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Discuss Liklihood of adjacent RCBO tripping due to fault on another circuit? in the Electrical Forum area at ElectriciansForums.net

GBDamo

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Got an odd one.

Supply is TPN TN-CS and all looks reasonably tidy but the circuit schedules bear little resemblance to the DB contents.

I have a piece of fixed equipment that is generating intermittent faults and tripping the C16 RCBO. The circuit tests fine at 999MOhms at 500V on IR. So it's looking like the fixed equipment or it's associated wiring.

The curious thing is that they are claiming that when it trips it takes down the adjacent B32 RCBO.

I have ramp and RCD tested the C16 20 times and not got the B32 to trip.

The wiring in the board is untidy but all is secure and correctly wired.

My theory is that when restting the faulty C16 they are hitting the test button of the B32.

But thought I'd ask if there were any exotic scenarios where one circuit fault can cause another to trip?
 
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GBDamo

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a N-E fault on a circuit can cause an unrelated RCD to trip when a load is switched on on the non-RCD (or a second RCD) side.
Thanks but, to clarify.

I have a full RCBO board.

Are you suggesting that if my fixed equipment circuit, the C16 had a N-E fault it could cause another RCBO to trip when put under load?

As all the IRs test fine this is unlikely, yes?

Or...

That when another circuit has, when under load, a N-E fault that may be causing the C16 to trip?

At the moment I'm going for fat fingers.
 

telectrix

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had a N-E fault on a shower once. the shower was on RCD1. as soon as a load (kettle) was switched on on RCD2, RCD1 tripped. something to do with the N current finding it's way through parallel paths like bonding through the tripping RCD. can't explian the theory without burning my few brain cells out.
 

Rockingit

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Given that magnetic fields don't respect a plastic housing, I guess it's not impossible that if you had a large enough spike in one device that it might cause some disruption to an adjacent coil, possibly encouraged if there were some harmonics involved as well. A simple test would be to swap them around on the bar and see what aspect the fault decides to follow.
 

GBDamo

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Just been testing the ZDB and got 0.06 L-E and 0.05 L-N so no issues with the supply.

Id like to ramp test the B32 to see if it is failing early but that circuit has the server on and shuts down the site.

Think I get my super precise Tacklife earth leakage clamp meter out and have a root round.

The B32 may have a high baseline leakage???
 

GBDamo

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Given that magnetic fields don't respect a plastic housing, I guess it's not impossible that if you had a large enough spike in one device that it might cause some disruption to an adjacent coil, possibly encouraged if there were some harmonics involved as well. A simple test would be to swap them around on the bar and see what aspect the fault decides to follow.
Like that, problem is I can't isolate without shutting the site down.

Will likely be returning out of hours so would like to have potential solutions ready along with parts.
 

Rockingit

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Just been testing the ZDB and got 0.06 L-E and 0.05 L-N so no issues with the supply.

Id like to ramp test the B32 to see if it is failing early but that circuit has the server on and shuts down the site.

Think I get my super precise Tacklife earth leakage clamp meter out and have a root round.

The B32 may have a high baseline leakage???
If that's a circuit supplying solely IT then I'd be tempted to put a B type RCD at 100mA anyway, but depends on how it's all wired - socket outlets etc (and also if you can get a B32 B100 RCBO for that board!!)
 

GBDamo

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Unf
If that's a circuit supplying solely IT then I'd be tempted to put a B type RCD at 100mA anyway, but depends on how it's all wired - socket outlets etc
Unfortunately not, it does a staff kitchen as well.

Need really to get that circuit tested just can't at the moment.
 

Lucien Nunes

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Are you suggesting that if my fixed equipment circuit, the C16 had a N-E fault it could cause another RCBO to trip when put under load?

No, the N-E fault would be on the B32 circuit. With N-E fault trips, the load / overload / fault that triggers the trip event can be on any circuit, but the pre-existing N-E fault that will be on the RCD / RCBO that trips unexpectedly. Rather than a solid fault, it can also be borderline operational leakage plus the effect of the supply disturbance.
 

pc1966

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If the fault is a big one, then it is possible both for magnetic coupling to be a culprit (as mentioned above) or even the dV/dt on the supply as it clears huge currents resulting in enough capacitive flow to trip a RCD/RCBO.

Certainly it sounds like a hard fault as IR results are reported to be good. Though I guess it is theoretically possible for vibration on tripping to do it, but you could rule that out by tripping the 'faulty' circuit using your MFT and see if a low-current fault ever does it.
 

UNG

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Had something similar on a dual RCD board, testing one RCD and the other tripped as well, what was more confusing I inavertantly did an RCD test on the outgoing terminals of the main isolator and RCD No2 tripped again, I eventually located some minor cable damage on one of the outgoing circuits that appeared to be causing the problem
 

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