Welders Yard, major problems!

[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.

 

[Sidewinder]

Any pics?

Welcome to the forum by the way!

Not sure of some of the terms you are using as they don't quite comply with those in 7671, so I will have to guess a bit, the written word can be confusing without all the other things that go with a face to face communication.

First thing then is a PIR, possible a few EDN's?

If the EFLZ is the Ra reading then this is unacceptable, if this is a Ze then again unacceptable unless the install is on a 10mA RCD.

The DNO are legally obliged under ESQCR to inform you of the supply type FOC, end of download a copy of the regs and quote the reg no at them, no compliance then OFGEM here we come (well I think it's OFGEM, they may have changed their name again this month).

What was the Zs at the pillar drill?

What welding sets are they using, make, model, and design/build standards please? (This IS relevant!)

How are they configuring their welding return leads?

I think this will do as a start...

 

[NozSpark]

Your DNO have to provide this information under ESQCR

So just ask them again,,,

However if the decide that the installation is dangerous from what they can see, the can isolate the supply

 

[scary cakes]

Sorry if my terminology is wrong. PIR I mean to be a Periodic Inspection Report. Don't know what EDN'S are, forgive my ignorance.

I do not know with any certainty the type of earthing supply, the Ze at origin is 0.29Ohms and the highest Zs i measured was 0.53Ohms at an isolator approx 7-10 mtrs from head.

I feel I should know this abbreviation but DNO? and ESQXR, FOC?? I will look this up asap.

No idea on welding sets, type, leads configuration etc..

Will find out tomorrow. Can you tell me why so relevant?

 

[NozSpark]

Just thinking about it, it sounds like they aren't using a return to the welding set and it's using any which way it can?

If you see an acronym you are uncertain of and it's underlined you can hover your mouse pointer over it and it'll give you a meaning

ESQXR is probably a typo,,, Sidey probably mean't ESQCR?

 

[Sidewinder]

There are standards for welding sets that provide mains isolation so knowing this would give me an idea if you had welding set faults or not.

 

[NozSpark]

There are standards for welding sets that provide mains isolation so knowing this would give me an idea if you had welding set faults or not.

Yes, there is that:O

 

[Doc Hudson]

Welcome to the forum. I imagine most electricians with a bit of initiative would be quite clear what is the best course of action if they know its a "Very old installation in poor condition, never had a PIR and no sign of any maintenance". It sounds to me as though it needs a comprehensive PIR, a call to the DNO for them to confirm what they consider the supply characteristic should be. Maybe you could ask for someone to attend on site and assist you with working through this problem. Are you a recently qualified electrician?

Doc H.

 

[scary cakes]

No not recently qualified, unless 7 years in recent. I primarily do PIRs of commercial properties, never before a welders yard. Its obvious it needs a comprehensive PIR which I will be doing tomorrow, I have already called the DNO today and they are unable to confitm the supply type. I would welcome some assistance but in reality it boils down to money and its not my choice, this job is a present from my company and its between them and the client as to the level of manpower.

 

[apprentice87]

Hi all,

Now, i am no electrical expert, very far from it!!! But i might just be able to point you in the right direction with this!!!!!!

Let me guess...The welding set they are using is ANCIENT

In any "not ancient" welding set, at least ones built to proper standards, the secondary windings are obviously separated from the primary ones, and they are ALSO INSULATED FROM THE FRAME OF THE WELDER.

At one time, many years ago, some genius decided that, in the interests of safety, the secondary windings would be connected to earth, internally in the set itself, presumably to try to stop mains voltage appearing on the secondary side in the event of an insulation failure in the welding transformer.

Now for some welding terminology;

1,The "welding cable" is the one connected to the electrode.

2, The "welding return cable" is the one that goes from the set and clips onto the job to complete the welding circuit. IT IS NOT THE "EARTH CABLE"

3, The "welding earth" cable, goes from the job to the metal frame of the building [or wherever else you can earth it] Idea being to prevent there being a PD between the "job" and surrounding metalwork. Also, say you squashed a mains extension lead on the job, it would obviously raise the entire job to mains voltage, not very good!!!!

Now here is the first problem....... Remember now, one end of the secondary windings is earthed in the set. The job is earthed too.

Now, what happens if the "welding return" lead falls off????? The welding circuit is now completed by the welding cable with the electrode in the end, and the current flows through the welding job, down the "welding earth" through whatever the welding earth is earthed to, down to your MET [via bonding] and back along the various CPC's till it gets back to the earthed secondary of the set.

As a result, when the "welding return lead" falls off, Mr welder has no idea, and carrys on welding. Meanwhile the hundreds of amps of welding current cooks all the CPC's etc that it flows along..

Result is that very soon, the earthing system is destroyed, so that when Mr Pillar drill then develops an earth fault, the OCPD will not operate, as the earthing system has been destroyed....

So, how do you test for all this???

Well, the prime test is to earth the job to the frame of the shed with the "welding earth" disconnect the welding return cable, and then see if Mr welder can strike an arc, if he can, then there is a serious problem with his welding set.....

Also, you can physically check whether there is any internal connection between the secondary windings of the set and the earthed frame of the set.

I should add, that at one time, it was a condition imposed by the "british standards" for welding sets, that the secondaries WERE earthed. Then, they changed their minds, and now, the secondaries MUST NOT be earthed for the reasons i have given.

