Ret. wrote:
12 months or so ago I had my old fuse box replaced with a modern CU.

I have problems with the RCD tripping whenever I first switch on my
pressure washer - and occasionally when I turn on the waste disposal
unit in the kitchen sink.

Strangely - with both, once the RCD has been reset, I can restart both
without problem.

I am assuming that it is the electrical spike caused by these motors
suddenly demanding power that is causing the trip - but is there
anything I can do about it?

Added to uk.d-i-y.

As your CU is less that 12 months old I would expect it to have two RCDs. Is
it the same RCD that trips with both the pressure washer and the waste
disposal unit?

--
Adam

ARWadsworth wrote:
Ret. wrote:
12 months or so ago I had my old fuse box replaced with a modern CU.

I have problems with the RCD tripping whenever I first switch on my
pressure washer - and occasionally when I turn on the waste disposal
unit in the kitchen sink.

Strangely - with both, once the RCD has been reset, I can restart
both without problem.

I am assuming that it is the electrical spike caused by these motors
suddenly demanding power that is causing the trip - but is there
anything I can do about it?

Added to uk.d-i-y.

As your CU is less that 12 months old I would expect it to have two
RCDs. Is it the same RCD that trips with both the pressure washer and
the waste disposal unit?

Yes - ground floor ring main.

--
Kev

Ret. wrote:
ARWadsworth wrote:
Ret. wrote:
12 months or so ago I had my old fuse box replaced with a modern CU.

I have problems with the RCD tripping whenever I first switch on my
pressure washer - and occasionally when I turn on the waste disposal
unit in the kitchen sink.

Strangely - with both, once the RCD has been reset, I can restart
both without problem.

I am assuming that it is the electrical spike caused by these motors
suddenly demanding power that is causing the trip - but is there
anything I can do about it?

Added to uk.d-i-y.

As your CU is less that 12 months old I would expect it to have two
RCDs. Is it the same RCD that trips with both the pressure washer and
the waste disposal unit?

Yes - ground floor ring main.

OK. Is it possible to try either of the two appliances out via a circuit
from the other RCD to see what happens? eg extension lead from upstairs.
Note that the circuit MUST be fed from a different RCD than the one that
feeds the ground floor ring not just a different circuit.

I strongly suspect that you have a live-neutral or live-earth low resistance
on one of the circuits protected by the RCD that covers the ground floor
sockets.

There is no reason why either of the appliances should trip an RCD unless
there is a fault somewhere.

--
Adam

John Rumm wrote:
On 11/01/2011 18:02, Ret. wrote:
ARWadsworth wrote:
Ret. wrote:
12 months or so ago I had my old fuse box replaced with a modern
CU. I have problems with the RCD tripping whenever I first switch on my
pressure washer - and occasionally when I turn on the waste
disposal unit in the kitchen sink.

Strangely - with both, once the RCD has been reset, I can restart
both without problem.

I am assuming that it is the electrical spike caused by these
motors suddenly demanding power that is causing the trip - but is
there anything I can do about it?

Added to uk.d-i-y.

As your CU is less that 12 months old I would expect it to have two
RCDs. Is it the same RCD that trips with both the pressure washer
and the waste disposal unit?

Yes - ground floor ring main.

The thing that your waste disposal and pressure washer possibly have
in common is they typically have induction motors. These have quite
high inrush current when first turned on (can be anything from 5 to 9
times their operational current). If your RCD is operating close to
its trip current anyway, this inrush can be enough to push it over
the edge.
See the sensitising RCD section he

http://wiki.diyfaq.org.uk/index.php?...Nuisance_trips

Fixing this can be tricky, since it may not actually be the result of
a true fault (having said that, its worth working through some of the
suggested tests, just in case it is). It could just be too many
circuits sharing the same RCD and the small leakages from various
appliances adding up. If this is the case, you may be able to reduce
the effects by swapping which RCD the problem circuit is on, or
possibly installing a dedicated RCBO for that circuit to give it its
"own" leakage budget that does not need to be shared with other
circuits.

Thanks for the advice and the link John. I'm not sure that I have the
necessary expertise to sort this out for myself. The electrician who
installed my CU lives on the same estate as me - just around the corner, so
if I can't resolve it myself I may ask him to come and take a look.

--
Kev

John Rumm wrote:
On 11/01/2011 19:49, Ret. wrote:
John Rumm wrote:
On 11/01/2011 18:02, Ret. wrote:
ARWadsworth wrote:
Ret. wrote:
12 months or so ago I had my old fuse box replaced with a modern
CU. I have problems with the RCD tripping whenever I first switch
on my
pressure washer - and occasionally when I turn on the waste
disposal unit in the kitchen sink.

Strangely - with both, once the RCD has been reset, I can restart
both without problem.

I am assuming that it is the electrical spike caused by these
motors suddenly demanding power that is causing the trip - but is
there anything I can do about it?

Added to uk.d-i-y.

As your CU is less that 12 months old I would expect it to have
two RCDs. Is it the same RCD that trips with both the pressure
washer and the waste disposal unit?

Yes - ground floor ring main.

The thing that your waste disposal and pressure washer possibly have
in common is they typically have induction motors. These have quite
high inrush current when first turned on (can be anything from 5 to
9 times their operational current). If your RCD is operating close
to its trip current anyway, this inrush can be enough to push it
over the edge.
See the sensitising RCD section he

http://wiki.diyfaq.org.uk/index.php?...Nuisance_trips

Fixing this can be tricky, since it may not actually be the result
of a true fault (having said that, its worth working through some
of the suggested tests, just in case it is). It could just be too
many circuits sharing the same RCD and the small leakages from
various appliances adding up. If this is the case, you may be able
to reduce the effects by swapping which RCD the problem circuit is
on, or possibly installing a dedicated RCBO for that circuit to
give it its "own" leakage budget that does not need to be shared
with other circuits.

Thanks for the advice and the link John. I'm not sure that I have the
necessary expertise to sort this out for myself. The electrician who
installed my CU lives on the same estate as me - just around the
corner, so if I can't resolve it myself I may ask him to come and
take a look.

You may be able to do some preliminary stuff to help him track it
down. Stuff like unplugging all the other appliances from the
circuits that are protected by the RCD that trips, and then seeing if
you can still get it to trip with just the pressure washer or waste
disposal. If you can, then that would point to a neutral to earth
short somewhere in the wiring.

Okey doke -I'll give that a try. The waste disposal trip is infrequent and
so I don't think I can do much with that - but the pressure washer trips it
every time I first switch it on. Can't quite understand why it should do it
the first time I turn the washer on - but not the second time after
resetting the RCD.

--
Kev