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.​

 

[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?

 

[Engineer54]

If your working for a company, then i would strongly suggest/advise that you request a colleague of some experience to assist you, or visa versa. This welding shop is in all honesty a can or worms, where disaster is potentially just around the corner. If you miss something, on this PIR that later rears it's ugly head and injures, maims or kills a worker, guess who they will be looking for as the scapegoat??

 

[scary cakes]

Ze was 0.29 Ohms. Supply neutral has 10mm earth cable running to MET.

 

[trev]

Ze was 0.29 Ohms. Supply neutral has 10mm earth cable running to MET.

Ze suggests TNCS but I'm sure you thought the same. In your position I'd want independent confirmation too

 

[GLENNSPARK]

Ze was 0.29 Ohms. Supply neutral has 10mm earth cable running to MET.

Would that be a 10mm earth from the neutral-earth link in the cutout?....

 

[scary cakes]

Yes 10mm earth from neutral-earth link in the cutout

 

[Knobhead]

We may be at cross-purposes here. I was referring to the earth return for the welding current to the set. Nothing to do with earthing of the supply or the kit in general. If the welding set return isn’t connected directly to the piece being welded the current will find it’s way back somehow.

To be honest if you don’t know about welding plant, find the quickest way out. Like Glenn I’ve seen cables, panels and motor bearings going up in flames due to the welding current.

 

[GLENNSPARK]

Well that would suggest a TN-C-S but you would need confirmation and as you have already said the DNO have no record of such an arrangement it makes you think maybe they have just stabbed that 10mm (which isn`t big enough csa for PME anyway) into the neutral-earth link they have discovered in order to get a better earthing for here....so maybe a sparks has been there before and they have been listening to what he has been on about (haphazard install) and decided to do something about it on the cheap............

 

[GLENNSPARK]

We may be at cross-purposes here. I was referring to the earth return for the welding current to the set. Nothing to do with earthing of the supply or the kit in general. If the welding set return isn’t connected directly to the piece being welded the current will find it’s way back somehow.

To be honest if you don’t know about welding plant, find the quickest way out. Like Glenn I’ve seen cables, panels and motor bearings going up in flames due to the welding current.

same here tony....even a dodgy clamp when you crank up the current (for thicker materials) will run hot enough to melt solder.....easily.........

 

[johnboy6083]

if i were to PIR this job, going on what youve said, and the other lads experience id be going for 100% sampling.

 

[GLENNSPARK]

if i were to PIR this job, going on what youve said, and the other lads experience id be going for 100% sampling.

1s and 2s galore...lol.......