I have a workshop a distance away from the house (approximately 60m).
It is fed from an MCB in a consumer unit (with an RCD as a main breaker)
through two x 2.5mm FTE. At the workshop it enters through another RCD
then into a consumer unit with three MCB, two at 20A feeding two
workshops and one at 6A feeding all lights. This consumer unit also
feeds the underfloor heating and the immersion heater.

There is a second consumer unit that does the rest of the house -
lighting circuits (protected by a single RCD) and upstairs and
downstairs sockets on RCBOs and cooker, shower etc., also covered by an
RCD. The incoming mains (pole route) is also protected through and RCD.

The reason for the RCBOs is that for a while, from what we believed to
be an external influence, the "whole house" RCD would trip and we would
lose everything. Now we have RCBOs protecting some circuits, so the
losses are contained.

That's the background!

I am currently getting "nuisance" trips of the workshop RCD, although
sometimes it also trips out unrelated RCBOs on the upstairs and
downstairs sockets (a different consumer unit to the workshop supply in
the house). At other times, just the RCD at the workshop trips.

I am trying to work out where to look. I have turned the workshop off
totally at night (through the workshop RCD) and the house hasn't
tripped. Not conclusive, but a start. I have removed circuits one by
one from their MCBs and neutral bars (stopping the neural/earth fault as
well) and this has shown that in two cases tried so far, disconnecting
these circuits, leaving the others connected, doesn't stop the trips. I
have two more circuits to work through (thank goodness it is cold as the
freezer is on one of them!)

I haven't meggered the cables between the house and workshop yet (next
weekend job when it is light) but my question is, could a fault in the
house affect the "downstream" RCD in the workshop and how can the
workshop RCD tripping affect "upstream" RCDs and RCBOs?

In other words, am I looking in the right place at the workshop end, or
could I have a house fault reflected into the workshop RCD and I'm just
wasting my time in the workshop?

Confused of Wiltshire!

"puffernutter" wrote in message
...
I have a workshop a distance away from the house (approximately
60m).
It is fed from an MCB in a consumer unit (with an RCD as a main
breaker)
SNIP
I am trying to work out where to look. I have turned the workshop
off
totally at night (through the workshop RCD) and the house hasn't
tripped. Not conclusive, but a start. I have removed circuits one
by
one from their MCBs and neutral bars (stopping the neural/earth
fault as
well) and this has shown that in two cases tried so far,
disconnecting
these circuits, leaving the others connected, doesn't stop the
trips. I
have two more circuits to work through (thank goodness it is cold as
the
freezer is on one of them!)

I haven't meggered the cables between the house and workshop yet
(next
weekend job when it is light) but my question is, could a fault in
the
house affect the "downstream" RCD in the workshop and how can the
workshop RCD tripping affect "upstream" RCDs and RCBOs?

In other words, am I looking in the right place at the workshop end,
or
could I have a house fault reflected into the workshop RCD and I'm
just
wasting my time in the workshop?

Confused of Wiltshire!



Peter,

We went through a long period of RCD trips - always in the small hours
of the night. I isolated and meggered everything but found nothing.
Eventally I changed the RCD (it was a Wylex 100A/30mA of 1996 vintage)
and it totally cured the problem. The removed RCD would latch on ok,
but the slightest tap with a screwdriver handle would trip it. It had
gone over sensitive and I suspect triggered on perturbances on the
(overhead) supply when the voltage was high.

(Incidentally I dismantled it and to my suprise it contained small
electrolytic capacitors - so they must have a finite life)

AWEM

Andrew Mawson wrote:
"puffernutter" wrote in message
...
I have a workshop a distance away from the house (approximately 60m).
It is fed from an MCB in a consumer unit (with an RCD as a main
breaker)
SNIP
I am trying to work out where to look. I have turned the workshop
off totally at night (through the workshop RCD) and the house hasn't
tripped. Not conclusive, but a start. I have removed circuits one
by one from their MCBs and neutral bars (stopping the neural/earth
fault as well) and this has shown that in two cases tried so far,
disconnecting these circuits, leaving the others connected, doesn't
stop the trips. I have two more circuits to work through (thank
goodness it is cold as the freezer is on one of them!)

I haven't meggered the cables between the house and workshop yet
(next weekend job when it is light) but my question is, could a
fault in the house affect the "downstream" RCD in the workshop and
how can the workshop RCD tripping affect "upstream" RCDs and RCBOs?

In other words, am I looking in the right place at the workshop end,
or could I have a house fault reflected into the workshop RCD and
I'm just wasting my time in the workshop?

Confused of Wiltshire!



Peter,

We went through a long period of RCD trips - always in the small hours
of the night. I isolated and meggered everything but found nothing.
Eventally I changed the RCD (it was a Wylex 100A/30mA of 1996 vintage)
and it totally cured the problem. The removed RCD would latch on ok,
but the slightest tap with a screwdriver handle would trip it. It had
gone over sensitive and I suspect triggered on perturbances on the
(overhead) supply when the voltage was high.

(Incidentally I dismantled it and to my suprise it contained small
electrolytic capacitors - so they must have a finite life)

Photos? I would love a look.

--
Adam

"ARWadsworth" wrote in message
-

SNIP
(Incidentally I dismantled it and to my suprise it contained small
electrolytic capacitors - so they must have a finite life)

Photos? I would love a look.

--
Adam



Sorry Adam but they've been binned. It was a small bit of pcb maybe
1cm square or less, with two diodes and an electrolytic capacitor - I
assumed it was forming DC for the trip circuit

AWEM