Earth cable testing with some positive signs??

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wombweller

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Hi

I've just been testing and old Electric double dial railway station clock to make sure it's safe.

The surround for the clock is metal of some description it is covered with a thick layer of paint.I plugged it in to the 240v mains to see if the internal light works and while doing this I decided to put my electrical test screwdriver on the Earth contact that's connected to the metal housing.I found that when I did this the light within the screwdriver glowed red.I stripped back everything as I assumed I had something leaking from the positive wire.I ended up taking the power lead right out as I could not find any bare wires.

I connected a 3way terminal block to the cable and then tested the earth again, it once again made the test light glow but not a bright glow like the positive wire??

I am baffled and it makes me a little worried as it seems the metal case of the clock was live!!

What going on as I can't find any leakages from the positive side????? and why does it not trip the fuse box?
 
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Do you have DC 240V mains?

If they are AC, which are you calling "positive" and which "negative"?
 
Hi

The lead is connected via a 3 pin plug (UK.) to 240v AC. Brown(live),,Blue(Neutral) and green/yellow is (negative Earth). It's the Earth cable that is making the test screw driver light up, it's not as bright as when testing the live wire but it's a glow.

Colin55, I'm not sure what you are saying.

Cheers
 
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colin55 said:
The earth lead is not connected and is picking up hum from the active.
Click to expand...

Are you suggesting that the Earthing cable is not connected to earth at any point and so is picking up something from the live?

How do I test to make sure my Garage is Earthed accordingly?

Cheers
 
colin55 said:
Try shorting the active to earth and see if the circuit breaker trips.
Click to expand...

Are you mad!

If the earth is connected, there will be one hell of a flash and a bang!
If the earth is high resistance, it may cause big problems elsewhere.

Wombwell, have you tried the earth contact in the power socket in your garage using the neon screwdriver?
How did that test out?
If it glows, you have a problem.

Just a note on terminology, in a mains cable, the three wire are Line (live), Neutral and Earth. Never positive and negative.

JimB
 
If you don't want to short the active to earth, place a 2kw radiator between active and earth and see if it heats up.
 
Hi All

I tested the wall socket Earth and that tested OK!! I test another and again OK!!
I now think the problem area is my extension reel, not sure whats going on with it but when I plug in to the mains wall socket direct the Earth issue is fine.

Why use a Tufnol insulator strip to protect the metal case from the terminal block when steel screws are used to connect the block to the case? (old hard plastic terminal block not new)


Cheers!!
 

hi Mark,
As a general guide line I would say connect ALL mains powered projects to the mains via a RCD plug.

I would replace the old mains connector blocks, the fixing screws for the TB are insulated from the eletrical terminals of the block.[ also any rubber insulated wires]

NEVER use over diameter sized screws for fixing the TB down.

The mains extension cable should be easy to check out use a DVM [meter] set to ohms.
All 3 wires Live, Neutral and Earth should be continuous from one end of the cable to the other [Very Low resistance ] and high resistance between the 3 wires.

If you are using an extension cable check the plug and socket terminal screws for tightness and the wires are held firmly in place.
 
Back decades ago the standard test was to place a 100W bulb between live and earth - that met the requirements of the time, and was well before the use of earth leakage trips.
 
Hi

What worries me now is my Garage Earth line as if my extension reel is faulty then why didn't the fuse box trip, normally a light blowing trips the box.

How can I simply test my Earth cable?

Cheers
 
wombweller said:
Hi

What worries me now is my Garage Earth line as if my extension reel is faulty then why didn't the fuse box trip, normally a light blowing trips the box.

How can I simply test my Earth cable?

Cheers
Click to expand...

hi Mark,
Like I said, use an ohm meter, measure from one end of the green/yellow EARTH wire to the other end.. it should be almost zero ohms..

Is that what you mean.?
 
wombweller said:
Hi

What worries me now is my Garage Earth line as if my extension reel is faulty then why didn't the fuse box trip, normally a light blowing trips the box.
Click to expand...

The earth wire breaking, or any other wire breaking for that matter, wouldn't blow a trip.
 
ericgibbs said:
hi Mark,
Like I said, use an ohm meter, measure from one end of the green/yellow EARTH wire to the other end.. it should be almost zero ohms..

Is that what you mean.?
Click to expand...

Hi Eric

I was assuming that because the Earth cable had some signs of live running though it then my fuse box would trip out, not talking about the reel but the main Earth!!

I understand what your saying about testing the reel.!!
 
Ha!! cheers Nigel. think it's me who would have blown then!! not sure how much Live the Earth had running though it but it didn't look to be the same as Live was with the screwdriver!
Good job I didn't go in gung ho!!!

Cheers
 
Neon screwdrivers should be banned.


Never use a neon test screwdriver to test for the presence of mains voltage.

They aren't safe, there's a chance the current limiting resistor could fail, connecting you directly to the mains power and what's even more dangerous if you're not properly earthed, there might be mains present but the neon won't light leading you to believe the circuit it dead, when it isn't.
 

hi hero,
When I was a young TV service engineer I used a neon screw driver for a number years, it never failed for me and it warned me when I had a live TV or Radio chassis.
I still use a neon screwdriver to check before I touch any any chassis that I am unsure about.

If you take care of your neon screwdriver it a safe piece of kit
 

Gibbs in his younger days...

**broken link removed**
 
hi Mike,
I was NEVER that young or relaxed.

That image would make a nice avator..
 
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