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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> Wiring garage https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1087983187 Message started by John Davies on Jun 23^rd, 2004, 10:33am

Title: Wiring garage
Post by John Davies on Jun 23^rd, 2004, 10:33am

We have just bought a house and I need to rewire it, and wire the garage to suit the needs of a MIG welder. These sometimes can cause mcb's to become weak, and I have been told it is the done thing to have a socket wired direct off the supply side of the fuseboard. Is this correct? The fuseboard is some way from the garage, and I don't much like the idea of wiring from the supply side without fused protection, especially as the feed wire would be running under a bedroom floor.

Wouldn't it be better to wire from a 40 amp mcb at the consumer unit via an isolating switch in 6 mmm cable from the supply side of the fuseboard to 32 amp and 6 amp MCB's within garage so that the system was fully protected and at least if any tripped they could be easily reset?

All advice welcome.

Thanks

John

Title: Re: Wiring garage
Post by plugwash on Jun 23^rd, 2004, 12:12pm

wiring from the supply side of the board is very dangerous and i wouldn't take any advice from him on electrics

i presume this mig welder is plug in?

id imagine a C32 or D16 should be fine

the problem is that with those breakers you are really pushing it on disconnect time and you need to get your Ze mesured with proper test gear to be sure its safe to use them

Title: Re: Wiring garage
Post by Lectrician on Jun 23^rd, 2004, 4:51pm

We generally use a 16amp socket, on a D20 breaker in the board (if its a submain, you have to be careful about discrimination).

Like plug says, get a spark to calculate the cable size to ensure the Zs is low enough. He will need to know the cable length, and the Ze at the origin of your supply (he could take 0.35 as the Ze, as this is the max the REC will give, but usually it is a lot lower, and this 'rule of thumb' figure may lead to un-necessarily large cables.

Anyone on here could calculate for you if you give us the distance, and if the cable proves to large, then we could recalculate if we knew the Ze.

Confussing??

Title: Re: Wiring garage
Post by plugwash on Jun 23^rd, 2004, 5:21pm

i thought the rec were allowed to give a Zs of 0.8 on TN-S

and i did the sums once for a C32 on worst case TN-S and found it was impossible to make it meet

Title: Re: Wiring garage
Post by Lectrician on Jun 23^rd, 2004, 5:44pm

sorry, yea, 0.8 for TN-S, 0.35 for TN-C-S, making asumptions :-)

Title: Re: Wiring garage
Post by Lectrician on Jun 23^rd, 2004, 5:45pm

max Zs for a D20, 0.6ohm!!

Title: Re: Wiring garage
Post by Lectrician on Jun 23^rd, 2004, 6:20pm

If TN-C-S(PME) or TN-S, then you could use a D20 MCB with 4mm/4mm cable(4mm L and N with 4mm earth) over a distance of 46m maximum. This is assuming the welder is fixed equipment with a disconnection time of 5sec's.

If 0.4sec's is required, a D20 MCB with TN-S would not be possible, but the above spec on TN-C-S would be ok(just).

T+E with its 1.5mm earth in the 4mm size would be too small, a seperate earth would need to be run.

Title: Re: Wiring garage
Post by Lectrician on Jun 23^rd, 2004, 6:22pm

Thanx to Amtech Cable Calculator for those results ;-) �

It would have taken ages by hand �;D

Title: Re: Wiring garage
Post by John Davies on Jul 1^st, 2004, 9:56pm

Sorry folks,

What exactly does TN-C-S

PME

and

TN-S

actually mean?

Thanks

John

Title: Re: Wiring garage
Post by L.Spark on Jul 1^st, 2004, 10:29pm

it's the way the main earthing is done

in a TN-C-S the earth is combined with the neutral conductor

TN-S the earth comes from the steel armour on the incoming cable or the lead sheath on the incoming cable

PME is Protective Multiple Earthing (PME), which is what TN-C-S is technically speaking.

please note none of these supplys can be supplied personaly, only by the regional electricity company. its illegal to personaly combine neutral with earth.

hope this helps

Title: Re: Wiring garage
Post by greg on Jul 2^nd, 2004, 6:36pm

so on a TN-C-S arrangement the earth is combined with the N - how does it get separated at the CU

Title: Re: Wiring garage
Post by plugwash on Jul 2^nd, 2004, 6:41pm

its generally sperated at the service cutout
either by sticking an extra cable in the neutral (most service sutouts have 2 neutral terminals) or by a specific contact on the side

Title: Re: Wiring garage
Post by Lectrician on Jul 2^nd, 2004, 6:57pm

From looking at a cutout, sometimes you cant figure out if it is TN-S or TN-C-S. The rec's use concentric for TN-C-S, and sometimes split concentric for TN-S down here. The only way to tell is with a loop tester, and this isn't a deffinate answer!

Title: Re: Wiring garage
Post by John Davies on Jul 2^nd, 2004, 10:10pm

Thanks very much :)

John

Title: Re: Wiring garage
Post by plugwash on Jul 3^rd, 2004, 2:00am

i suppose the other option is to open the cutout and find out for sure ;)

or ask the rec directly

iirc pme should have a warning label but often doesn't

Title: Re: Wiring garage
Post by L.Spark on Jul 3^rd, 2004, 2:03am

wrote on Jul 2^nd, 2004, 6:36pm:

so on a TN-C-S arrangement the earth is combined with the N - how does it get separated at the CU

TN-C-S is PME as said which is Combined Neutral Earth (CNE) it's split at the cut out as plug suggested.

Title: Re: Wiring garage
Post by rabbit_rabbit on Jul 3^rd, 2004, 7:50pm

Chubby - that sort of thing may go down well over at Screwfix but we do try to avoid it over here. Do try and remain civilised on this Forum not a prat - save that for SF coz they deserve you over there and you them.

Many Thanks

RR