residual current?

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Many years ago I rewired my own houses and fitted fuse boards etc,so not a complete noob, I have test gear , Working on fitting extra sockets with the ring unpowered I still get minor shocks and tripping out , what is the likely source ? the only thing left would seem to be a leak onto the earth somewhere,
 
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Do you mean you are surprised that the RCD trips when the neutral and CPC are touched together?

I think more specific details are required.
 
...Working on fitting extra sockets with the ring unpowered I still get minor shocks and tripping out , what is the likely source ?
I don't know about the 'minor shocks' (which are obvioulsy potentially worrying), but assuming that you have 'unpowered' the ring by switching a (single-pole) MCB (or removing a fuse), then you would usually get an RCD trip if you allowed neutral and earth to come into contact, even those the circuit was 'unpowered'.

Kind Regards, John
 
Yes even with the circuit isolated via MCB, when CPC (earth) and neutral touch, the RCD will trip. To prevent this you can disconnect the neutral from the neutral busbar.
An understanding of this can be found here:


Although I am concerned that you say that you are getting shocks from an isolated circuit, could you take some voltage readings from this circuit whilst isolated?
Then test with neutral disconnected and then with CPC disconnected.
 
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Powering down and isolation are different. An isolator will disconnect all live wires both line and neutral but a MCB will not normally switch neutral.

Except as required by Regulation 537.1.4, in a TN-S or TN-C-S system the neutral conductor need not be isolated (537.1.2) but with a TT system the neutral will need isolating.

You have test equipment so use it and check the earth loop impedance if under 0.35 likely it's TN-C-S if under 0.8 then likely TN-S and above 0.8 likely TT what reading do you get?

Same with RCD does it fail to trip at half pos and neg trip at full and trip within 40 ms at 5 times full?
 
You have test equipment so use it and check the earth loop impedance if under 0.35 likely it's TN-C-S if under 0.8 then likely TN-S and above 0.8 likely TT what reading do you get?

You are talking about the Ze here.

But, when looking solely at the Zs, it is often impossible to say.

I would say the first two are a reasonable test for their respective supply types (if they are wildly out, there is a problem the DNO needs to be called out to investigate).

However, TT installs can (but not always) present decent sub-1 Zs readings due to parallel paths with various types of bonding.

Just something for the wary to watch out for!
 
You have test equipment so use it and check the earth loop impedance if under 0.35 likely it's TN-C-S if under 0.8 then likely TN-S and above 0.8 likely TT what reading do you get?
You are talking about the Ze here. But, when looking solely at the Zs, it is often impossible to say. I would say the first two are a reasonable test for their respective supply types (if they are wildly out, there is a problem the DNO needs to be called out to investigate). However, TT installs can (but not always) present decent sub-1 Zs readings due to parallel paths with various types of bonding. Just something for the wary to watch out for!
All true (and, as you may recall, I have such a TT installation with Ze under 0.5Ω). However, I would have thought that it would be a bit odd if someone equipped to measure Ze/Zs (and therefore presumably with some knowledge and understanding of electrical matters/installations) needed to undertake measurements in order to ascertain whether an installation was TN or TT!

If I wanted to be controversial, I might suggest that, from the safety viewpoint, requiring DP isolation with TT supplies is being ultra-cautious, to say the least. Also, as I've observed before, given the apparenly perceived need for that degree of ultra-caution, I'm rather surprised that the requirement doesn't extend to TN-S - it's only really with TN-C-S, where N and 'E' are connected within the premises, that one can be absolutely certain that there is no N-'E' potential difference within the installation.

Kind Regards, John
 
I seem to have landed on another planet, no idea what you are talking about!!,the residual current is not 250v but as I have a pacemaker I have to be cautious. Can't turn off the supply to the other floors as causes days of problems with new heating system which will not re-boot without a whole team of super geeks input. Should not have said test equipment as it means something else to you! . Did you know you can test for polarity with a spud? (':p')
 
I seem to have landed on another planet, no idea what you are talking about!!,the residual current is not 250v but as I have a pacemaker I have to be cautious.
That is very wise. Give or take the fact that it's not really correct to talk about a voltage as a current, it would certainly be interesting to know what voltage exists between neutral and earth (CPC) when your circuit is powered down. Even though you say "Should not have said test equipment as it means something else to you!", I presume that whatever you have is able to make an attempt at measuring that voltage?

However, I and others have explained how you can get RCDs tripping when a circuit is just 'powered down' (by operation of an MCB or removal of a fuse), so maybe that's at least partially answered your initial question.

Kind Regards, John
 
Thanks John, could not get a voltage but certainly a good spark when crossed up. I plugged in my Makita charger and that seemed to drain off the problem.Have to be very carefull not to trip off the main RCD as it causes agro with the central heating remote access system.
 
I seem to have landed on another planet, no idea what you are talking about!!,the residual current is not 250v but as I have a pacemaker I have to be cautious. Can't turn off the supply to the other floors as causes days of problems with new heating system which will not re-boot without a whole team of super geeks input. Should not have said test equipment as it means something else to you! . Did you know you can test for polarity with a spud? (':p')

OK my post worked and you have admitted you don't have the test equipment so now we return to basics.

Any cables running together will with either inductance or capacitance put energy into the other cable plus likely the neutral is not switched off anyway so we have to work as if the system is still live when only switching off at the MCB.

I have had these computer guys before with "You can't turn that off it supplies the server" and my answer is if so important clearly it will be on battery back-up and what I want is the time I can have it off for. When they say there is no back-up I reply then clearly not a problem or it would have a back-up.

OK I know not strictly true, but if a power cut does cause such a major problem then it clearly needs a UPS fitted. All the central controlled heating systems I have worked on have been commercial never seen one in a house and with commercial one really does have to follow the rules DIY is really out.

As to pace makers yes there are problems. Had to have my mothers induction hob removed because the pace maker did not comply with EU rules then they changed the pace maker so now she could have one. I would say in view of that just don't touch it let some one who knows what they are doing do the work for you just not worth the risk.
 
Only joking with the spud, don't want to cash in my chips yet.I can test for voltage ,polarity and resistance . I will have to get a dedicated separate supply for the router and control hub for the central heating, and just hope for no power cuts as 2-3 days of phone calls is wearing and a waste of my life.
 

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