Change to circuit in garage

[coshhassessor]

I want to change / have altered the circuit in my garage. The garage is attached to the house (i.e. NOT separate, outdoors etc), and currently has a radial circuit (about 15m total length) wired with 2.5mm2 (surface clipped) T&E to a 16 amp type B MCB. The whole system is a TT, for reference (30mA RCD in situ).

This is inadequate for welding, except at the lowest current levels. I need to go up to a 30A nominal current draw, so was thinking in terms of 6mm2 T&E and a 32A type B MCB.

Based on my calcs. this is adequate. Any (helpful, please) comments?

My reading, since this is an upgrade to an existing circuit, not in a special location, is that this is NOT Part P notifiable. Comments?

 

[andy]

1: you could use 4mm instead of 6mm.

2: its in a special location so it is under part P

might be easier just running a seperate B16 radial to 1 socket for just the welder

 

[coshhassessor]

Why is it a special location? It's an attached garage, with a door that goes directly into the house (i.e. not an outside door). By that logic, any living room with patio doors is a special location

The circuit NEEDS to be able to carry 30 amps: to use a 130 / 150 amp welder you will need that level of supply. Notwithstanding the duty cycle is about nothing at that sort of draw, I don't want to put unnecessary stress on the circuit, especially for the relativley small amount of additional grief that a 32A MCB and 6mm will be over 4mm

 

[andy]

Why is it a special location? It's an attached garage, with a door that goes directly into the house (i.e. not an outside door). By that logic, any living room with patio doors is a special location

The circuit NEEDS to be able to carry 30 amps: to use a 130 / 150 amp welder you will need that level of supply. Notwithstanding the duty cycle is about nothing at that sort of draw, I don't want to put unnecessary stress on the circuit, especially for the relativley small amount of additional grief that a 32A MCB and 6mm will be over 4mm

i think that the garage is a special location, but it might not be



and since its 30A, i assume you have a BS4343 32A plug on the welder?
prob be best do do as i said, but make it 32A instead of 16A

 

[coshhassessor]

re. The plug on the welder - if necessary, it will have - and if so there will be a suitable outlet set aside for it!

Given that you end up stepping up to really fairly hairy currents, it must come as a surprise to some people that the lights dim when they start welding... The maximum you are going to be able to produce on a "normal" outlet is about 120-130 amps. On the sort of machine you can run on a normal 13A type outlet, you get a duty cycle of about 5%! Places like machine mart make a good deal of the fact that you can run a 150A welder off a single phase 240v supply - but neglect to tell you it needs a different outlet, other than to say "30A supply needed". I think this is a bit disingenous. Fortunately, you can weld 2-3mm without this sort of malarkey. My concern re. a 30A supply is that I really only want to go through this once, and be reasonably sure I'm at the top of the envelope.

As for the separate outlet - great idea. If the CU had sufficient spaces on it I would, but with a radial in there at present, I would have to have a fairly radical redesign to give me the same number of outlets in the garage plus a dedicated welder point. If only I was having it done from the ground up from scratch, with unlimited funds

 

[andy]

might also be a good idea to use a C32 rather than B32... just to avoid nuisence trippin

and you will have to use a BS4343 32A plug and socket... either that, or melt a 13A socket

 

[coshhassessor]

Strewth! That was quick! Info by return - more or less.

Good point about the type C - I need the rest of the household bending my ear 'cos the telly's gone off as I weld like I need a third shoe - especially if I'm in the middle of running a bead!

Anyway, in the mean time, back to MMA for thick stuff...

Cheers for the (very helpful) advice.