I have a mains pond pump which is connected to a Garage Consumer unit
via outdoor douple pole switch. The consumer unix is RCD protected.
When I switch the pump on everything works as it should and the pump
will run all day without any problem. However, when I switch the pump
off using the outdoor switch, the RCD on the consumer unit trips. This
is not intermittent; it happens every time.

The same consumer Unit supplies an outdoor socket which we use for a
lawn mower without any problems.

Does anyone know what could be causing the RCD to trip when I switch
the pump off? I am guessing that the pond pump is faulty, but why does
switching it off trip the RCD?

In article .com,
Peter M wrote:
I have a mains pond pump which is connected to a Garage Consumer
unit via outdoor douple pole switch. The consumer unix is RCD
protected. When I switch the pump on everything works as it
should and the pump will run all day without any problem.
However, when I switch the pump off using the outdoor switch, the
RCD on the consumer unit trips. This is not intermittent; it
happens every time.

Ha! Seen something similar twice now. On our old
Hotpoint built-in fridge, and my pal's well pump.

If it is the same, there is a Neutral wire somewhere
in the motor that is nearly touching Earth. As the
motor runs down, the vibration is enough to cause
a transient N-E short.

--
Tony Williams.

Thanks,

I think I'll wire it up off the RCD

"Peter M" wrote in message roups.com...
I have a mains pond pump which is connected to a Garage Consumer unit
via outdoor douple pole switch. The consumer unix is RCD protected.
When I switch the pump on everything works as it should and the pump
will run all day without any problem. However, when I switch the pump
off using the outdoor switch, the RCD on the consumer unit trips. This
is not intermittent; it happens every time.

The same consumer Unit supplies an outdoor socket which we use for a
lawn mower without any problems.

Does anyone know what could be causing the RCD to trip when I switch
the pump off? I am guessing that the pond pump is faulty, but why does
switching it off trip the RCD?


The RCD trips when there is an imbalance of current in the phase and
neutral supply to the pump.This normally occurs if there is a fault to
earth from phase or neutral but I am guessing the pump is double
insulated and there is no earth wire (cpc).The double pole switch
might be causing the problem, if both contacts do not disengage at the
same time then this could cause a momentary imbalance of current.

Peter M wrote:

I think I'll wire it up off the RCD


Not the best idea you've had all year, I'd suggest. Outdoors, mains,
some distance from the house, water ("impure", so probably more
conductive than what's in your tap). I'm not paranoid about electrical
safety, but I'd *really* not want anything mainspowered in a pond of
mine which *wasn't* on an RCD.

Rather, I'd try to sort out what the pump problem is. Tony's experience
suggests one intriguing possibility. You can do some faultfinding by
visual inspection - is it possible that the switch you're using has some
loose wiring, making either L-to-E or N-to-E contact when it's operated?
Can you put another switch temporarily in (alternately) the L and the N
conductors, to try to give a clue as to whether it's the pond switch
itself, or the pump (and on which side the return route is?) Do you have
a long enough extension lead - and/or access to the garage CU - to
supply the pump through a different (but 'known' to work) plug-in RCD,
to see whether the garage RCD is 'oversensitive'? Do you get the same
nuisance trip supplying the switch and pump from that long extension
lead (which suggests a problem at the switch-and-pump end), or does it
go away (suggesting maybe a 'sensitising' fault - rodent damage? - in
the buried cable - 'nearly' enough to trip the RCD, which gets added to
the switch-off transients (suppressors, collapsing magnetic field,
handwave ;-) to make the garage RCD trip?

Hope something in there gives you some fault-finding ideas, and allows
you to avoid the 'bypass the RCD and hope' non-solution...

Stefek

In article ,
Stefek Zaba wrote:

Rather, I'd try to sort out what the pump problem is. Tony's
experience suggests one intriguing possibility.

I think it is to do with the way in which a motor twists
on start or stop. If the motor is soft-mounted, the
flying leads to it will get a bit of a workout at every
start/stop twist. If one of the leads is touching the
metalwork there is a chance that it will eventually chafe
through.

Our fridge was a bummer..... it took months to find out
what was doing the random trips. I only discovered it
when the N-E short got permanent enough to be sometimes
seen with the Megger.

