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In my Electrical Installation, the Main RCD (300mA) trips before the second RCD (30mA). This has been happening in various occasions. Does anyone know why this is happening? As far as I know, it should have been the other way round.
 

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MS Lady said:
In my Electrical Installation, the Main RCD (300mA) trips before the second RCD (30mA). This has been happening in various occasions. Does anyone know why this is happening? As far as I know, it should have been the other way round.
First thing that comes to mind is that you have a ground (earth) fault between the Main and the Branch.

For all the Americans here, an RCD (Residual Current Device) is the equivalent of an Equipment Ground Fault Interruptor. The 300ma and 30ma refer to the ground fault trip settings.
 

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fertilizer distrubuter
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In my Electrical Installation, the Main RCD (300mA) trips before the second RCD (30mA). This has been happening in various occasions. Does anyone know why this is happening? As far as I know, it should have been the other way round.
Is it possible the ground fault is detected by both is above 300ma and the unlatching time on the 30ma rcd is not fast enough to provide coordination.
 

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WHAT THEY SAID and

If there are grounds on the grounded conductor down stream of the main bond (I would think at this level through a load), you could have some issues with nuisance tripping. The level of fault current seen by the main could be constant while the branch circuit is seeing nothing until the fault. Main exceeds it preset level and trips.
 

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Buzzy304E
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Simply change out the branch circuit RCD breaker, I'll bet that solves it.

Not sure of your brand, but when I returned from Iraq, I had a stack of papers showing real and counterfeit breakers. There were almost as many counterfits as real ones, we knew it , and they were sometimes installed because that was all that was available. Some functioned equally as well as the real deal, though all bets are off as to their long term safety

That is not to say a conterfeit is at fault, but changing out a breaker is cheap. If that doesn't do it, change out the main breaker.
 

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Simply change out the branch circuit RCD breaker, I'll bet that solves it.

Not sure of your brand, but when I returned from Iraq, I had a stack of papers showing real and counterfeit breakers. There were almost as many counterfits as real ones, we knew it , and they were sometimes installed because that was all that was available. Some functioned equally as well as the real deal, though all bets are off as to their long term safety

That is not to say a conterfeit is at fault, but changing out a breaker is cheap. If that doesn't do it, change out the main breaker.
If both breakers are tripping at various times, I think it's safe to say that she has a ground fault issue and changing out breakers would be a waste of time and money. I would look first for a specific load that's on when it trips and then work backwards from there
 
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