Any set with an earthed secondary is obsolete, illegal, and must be scrapped.......

Current thinking is apparently, NOT to use a "welding earth" at all. This [in my opinion] is another idea dreamt up by numpties. What happens if Fred is using his magnet drill and it develops a fault and makes the entire job "live"... Fred does not know, because he is sitting on the job. You walk past and lean on it and get electrocuted.....

So, finally, why is the portable 13A "pistol drill" cooking???? because the set secondary windings are earthed to the frame of the set, so the drill and it's lead are now forming, [especially if they have not got a proper "welding earth"] part of the welding circuit, carrying maybe 400 Amps....

So first off, see if the set is an ancient british one, or one made to funny foreign standards with an earthed [highly illegal] secondary and also see if the set works under their normal working conditions [obviously not just a bit of metal on the floor] with the "welding return lead" disconnected....

Hope this helps!!!!

john

 

[Sidewinder]

Well I guess my oil cooled Oxford is out then, however, there is NO WAY is this going ANYWHERE!

 

[Evans Electric]

John, I feel that your Forum name causes some confusion , unless you've been an "Apprentice" for 20 years

 

[scary cakes]

Thanks apprentice87 and everyone else. I am digesting your comments and will speak with my manager to discuss the best thing to do next. I really would like to resolve these problems but I am not experienced with welding sets.

 

[apprentice87]

Hi Paul,

Yes....I tried an oxford up here a few months ago....To be honest i thought it was absolutely LOVELY to weld with [and believe me i have used a few!!]

Just don't leave your "Class one" drill resting on the job whilst welding!!!!!!

john....

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Hi Deke,

I will take that as a compliment!!! Thank you very much!!!

Believe me, i am not even an apprentice, only an interested amateur....I have not even been brave enough to go in for 2382 yet.... But i will!!! [sometime...!!!!]

john....

 

[apprentice87]

Hi Canoe,

Thanks for that!!!! I just wish i had a merest fraction of the knowledge that you guys possess.....

I do try though....

john.....

 

[apprentice87]

Hi all,

I do not know what to say.... but thank you so much.....

I really do try to understand the principles behind it all, i really do...

Owing to the other problems i have, [Paul and Canoe understand...] i wonder if i will ever be able to actually DO any qualifications, as apparently you have to clock up so many "guided hours" in a college. This would not be possible for me.......

I would really like to though...... Not saying i would pass anything mind you!! but i would like to have a go if i could.....

Thanks everyone....

john

 

[Sidewinder]

john,

I think you could clock up the hours with the correct college or training provider, as you say I do know your problems a little.

You are very committed and I believe capable of learning, don't let others tell you that you are not, nor let other things hold you back.

 

[Sidewinder]

Canoe,

He's about 60 miles East of me down the M4.

A bit far to come to the trg ctr I work with?

 

[apprentice87]

Hi Paul,

Perhaps not....

john...

 

[SLIPSHOD & SLAPDASH]

There was an identical thread to this on the IET website some months back, i've had a look but cant find it.

This same type of problem can happen on any age and type of welding kit. Last year i wired a home workshop for a friend. He asked me to pop round and explain a problem he had, he was Mig welding a car and not getting good results. He then noticed he had forgotten to clamp the return lead to the chassis. He then noticed a 240 volt metal cased lead light (which was switched off) and was laying on the engine had had its lead completely melted, no breakers or the RCD had tripped.

The welding kit had used the earth of the lead light, cpc of the socket circuit back to the board and down a different cpc to the socket where the welder was plugged to complete its ground circuit. There was no imbalance of current across the RCD & no overload of the breaker so neither tripped. The fault had however, as well as ruining the lead lamp cooked the 1.5 cpc from the local socket circuit the light was plugged into (which was on a 20A b type mcb)

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Found this text at the IET,

This is something that rears it's ugly head now & then.

In the average welding shop, the earth clamps tend to be tatty, bad or loose connections from the earth lead to the clamp.

In a recent PIR, a distribution board was found to have the earths within the board melted on circuits feeding several outside lights & some metal 13a sockets, all wired in swa. There were obvious signs of the panel metalwork overheating where the swa's were glanded.

This board did not feed welder outlets, but all the lights & sockets were mounted on the metal structure.

Within the shop, metal beams were cast into the concrete floor, flush with the surface, these were used to 'tack' larger welding jobs onto while they were being constructed, these were bolted to the structure columns.

Inspection of several welder earth clamps found overheated cable ends where the connection to the clamp was made.

Due to these bad clamp connections, the preferential return path for the welder current was via the building structure, the various lights & sockets and the earths from them to the DB.

There was correct bonding from the met to the structure, I can only surmise the lower impedance path for the welding return currents was via the lights & sockets. All the swa's feeding these were damaged along the entire length.

The structure bonding was uprated well in excess of that required, new earth clamps & crimped lugs were fitted to all the welders used, and a management instruction to make sure all welder earth clamps were properly secured & maintained.

Since then there has been no more problems.

Tig welders are a special case, as on most of them, RF is used to start the arc, the preferential earth path for this may not be what you expect it would be at 50Hz, bigger Tig welders have some inductance in the supply connections to keep this RF out of the supply conductors.