electrical problems at welders yard, supply mystery?

[scary cakes]

Hi All,
I attended a welders yard today with numerous electrical problems.
Very old insatallation in poor condition, never had a PIR and no sign of any maintenance, a total mess.
Firstly they had a large 3 phase pillar drill whose metal casing went live when switched on. I found a short between a phase and earth from the commando plug which would explain the fault but why did it not blow the fuse? Old MEM DB, rewireable fuses.
Secondly they had a cooked earth cable within a control box for a large saw. Apparently, the staff told me they were welding nearby when it started to cook and it stopped when they finished welding. the commando in which the welding unit was plugged into and the saw supply are on separate curcuits.
They went on to tell me they previously had a drill plugged into a switched on 13a socket resting on a table not being used whilst on the same table they started welding, the cable from plug to drill started to burn out.
The yard is in a semi-rural location and at first glance it appeared to be a TT, as there is a tatty old approx 10mm cable running from the MET to the factory floor and is then untraceable, however there is a 10mm earth terminated into the neutral block at the head which would suggest PME. We attempted to get confirmation from the LEB as to the supply earthing type but to no avail.
I have taken loops at head, main switch, isolators and commandos and the reading are from 0.28 Ohms to 0.53 Ohms, acceptable.
I have also disconnected the suspected earth rod fly lead and taken a EFLZ and it was 1683 Ohms.
We suspect that it may have been TT originally and due to a poor earth perhaps they decided to jab into the neutral, but its not designed for PME.
To be honest really not sure.
Can anyone help is there a way I can determine the supply type?
Any help is appreciated.​

 

[Craig1982]

They went on to tell me they previously had a drill plugged into a switched on 13a socket resting on a table not being used whilst on the same table they started welding, the cable from plug to drill started to burn out.
​

I have seen this before, tell them to stop welding on the same table as the drill as I think it earths back through the cable. I done it with a 240v grinder that I left on the bench when I was a lad and got a bollcking for it.

 

[GLENNSPARK]

would not Prospective fault current be the same (PSCC and PEFC) for a tn-c-s..?

 

[Engineer54]

First and most important question for you, ....Are the owners of this welders yard prepared to put all there electrical deficiencies right?? If there not and just after a quick fix here and there, ...Walk away!!! You will be up to your head in trouble if anyone gets injured after you have left.

Secondly, And i'm not being funny here, do you feel confident enough to be able to bring this installation up to a safe and decent standard?? This sounds like a can or worms that needs a fair bit of experience and know how, to bring back to any form of normality.

 

[GLENNSPARK]

But that would depend on it being single phase...

 

[Darkwood]

The welding kit is finding alternate route and using the ground and into the nearest earth cable it finds, this is a highly dangerous set-up as it sounds like a faulty welding set or poor connection on his out going leads, this can and has killed many ppl in the past the amount of current flowing is extremely high and with burn out any earths its tracks to, as goes the pillar drill obvious earth path fault and again could kill or injure anyone using them, you need to express how dangerous the installation is and because the welder could have burnt out various earths he needs to stop production and have an immediate pir done, there isnt any half way mark here if someone dies while your there they will say he didnt tell us to stop using anything, i would condem any items effected with warning notices and padlock off supplies till route of problem found this way they cant say you didnt tell them not to use them.

 

[Guest123]

The welding kit is finding alternate route and using the ground and into the nearest earth cable it finds, this is a highly dangerous set-up as it sounds like a faulty welding set or poor connection on his out going leads, this can and has killed many ppl in the past the amount of current flowing is extremely high and with burn out any earths its tracks to, as goes the pillar drill obvious earth path fault and again could kill or injure anyone using them, you need to express how dangerous the installation is and because the welder could have burnt out various earths he needs to stop production and have an immediate pir done, there isnt any half way mark here if someone dies while your there they will say he didnt tell us to stop using anything, i would condem any items effected with warning notices and padlock off supplies till route of problem found this way they cant say you didnt tell them not to use them.

Absolutely what he said^^^!!!

 

[trev]

As it is not within an electrician's power to disconnect any supply would it be prudent to get in touch with the DNO advise them of the potentially lethal condition of this installation and get them to come and pull the supply?

