RCD tripping.

[hsrry Electrical]

So I’ve been working at a cafe and I have an RCD as main switch by the incoming supply which is up the drive and it comes into the cafe fuseboard which is a split load with two 63A RCDs. They’ve been having the RCD trip constantly at the end of the drive and not the ones INSIDE the cafe fuse board. Why are the ones in the cafe CU not tripping before the one at the end of the drive? (All RCDs work)

please help
Thank you

 

[Phil L]

Possible cable fault along the drive?

 

[SJD]

What are the rated tripping currents of the various RCDs. Hopefully the up-front one is not the same value as the cafe ones!

 

[OnlQQker]

What's the cable between main switch RCD and consumer unit in cafe?
Is it testing out ok?

 

[littlespark]

I would assume all rcd’s are rated at 30mA, but one could be 25, the other 26. Just the sensitivity of each.

Also the main one is measuring the cumulative effect of all circuits, whereas the other 2 are half each.

 

[pc1966]

First question, is the up-front one at least 100mA and a delay (type-S) trip? If not you have a very likely likely answer of no (usable) RCD selectivity and a final circuit fault (might even be N-E so MCB isolating Ls might not locate it).

If it is a selective arrangement, then next most likely is a real fault in the feed cable or other loads at the sending end tripping the RCD.

If you isolate the final board (incomer switch or both RCD opened) is the supply end RCD still tripping? That would point to the feed cable.

 

[Strima]

As above, what size upfront RCD? Cable type and installation method? Earthing arrangement? Any test results (IR, R1+R2) etc?

 

[hsrry Electrical]

First question, is the up-front one at least 100mA and a delay (type-S) trip? If not you have a very likely likely answer of no (usable) RCD selectivity and a final circuit fault (might even be N-E so MCB isolating Ls might not locate it).

If it is a selective arrangement, then next most likely is a real fault in the feed cable or other loads at the sending end tripping the RCD.

If you isolate the final board (incomer switch or both RCD opened) is the supply end RCD still tripping? That would point to the feed cable.

It’s tncs, and has an 80a 30ma rcd which is tripping and melted at the top. Supply cable is fine from it to the board