RCD on Outside Water Proof Socket?
- Thread starter Minatoar
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No.
The socket one might trip first. Or the house one. Or both of them.
The socket one might trip first. Or the house one. Or both of them.
You need to fix the problem. It may be with the water feature or the connecting wiring. The RCD is doing its job. Adding another one, or changing the existing RCD, is pointless.
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You can get 10 mA RCD's, however the one I had at work, and good make MK, pressing the test button would trip the socket, and the 30 mA in local board and 100 mA in main board, and caused many problems as people would press the test button.
We work with a third of the rating, so we can allow a back ground leakage of under 10 mA for a 30 mA RCD, so 9 mA max. And we tend to use RCD's in series with a times 3 basis, so 10, 30, 100, 300 etc. But the time is the same, they all trip within 40 mS, so any fault trips them all.
3.5 mA leakage is the limit for any single item, unless special measures taken, but we use AC and there is always some leakage with AC due to capacitive and inductive linking, also any filters used.
So the electrician may use his insulation tester and get a reading of many MΩ but he is testing with DC. Using a clamp on ammeter around both line and neutral we can measure the leakage, my whole house is around 24 mA, but since split into 14 circuits with RCBO's (a MCB and RCD combined) no circuit is near the tripping limit, remember 30 mA RCD must trip between 15 and 30 mA often they do trip at over 25 mA but it is acceptable to trip at 16 mA.
So if the back ground leakage is 9 mA and the RCD trips at 16 mA then you have 7 mA to play with, so a 10 mA RCD is very likely to trip at same time as the 30 mA RCD, which is why I have spent the extra and have RCBO's not RCD's so if one trips I loose less.
In the main water is the reason for tripping, however once water allows electric to flow, it can burn a carbon track, I well remember drilling holes in distributor caps to break the carbon track until we could get a new one, when cars had such things, so get water in a socket, and if the socket it powered once it tracks, only cure is new socket.
If you want to test an insulation tester
and a clamp on ammeter 
both cost around £35 there are clamp ons for less, but not to measure down to 1 mA, so in your case best option is likely just to replace the pump. I think the one I got from Lidi was less than £15 and likely even if tested you will still need a new pump, so just replace it.
We work with a third of the rating, so we can allow a back ground leakage of under 10 mA for a 30 mA RCD, so 9 mA max. And we tend to use RCD's in series with a times 3 basis, so 10, 30, 100, 300 etc. But the time is the same, they all trip within 40 mS, so any fault trips them all.
3.5 mA leakage is the limit for any single item, unless special measures taken, but we use AC and there is always some leakage with AC due to capacitive and inductive linking, also any filters used.
So the electrician may use his insulation tester and get a reading of many MΩ but he is testing with DC. Using a clamp on ammeter around both line and neutral we can measure the leakage, my whole house is around 24 mA, but since split into 14 circuits with RCBO's (a MCB and RCD combined) no circuit is near the tripping limit, remember 30 mA RCD must trip between 15 and 30 mA often they do trip at over 25 mA but it is acceptable to trip at 16 mA.
So if the back ground leakage is 9 mA and the RCD trips at 16 mA then you have 7 mA to play with, so a 10 mA RCD is very likely to trip at same time as the 30 mA RCD, which is why I have spent the extra and have RCBO's not RCD's so if one trips I loose less.
In the main water is the reason for tripping, however once water allows electric to flow, it can burn a carbon track, I well remember drilling holes in distributor caps to break the carbon track until we could get a new one, when cars had such things, so get water in a socket, and if the socket it powered once it tracks, only cure is new socket.
If you want to test an insulation tester
and a clamp on ammeter both cost around £35 there are clamp ons for less, but not to measure down to 1 mA, so in your case best option is likely just to replace the pump. I think the one I got from Lidi was less than £15 and likely even if tested you will still need a new pump, so just replace it.
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AND HOW, EXACTLY, is that going to help the situation???? The fault is with the water feature or the wiring.......
Yes, of course it will trip them all, and you know this, so i dont know why you posted all that stuff....
You cannot discriminate RCDs on the basis of current. Consider the real world. Three parts of an installation with 2 separate DBs
The source has a 100mA RCD, the middle has a 30mA and the end device has a 10mA RCD.
An earth fault develops in the end device, like most earth faults, its a big one, lets say its 200mA. That's probably gonna trip all of the RCDs - perhaps not all - certainly the one with the fastest trip characteristic might go first, or it might be the only one to trip.
That isnt the way to design a circuit!
A chain of RCDs can ONLY discriminate on the basis of TIME. So we have a long time delay S-type RCD at the source end, Medium in the middle and a standard one at the device.
Quite. Indeed, if changing from 30mA to 10mA protection made any difference (in the context of a fault, water ingress or whatever) it would presumably do the opposite of 'helping' (other than somewhat reducing the chance of the house's RCD tripping)!
Kind Regards, John
Apologies for living down to my moniker (again).
I believe Eric means 40ms.
I'm sure he does, but even when that is corrected I do not really agree with eric's assertion that "... they all trip within 40 ms, so any fault trips them all.". As has been said, it is quite possible that only one (either one) will trip, as well as possible that both will trip.
Only with a slowly-developing residual current fault could one be reasonably confident that a 10ma RCD would probably trip before a 30mA one.
Kind Regards, John
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Final line was "you will still need a new pump, so just replace it." However in the main the fault takes time to develop so 10 mA will trip first if no other leakage, but likely there is other leakage, so back to orignal advice just replace the pump.
Sorry a is next to s and clearly I did mean mS.
Sorry a is next to s and clearly I did mean mS.
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