The testing required before cu change

[MrsS]

I’m about to change an CU with rewireable fuses to one with RCBOs, the reasoning behind this is, only a small CU will fit the space and the property only has 4 circuits
5amp Upstairs Lights
5amp Downstairs Lights
30amp Sockets
30amp Cooker
If I use MCB all circuits are protected by an RCD, therefore all circuits would be interrupted under fault conditions; an RCBO ensures that only the circuit with the fault is interrupted.
I plan to test the installation before removing the old CU and because I will be fitting RCBOs I want to avoid any problems with N-E.
Now I’ll get to the point (typically of a woman to go all around the houses)
Tests are:
Ze and Psc tests
Continuity of protective conductors test ( R1 & R2 test at the furthest of the 2xlight circuit and the cooker circuit, adding it to Ze to get Zs). But how does this test check neutral
Then the end to end testing on the sockets circuit
Followed by the cross over test, I know the reading at each socket should be (R1+Rn)/4 or (R1+R2)/4 (spurs higher)
Then Insulation resistance test on all circuit.
Then Zs test of all circuits
Is there anything else I should do or lookout for to avoid problems with the RCBOs
By the way, Which RCBOs are the best to use.
Feedback Welcome
Many Thanks

 

[Sparky Ninja]

The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.

I often prefer MK RCBO's


Often when I introduce RCDs to an existing installation I will carry out a continuity test between neutral and cpc, to see if any leakage is already existing.
Another thing i do is carry around with me a plug in RCD unit, which I will try out on any suspect old appliances prior to installation. It isn't guaranteed to pick out problem appliances (RCDs have different sensitivity) but it does Ilustrate to the clients your concern prior to installation.

 

[MrsS]

Many Thanks

[The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.]

To complete this test, would I link neutral to cpc at CU just like R1&R2, and what reading should I expect?
Just look up the plug in RCD units, does it indicate if a electrical appliance is faulty.

 

[ezzzekiel]

would a split load consumer unit not suit your purpose?
assuming by post you are new - if so life would be made much easier and cheaper this way.

dont go overboard on initial testing,
ze
ring continuity
basic ir test

 

[Amp David]

Your readings will all depend on your circuit length and if you have spurs or not.

Soulnds like another diyer taking work of the good old sparky again

 

[ezzzekiel]

Your readings will all depend on your circuit length and if you have spurs or not.

Soulnds like another diyer taking work of the good old sparky again

seems a little well informed for a diyer - im thinking new partp or trainee

 

[MrsS]

Thank you Widdler and Ezzzekiel for the advice
Looked at split load consumer unit first but can’t find one that would fit the space I’ve got to work with, which is measured at
W- 250, D - 120mm & H - 260mm
I am new to the forum, and qualified in June NOT A DIYER TAKING WORK OFF THE GOOD OLD SPARKY AGAIN as Amp David suggested.
Just look for some advice like anyone else.

 

[Amp David]

Feel for the customer

 

[Sparky Ninja]

Many Thanks

[The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.]

To complete this test, would I link neutral to cpc at CU just like R1&R2, and what reading should I expect?
Just look up the plug in RCD units, does it indicate if a electrical appliance is faulty.

The plug in tester should work like a normal RCD and hopefully trip if an individual appliance was giving off sufficient leakage to cause problems upon completion. Suspect appliances can be old fridges, washing machines or PC's etc. This won't account for the quantiy of appliances though, which may when all in operation, build up an amount of leakage sufficient to also trip the RCBO anyway.

As for the neutral, yes you could connect it to CPC at the board. Assuming that you have T&CPC cabling, you could play around with the data to verify readings for comparison. (R1&Rn)/2= R1 or Rn. Therefore R1&R2 should equal (R1x1.67)+R1. Then you will have the figures for R1, Rn & R2.

This is all unnecessary though for current requirements, and so I'm sure others here are probably wondering what the heck I'm talking about.

