K
kai
No you can't, as BS7671:2001, states that no switch or similar shall be placed in the Earthing Conductor.
main service earths
- Thread starter keenamateur
- Start date
Sponsored Links
I had read that to mean that multi-pole switches and sockets would be alright, but that the earth pin has to leave last and make contact first.
- I haven't got the regs here but certainly isolators, and, of course plug/socket as means of isolation, working on all 3 poles are common, but no one, as far as I know makes RCDs that do this.
However, in countries like south Africa, where theft of the neutral/earth wire is common (for the copper to be re-sold...) they do use a different type of trip, but I'm not sure what it disconnects.
M.
- I haven't got the regs here but certainly isolators, and, of course plug/socket as means of isolation, working on all 3 poles are common, but no one, as far as I know makes RCDs that do this.
However, in countries like south Africa, where theft of the neutral/earth wire is common (for the copper to be re-sold...) they do use a different type of trip, but I'm not sure what it disconnects.
M.
- Joined
- 30 Aug 2004
- Messages
- 23
- Reaction score
- 0
- Country
I doubt keenamateur expected such a debate!
I,m glad to have stimulated a debate and drawn out the "big guns" on the forum.
There are a lot of knowledgable people out there, and i've learnt alot through this debate, and the answers to my original question
Just to clarify if you run a supply from a PME fed house to ,say, a shed/garage do you use the pme earth or bang in a rod.
It's been talked about before but I'm still unclear
[/quote]
I,m glad to have stimulated a debate and drawn out the "big guns" on the forum.
There are a lot of knowledgable people out there, and i've learnt alot through this debate, and the answers to my original question
Just to clarify if you run a supply from a PME fed house to ,say, a shed/garage do you use the pme earth or bang in a rod.
It's been talked about before but I'm still unclear
[/quote]Sponsored Links
Its interesting how its gone off on a PME tangent this topic.
The majority buildings are underground cable fed, protected by a metallic sheath/armouring, so why not use the TN-S method? and use the supply companys cable armouring.
(with their permission of course!!)???
Use PME ensure that you have sockets protected by a 30ma rcd.
The majority buildings are underground cable fed, protected by a metallic sheath/armouring, so why not use the TN-S method? and use the supply companys cable armouring.
(with their permission of course!!)???
Use PME ensure that you have sockets protected by a 30ma rcd.
Well, tangent or not, the point is that if you don't have a TN-S supply you can't use a "TN-S method" to provide an earth for your outbuilding, with or without permission. The discussion that arose was around the contentious subject of exporting PME earths. I agree that if you have a TN-S supply then use the earth from that.mingmong said:Its interesting how its gone off on a PME tangent this topic.
The majority buildings are underground cable fed, protected by a metallic sheath/armouring, so why not use the TN-S method? and use the supply companys cable armouring.
(with their permission of course!!)???
If what I read somewhere is true, however, I wonder how many people who think they have a TN-S supply actually don't, because the armour of the cable has rotted away.
That will be the same earth loop test needed for the rod, that makes it so difficult to DIY install!
Actually I don't think it is that difficult, to test an earth rod, if you already have mains. For a generator or a substation where there is no pre-existing main supply to work against, so then it is complex, as you do indeed need additional current injection and voltage monitoring electrodes, but if you already have a trusted earth from the main supply, whether PME neutral or TNS, you can either do an live-earth loop measurement with the ordinary high current pulse type meter, or if you don't have one, one could set up a quasi-static test with a transformer and an AC ammeter, and just measure the current flowing to the earth under test, when driven against the test supply with the other limb going to the 'good' existing earth.
As an aside one way that I know at least some Radio Hams have tested their RF earths integrity at low frequency is with a 6.3V heater transformer, and measure the AC milliamps that flow when one side is temporarily connected to mains supply earth, and the other to the antenna earths. Typically a few hundred milliamps will flow. The resistance is then 6.3/I where I is the current measured. To eliminate supply neutral earth currents distorting the reading, the transformer is reversed and the reading repeated. If the results are widely different, then the average value of the two 'I's should be used. The resistance deduced number is slightly pessimistic, as the supply earth impedance is also in the calculations. However, for sensible rod impedances of 10s of ohms to hundreds, that is a small error compared with the effects of the weather !
(Obviously after the test the temporary connections between the two earths and the transformer are removed.)
It would be possible to adapt this technique for home earth spikes, though I think a larger test current would be in order (several times the rating of the RCD ) to make the test more realistic, though nothing beats the proper earth loop tester (but not the 15mA never trip the RCD kind - the test current is really too low to be representative)
regards M.
Actually I don't think it is that difficult, to test an earth rod, if you already have mains. For a generator or a substation where there is no pre-existing main supply to work against, so then it is complex, as you do indeed need additional current injection and voltage monitoring electrodes, but if you already have a trusted earth from the main supply, whether PME neutral or TNS, you can either do an live-earth loop measurement with the ordinary high current pulse type meter, or if you don't have one, one could set up a quasi-static test with a transformer and an AC ammeter, and just measure the current flowing to the earth under test, when driven against the test supply with the other limb going to the 'good' existing earth.
As an aside one way that I know at least some Radio Hams have tested their RF earths integrity at low frequency is with a 6.3V heater transformer, and measure the AC milliamps that flow when one side is temporarily connected to mains supply earth, and the other to the antenna earths. Typically a few hundred milliamps will flow. The resistance is then 6.3/I where I is the current measured. To eliminate supply neutral earth currents distorting the reading, the transformer is reversed and the reading repeated. If the results are widely different, then the average value of the two 'I's should be used. The resistance deduced number is slightly pessimistic, as the supply earth impedance is also in the calculations. However, for sensible rod impedances of 10s of ohms to hundreds, that is a small error compared with the effects of the weather !
(Obviously after the test the temporary connections between the two earths and the transformer are removed.)
It would be possible to adapt this technique for home earth spikes, though I think a larger test current would be in order (several times the rating of the RCD ) to make the test more realistic, though nothing beats the proper earth loop tester (but not the 15mA never trip the RCD kind - the test current is really too low to be representative)
regards M.
As I sit here reading this, I can't help but think that I possibly owe my life to a poor Ze......
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