 

[scary cakes]

Hi All, they have asked for a PIR of the installation which I will be doing tomorrow. In terms of there intentions, I suspect they want to make the present problems safe but I very much doubt they will want to rectify the problems arising from the PIR which will be very costly. I would not choose to take this job myself it was kindly given to me from the company I work for. Its a 3 phase supply

 

[trev]

In terms of there intentions, I suspect they want to make the present problems safe but I very much doubt they will want to rectify the problems arising from the PIR which will be very costly.

By the sound of it I'd guess that making the present problems safe and rectifying all problems arising from the PIR are going to be one and the same mate.

 

[Darkwood]

As it is not within an electrician's power to disconnect any supply would it be prudent to get in touch with the DNO advise them of the potentially lethal condition of this installation and get them to come and pull the supply?

I beg to differ, although he can isolate downstream on this occasion you are within your rights in certain situations to break a dno seal and remove supply fuses if you deam not doing so would be a greater risk of fire or safety (normally if the tails are exposed live parts etc)

 

[trev]

I beg to differ, although he can isolate downstream on this occasion you are within your rights in certain situations to break a dno seal and remove supply fuses if you deam not doing so would be a greater risk of fire or safety (normally if the tails are exposed live parts etc)

I thought we couldn't do it but I stand corrected

 

[Knobhead]

When they use the welder are they running the earth return from the set to the work piece? It’s a common failing they just clip on to any old steelwork near the set and rely on what ever return path that happens to be there. Over the years I’ve had SWA’s by the dozen toasted by welding currents.
Welders are in a class of their own, they can destroy anything.

 

[Kamikaze]

Just be careful, as all the experienced guys above have said. It’s got disaster written all over it.

 

[GLENNSPARK]

When they use the welder are they running the earth return from the set to the work piece? It’s a common failing they just clip on to any old steelwork near the set and rely on what ever return path that happens to be there. Over the years I’ve SWA’s by the dozen toasted by welding currents.
Welders are in a class of their own, they can destroy anything.

Used to work as a welder before i got into sparkying and believe me...any loose connections/joints and they really cook when connected to welding plant....i`v seen tough insulation on heavy cable just wilt and drop off due to heat generated............

 

[Darkwood]

I thought we couldn't do it but I stand corrected

As long as you are qualified and knowledgeble about what you are doing then you can but is a rare thing many ppl never come across a situation in there career, i myself have once when a builder dropped something on the meter and it smashed it and also dragged tail (live) out of dis' board without shorting out, only safe way was to cut seal and withdraw fuse to which the dno had no issue.

 

[scary cakes]

Thanks guys. I do not know how they are running the earth return for the welder but I will ask tomorrow. In actual fact can you explain this further as I am not familiar with the earthing practices when using welding equipment. No matter how much I would like to pull the head fuses and shut down the site I really would not be able to get away with it. The PIR will highlight broken/damaged accessories, open rings, high loops poss but all these may not rectify the underlying big problem they have. Does anyone have any thoughts as to how I can clarify the earthing arrangements for the supply.

 

[Darkwood]

just to add experience on this thread ive seen a 800amp welding kit take out a 50mm earth in seconds thus melting it in the trunking to various cables blowing 8 fuses and a need for lot of replacement wiring, even after expressing the cause and what to avoid the same lad did it again 1month later thus welcome to the dole queue for him, cost them thousands, but hey one dumb b.........d mistake is anothers mans opportunity to earn a living

 

[GLENNSPARK]

Thanks guys. I do not know how they are running the earth return for the welder but I will ask tomorrow. In actual fact can you explain this further as I am not familiar with the earthing practices when using welding equipment. No matter how much I would like to pull the head fuses and shut down the site I really would not be able to get away with it. The PIR will highlight broken/damaged accessories, open rings, high loops poss but all these may not rectify the underlying big problem they have. Does anyone have any thoughts as to how I can clarify the earthing arrangements for the supply.

Surely there would be evidence of an earthing connection at the incoming supply cable if tns or cutout if tn-c-s?

 

[GLENNSPARK]

Would not doing a Ze give you a start?