mbrooke
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Disregard the first link, the network was determined to be 220/380.
TT earthing... Why?
- Thread starter mbrooke
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Tony S
Senior Member
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The house was on a TT system which I thought is what we set out discussing.
Why do you find it difficult to accept <1ohm is achievable?
This may help you understand how we did the measurements at my house.
http://www.fluke.com/fluke/inen/solutions/earthground/Fall-of-Potential.htm
As I said it was verified by the then electricity board (pre DNO) as a favor to me.
mbrooke
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It is, just comparing systems :angel:
1 ohm is very hard to get in the US, even with 3 ground rods. I mean it is possible, but not in all conditions.
Did the home have RCDs at the time?
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
I did install RCD?s even though in the mid 70?s they were prohibitively expensive and not a requirement only a recommendation under BS7671-14th edition.
Prior to this time many TT installations relied on VOELCB?s (voltage operated). The most unreliable thing you could think of.
Prior to this time many TT installations relied on VOELCB?s (voltage operated). The most unreliable thing you could think of.
mbrooke
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How do VOELCBs work? Any links?
Tony S
Senior Member
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- Resting under the Major Oak UK
I?ve just worked it out, the two Crabtree RCD?s I fitted in 1974 cost ?55 each, in today?s money that would be an eye watering ?554 each! Nowadays it?s a wonder they don?t come free with a pack of breakfast cereal.
No wonder my new wife went mad at me over ?a waste of money!? ?1108 for two black boxes that she could see no reason for.
By the time it came to improving the earth nest from its original single rod she?d got to the ?just let him get on with it? stage.
No wonder my new wife went mad at me over ?a waste of money!? ?1108 for two black boxes that she could see no reason for.
By the time it came to improving the earth nest from its original single rod she?d got to the ?just let him get on with it? stage.
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
I've a drawing of them somewhere on this black hole that pretends to be my computer. I?ll look it out.
It may be tomorrow, its now 05:00 here.
mbrooke
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Fair enough, my computer can be the same. But either way I want to thank you for your knowledge of the subject
Very well informed.
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
VOELCB
Voltage Operated Earth Leakage Circuit Breaker.
For the CB to operate the voltage across the coil needs to reach 50V. All cross bonded exposed metalwork has to reach this level. Take into account possible parallel paths to earth such as gas and water services this is going to require a sizable leakage current.
Houses with no gas service the incoming water pipe could be cut and a section of alkathene pipe inserted so that the VOELCB provides the only path. This brings another problem as the sensing coil could burn out leaving the house with no connection to earth at all.
The earth electrode has to be of a low impedance for the CB to even stand a chance of operating. The electrode has to be as far as possible from other electrodes otherwise a fault in a neighbouring house could cause an imported fault which will trip the CB.
You can imagine just how unreliable and unpopular these things were.
Voltage Operated Earth Leakage Circuit Breaker.
For the CB to operate the voltage across the coil needs to reach 50V. All cross bonded exposed metalwork has to reach this level. Take into account possible parallel paths to earth such as gas and water services this is going to require a sizable leakage current.
Houses with no gas service the incoming water pipe could be cut and a section of alkathene pipe inserted so that the VOELCB provides the only path. This brings another problem as the sensing coil could burn out leaving the house with no connection to earth at all.
The earth electrode has to be of a low impedance for the CB to even stand a chance of operating. The electrode has to be as far as possible from other electrodes otherwise a fault in a neighbouring house could cause an imported fault which will trip the CB.
You can imagine just how unreliable and unpopular these things were.
mbrooke
Batteries Included
- Location
- United States
- Occupation
- Technician
VOELCB
Voltage Operated Earth Leakage Circuit Breaker.
For the CB to operate the voltage across the coil needs to reach 50V. All cross bonded exposed metalwork has to reach this level. Take into account possible parallel paths to earth such as gas and water services this is going to require a sizable leakage current.
Houses with no gas service the incoming water pipe could be cut and a section of alkathene pipe inserted so that the VOELCB provides the only path. This brings another problem as the sensing coil could burn out leaving the house with no connection to earth at all.
The earth electrode has to be of a low impedance for the CB to even stand a chance of operating. The electrode has to be as far as possible from other electrodes otherwise a fault in a neighbouring house could cause an imported fault which will trip the CB.
You can imagine just how unreliable and unpopular these things were.
Things like that make me wonder why TT earthing has ever been considered.:?
Fascinating, stuff though I have to admit.
Thanks!- Status