Fixed portacabin supply

[Set s]

Hey all,

Got a few questions about a portacabin that's going to be used as an office block. Unfortunately I have not seen the cabin and doubt I will until it turns up unannounced no doubt. The cabin is 75m away from the closest supply which will be run underground in ducts (already in place). I am planning on supplying a 63A single phase supply using 25mmsq 3C swa (due to length of the run). The supply is TNS so no need to earth rod. Do I need to make any other considerations? Input greatly recieved.

S

 

[Evans Electric]

Can't think of any Set.

Just check the heating load in the cabin , someone must know.

 

[Set s]

Been trying to get a spec off the supplier for the cabin. Cheers for getting back to me.

S

 

[Evans Electric]

Don't order the cable till you know. On the face of it it should be fine.

 

[Sharpend]

Set, is this a single cabin or part of a multiple system that you are supplying? A little confused by the terminology office block.

 

[a12jpm]

If it is just a standard single office cabin then they normally have 6 double sockets, 5 fluro, pos hand wash/dryer, wall heaters and possible water heater and that's about it.

You could probably get away with a lot smaller than 25mm, even on that long a run. Normally 6/10mm is enough, even on a drying room/canteen. Portacabin will supply you with a layout/spec if you ask, normally sen one for setting out of pads.

 

[Evans Electric]

Threw me where you said 63A I thought you knew the load. A12JPM s probably nearer the mark .

Is it just a builder's cabin . Office block sounds big.

 

[androidlee]

diversity

 

[Set s]

I have been told it is to accommodate 12 office staff. No provision is to be made for canteen facilities as far as I am aware. It is on 40ft long x 20ft and allegedly open plan. So I'm expecting a fair few sockets and at least 3 convector heaters. Unfortunately getting info from those above me is like getting blood from a stone. They must think it will all magic itself in!!!!!

 

[apprentice87]

Hi There,

Where are you getting the supply from?? Owing to length of run, even if it is direct from the meter, if Ze is getting towards the max quoted 0.8, things are going to be awful close with your 63A MCB even if it is a "B" curve one.

If you have got the supply from an existing DB, then things might be worse, so, TNS or not, you might have to fit an RCD at the origin of your 75 meter distribution circuit, purely to be able to achieve the required disconnection time for the distribution circuit itself, even though the final circuits [due to having smaller MCB's, might already be ok]

john..

 

[Set s]

Sorry I should have given the details better. Supply is coming from a rcd protected 3ph db.

 

[a12jpm]

That will probably be 2 open sided cabins joined in the middle. You'll find each cabin/section has its own CU serving only what's installed inside that section. So you'll need to run in your SWA to a DB then run your feeds off to each CU. I normally run it to a box mounted on the outside of the cabins with a isolator/RCD then each unit is fed from a mcb.

That's how I do it, others will do it different.

 

[apprentice87]

Hi Set s,

"Sorry I should have given the details better. Supply is coming from a rcd protected 3ph db"

All sounds well then!!

Personally, I would use the 25mm too.... Better a few quid more to do a proper job now than have them all whinging come the winter and loads of heaters all plugged in!!

john....