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clanky

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Hello.
Im an enthusiastic diy'er and whilst finishing off a job that a local sparky came to do, i came across this 'fault' that i find a bit worrying.

My house is split up into to two section with separate consumer boards fed from henly blocks. When i was rerouting the earth cables for an additional supply i got a mild belt off one of them. Long and short of it after some testing, i found there was around 75 ish V present on the earth line. I disconnected everything and carried out an insulation test (500vdc) on the supply cable (16mm SWA - around 12m long) and all tested good except even with everything disconnected, i was still seeing 30v on the earth when live.

This is between the earth on that particular supply cable and the main incoming earth. Im presuming that this is an induced voltage? I know that this wasn't strictly safe as i essentially had a live supply with no cpc but i felt i needed to investigate this problem and i was as careful as can be.

Further testing on all the individual circuits from that board showed a few adding (around 8v) to the overall problem but i eventually traced the main culprits to the washing machine (40+v) and a dryer (15V). Is this normal? Obviously with all the earth lines connected this problem doesnt actually exist as any residual voltages would be 'drained' and would therefore be undetectable under normal circumstances so am i creating a problem where one doesnt actually exist? Currently my main concern is that the washing machine, being a cheap indesit, could be on its way out and would best be changed.
 
I know that this wasn't strictly safe as i essentially had a live supply with no cpc
I think that's your issue.
A lot of appliances leak to earth as a noise suppression measure, this is normal and wouldn't generally be enough to trip an rcd.
However it's very foolish to break an earth connection on a supply that's not otherwise isolated.
Even the gas guys have huge croco clips to connect across any gas pipes they break into in case of differences between the supplierss earth and the gas pipe/local earth.
 
Hello.
Im an enthusiastic diy'er and whilst finishing off a job that a local sparky came to do, i came across this 'fault' that i find a bit worrying.

My house is split up into to two section with separate consumer boards fed from henly blocks. When i was rerouting the earth cables for an additional supply i got a mild belt off one of them. Long and short of it after some testing, i found there was around 75 ish V present on the earth line. I disconnected everything and carried out an insulation test (500vdc) on the supply cable (16mm SWA - around 12m long) and all tested good except even with everything disconnected, i was still seeing 30v on the earth when live.

This is between the earth on that particular supply cable and the main incoming earth. Im presuming that this is an induced voltage? I know that this wasn't strictly safe as i essentially had a live supply with no cpc but i felt i needed to investigate this problem and i was as careful as can be.

Further testing on all the individual circuits from that board showed a few adding (around 8v) to the overall problem but i eventually traced the main culprits to the washing machine (40+v) and a dryer (15V). Is this normal? Obviously with all the earth lines connected this problem doesnt actually exist as any residual voltages would be 'drained' and would therefore be undetectable under normal circumstances so am i creating a problem where one doesnt actually exist? Currently my main concern is that the washing machine, being a cheap indesit, could be on its way out and would best be changed.
What readings did you get on your IR tests?
 
My house is split up into to two section with separate consumer boards fed from henly blocks. When i was rerouting the earth cables for an additional supply i got a mild belt off one of them.
one for those consumers must have been live ,did you not know to isolate the c/u.s before hand .
or did you think ,its ok :eek:
 
Not you John just in general mate, just thought the Ohms law thingy regarding neutrals using parallel paths as returns.
 
What were the IR results?
 
I would be doing basic dead tests ...
.. Not the diy hit and miss.

Why didn't the spark do this?
 
Hi - out of interest, what earthing system is used in this installation? In my view, you've had a "near miss" at 75 V, indicating a fault is present. So please get an experienced Electrician with test equipment to review it on site. Otherwise may think you've "fixed it" but just left a hazard.
 
Just back. In answer to a lot of the posts, yes it wasnt probably the wisest thing to break the earth to a live con board but i did.

Insulation test showed pretty much infinity with cable disconnected at both ends.
 
I don't agree that 75v measured on a high impedence multimeter is a problem in itself. (Aside from the fact that the earth has been disconnected which is a problem)
50v is the limit of touch voltages of supplies of high current, but 75v that causes a tingle could be 1mA or less.
If it's failing ir tests or tripping an RCD, definitely a danger, but if it's just a low current not dangerous as many appliances leak to earth.
Having said all that, to be clear, none of the above detracts from the fact that the supply should be isolated before removing the earth, and the bonding should really be connected at all times especially on a pme system. Oh, and that the op needs someone competent with suitable test equipment
 
Hi - out of interest, what earthing system is used in this installation? In my view, you've had a "near miss" at 75 V, indicating a fault is present. So please get an experienced Electrician with test equipment to review it on site. Otherwise may think you've "fixed it" but just left a hazard.

As per my first post, the fault is with the washing machine and dryer. Both are now unplugged until i can find a reasonable explanation for their behaviour.
 
I don't agree that 75v measured on a high impedence multimeter is a problem in itself. (Aside from the fact that the earth has been disconnected which is a problem)
50v is the limit of touch voltages of supplies of high current, but 75v that causes a tingle could be 1mA or less.
If it's failing ir tests or tripping an RCD, definitely a danger, but if it's just a low current not dangerous as many appliances leak to earth.
Thanks John, i wondered whether this was normal but the fact that indesit always top the tables on fire hazards had me thinking there may be a fault with the machine. For the record, the circuit is on an RCD and has never tripped.
 

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