Ask The Trades - Wiring in metal portacabin

andymac

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Wiring in metal portacabin
Dec 29^th, 2004, 6:19pm

I wonder if I could take advantage of those more knowledgeable than me in matters of electrickery? I'm not a sparky, don't profess to be and don't do sparky stuff for other folk so please excuse any mistakes with the terminology Grin

I have half a 40' portacabin that I use as my metalwork/fabrication workshop and I've just rewired it to suit my own needs with three double sockets on a ring main with a 15 amp fuse, four 80w striplights on a radial with a 5 amp fuse and a 500w floodlight (external) on another radial, also with a 5 amp fuse, with everything on a 27 amp, 30 mA rcd. Fuses rather than breakers because I recycled an old consumer unit.

The old supply was spurred off the existing wiring in the cabin but kept tripping when I overloaded it with my welder (single phase) so I've flown the new supply (with sufficient capacity this time) from another, totally separate, cabin.

The new sockets are plastic and all the cables are run through plastic trunking, because the cabin is metal clad. The old sockets and boxes were metal and were earthed to the cabin walls

Two questions:

Does each socket need earthing to the structure of the cabin or does the earth in the cabling take care of that?

I can't see any evidence of an earth rod on any of the three cabins that are all wired together (although it is very dark and dingy underneath, so I might have missed it). Should there be one? The old wiring has never given any problems and, as far as is known, is correctly wired up.

Note to mods: please feel free to shift this into the DIY bit if you think it might benefit.

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plugwash

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Re: Wiring in metal portacabin
Reply #1 - Dec 29^th, 2004, 6:59pm

you need to be carefull with metal structures

probablly worth reading the caravan regs especially the ones as to why you shouldn't put caravans on PME they seem rather applicable here too

possiblly those for construction sites too

neither of theese are directly applicable in this case but both of them will give you usefull hints as to possible safety problems with installing in this kind of situation

the body of the building should definately be main bonded to the CU in there and it is probablly best to avoid conecting it to a PME earth (use a seperate rod if needed)

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andymac GDPR opt-out Total Thanks: 0 For This Post: 0	Re: Wiring in metal portacabin Reply #2 - Dec 29^th, 2004, 7:06pm Cheers Plugwash, I'll have a search on those regs. I have a static caravan, as it happens, and I'm pleased to say it's got a rod of its' own. What's PME? I know (well, I think...) it stands for protective multiple earthing, but what does that actually mean?
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LSpark

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Re: Wiring in metal portacabin
Reply #3 - Dec 29^th, 2004, 7:49pm

Quote:

What's PME? I know (well, I think...) it stands for protective multiple earthing, but what does that actually mean?

That's corrcect, PME is sourced from a TN-C-S supply, which means that the Earth & Neutral are common up to the consumer's terminals where they are then seperated, when you break it down you see that the C n TN-C-S is common as in both neutral and earth are one conductor, and S is for seperated, where the earth is seperated from the neutral at the supply point.

Quote:

Does each socket need earthing to the structure of the cabin or does the earth in the cabling take care of that?

No, The earth from the circuit should only protect the circuit, but you would need to properly investigate what the bonding requirement's are for the porta-cabin, all this would be supplementary to the circuit earthing, or circuit protective conductors (CPC's)

Quote:

I can't see any evidence of an earth rod on any of the three cabins that are all wired together (although it is very dark and dingy underneath, so I might have missed it). Should there be one?

I would think there should be one, and there probably is, this is usualy in the style of a small black box which is visible from the surface up to about 2 inches, sometimes more, and will or should be marked with 'earth - do not remove'

Quote:

The old wiring has never given any problems and, as far as is known, is correctly wired up

It probably is, however testing & inspection would be the only way to confirm the safety of the installation, however I have no doubt you have correctly wired it and are more than happy with your arrangement.

Quote:

the body of the building should definately be main bonded to the CU in there and it is probablly best to avoid conecting it to a PME earth (use a seperate rod if needed)

Definatly

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« Last Edit: Dec 29^th, 2004, 7:56pm by LSpark »

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andymac GDPR opt-out Total Thanks: 3 For This Post: 0	Re: Wiring in metal portacabin Reply #4 - Dec 29^th, 2004, 8:42pm Cheers, L.Spark. Very much appreciated and I'm learning fast here
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Lectrician

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Re: Wiring in metal portacabin
Reply #5 - Dec 29^th, 2004, 8:59pm

Plugwash and L.Spark have all your answers........Can't add a thing really.

