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Re: OT what is that vibrating sensation you get when you lightly touch the metal on a mains appliance? |
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| message from Pete C on 19 May 2004 |
Hi,
Sound like the appliance needs an insulation test, to check there is
no leakage to earth and that the earth is connected (AFIAK).
If this passes then it could be an earthing fault with the supply.
cheers,
Pete,
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| Pete C replied to Pete C on 23 May 2004 |
Hi,
You really need to prove the appliance earth and the supply earth are
OK.
cheers,
Pete.
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| Lobster replied to Pete C on 19 May 2004 |
Several people have suggested something along the above lines -
assuming the appliance checks out OK, then what tests should be
carried out to check house earthing in general and/or isolate any
fault?
Thanks
David (who has the same problem has the OP - see other post)
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| Lurch replied to Lobster on 20 May 2004 |
Basically, a full periodic installation test. Then you'll have all
earth paths, external and internal, tested and verified. You could
just check the Ze, the Zs on the affected circuit and the R1\R2 and an
insulation test. I'd have a full test though, for what they cost.
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| N. Thornton replied to Lurch on 23 May 2004 |
Now the OP has told us its a 1950s install, with MCBs (retrofitted??).
If it really is 50s it will inevitably fail on a wide range of counts.
Regards, NT
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| Lurch replied to N. Thornton on 23 May 2004 |
Yes, I've just noticed that. I can see it either being a PITA to find the actual
fault that's causing this problem, in a sort the wheat from the chaff stylee.
Either that or just go straight for a rewire! Either way, I'm glad he doesn't
live near me!
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| N. Thornton replied to Lurch on 23 May 2004 |
I have to say I have my reservations about it being 1950s with MCBs
though :) Possible I suppose, but my gut feeling is 'are you sure?' I
can just imagine an MCB feeding the electrode heater that supplies the
bath :)
Regards, NT
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| Pete C replied to Lobster on 20 May 2004 |
Hi,
First it would be worth checking if their is a connection between the
metal case of the appliance and the earth pin on the plug, this can be
done with a continuity test on a cheap DMM.
If that's OK, check the connection between the earth on the socket and
the earth on another socket and a metal water pipe that goes down to
ground level.
A full insulation test is not really a DIY job unless you have the
right equipment, but insulation failure is pretty rare AFAIK.
cheers,
Pete.
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| Dave Plowman replied to Lobster on 20 May 2004 |
The correct way is with a purpose made meter. It dumps a large voltage
pulse to earth and measures the resistance by checking what current flows
in that split second. But they're expensive, so not really worth it for a
DIY toolbox. So most would get an electrician in to do it for them.
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| N. Thornton replied to Dave Plowman on 20 May 2004 |
Have come across buildings like this. The mains earth isnt always at
earth potential. On a ground-rod earthed system, persistent leakage
can set up an ac potential on the earth wiring. If there is no RCD, as
is the case with a lot of such installs, particularly older ones,
generally nothing will trip, and you may notice that earth isnt quite
earth. There are plenty of installs like this around. Most are
protected by v-ELCBs, which will not trip on these kind of minor
faults.
Is it dangerous? No, although it has to be a risk factor to more than
a zero extent, since it indicates there is leakage to earth somewhere,
plus less than perfect earthing, plus no RCD. Nonetheless the risk
factor would normally be very small.
OTOH it could be something more problematic, which might indicate a
greater risk. We cant know from here.
You could work out what your installation setup is by looking at the
CU and asking, maybe you could locate leaky appliances with a very
simple homemade tester, applying mains live to appliance L and N,
earthing E, and a meter in the live to measure i flow. However you
should only use mains voltage appliance tests if youre competent to do
so safely: one must appreciate and manage the risks.
Some qs to get you started:
Do you have wire fuses or switchable trips?
Do you live in town or country?
Do you know when the house was last rewired?
Do you know if you ahve an earth rod?
It might be necessary to take matters further, though usually not.
Calling an electrician for a whole house install and appliance test
seems rushing it to me, but for all we know it could possibly be very
necessary. Only you can decide which course of action to take.
Regards, NT
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| N. Thornton replied to N. Thornton on 23 May 2004 |
In that case something may be wrong. You shouldnt get this on a town
no earth rod install.
Regards, NT
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