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My instinct here will be to replace the MCB With a Rcbo, tell the Client a FI will be required,& appropriate tests to be made on that circuit.
At least for now an Earth fault will be protected by the Rcbo…..which will be better than it is now.
My attachment above states that reasoning too.
I cannot quite understand why a few of you disagree with that option…& I fully understand the short circuit requirements…& that is typically of the high Zs reading on circuits where the Zs are high.
My concerns will also be directed @ the Company I work for…
 
I have to agree that attempting to temporarily mitigate this CPC fault by installing an RCBO is not an acceptable approach.

The allowance in the regs for using an RCD as supplementary protection is a design consideration, not a fault correction provision.

If you had not been given time to locate and correct the fault, the circuit should have been disconnected as it is potentially dangerous.

At least that's the way I look at it...
 
My instinct here will be to replace the MCB With a Rcbo, tell the Client a FI will be required,& appropriate tests to be made on that circuit.
At least for now an Earth fault will be protected by the Rcbo…..which will be better than it is now.
My attachment above states that reasoning too.
I cannot quite understand why a few of you disagree with that option…& I fully understand the short circuit requirements…& that is typically of the high Zs reading on circuits where the Zs are high.
My concerns will also be directed @ the Company I work for…
It is you that doesn't understand. Further dead tests should have been undertaken to establish the issue. How do you know the rcbo will protect under earth fault conditions the earth may totally break down under fault.
 
I have to agree that attempting to temporarily mitigate this CPC fault by installing an RCBO is not an acceptable approach.

The allowance in the regs for using an RCD as supplementary protection is a design consideration, not a fault correction provision.

If you had not been given time to locate and correct the fault, the circuit should have been disconnected as it is potentially dangerous.

At least that's the way I look at it...
Agree… so what about the high loop impedances found on other citcuits that do not comply eg ring main circuits just stick a Rcbo on it…
 
When I have trainess/improvers working with me I always insist they work out the expected value of R1/R2 etc. Also for Ring Final Circuit tests, always calculate the expected value before measuring. So in the case above you would have an expected value derived from the estimated length of the circuit and so on. This would the verify if the circuit is too long of there a comparable value which can indicate a definite fault. I guess I would be out with the wander lead going light to light getting R2, or even between lights if the circuit is too long.
 
When I have trainess/improvers working with me I always insist they work out the expected value of R1/R2 etc. Also for Ring Final Circuit tests, always calculate the expected value before measuring. So in the case above you would have an expected value derived from the estimated length of the circuit and so on. This would the verify if the circuit is too long of there a comparable value which can indicate a definite fault. I guess I would be out with the wander lead going light to light getting R2, or even between lights if the circuit is too long.
Thanks
 
As said needs a good looking at, and rcbo would temporary protect until powers that be sort out a plan. But doesn't sound good. Like for like, many would swap and walk away without testing.
 
I did ask what test had been done earlier but the OP has not as yet answered.
 
As said needs a good looking at, and rcbo would temporary protect until powers that be sort out a plan. But doesn't sound good. Like for like, many would swap and walk away without testing.
Thank you…it’s now become a major problem & who is going to pay.
 
Personally I'd stick the live in the earth bar, open up a few car park lights, measure R1+R2 and form a picture of where the resistance jumps high. It shouldn't take that long to get a better understanding of what's going on.
Leaving the live in the earth bar is also an option I'd prefer to installing an RCBO. Leaving part of the circuit functional is also an option if you find good Zs for part of it, while the remainder is investigated more.
You need to talk to your boss again about this. Mistakes happen. He or she will know that.
 
Walk in turn the breaker off or remove the Live or if you have time do as tim says, find that car crash and disconnect at that point.
 
Yes the Swa been in some time, 2 core only,armourping used for cpc.
that is most likely the problem. as someone has already stated, corroded armour. also depends on if the SWA has been correctly glanded in the first place, not just bodged. definitley needs investigation.
 

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