A Rod will be required if you intend to run a TT system, and this will be connected via the CU and an RCD will also be required.

In the old days, all caravans and portacabins used to have the chassis rodded down at one corner (this is no longer neccessary).

Also pay attention to any main equipotential bonding required - external gas/water/oil supplies.

Where is the cabin fed from? Can you determine the earthing system at the origin (metr position)?

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« Last Edit: Dec 29^th, 2004, 9:04pm by Lectrician »

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LSpark

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Re: Wiring in metal portacabin
Reply #6 - Dec 29^th, 2004, 9:19pm

Actualy just been talking to someone, if the earth is good enough then a rod is not always required, however you have no wat to verify the earth without calibrated impedance test equipment.

Quote:

A Rod will be required if you intend to run a TT system, and this will be connected via the CU and an RCD will also be required.

Yea

an RCD is Always required by regulations for a TT supply if you have one andymac

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« Last Edit: Dec 29^th, 2004, 9:21pm by LSpark »

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BigT

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Re: Wiring in metal portacabin
Reply #7 - Jan 17^th, 2005, 2:53am

to reply to this I would say this. You say it is a workshop so I feel that all switches and sockets should in my opinion be installed to suit the surroundings. In this case I would of installed more robust accessories for safety and not plastic as this would be much safer.

You also say sockets on 15amp ring, well depends on loading and what your using, sounds to me your not using high enough MCB. Also all metalwork should be bonded and also make sure main earth is adequate. I would ask a qualified electrician from your local area to check all is correctly installed, as long as he is competant electrician that is. Life is worth more than money however much it costs within reason get it checked out.

hope this helps

from BigT with 32 years experience, City & Guilds in 2380, 2392, and a JIB approved apprenticeship, I passed on the 14th edition and joining a scheme but not giving up the fight against some of part P but classed as a DIY person

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LSpark Global Moderator Trade Member Author Offline Posts: 8069 Total Thanks: 3 For This Post: 0 London, UK United Kingdom Gender: Trade: Electrician	Re: Wiring in metal portacabin Reply #8 - Jan 17^th, 2005, 10:50am 2392 ??? Don't be too eager BigT, this post is around 18 days old and usually the person who made that post is gone by now, this is an exception I can see you have allot of help and knowledge to share
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BigT

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Re: Wiring in metal portacabin
Reply #9 - Jan 17^th, 2005, 11:15am

Yes I have put a few hours in like everyone else. Yes I like to help people but I dont like being forced into things unwillingly, if I am I bite back and keep on till the bitter end.

Whats up with all the electricians on this planet, the ones I use to know would never give up without a fight. Yes its now law but laws can be changed, so show your hands fellers and keep showing them till law is changed.

I do want the cowboys stopped like everyone but not the way its been done sofar. The person who thought this up cant be an electrician, probably cant even change a light bulb, be he or she isnt Part P registered though.

regards to all T

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LSpark

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Re: Wiring in metal portacabin
Reply #10 - Jan 17^th, 2005, 11:42am

Hi T

Perhaps I could suggest you register for a trade account here, it doesn’t cost anything and you can get a better idea of how we all (The sparks) feel about these issues as your see the 'trade only' forums

All you need do is provide something which shows us your trade such as a scanned copy of the 2391/2392 certificate, cut out anything you don't want us to see

This just ensures we get only trade members in the trade forums.

Please PM me for more information or go to the 'Just Talk' section where you can make a post in the trade access thread.

Thanks & Regards

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andymac

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Re: Wiring in metal portacabin
Reply #11 - Jan 17^th, 2005, 8:57pm

[quote author=L.Spark link=1104349267/0#8 date=1105959018]2392 ???

Don't be too eager BigT, this post is around 18 days old and usually the person who made that post is gone by now, this is an exception Grin

[/quote]

Oh aye, I'm still about. Don't post a lot because I'm not as experienced or as knowledgeable as most of the folk on here (yet... Grin

) . I just read and learn Wink

BigT, thanks for the input. Because of the space constraints in the workshop I can physically only use one thing at a time. The most power-hungry item is a single-phase welder and that never gets wound up very high as I generally only use 2.5mm rods.

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