Another electrics question...dodgy workshop supply

[mattg]

Hello
I wondered if anyone can advise on a little problem we have in our workshop:

Somtimes, particularly in damp weather, you can get a bit of a shock off some metal bodied stuff- pillar drill, welder etc. I did some investigation- used a FLuke socket tester (one of the wee things you stick in the socket and read the LED's). It beeps away indicating that live and neutral have been swapped around.

First off, is this the reason for the shocks, and if so why?

Second, the landlord got an electrician in a while back who appeared to do nothing. If its as simple as just swapping the live and neutral over a the fuse box, is this a sensible thing to do, or are there potential knock on effects?

Third, are there more dangerous things that will happen if its left- like mcb's or rcd's not operating as intended?

Any advice appreciated.
Cheers
matt

 

[piman]

Hello Mattg,

swopped polarity won't be the cause of your shocks, if the metal work is live the earthing is not right.

The main reason for polarity being correct is that a lot of equipment switches the live. If the polarity is swapped , the machine will still switch off as normal but it will still be live internally. Yes, to answer your question it should be corrected but you need to check that all sub circuits are affected as it may be just the sockets? It won't affect the MCB's operation and probably not the RCD either. If you have RCD's, they should be tripping with the leakage to earth?

I suggest that a thorough check is carried out as it sounds substandard at present?

Alec

 

[mattg]

Thanks for the reply
Ill check the other circuits polarity. As an aside, how does the little fluke plug in thing know what is live and what is neutral?

Ill also check the earth continuity and generally have a little explore of the circuits. The RCD has never tripped, but from now on il use a plug in one on on the pillar drill etc and see if it goes.

You're right it is substandard...but you know what its like trying to get a landlord to do anything!

Thanks again
matt

 

[piman]

Hello Matt,

not sure how your tester works but using a meter it is a simple matter to compare voltage to earth (With reversed polarity, neutral will have 240v and neutral almost zero). I assume it works on that principle?

Alec

 

[rtbcomp]

Fixing the earth will divert fault current to ground, you also need to find where this current is actually coming from.

Are all sockets showing live & neutral reversed? The tester will probably rely on a good earth to recognise crossed live/neutral so you may be getting a false reading with a faulty earth.

Try one of the neon screwdriver testers, they rely on the capacitance to ground through your body.

 

[mattg]

Yes all sockets show live and neutral reversed.

Alec said-
'With reversed polarity, neutral will have 240v and neutral almost zero'

So in a correct system neutral to earth should be about zero volts, and earth to live should be 240V, I didnt quite understand what you meant.

Ill check this with a meter later. Yeah thats a good point rtbcomp- I was just blindly blaming the problems on the polarity, and blindly trusting that the fluke was correct. Always good to engage the brain...

matt

 

[tigler]

Suggest to you landlord that he may be in quite a difficult situation if someone is killed by a defective electrical installation !

 

[piman]

Hello Matt,

sorry, I mis-typed it, the second neutral, as you worked out, should be live to earth will have near zero.

Alec

 

[brightspark]

as said above get it checked out sort the crossed polarity out and also check the earths feeding all the circuits back at source. what u will find is if the earth is broken u will get aprox 50 volts through residual current down to earth on all metalwork and apliances enough to lift u and make u jump if there was a full 240v fault developed to earth it wouldnt blow the fuse and then would be real dangerous .test the eath back at source if its ok work out over down line to establish where the break is u need to know if its overhead suply using an rcd and an earth rod or if underground with electricity board earth . if metal building with water supply water pipes and metal framework of building need to be bonded .a good insulation test is in order as well

 

[gridley51]

If your installation is a PME type,the neutral and earth are connected together at your meter.Be very careful of swapping polarity if you`re not 100% sure of what you`re doing.
Mark.

 

[mattg]

thanks for all the advice!
I tested and in fact rtmcomp might be right- the plug polarity seems fine when tested with a meter- earth to neutral = 0, earth to live = 240ish.

Hmmm might be time to put some pressure on the landlord.

It sounds like from what brightspark said we have an earth problem...and come to think of it, the shocks feel familiar....once was fixing an off grid system where neutral was floating at about 50V, great fun.

 

[piman]

Hello Matt,

as a matter of interest, I was visiting a colleague at Wylfa Power Station switching yard. He put a neon screwdriver on the earth tape and it lit up.

Alec

 

[gridley51]

Hello Matt,

as a matter of interest, I was visiting a colleague at Wylfa Power Station switching yard. He put a neon screwdriver on the earth tape and it lit up.

Alec

These neon screwdrivers are ultra unreliable for testing.The only good thing about them is if you heed the warning they give you should never be electrocuted.D:
They pick up anything and are extremely misleading.
Mark.

 

[piman]

Hello Mark,

well my colleague certainly never used it for checking voltage at supergrid levels :-)

Alec

 

[Robotstar5]

well my colleague certainly never used it for checking voltage at supergrid levels :-)

Unlike a plonker at the foundry where I did my apprenticeship - tried to test 11Kv to earth with the old Martindales! - all that was left was the insulated probes and he spent a few weeks in hospital with serious burns...

 

[gridley51]

When I was a young apprentice fitter in the early sixties I was in a mill with a tradesman who went to check if something was live with the sparky`s Avo.Being a bit short of hands he stuck a lead in his mouth while he tried to clip the other one on....
The sparky appeared screaming STOP!!!!
I spend over sixty percent of my time in panels with a meter in my hand and often remember that. :-)

 

[rtbcomp]

A boss of mine (with a degree, and in charge of a computer repair shop) nearly tested an RCD with his fingers accross live & neutral. Against my better judgement I managed to stop him in time.

BTW if you see someone going to touch something live don't grab hold of them!

A good tip for working on live stuff is to keep one hand in your pocket.

As for neon testers, if it lights up you'll get a shock, if it doesn't you may not.

 

[Robotstar5]

A good tip for working on live stuff is to keep one hand in your pocket.

Which means you have to hold the other tester probe with your teeth?

I was told something similar, always keep one hand outside a live panel when working on it.

 

[madkayaker]

touch with back of hand first then if it is live you only slap yourself in face (not on high voltage DC where you will stick to it and go all crispy)

 

[brightspark]

better still use a set of test probes and put them on your proving unit first neon testers and volt sticks are half reasonable but definately not to be relied upon . the buisness of wetting of ones finger or otherwise and having a touch is a fools game ive nearly snuffed it twice by other peoples mistakes and have learned from it