Workshop electrical wiring upgrade advice

Hi Everyone,

I have recently purchased a spot welder- Celette Scorpion 2400R.
Plugged it into my three phases and it blew fuses(3x20A) with the first weld attempt.
Changed old fuses like for like with new ones and tried the machine on the lowest setting, then upped it, and fuses were blown once again, so it's clear I need some upgrades.

The machine has settings from 0.8mm to 3mm, I got to 1.5mm and the fuses went.
I'm attaching pictures of the current setup. I also wanted to make another three-phase socket about 15m away from what you see in the pictures.

Thank you for all bits of advice.

And the machine load spec is????

You seem to have a 32A socket protected by 20A fuses, rather than the expected 32A. Where does the supply come from and what do you know about its characteristics? That might be the limiting factor as to how much you can increase the fuse rating. What fuse does the welder manufacturer recommend? Aside from the current rating, are they supposed to be slower than the gG fuses fitted now?

On a separate note I am not 100% convinced by what I can see of the earthing. It might be local TT in which case the body of the fuse-switch shouldn't be connected to the supply earth if that's TN, but it doesn't seem to be connected to the earth passing through either. Or if it's earthed via the armour, why isn't the green/yellow cable connected to the casing stud? Presumably the DB is connected to the MET below it?

Lucien Nunes said:

You seem to have a 32A socket protected by 20A fuses, rather than the expected 32A. Where does the supply come from and what do you know about its characteristics? That might be the limiting factor as to how much you can increase the fuse rating. What fuse does the welder manufacturer recommend? Aside from the current rating, are they supposed to be slower than the gG fuses fitted now?

On a separate note I am not 100% convinced by what I can see of the earthing. It might be local TT in which case the body of the fuse-switch shouldn't be connected to the supply earth if that's TN, but it doesn't seem to be connected to the earth passing through either. Or if it's earthed via the armour, why isn't the green/yellow cable connected to the casing stud? Presumably the DB is connected to the MET below it?

Click to expand...

1.15 a.m. you wet the bed?

Was online anyway in a long rambling meeting with some guys on the other side of the world.

Lucien Nunes said:

On a separate note I am not 100% convinced by what I can see of the earthing.

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I happen to know the person who's sticker is proudly displayed there and I'd say from the pictures that their standards have improved!

davesparks said:

I happen to know the person who's sticker is proudly displayed there and I'd say from the pictures that their standards have improved!

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Good to see you back

Lucien Nunes said:

You seem to have a 32A socket protected by 20A fuses, rather than the expected 32A.

Click to expand...

The box above the 32A socket has "temp supply" written on it. If "temp" is short for "temporary" (which has a habit of often becoming permanent), then there might be good reasons why the fuses are 20A.
This needs looking at by an experienced sparky.

UNG said:

And the machine load spec is????

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Unfortunately, the spot welder came without a manual. I have messaged manufacturer and waiting for a reply. The only bit I have is rating on spot welder

Lucien Nunes said:

You seem to have a 32A socket protected by 20A fuses, rather than the expected 32A. Where does the supply come from and what do you know about its characteristics? That might be the limiting factor as to how much you can increase the fuse rating. What fuse does the welder manufacturer recommend? Aside from the current rating, are they supposed to be slower than the gG fuses fitted now?

Click to expand...

I think the socket is 64A. I'm waiting for the spot welder manufacturer to reply. The machine is quite old, will see what fuse they recommend once I get my hands on manual

Lucien Nunes said:

On a separate note I am not 100% convinced by what I can see of the earthing. It might be local TT in which case the body of the fuse-switch shouldn't be connected to the supply earth if that's TN, but it doesn't seem to be connected to the earth passing through either. Or if it's earthed via the armour, why isn't the green/yellow cable connected to the casing stud? Presumably the DB is connected to the MET below it?

Click to expand...

There is earthing pole just outside the workshop. See pictures of supply attached.

brianmoooore said:

The box above the 32A socket has "temp supply" written on it. If "temp" is short for "temporary" (which has a habit of often becoming permanent), then there might be good reasons why the fuses are 20A.
This needs looking at by an experienced sparky.

Click to expand...

Someone will be coming round to have a look.

brianmoooore said:

The box above the 32A socket has "temp supply" written on it. If "temp" is short for "temporary" (which has a habit of often becoming permanent), then there might be good reasons why the fuses are 20A.
This needs looking at by an experienced sparky.

Click to expand...

It does indeed stand for temporary in this case.


I've even seen that socket before and still can't work out whether it is PNL or PWL written on it.

Same thing happened the other day for me on another thread. There's a label belonging to a spark whose work (and level of knowledge) I'm familiar with. I'd say more, but this is a public forum.

I have edited out the details of the company in question.

westward10 said:

I have edited out the details of the company in question.

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I've only been back 5 minutes and you're already censoring me!

Welcome back Dave.

Spot welders take short, sharp gulps of power and this is no exception. It is rated at 70kVA which corresponds to a peak line current of 100A. The average current will be much lower, so the built-in D32 (32A, D-curve) MCB suffices. Like any 32A MCB this will react to a prolonged steady current exceeding 32A by a certain factor, but different tripping curves allow different maximum peak currents before their instantaneous magnetic trip mechanism reacts. Most wiring uses B-curve or for more demanding loads C-curve MCBs, with D-curve being reserved for very high-inrush and surge loads such as this. It is designed to ride out brief pulses of up to 10xIn = 320A, which allows for the momentary 70kVA demand of the welder.

Since the manufacturers will have chosen the MCB with knowledge of the demands of the unit, that is probably the minimum rating that will allow it to be used to its full capability without nuisance tripping, so you would need to provide equal or greater rating upstream. The challenge is that the low sensitivity of a D-curve MCB to short-circuit currents puts more onerous requirements on the loop impedance of the wiring to ensure faults are cleared rapidly. Sometimes that is easy to satisfy, sometimes not.

Because of the unusual nature of the load, the suitability of the supply should be checked, preferably by someone familiar with industrial equipment as this is rather out of the sphere of many electricians. Spot-welders and their like can be so disruptive to supplies that in an industrial setting, it is sometimes necessary to advise the DNO that such a load is to be connected and they are at liberty to limit the maximum rating to avoid other customers' lights pulsating in response to the voltage fluctuations it creates.