earth loop impedence values
- Thread starter neilyboy1961
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You don't. It is dangerous. Only a competent person, i.e. an Electrician can do it.
It's not dangerous when it's plugged in via a socket (like the gas man did 
)
To the OP - did the guy find >200ohm at all the sockets he tested on?
Were they all part of the same circuit (on the same MCB) or on different socket circuits?
The >200 reading means there is a bad earth at the points he tested at. This could mean the suppliers earth is bad, or the earth wires for the circuits(s) tested are bad.
If the same reading on different circuits then it is likely it is a problem with the suppliers earth, especially if the tested circuits were rings as you need 2 faults/loose wires to break the earth completely in a ring.
)To the OP - did the guy find >200ohm at all the sockets he tested on?
Were they all part of the same circuit (on the same MCB) or on different socket circuits?
The >200 reading means there is a bad earth at the points he tested at. This could mean the suppliers earth is bad, or the earth wires for the circuits(s) tested are bad.
If the same reading on different circuits then it is likely it is a problem with the suppliers earth, especially if the tested circuits were rings as you need 2 faults/loose wires to break the earth completely in a ring.
How do you conduct an external earth fault loop impedance test via a socket outlet?
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It's not dangerous when it's plugged in via a socket (like the gas man did
To the OP - did the guy find >200ohm at all the sockets he tested on?
Were they all part of the same circuit (on the same MCB) or on different socket circuits?
The >200 reading means there is a bad earth at the points he tested at. This could mean the suppliers earth is bad, or the earth wires for the circuits(s) tested are bad.
If the same reading on different circuits then it is likely it is a problem with the suppliers earth, especially if the tested circuits were rings as you need 2 faults/loose wires to break the earth completely in a ring.
He only tested 1 socket,and using his plug in meter what reading should it be ?
Oops missed that, apologies. Though it was Zs for some reason
Neily - a normal reading for TNS (or TNCS) would be under 1.2 ohms
Hey, who knows, perhaps his meter was faulty, I must admit, it seems a bit crazy to have a gas man inspect your electrical installation, would you want an electrician testing your gas install??
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Ze is the earth loop impedance where the power comes into the house. There are three methods to find it out.
Inquiry which means you phone the supply company (Not billing agent) and ask them what it is and they are duty bound to tell you if it is a earth provided by them. This is rather useless in your case as we are trying to fault find and we know the supply company will quote 0.35 for a TN-C-S and 0.8 for a TN-S earth system.
Second is a very special earth meter used with earth rods. Again forget that as from what you now say seems unlikely you have a TT system.
Third is with an Earth Loop impedance meter.
click on picture to see advert but as you can see around the £300 mark. These meters can produce dangerous voltages and as a result not really the tool for the DIY'er to use.
The normal procedure would be first to check Ze this is the value as it comes into the house then check Zs this is the value at the socket or other outlet.
If we assume that the supply to the house is 0.35 if we get a reading of >200 at a socket we would assume some where the earth wire has become disconnected. We would switch off the mains supply and then remove one socket. We would hope part of ring main and we should see two wires in each hole and we should be able to part each pair and measure continuity between each pair of wires. This proves it is a ring. To lose the earth both earth wires would have to become disconnected and so likely we would find a broken ring.
However if we didn't we would then look in the consumer unit although the whole test could be done from consumer unit often it is hard to trace wires.
The first method is stab in the dark at where one thinks the fault may lie. We ask the occupier if any work has been done etc. And try to guess where the fault may be. If this fails it is a step by step which can take a long time.
It is unusually to have lost the earth on a ring main as by very nature there are two independent supplies and in the past when on a ring main I have had a reading >200 it has been traced to a faulty ELI meter. The normal is to go home and re-test ones meter on a known socket and see if the meter reads the same as normal. Losing ELI at whole house does happen but even then an electrician would be able to test his meter by using the neutral supply with wandering leads so an electrician would be sure it was really a lost earth and not a faulty meter.
At the price involved to get your own meter even to hire it does not make sense to DIY. Although the LED go - no go type tester will high light there is likely a fault they do not really replace the meter giving values and although as already shown you could buy one of these cheap boxes as used by gas man I do think you would be wasting your money.
Inquiry which means you phone the supply company (Not billing agent) and ask them what it is and they are duty bound to tell you if it is a earth provided by them. This is rather useless in your case as we are trying to fault find and we know the supply company will quote 0.35 for a TN-C-S and 0.8 for a TN-S earth system.
Second is a very special earth meter used with earth rods. Again forget that as from what you now say seems unlikely you have a TT system.
Third is with an Earth Loop impedance meter.
click on picture to see advert but as you can see around the £300 mark. These meters can produce dangerous voltages and as a result not really the tool for the DIY'er to use. The normal procedure would be first to check Ze this is the value as it comes into the house then check Zs this is the value at the socket or other outlet.
If we assume that the supply to the house is 0.35 if we get a reading of >200 at a socket we would assume some where the earth wire has become disconnected. We would switch off the mains supply and then remove one socket. We would hope part of ring main and we should see two wires in each hole and we should be able to part each pair and measure continuity between each pair of wires. This proves it is a ring. To lose the earth both earth wires would have to become disconnected and so likely we would find a broken ring.
However if we didn't we would then look in the consumer unit although the whole test could be done from consumer unit often it is hard to trace wires.
The first method is stab in the dark at where one thinks the fault may lie. We ask the occupier if any work has been done etc. And try to guess where the fault may be. If this fails it is a step by step which can take a long time.
It is unusually to have lost the earth on a ring main as by very nature there are two independent supplies and in the past when on a ring main I have had a reading >200 it has been traced to a faulty ELI meter. The normal is to go home and re-test ones meter on a known socket and see if the meter reads the same as normal. Losing ELI at whole house does happen but even then an electrician would be able to test his meter by using the neutral supply with wandering leads so an electrician would be sure it was really a lost earth and not a faulty meter.
At the price involved to get your own meter even to hire it does not make sense to DIY. Although the LED go - no go type tester will high light there is likely a fault they do not really replace the meter giving values and although as already shown you could buy one of these cheap boxes as used by gas man I do think you would be wasting your money.
Or check Zs, and if not right check R1+R2 at the CU....?
And with Zs.
But if you've got a 200+Ω Zs, and then your R1+R2 comes in at 0.2, you'd probably be more correct to assume a high Ze than misleading parallel paths....
But if you've got a 200+Ω Zs, and then your R1+R2 comes in at 0.2, you'd probably be more correct to assume a high Ze than misleading parallel paths....
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I had returned to page through email link and I missed the bit were he only tested one socket.
In which case it could be as simple as earth wire fallen off behind just that one socket. And if it was a spur same could be true on the socket supplied from.
Although the links show a tester far cheaper than I ever expected to see at £60 can't really see the point in buying one for you as even if you test the rest of the sockets you don't know how to correct the faults if you find any so rather pointless.
He has identified there is a problem. And so really the only way is to get some one able to not only test but able to correct the problem.
In which case it could be as simple as earth wire fallen off behind just that one socket. And if it was a spur same could be true on the socket supplied from.
Although the links show a tester far cheaper than I ever expected to see at £60 can't really see the point in buying one for you as even if you test the rest of the sockets you don't know how to correct the faults if you find any so rather pointless.
He has identified there is a problem. And so really the only way is to get some one able to not only test but able to correct the problem.
The supply voltage doesn't make any difference, the calculation is on a maximum permissable touch voltage of 50v hence the max Zs for a 100mA RCD is 50v/0.1A=500 ohms
I'll 2nd the need to contact a competent electrician.
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