Advice on cable size to supply a caravan.

[stevie22b]

Im going to need to run a cable about 40 metres in length to supply a static caravan in my garden. I will be living in the caravan for a few months so i will need the cable to be big enough in order to meet the demand - lighting, tv, computer, combi boiler pump, electric kettle etc, and probably a washing machine. I guess i will have the potential of drawing upto 7-8 kw at any given time.
I was thinking of using something like 6mm armoured cable, but not sure if it would be big enough given the length of run?

Would appreciate any advice. Thanks.

 

[plugwash]

This is somewhat different from an outbuilding supply in that you want to pay far more attention to minimising the chance of tripping the house breaker. That means that the largest breaker in the caravan unit should be at most half the breaker in the house unit so that a short on one of the circuits in the caravan does not trip the breaker at the house end. For the same reason the circuit should be fed from the non RCD side of the house CU with any RCD protection being placed at the caravan end (I would probablly use a RCD incomer unit, it's not ideal but given the lack of stairs in a caravan I don't think losing lighting on a RCD trip is that big an issue in this case).

I would use a 40A circuit to feed the caravan. Then in the caravan CU put a 16A breaker for a dedicated washer circuit, a 6A breaker for lighting and a 20A breaker for a general power circuit.

Given the run length 10mm cable is required and if it is going to be burried it obviously needs to be armoured.

If your house is on a TN-C-S supply you MUST use a seperate earth rod for stuff inside the caravan (the cable amrmour can and generally should be protected by the house earth but if it is it must be completely covered when in the caravan). Earth rods absoloutely MUST be tested before use.

This work is notifiable under part P

If you plan to use an electrician get them involved from the start, they will probablly be able to source stuff cheaper than you can, they will have thier preffered brands and many electricians are set in thier ways and will want things done their way.

 

[Lectrician]

The armour MUST be earthed at the house end, and isolated at the caravan end if using a PME TN-C-S supply. You may as well only use 2 core in this case too.

I would terminate the SWA into a gewiss box under the van, and use some 10mm Split Concentric or T+E to make the final couple meters to the CU already fitted in the caravan.

The caravan is likely to have a consumer unit already which will have 30mA RCD protection as the main switch. This is very typical. Depending on size, you could expect a lighting circuit or two, and one or two socket circuit, either a ring or a couple radials. Earth rod connected to CU earth bar, and the house earth kept isolated from this earth bar.

 

[stevie22b]

Rather glad i asked now, i had not given any thought to the regs regarding the earthing, i was going to use the earth from the house. Im going to get an electrician to check and sign off the install, so i will also get him to deal with the earthing - im not certain about how to fully check an earth, or even what length or rod i would need, so will leave that to someone who knows about it.
I am waiting for delivery of the caravan - a ten year old 12'x35' static, so not sure what electrics it will have, though im expecting to have to run a new ring main for general use as i should imagine that sockets are going to be few and far between, may also fit a new CU depending on whats currently installed. Do you know if its acceptable to run standard 2.5 t/e under the floor on a caravan?, will make the install of the new ring much easier if it is. Obviously being under the floor U/V should not be a problem.
I think that the vans current incoming supply terminates in a gewiss or similar ip65 rated box under the floor, if not i will impliment that arrangement.
Thank for your replies, have been a great help, and if you could advise on whether i could run standard 2.5 T/E under the floor it would be appreciated.