higher Zs with RCD

[diditrain]

When testing Zs for circuits which also have RCD protection, what figure do you record onto your test sheets? when you exceed the max value for a specific MCB, due to the rcd. Do you just use a calculated value or do you actually record the value that you get even though it exceeds the max allowed for the MCB

Ze, R1R2 are within spec as is Zs when the RCD is taken out of the equation but when the RCD is connected it exceeds the max allowed for the MCB`S.
I am aware of the 1667 figure when an RCD is used

Hope my question is clear

 

[Octopus]

If the recorded value is above what you are expecting I would be investigating the cause rather than entering a high value and moving on.

Its all wellk and good saying the 1667 value is OK as I've got RCD's but I've seen several faulty RCD's recently so relying on them isn't the best plan.

 

[Top Cat]

When testing Zs for circuits which also have RCD protection, what figure do you record onto your test sheets? when you exceed the max value for a specific MCB, due to the rcd. Do you just use a calculated value or do you actually record the value that you get even though it exceeds the max allowed for the MCB

Ze, R1R2 are within spec as is Zs when the RCD is taken out of the equation but when the RCD is connected it exceeds the max allowed for the MCB`S.
I am aware of the 1667 figure when an RCD is used

Hope my question is clear

Do you mean on a TT system?

 

[ringer]

What instrument are you using to measure Zs? What setting is it on? How are you including/excluding the RCD in these tests?
And remember, the RCD is there for additional protection rather than for fault protection (unless this is a TT installation).

 

[Amp David]

Think he mean when the test with non trip setting is throwing up higher than calculated figures.

 

[diditrain]

As Amp david states that is exactly what is happening. I thoiught that i had explained how i had verified that there was not an underlying issue Murdoch in my initial post

 

[Top Cat]

If the recorded value is above what you are expecting I would be investigating the cause rather than entering a high value and moving on.

Its all wellk and good saying the 1667 value is OK as I've got RCD's but I've seen several faulty RCD's recently so relying on them isn't the best plan.

Something fishy going on here. Lol

 

[telectrix]

sometimes it's not the fact that you are using no-trip test, it's the RCD having internal components pushing up the reading.

 

[diditrain]

I know that, but thank`s anyway. That is why i am asking.
Tester is used on ATT due to there being an RCD. There is nothing wrong with the circuit. I have seen many a previous similar post on the same subject

 

[derek preece]

Sorry miss-read the op

 

[c.boy]

Hi.
If you want to follow the e.a.w.r,reg 14 a think?? Then the only zs to be taken shall be at the sockets or lights if you have the suitable adaptor!!Under no circumstances should you work live unless totally unavoidable!!

 

[sedgy34]

When testing Zs for circuits which also have RCD protection, what figure do you record onto your test sheets? when you exceed the max value for a specific MCB, due to the rcd. Do you just use a calculated value or do you actually record the value that you get even though it exceeds the max allowed for the MCB

Ze, R1R2 are within spec as is Zs when the RCD is taken out of the equation but when the RCD is connected it exceeds the max allowed for the MCB`S.
I am aware of the 1667 figure when an RCD is used

Hope my question is clear

investigation to the high reading should be the next thing you do

 

[telectrix]

take a Zs reading on the busbar in the CU, with only the MCB for the circuit/s you are concerned with. if that is higher than expected, then it's the rcd affecting the reading. i've posted before about having the RCD add 349 ohms !!!

 

[Amp David]

Do a no trip test on each side of each RCD, then you'll know if the RCDs are increasing the reading or if it's your no trip test itself.

 

[telectrix]

just thinking out loud here. somebody correct me if i'm wrong.

fault path is from load side of MCB through circuit to location of fault, then either through N or E. now, if it's an earth fault, the actual resistance of the fault is not affected by the RCDs internal impedance so that the OCPD will react accordingly. (assuming the RCD has not tripped first)..a L-N fault, however will have the effective impedance of the fault path increased by whatever the RCD adds, so fault protection may not be compliant. rambling on a bit, but food for thought???