 

[davelerave]

amazing really the simple things


customer can see it for himself -before you changeover to 30mA protection

and have to explain it


err you need to order a skip for all your equipment that worked before i started

 

[MrsS]

Got to get myself a plug in RCD tester, always handy to help sort out faults.
I’ll give the neutral test ago. Many Thanks

 

[pushrod]

Separate all your neutrals and IR test (or you could continuity test) between them - (there are 6 different combinations with 4 circuits) If you get a zero on any of them chances are you have a shared neutral and potential problems with your RCBOs. If you do have this problem then at least with a split board, although not ideal, you have the opportunity to put the offending circuits on the same rcd and save taking up floorboards/chopping out walls etc.
Of course do the other tests as well to check for other problems. Good luck

 

[MrsS]

Many Thanks Guys, you’ve all give me lots of good advice .

 

[brucelee]

Many Thanks

[The R1&R2 test is for continuity of protective conductors and so neutral isn't included, you could however carry out a test to neutral to assist in polarity check.]

To complete this test, would I link neutral to cpc at CU just like R1&R2, and what reading should I expect?
Just look up the plug in RCD units, does it indicate if a electrical appliance is faulty.

hi mrs s
to do the continuity of protective conductors
1 link line and cpc at db test between line and cpc at all relevent points if its a lighting circuit test at the ceiling rose between sw/line and cpc record highest as R1+R2 value for the circuit operate switches to confirm polarity whilst carrying out the test
2 if you want to you can also measure L- N by linking line and neutral at DB the tesing at all relevent points between line and neutral this result not recorded and value will be substantially the same if same size conductors are used ie 1mm T/E the line , neutral and cpc will give same results as they have same csa
if 1.5mm T/E used then the line to cpc will be higher than the line to neutral as cpc has a smaller csa
use this test for line to neutral (R1 + RN) when testing radial socket outlets to confirm polarity

 

[WayneL]

Separate all your neutrals and IR test (or you could continuity test) between them - (there are 6 different combinations with 4 circuits) If you get a zero on any of them chances are you have a shared neutral and potential problems with your RCBOs. If you do have this problem then at least with a split board, although not ideal, you have the opportunity to put the offending circuits on the same rcd and save taking up floorboards/chopping out walls etc.
Of course do the other tests as well to check for other problems. Good luck

Hmmm

 

[Amp David]

Don't understand this method very well

 

[WayneL]

hi mrs s
to do the continuity of protective conductors
1 link line and cpc at db test between line and cpc at all relevent points if its a lighting circuit test at the ceiling rose between sw/line and cpc record highest as R1+R2 value for the circuit operate switches to confirm polarity whilst carrying out the test
2 if you want to you can also measure L- N by linking line and neutral at DB the tesing at all relevent points between line and neutral this result not recorded and value will be substantially the same if same size conductors are used ie 1mm T/E the line , neutral and cpc will give same results as they have same csa
if 1.5mm T/E used then the line to cpc will be higher than the line to neutral as cpc has a smaller csa
use this test for line to neutral (R1 + RN) when testing radial socket outlets to confirm polarity

Would you really do all this before a CU change??


MrsS, have a read of this : http://www.esc.org.uk/pdfs/business-and-community/electrical-industry/BPG6_09.pdf

 

[brucelee]

no mate not before changing cu she was asking how to check the neutral in post 3 and she put
neutral to cpc i was just explaining that its carried out between line and neutral R1+RN and its whats used to check radial socket outlets to confirm polarity and doesnt have to be carried out for lighting circuits
but not neded before a board change

 

[pushrod]

Don't understand this method very well

I am not surprised on reading my explanation again!

Interestingly it does make some sort of sense and would identify a circuit that for some reason had its own neutral and another neutral from another circuit which would cause rcd problems. This is not the usual problem though and it was not what i meant to say.
I managed to miss out was that you test between the "live of a circuit and the other" neutrals. As the more usual problem especially with 2-way lighting is that the current returns via another circuit.

If IR testing you need to do it at 250v and obviously light switches should be closed.

The easiest way of doing it is to just take the neutral, of say, upstairs lights out of the neutral bar and then test between the live of that circuit and the remaining neutrals on the bar - you only have to separately test all the neutrals if you get a zero reading. Then do the same for downstairs lights. As i'm sure you know it is most likely to be the lighting if there is a problem and it is a quick way of checking.

Hope that makes it a bit clearer and apologies for the confusing first post

 

[WayneL]

Much Better, Pushrod