--
Tony Williams.

I think I'll wire it up off the RCD

Customer: My brakes appear to be seized on.
Mechanic: No problem. I'll cut all the brake lines. That will solve the
problem.
Customer: Thank you!

Hint: The RCD is there is save your life. Having done its job, please don't
throw it away!

Christian.

The double pole switch might be causing the problem, if both contacts
do not disengage at the same time then this could cause a momentary
imbalance of current.

So how would that work then?

Christian.

Tony Williams wrote:
In article .com,
Peter M wrote:

I have a mains pond pump which is connected to a Garage Consumer
unit via outdoor douple pole switch. The consumer unix is RCD
protected. When I switch the pump on everything works as it
should and the pump will run all day without any problem.
However, when I switch the pump off using the outdoor switch, the
RCD on the consumer unit trips. This is not intermittent; it
happens every time.


Ha! Seen something similar twice now. On our old
Hotpoint built-in fridge, and my pal's well pump.

If it is the same, there is a Neutral wire somewhere
in the motor that is nearly touching Earth. As the
motor runs down, the vibration is enough to cause
a transient N-E short.

It's not likely to be the same: fridges are metal and earthed, pond
pumps are usually plastic and don't have an earth.

Christian McArdle wrote:
The double pole switch might be causing the problem, if both contacts
do not disengage at the same time then this could cause a momentary
imbalance of current.


So how would that work then?

Well it's probably all running in to the circuit but it can't get out
again. You shold notice a little bulge in the cable while this happens.

Christian McArdle wrote:
The double pole switch might be causing the problem, if both contacts
do not disengage at the same time then this could cause a momentary
imbalance of current.


So how would that work then?

Actually it might work like this:

The pump motor is just a mains coil embedded in plastic. and say this
insulation is going and water getting in to the coil at the neutral end.
While both live and neutral are connected the current flow from neutral
to earth is low enough not to trip the RCD but if the neutral pole of
the switch opens first you momentarily have a flow from live through the
coil (negligible resistance) through the dodgy insulation to earth, so
the RCD trips.

John Stumbles wrote:
Christian McArdle wrote:
The double pole switch might be causing the problem, if both
contacts
do not disengage at the same time then this could cause a momentary
imbalance of current.


So how would that work then?

Well it's probably all running in to the circuit but it can't get out

again. You shold notice a little bulge in the cable while this
happens.

Lol, good one.

Maybe Cable capacitance to earth/water, add inductive spike from motor
being switched off tog enerate a high peak v and thus push more joules
through given capacitance. Cant say Im very convinced by that
explanation though. Just megger and see what fails is the sensible
approach.


NT

Peter M wrote:
Thanks,

I think I'll wire it up off the RCD

We really need a gallery for posts like this. Trouble is, some pros are
no better.

NT

In article .com,
Peter M wrote:
Does anyone know what could be causing the RCD to trip when I switch
the pump off? I am guessing that the pond pump is faulty, but why does
switching it off trip the RCD?

I'd start by checking inside the switch housing to make sure it's still
dry and clean. The travelling part of the switch mechanism may be hitting
damp etc one way, but not the other.

--
*Some people are alive only because it's illegal to kill them *

Dave Plowman London SW
To e-mail, change noise into sound.

John Stumbles wrote in message ...
Christian McArdle wrote:
The double pole switch might be causing the problem, if both contacts
do not disengage at the same time then this could cause a momentary
imbalance of current.


So how would that work then?

Actually it might work like this:

The pump motor is just a mains coil embedded in plastic. and say this
insulation is going and water getting in to the coil at the neutral end.
While both live and neutral are connected the current flow from neutral
to earth is low enough not to trip the RCD but if the neutral pole of
the switch opens first you momentarily have a flow from live through the
coil (negligible resistance) through the dodgy insulation to earth, so
the RCD trips.

Thanks for the support, I did feel a bit stupid after the responses to
my idea about the double pole switch but feeling much better now.

In article ,
John Stumbles wrote:

Tony Williams wrote:
If it is the same, there is a Neutral wire somewhere
in the motor that is nearly touching Earth. As the
motor runs down, the vibration is enough to cause
a transient N-E short.

