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S

Strawbs

Circuit: -
17th edition board with 30mA RCD
Pond pump circuit is a 16A MCB feeding double pole FCU with 3A fuse, this feed an electronic immersion heater timer, this is connected to a pond pump/filter unit via SWA.

Problem: -
RCD trips every time the pump switches OFF

What is connected to RCD: -
Socket ring for garage
House alarm system
Garage Door
Pond pump

What has been done so far: -
Initially the circuit was good and has worked well for several months, but recently the RCD started to trip when the pond pump switched OFF
Initially there were two pumps and a UV filter box, being controlled by a mechanical immersion heater timer, but one of the pumps started to fail so I obtained a new pump with an integral UV filter, so this combined pump has replaced the two pumps and the UV filter box. But the RCD kept tripping, so I replaced the mechanical timer with an electronic one, RCD still tripping.
Carried out insulation resistance on cables from CU to FCU and SWA cable, all OK (FCU, Timer and pump disconnected for test)
All cable connecting checked for security of attachment
Carried out RCD test, the RCD trips within 20ms @ 5I and trips at 27mA
All the cabling is less than 12 months.
L & N cabling within garage is 2.5mm singles in trunking with 1.5mm for the earth cable.

I do not have an earth leakage tester

Any ideas?
 
Do an IR test on everything supplied by the RCD; L+N to E. You might have a high standing leakage with a small additional spike when the pump switches of just tipping it over the edge.
 
Do an IR test on everything supplied by the RCD; L+N to E. You might have a high standing leakage with a small additional spike when the pump switches of just tipping it over the edge.

Hi

Sorry about the delay in getting back, but the day job has gotten in the way.
I have carried an IR of the circuits on the RCD with my Megga at 250V, 500V and 1000V and all circuits are good. The loop resistance of the ring main is 0.27Ohms (L+N & E). I have replace the FCU with a cooker connector and down rated the MCB to 6A, but the RCD still trips when the pump switches OFF.
If it comes to it I will:-
a) Think of uprating the 30mA RCD to a 300mA
b) Thinking of replacing the board with a RCBO board. At least this way is wont take every thing else out with it.
 
Hi

Sorry about the delay in getting back, but the day job has gotten in the way.
I have carried an IR of the circuits on the RCD with my Megga at 250V, 500V and 1000V and all circuits are good. The loop resistance of the ring main is 0.27Ohms (L+N & E). I have replace the FCU with a cooker connector and down rated the MCB to 6A, but the RCD still trips when the pump switches OFF.
If it comes to it I will:-
a) Think of uprating the 30mA RCD to a 300mA
b) Thinking of replacing the board with a RCBO board. At least this way is wont take every thing else out with it.
eh?
i take it this is a domestic setup?
 
On some RCDs there are earth flyleads and they are there in case there is a momentary loss of neutral, ie when switching off florries and motors , if you can try one of these , such as on some RCBOs , I found that this usually cures the problem.
 
Back feed from the motor slowing down (Ie acting as a generator).
could be talking nonsense but I seem to think I've heard this before.
perhaps a diode on the live side could eliminate any backfired issues?
 
Back feed from the motor slowing down (Ie acting as a generator).
could be talking nonsense but I seem to think I've heard this before.
perhaps a diode on the live side could eliminate any backfired issues?

I have replaced the RCD like for like and now I do not have any problems with it tripping when the pump switches OFF:clap:.
Even though the old unit tested out OK, it appears that it was at fault.
 

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