in effect create a new TNs

    At the moment the O-PEN solution is still quite novel, and in regs at least has only really been considered for the EV case, although as noted, the actual electrons don't know that, and the risk is very similar.

    If the O-PEN operated the vehicle would be disconnected, but any metal bits of building would still be live so its not that complete in terms of removing the danger.

    Mike.

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  • 0

    Putting the regs aside for a moment, electrically this is similar to a caravan, albeit a very cold one, where no one sleeps (though some caravan holidays have felt like sleeping in an ice box, so maybe not so different) and normally for that PME would not be permitted. The risks are about the same as a car on charge, as the body of the vehicle - I presume - is at mains earth potential while connected to shore power, and folk do presumably touch the thing as part of normal operations of loading and unloading.

    This would normally be solved in the caravan case by wiring the 'shore power' sockets as TT. But that may mean the whole site has to be TT if you cannot get far enough away from bonded services and bits of the 'indoor' installation. (which is possible - farms with supplies of hundreds of amps are often TT, but it needs some more planning.)

    for small loads (trucks full of radio gear for example) a transformer is used, either in the truck or static, to in effect create a new TNs

    At the moment the O-PEN solution is still quite novel, and in regs at least has only really been considered for the EV case, although as noted, the actual electrons don't know that, and the risk is very similar.

    If the O-PEN operated the vehicle would be disconnected, but any metal bits of building would still be live so its not that complete in terms of removing the danger.

    Mike.

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