High Zs for circuit with metal conduit earth
- Thread starter endecotp
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I suspect the r2 value is the dubious one, and the Zs is accurate.
Interesting idea, but I think there were similar numbers (i.e. > 1 ohm) on a couple of sockets.
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I had a call to a 60's house a while back. There was no earth on any of the sockets in the lounge.
Fearing a problem with the supply, I started to think I needed to settle down to some fault-finding.
Before I did, I had an idea and checked the Zs from the back of the socket. It was more than fine!
The old 60's sockets were worn and sloppy and were not making contact with the earth pins of the plugs.
Weird that it was every single socket in the room, though!
The rest of the house had more modern sockets, but the lounge must have been forgotten or left as it was OK at the time.
Fearing a problem with the supply, I started to think I needed to settle down to some fault-finding.
Before I did, I had an idea and checked the Zs from the back of the socket. It was more than fine!
The old 60's sockets were worn and sloppy and were not making contact with the earth pins of the plugs.
Weird that it was every single socket in the room, though!
The rest of the house had more modern sockets, but the lounge must have been forgotten or left as it was OK at the time.
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Had they been using those silly socket covers?
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Can't remember...
In this case they're modern sockets, one of them fitted by me recently.
Any thoughts anyone about whether this is actually a problem or not?
Can you not check r2 ?
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Who?
How do I messure r2 in a conduit installation? I think I have to unscrew conduit fittings, don't I?
You can't.
R2, then.
Well, the Zs of 1.31 is just ok for a B32 without the temperature correction.
However, we have these figures:
r1 = 0.50
rn = 0.51
r2 = 0.68
(R1+R2) = 0.68
Zs = 1.31
Ze = 0.2
They can't all be correct.
See what R2 is first.
However, we have these figures:
r1 = 0.50
rn = 0.51
r2 = 0.68
(R1+R2) = 0.68
Zs = 1.31
Ze = 0.2
They can't all be correct.
See what R2 is first.
I have improvised a way of measuring R2, and a value of around 0.6 ohms is plausible.
(Method: two long wires from earth point near CU, two wires from earth of socket; measure DC volts between one pair, supply DC current to other pair using a variable-current-limit bench power supply.)
(Method: two long wires from earth point near CU, two wires from earth of socket; measure DC volts between one pair, supply DC current to other pair using a variable-current-limit bench power supply.)
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