Portakabin supply

There_we_go · May 14, 2020

Morning all,

Had a request to install a power supply to a temporary cabin which will have basic utilities like a heater, lighting and a socket. I have no details yet of the actual cabin so will need to get this information, what would you suggest for the circuits at the cabin end, an MCB? I can pick up a single phase power supply from a local switchroom where the majority of the cable run will be on overhead cable tray. Thanks in advance.

pc1966 · May 14, 2020

It kind of depends on how it is fed I guess, and access to the switchroom to reset anything that has tripped.

If the workers can't easily get to the switchroom or the options for RCBO use there are limited, then you really want to put the RCD protection in the cabin. That in turn means your feed has to be adequately protected against shock from any damage, so SWA or Flexishield.

An RCD at the cabin would also be essential if it is a TT supply (e.g. on building site with TN-C-S main supply), but if there is little worry over a PME fault then you could just use the supply earth and not a local rod.

You might find it already has a CU with incomer RCD and a few MCB anyway, so the only issue becomes back to the above of it not being selective with any switchroom 30mA RCD. Otherwise the cheap option is something like the garage CU with 2 or 3 MCB slots to play with:

Metal Clad Garage Unit with 40A RCD and 6A and 32A MCB

Metal IP65 enclosure c/w 20mm knockouts on all sides drillable to 32mm

www.cef.co.uk

Depending on the loads in the cabin, and the feed cable & OCPD, you might want to drop the sockets from a 32A MCB to 20A to try and gain a little more selectivity on over-current (but you will not ever do terribly well that way).

westward10 · May 14, 2020

The cabin will be prewired with its own consumer unit. 10.0 swa on a 50A mcb will be fine, you won't achieve selectivity but is only a temp supply.

There_we_go · May 14, 2020

Thanks for the info, I contacted the supplier and it comes equipped with a 32A mcb prewired to the circuits inside, also a local isolator on the exterior of the cabin. A 3 core swa 10mm2 cable shall be fine.