Pickhill Bantam Wiring

[indiananose]

Hi there,
I'm a newbie to welding so please bare with me if I ask something completely stupid! I've got a small amount of knowledge wiring residential premises but need to re-wire a Pickhill Bantam welder in an agricultural building on a TT system in the middle of nowhere for a neighbour, this is somewhat outside of my comfort zone. The re-wiring has to conform to part P.
For a start the existing installation is about 30 years old and so has no RCD protection whatsoever. It does have it's own 65Amp semi-enclosed fused supply in the main house, then a domestic 4mm twin and earth line is strung across to the shed which houses the welder, some lighting and a small ring main supplying 13A sockets. Currently the welder is switched by an electric cooker switch.
From what I can glean from the regs, the supply needs to be protected by RCD and the line needs to be raised to 6m above ground. Things I need to figure out are the type and size of the cable, which is the best RCD device to use given the surge, and the best switching device for the welder considering it's running on a TT system in agricultural premises!
Any help would be greatly appreciated

 

[oilcooled :)]

i have two bantams, dunno what tt means but mine are just wired for the standard blue 16amp socket with no problems, as for the welder its self under the cover plate there should be markings 240 brown 0 blue and centre is earth

 

[MarkMG]

Cable size, use this http://http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

I would then install a garage sized distribution board with RCDs etc

 

[Tomlt]

I'm not an electrician but 4mm^2 cable is awfully small to be protected by a 65amp fuse, I would think a 30A MCB and RCD or RCBO would be about right for that installation. However as you can appreciate that isn't going to give you much headroom from the supply, especially if running welder full out & the ring main.

Twin and earth should certainly not be used where abrasion can occur, since it has very low mechanical protection.

Best in my opionion would be to run SWA or Hi-Tuf cable either buried or strung across a suitable catenary wire as you stated.

With a 65A supply you'd want to be looking at 10mm^2 SWA or more depending on distance if you want to have that all useable, or you could fit a 40A MCB for instance and possibly get away with using 6mm^2.

Best to use something like this:

http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

To calculate your current and length to size the cable so that you get the correct size to match the allowable volt drop and impedance of the cable, that you will have to certify to for part p.

I'm not a sparky so this is my DIY and electronics engineering knowledge, so I'd strongly recommend consulting a competent electrician. Be aware that outside of the main home in outbuildings and gardens Part P applies to just about everything you do from my understanding. You can get the Part P cert from your local council inspector for ~£100-£150, or get a suitably qualified sparky to sign it off.

HTH, Tom.

 

[indiananose]

Hi All,
thanks for your help. Much appreciated.
oilcooled; tt refers to the supply from the grid, it's an old system which delivers no earth, instead the earth is supplied from the properties own earthing rod. My worry here is that would such a large current drain on the supply and such an unstable earth result in substantial current in the earth from the installation? meaning an RCCBO for example would just trip every time the welder was switched on :S
TomIt; the welder is about 25m from the meter so using your supplied link it looks like 6mm would be sufficient for 10Kw , does anyone know if using the welder at its max rated 180A low voltage would exceed 10Kw (40ish amps@240V)

thanks again

 

[oilcooled :)]

correct me if im wrong or if this is irrelevant but doesnt it say on the plate .5 kva max duty cycle, i know what duty cycle means but always had it expressed as a %

 

[MarkMG]

40ish amps at 240v is 10ish Kw

 

[brightspark]

40 amp will be fine for welder. mine knocks a 30 amp mcb out in startup now and then because of wirewound transformer . but runs at full current all day long if needed .one point with tt suply an earth rod must be used but also an rcd device fitted at source just past the meter eg 60 or an 80 amp double pole rcd with 30 miliamp trip. then through a switchfuse with 40 amp mcb or cartrige fuse/ as for the welder tripping it they shouldnt be any earth leakage of the welder .dont get confused with welder current and earth leakage current

 

[MarkMG]

With regards to earth, when i did a similar job on my garage I ran the earth back to the house earth. I understood that have different earth with different potential differences caused problems with the breakers.

 

[brightspark]

With regards to earth, when i did a similar job on my garage I ran the earth back to the house earth. I understood that have different earth with different potential differences caused problems with the breakers.

anything past the main cutout must be earthed back to source eg flat twin and earth or 3 core swa

 

[indiananose]

great stuff, thanks chaps