Patrick Benson said:

Also, would the use of a O-PEN protection device permit the use of the PME supply? Any comments would be much appreciated.

Not according to BS 7671.

An open-PEN protection device switches the protective conductor. According to BS 7671, a protective conductor may only be switched:

• Where permitted by Regulation 543.3.3.101; or
• Where an open-PEN protection device (OPDD) is used for an EV charging equipment installation (see 722.411.4.1).

Since connection of a mobile/transportable unit is neither of the above, use of an OPDD would NOT conform to BS 7671.

The same situation exists where an OPDD is considered for use for a heat pump or other fixed electrical equipment ... usually, the device contravenes BS 7671 (Regulation 543.3.3.101). The sole exception of the device being specified for EV charging equipment installations (722.411.4.1).

Even where 722.411.4.1 applies, it is only the charging point that is specified for protection by the OPDD.

Since connection of a mobile/transportable unit is neither of the above

Wouldn't a typical open-PEN device -which wouldn't allow the PE contacts to be open while any of the live contacts were closed -  meet 543.3.3.101 (ii) or (iii)?

   - Andy.

Thank you for your response, much appreciated.

AJJewsbury said:

Wouldn't a typical open-PEN device -which wouldn't allow the PE contacts to be open while any of the live contacts were closed -  meet 543.3.3.101 (ii) or (iii)?

The switching device would, but it's not simply a switching device. If it were that simple, I'm sure it would already have been implemented in 717.411.4.1.

In this particular case, refrigerated unit, the potential losses are a key consideration for unwanted operation.

mapj1 said:

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.

That is a key consideration.

mapj1 said:

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.

I think you have said yourself why the risks are NOT "about the same as a car on charge" - more risk of human contact, larger contact area - generally more probability of human contact if something does go wrong.

AJJewsbury said:

Wouldn't a typical open-PEN device -which wouldn't allow the PE contacts to be open while any of the live contacts were closed -  meet 543.3.3.101 (ii) or (iii)?

The switching device would, but it's not simply a switching device. If it were that simple, I'm sure it would already have been implemented in 717.411.4.1.

In this particular case, refrigerated unit, the potential losses are a key consideration for unwanted operation.

mapj1 said:

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.

That is a key consideration.

mapj1 said:

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.

I think you have said yourself why the risks are NOT "about the same as a car on charge" - more risk of human contact, larger contact area - generally more probability of human contact if something does go wrong.