RCD discrimination - 10mA?
 

I've had to connect an external pump controller (for a well) to a house
circuit that's on a 30mA RCD. I'd prefer to have some discrimination but
don't want a delayed RCD on the house circuit, any ideas?
I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well. If not, and nobody can suggest another solution, I'll
leave it as it is, or (possibly) use an isolating transformer.

RCD discrimination - 10mA?
 

On 24/04/2019 19:11, wrote:
I've had to connect an external pump controller (for a well) to a house
circuit that's on a 30mA RCD. I'd prefer to have some discrimination but
don't want a delayed RCD on the house circuit, any ideas?
I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well. If not, and nobody can suggest another solution, I'll
leave it as it is, or (possibly) use an isolating transformer.

I agree both or either would trip. You are probably not allowed a time
delay RCD on the house.

New dedicated circuit with it's own RCD?

--
Adam

RCD discrimination - 10mA?
 

On 24/04/2019 19:40, ARW wrote:
On 24/04/2019 19:11, wrote:
I've had to connect an external pump controller (for a well) to a
house circuit that's on a 30mA RCD. I'd prefer to have some
discrimination but don't want a delayed RCD on the house circuit, any
ideas?
I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well. If not, and nobody can suggest another solution, I'll
leave it as it is, or (possibly) use an isolating transformer.

I agree both or either would trip. You are probably not allowed a time
delay RCD on the house.

New dedicated circuit with it's own RCD?

A new circuit would be the "correct" answer but it's not really viable -
a large house with awkward runs and the need to drop down a plastered
wall. Having just looked at the price of 1kVA isolating transformers I
don't think they will be an option either.

RCD discrimination - 10mA?
 

On Wednesday, 24 April 2019 19:51:56 UTC+1, wrote:
On 24/04/2019 19:40, ARW wrote:
On 24/04/2019 19:11, wrote:
I've had to connect an external pump controller (for a well) to a
house circuit that's on a 30mA RCD. I'd prefer to have some
discrimination but don't want a delayed RCD on the house circuit, any
ideas?
I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well. If not, and nobody can suggest another solution, I'll
leave it as it is, or (possibly) use an isolating transformer.

I agree both or either would trip. You are probably not allowed a time
delay RCD on the house.

New dedicated circuit with it's own RCD?

A new circuit would be the "correct" answer but it's not really viable -
a large house with awkward runs and the need to drop down a plastered
wall. Having just looked at the price of 1kVA isolating transformers I
don't think they will be an option either.

You could just live with them being on the same RCD. Add an isolator if concerned in case the outdoor wiring goes wet, so you can continue using the indoor before solving it.


NT

RCD discrimination - 10mA?
 

On 24/04/2019 20:42, wrote:
On Wednesday, 24 April 2019 19:51:56 UTC+1, wrote:
On 24/04/2019 19:40, ARW wrote:
On 24/04/2019 19:11, wrote:
I've had to connect an external pump controller (for a well) to a
house circuit that's on a 30mA RCD. I'd prefer to have some
discrimination but don't want a delayed RCD on the house circuit, any
ideas?
I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well. If not, and nobody can suggest another solution, I'll
leave it as it is, or (possibly) use an isolating transformer.

I agree both or either would trip. You are probably not allowed a time
delay RCD on the house.

New dedicated circuit with it's own RCD?

A new circuit would be the "correct" answer but it's not really viable -
a large house with awkward runs and the need to drop down a plastered
wall. Having just looked at the price of 1kVA isolating transformers I
don't think they will be an option either.

You could just live with them being on the same RCD. Add an isolator if concerned in case the outdoor wiring goes wet, so you can continue using the indoor before solving it.


NT

Yes, that's the fallback plan

RCD discrimination - 10mA?
 

RCD discrimination - 10mA?
 

On 24/04/2019 19:11, wrote:

I've had to connect an external pump controller (for a well) to a house
circuit that's on a 30mA RCD. I'd prefer to have some discrimination but
don't want a delayed RCD on the house circuit, any ideas?