It's not likely to be the same: fridges are metal and earthed,
pond pumps are usually plastic and don't have an earth.

But the RCD is tripping so there is likely to be a
sideways path to Earth, somewhere.

--
Tony Williams.

Mortimer wrote:
John Stumbles wrote in message ...

Christian McArdle wrote:

The double pole switch might be causing the problem, if both contacts
do not disengage at the same time then this could cause a momentary
imbalance of current.


So how would that work then?

Actually it might work like this:

The pump motor is just a mains coil embedded in plastic. and say this
insulation is going and water getting in to the coil at the neutral end.
While both live and neutral are connected the current flow from neutral
to earth is low enough not to trip the RCD but if the neutral pole of
the switch opens first you momentarily have a flow from live through the
coil (negligible resistance) through the dodgy insulation to earth, so
the RCD trips.


Thanks for the support, I did feel a bit stupid after the responses to
my idea about the double pole switch but feeling much better now.

I wonder if the switch is wired back to front (L-N, N-L) as well? I
don't know, but I'd guess that a double pole switch is designed to break
the live first. If it's wired the other way then this would give the
effect described.

In article ,
Tony Williams wrote:

But the RCD is tripping so there is likely to be a
sideways path to Earth, somewhere.

Hmm.... I didn't notice 'double pole switch' in the
OP's original post. So my proposal of a transient
N-E short can be politely ignored.

--
Tony Williams.

OK, OK I'm an idiot!

The other idea I had was to never switch it off!

I have changed the switch, bypassed the buried cable and connected it
via a plug in rcd.
The plug-in rcd trips also.
I think I'll replace the pump with a low-voltage one!

On 23 Mar 2005 02:43:14 -0800, "Peter M"
wrote:

The other idea I had was to never switch it off!

I have changed the switch, bypassed the buried cable and connected it
via a plug in rcd.
The plug-in rcd trips also.
I think I'll replace the pump with a low-voltage one!

Hi,

Try running the pump in a bucket of water that is well insulated from
the ground, to see if the RCD doesn't trip off.

It could be that water is wicking down through the cable gland in the
pump body, which could be easily fixable with some sealant after
drying out the connections on the other side of the gland.

cheers,
Pete.

replying to John Stumbles, Jon R wrote:
As noted above, the coil in the motor is highly inductive, and when the pump
is switched off, it generates a short high voltage spike,. The cable to the
pump is probably long and submerged, so there is a fair capacitive coupling to
ground (through the water). So, although there is no fault with the pump and
wiring, there Is still a very brief capacitative pulse to ground. Try putting
a surge suppressor in line where the wiring emerges from the pond to flatten
the pulse.

--
for full context, visit https://www.homeownershub.com/uk-diy...cd-159345-.htm

On Monday, 10 September 2018 14:14:06 UTC+1, Jon R wrote:
replying to John Stumbles, Jon R wrote:
As noted above, the coil in the motor is highly inductive, and when the pump
is switched off, it generates a short high voltage spike,. The cable to the
pump is probably long and submerged, so there is a fair capacitive coupling to
ground (through the water). So, although there is no fault with the pump and
wiring, there Is still a very brief capacitative pulse to ground. Try putting
a surge suppressor in line where the wiring emerges from the pond to flatten
the pulse.

very useful to get debatable advice 13 years after the event.

replying to Jon R, JR wrote:
I'd just thought I would add my little bit. I just bought a brand new pump and
wired a plug to to it, plug it into the mains kitchen plug, and it trips my
RCD every time I switch it off. It's new and the wiring is not underground.
Awaiting an electrician.

--
for full context, visit https://www.homeownershub.com/uk-diy...cd-159345-.htm

On Thursday, 19 September 2019 13:14:04 UTC+1, JR wrote:
replying to Jon R, JR wrote:
I'd just thought I would add my little bit. I just bought a brand new pump and
wired a plug to to it, plug it into the mains kitchen plug, and it trips my
RCD every time I switch it off. It's new and the wiring is not underground.
Awaiting an electrician.

98% likely it's either the pump or the RCD.


NT