Pond Pumps ?

[John Barsby]

I've just had a call from a man who has 2 pond pumps that start up and run fine. The problem occurs when he turns them off it takes out the RCD. This guy has had a few electricians out already one advised to change his pumps which he has done.

Last summer they worked fine and in winter he had a new boiler fitted. Now summer is here he has started to use the pumps again and has this problem.

Not yet been out to this job but I will probably test the RCD first to see if its a bit too keen.

Any ideas appreciated.

JB

 

[chrish_1977]

I would be looking at the boiler wiring too, unless its on the existing spur. Might be coincidence, might not, but a full test wouldn't go amiss

 

[John Barsby]

Good point m8, could be coincidence but It has been known for boilers to be leaking onto electrical terminations etc and provide a bit of leakage to earth.

I was thinking there could be a neutral to earth fault anywhere on the system that only trips when enough power is pulled down a circuit but not sure why it only trips on power down of the pumps.

He did mention his washer has done it a couple of times on power off but an electrician replaced the socket outlet and it hasn't done it in that way since. Possibly another coincidence ?

 

[Tim]

I think there was a thread on here a while back about DP spurs. When you switch some of them off they take out the rcd because the line and neutral dont disconnect at the same exact monent causing an imbalence in the circuit.

Tim

 

[John Barsby]

Good info Tim, Any ideas what brands disconnect ok ?

 

[stuartcourt]

I dont think it discriminates but never had a prob with crabtree, mk etc and ask if he still has old pumps I will rewind motors for him (wink, wink)

 

[hubsy]

I switch my pond pumps using solid state relays, never had a problem with split board tripping.

 

[Tim]

Did you solve the problem?

 

[John Barsby]

Yes, After insulation resistance testing the whole property we put both his pond pumps on separate switches and he turns them off one at a time without problem.
Maybe something to do with turning them off simultaneously (collapse of magnetic field under momentum ?) , Starting them at the same time was never a problem.

 

[Tim]

Glad to hear you got it sorted

Tim

 

[Phoenix]

Yes, After insulation resistance testing the whole property we put both his pond pumps on separate switches and he turns them off one at a time without problem.
Maybe something to do with turning them off simultaneously (collapse of magnetic field under momentum ?) , Starting them at the same time was never a problem.

Seems odd!!! Not being current (pun intended) with magnets / generators / motors etc, would a contact suppressor across the L+N on each pump have fixed it? Was this because the motors continued to run after power off and 'generated' a voltage imbalance on L+N and tripped the RCD? I ask purely out of curiosity as I have a few pumps in my pond and have never (yet) encountered this problem, but you never know...