If you are cascading RCDs then the only reliable way to ensure
discrimination is with a time delay type upstream.

One way to avoid that would be to split the supply before the upstream
RCD and install a separate CU, and feed the pump controller from a
circuit on that.

I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well.

Indeed that is the problem - stick 50mA of leakage on the end of the
circuit and either one or both would trip. Most will react within two
mains cycles given enough trip current - so its harder to make a "fast"
one.

If not, and nobody can suggest another solution, I'll
leave it as it is, or (possibly) use an isolating transformer.

Here I split the incoming supply after a stand-alone main switch, and
have two CUs - one for the house, and one for anything outside. That way
regardless of what happens on on the outside circuits, problems can't
com back to affect the house CU.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

RCD discrimination - 10mA?
 

On 25/04/2019 11:04, John Rumm wrote:
On 24/04/2019 19:11, wrote:

I've had to connect an external pump controller (for a well) to a
house circuit that's on a 30mA RCD. I'd prefer to have some
discrimination but don't want a delayed RCD on the house circuit, any
ideas?

If you are cascading RCDs then the only reliable way to ensure
discrimination is with a time delay type upstream.

One way to avoid that would be to split the supply before the upstream
RCD and install a separate CU, and feed the pump controller from a
circuit on that.

I wondered whether there is a fast-acting 10mA RCD available that I
could use for the controller but I suspect the 30mA RCD would probably
trip as well.

Indeed that is the problem - stick 50mA of leakage on the end of the
circuit and either one or both would trip. Most will react within two
mains cycles given enough trip current - so its harder to make a "fast"
one.

If not, and nobody can suggest another solution, I'll leave it as it
is, or (possibly) use an isolating transformer.

Here I split the incoming supply after a stand-alone main switch, and
have two CUs - one for the house, and one for anything outside. That way
regardless of what happens on on the outside circuits, problems can't
com back to affect the house CU.
I've done that (with a split CU) at the other end of the house, which
feeds: the workshop, sheds, kitchen, car charger, utility area and some
other stuff. From there is a sub-main to a central CU with radials,
rings and light circuits for the main part of the house; the well is
connected, via a switched FCU, to one of these radials. It would be a
pain to get a dedicated circuit to where the SWA starts, whereas now
it's just a cable through the wall from the FCU to an adaptable box.
I think I'll have to live with it being on the one RCD for now (I may
change the MCB to be an RCBO to reduce the impact of any trip) and
when/if I next need to get the floorboards up I'll think about a new
circuit.

Now to confess my sins: as a short term solution I've exported the earth
about 45m to the well pump controller - an earth rod will be my next
purchase from SFix!

RCD discrimination - 10mA?
 

On 25/04/2019 13:46, wrote:
On 25/04/2019 11:04, John Rumm wrote:

Here I split the incoming supply after a stand-alone main switch, and
have two CUs - one for the house, and one for anything outside. That
way regardless of what happens on on the outside circuits, problems
can't com back to affect the house CU.

I've done that (with a split CU) at the other end of the house, which
feeds: the workshop, sheds, kitchen, car charger, utility area and some
other stuff. From there is a sub-main to a central CU with radials,
rings and light circuits for the main part of the house; the well is

I take it the house CU is all RCD in one way or another?

Any chance of introducing a non RCD split that you could then add a RCBO to?

(I did that for a kitchen circuit on my 16th edition style TT board,
when I was getting nuisance trips on the 30mA RCD side. Moved one
circuit to the 100mA time delayed side, and put in a single module RCBO
with 30mA trip just for the kitchen)

connected, via a switched FCU, to one of these radials. It would be a
pain to get a dedicated circuit to where the SWA starts, whereas now
it's just a cable through the wall from the FCU to an adaptable box.
I think I'll have to live with it being on the one RCD for now (I may
change the MCB to be an RCBO to reduce the impact of any trip) and
when/if I next need to get the floorboards up I'll think about a new
circuit.

