mains to portacabins

[reggie3363]

Hi All,

i'new to the board so please go easy.....been asked by my new employer to wire up a portakabin at the rear of his premises.

The cabin is already pre wired and is virtually new.The nearest D.B.has some spare ways and is aprox 20-25 mtrs away.

Cable run is internal mostly,then clipped surface onto a catenary wire across to the cabin.

The cabin D.B. is rated at 20A.Was thinking of running a 4mm swa protected by a 32A breaker.

Do you think i should be protecting the cable with an RCD?

 

[batty]

All depends on earthing at main DB if not TT then I would only RCD portacabin.

(and welcome to the forum)

 

[SLIPSHOD & SLAPDASH]

Most mobile or transportable buildings must be connected as a TT supply even if there are no other services. I have been through this very recently but can not remember if there is a specific Reg for it. Will check

Edit Section 717 starts with 717.411.1, Automatic disconnection of the supply shall be provided by means of an RCD

 

[Andy™]

buildings like this do not have to be made TT, however, if supply is TNCS, then i would TT it. if main supply is TT or TNS, then export it

 

[SLIPSHOD & SLAPDASH]

Why is that Andy ? We are currently wiring a large site and have been in deep discussion with the owners, designers & the Niceic about this. One of our units even has mains water (plastic), drainage and telephones connected but is still classed as Transportable

 

[a12jpm]

Spend most of my days doing site cabins at teh moment. Most site units have mains water and phones now, even on short contracts still worth it. As far as I can make out they are not a "fixed" installation, after all attach some chains and a hiab can lift it.

For my 2 pence I wire most from a large genny and we do each unit fed from a board on it's own MCB via a main distribution board which is in turn RCD protected at the genny. Each unit (normally 6 down 6 up) also has a RCD for the cabin and all circuits fed from this. Maybe overkill but these sites are uber safety aware at the moment so it's very much belt and braces. So much so I am not allowed to wear riggers any more - apparently they don't offer enough ankle protection! Oh and I have to wear gloves all the time now for hand protection - wtf!

 

[Andy™]

Why is that Andy ? We are currently wiring a large site and have been in deep discussion with the owners, designers & the Niceic about this. One of our units even has mains water (plastic), drainage and telephones connected but is still classed as Transportable

TNCS could be used. its no more dangerous if its a portacabin or small 'fixed' hut.

personally, if it was a TNCS supply, i would TT it because of the risks of TNCS

 

[sparkytim]

BRB Pg 204 717.414.4

 

[Lee321]

transportable is a unit that is expected to move surely and be supplied by plug and socket arrangement which is temporary. not swa feed being a fixed wiring installation

not applicable to a site cabin as it would be a disconnect/reconnect re test and cert if moved

 

[Andy™]

transportable is a unit that is expected to move surely and be supplied by plug and socket arrangement which is temporary. not swa feed being a fixed wiring installationnot applicable to a site cabin as it would be a disconnect/reconnect re test and cert if moved

but it may be on-site permanent. there are a few places i work on where they have portacabins permanently installed, and are fed from SWA

 

[Lee321]

[quote name='Andy

 

[SLIPSHOD & SLAPDASH]

All the above points and questions have already been addressed in various meetings and still no one is 100% sure so thats why we have Rcd'd (is that a word) everything and TT'd all the sites. The Niceic help-desk did advise that if the correct earth bond sizes from the MET to all extraneous metalwork were present then it would be ok on a TNCS.

However one of the sites we are fitting out for a utilities company is 3 acres and f**k that running all them expensive earth cables (we have 35mm 3 phase tails) so have TT that one. I made up a modular unit for the incomer housing a main switch feeding 3, 4pole 100A 100mA time delayed RCD's. One feeds the office, one the security hut & all the cameras, alarms etc and one for the general stores , yard and machinery on site. Apart from the large modular office all transportable buildings i have seen have a 30mA rcd main switch on their C/U.

 

[batty]

As slips says and as I have found most that I have wired have RCD built into cu in buildings. Cable will only need RCDing if supply is TT.

 

[Lee321]

sounds good slip. take some pics dude

deffo batty