earth loop impedance
- Thread starter oddball01
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could be any number of reasons..
cable size too small, cable run too long, lose or burnt connections on live or earth, broken leg on a ring etc...
could also be a socket fed of a fused spur from a ring with the fuse raising the live resistance...
disconnect from board and check circuit continuity and compare values..
earth value should be 3/5ths ( ration of 1.5 to 2.5 ) the value of the live and neutral.
cable size too small, cable run too long, lose or burnt connections on live or earth, broken leg on a ring etc...
could also be a socket fed of a fused spur from a ring with the fuse raising the live resistance...
disconnect from board and check circuit continuity and compare values..
earth value should be 3/5ths ( ration of 1.5 to 2.5 ) the value of the live and neutral.
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Chivers7 said:
Yes. Measure the Zs from the terminals behind the socket front.
I had a maintenance call to a house with high Zs on the ring final. The engineer had tested one socket, got a low reading, and tested 3 more, all low. He came to the conclusion that the circuit was down.
I get there and discover the Zs is fine from the socket terminals. All the sockets in that room (60's Volex) were sloppy, causing very poor readings.
yeah that's what i meant.. hadn't had my coffee...
isn't that the point though..
if it's a high reading at the socket front, and the fault is on the appliance then the Zs will still be high back to the breaker causing longer disconnect times?
although theoretically it should take the fuse in the plug first..
if it's good on the terminals but bad on the socket front I would recommend changing the socket outlets to new ones..
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ColJack said:
The Zs in my case wasn't high, it was non-existent.
Should it?
That's what I did...
yes it should..
discrimination..
a fault should take out the first over current device it comes to in a circuit.. otherwise whats's the point having it..?
you don't put 13 amp fuses on a 6 amp mcb do you?
discrimination..
a fault should take out the first over current device it comes to in a circuit.. otherwise whats's the point having it..?
you don't put 13 amp fuses on a 6 amp mcb do you?
A BS1362 fuse will rarely discriminate against an MCB during an earth fault.
Mates he's got high Zs. If its that high the fuse isn't going to blow in the event of an earth fault.
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Taylortwocities said:
That was what I was getting at.
If the loop's that high, nothing's gonna blow, the 1362, the breaker, nowt.
that's what I was getting at too
if the Zs at the terminals is fine, but at the socket front is high because of a worn socket or dodgy switch then the fuse / breaker aint gonna blow fast enough..
if the Zs at the terminals is fine, but at the socket front is high because of a worn socket or dodgy switch then the fuse / breaker aint gonna blow fast enough..
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ColJack said:
Is what you said...
Do I sense a little back pedalling?
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