Now to confess my sins: as a short term solution I've exported the earth
about 45m to the well pump controller - an earth rod will be my next
purchase from SFix!

What earthing system is in use in the house currently?


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

RCD discrimination - 10mA?
 

On 25/04/2019 15:48, John Rumm wrote:
On 25/04/2019 13:46, wrote:
On 25/04/2019 11:04, John Rumm wrote:

Here I split the incoming supply after a stand-alone main switch, and
have two CUs - one for the house, and one for anything outside. That
way regardless of what happens on on the outside circuits, problems
can't com back to affect the house CU.

I've done that (with a split CU) at the other end of the house, which
feeds: the workshop, sheds, kitchen, car charger, utility area and
some other stuff. From there is a sub-main to a central CU with
radials, rings and light circuits for the main part of the house; the
well is

I take it the house CU is all RCD in one way or another?
It's on a journey in that direction. It will be a mix of RCDs and RCBOs,
plus a couple of non-RCD-protected buried SWA circuits to sheds with
their own CUs.

Any chance of introducing a non RCD split that you could then add a RCBO
to?
That would still need me to run a dedicated cable - it may be the
eventual solution but it's not viable at the moment.

(I did that for a kitchen circuit on my 16th edition style TT board,
when I was getting nuisance trips on the 30mA RCD side. Moved one
circuit to the 100mA time delayed side, and put in a single module RCBO
with 30mA trip just for the kitchen)

connected, via a switched FCU, to one of these radials. It would be a
pain to get a dedicated circuit to where the SWA starts, whereas now
it's just a cable through the wall from the FCU to an adaptable box.
I think I'll have to live with it being on the one RCD for now (I may
change the MCB to be an RCBO to reduce the impact of any trip) and
when/if I next need to get the floorboards up I'll think about a new
circuit.

Now to confess my sins: as a short term solution I've exported the
earth about 45m to the well pump controller - an earth rod will be my
next purchase from SFix!

What earthing system is in use in the house currently?
TN-C-S

RCD discrimination - 10mA?
 

On 25/04/2019 16:15, wrote:
On 25/04/2019 15:48, John Rumm wrote:
On 25/04/2019 13:46, wrote:
On 25/04/2019 11:04, John Rumm wrote:

Here I split the incoming supply after a stand-alone main switch,
and have two CUs - one for the house, and one for anything outside.
That way regardless of what happens on on the outside circuits,
problems can't com back to affect the house CU.

I've done that (with a split CU) at the other end of the house, which
feeds: the workshop, sheds, kitchen, car charger, utility area and
some other stuff. From there is a sub-main to a central CU with
radials, rings and light circuits for the main part of the house; the
well is

I take it the house CU is all RCD in one way or another?
It's on a journey in that direction. It will be a mix of RCDs and RCBOs,
plus a couple of non-RCD-protected buried SWA circuits to sheds with
their own CUs.

Any chance of introducing a non RCD split that you could then add a
RCBO to?
That would still need me to run a dedicated cable - it may be the
eventual solution but it's not viable at the moment.

(I did that for a kitchen circuit on my 16th edition style TT board,
when I was getting nuisance trips on the 30mA RCD side. Moved one
circuit to the 100mA time delayed side, and put in a single module
RCBO with 30mA trip just for the kitchen)

connected, via a switched FCU, to one of these radials. It would be a
pain to get a dedicated circuit to where the SWA starts, whereas now
it's just a cable through the wall from the FCU to an adaptable box.
I think I'll have to live with it being on the one RCD for now (I may
change the MCB to be an RCBO to reduce the impact of any trip) and
when/if I next need to get the floorboards up I'll think about a new
circuit.

Now to confess my sins: as a short term solution I've exported the
earth about 45m to the well pump controller - an earth rod will be my
next purchase from SFix!

What earthing system is in use in the house currently?

TN-C-S

So non RCD head end of the circuit, exported earth just for the sub
main, and isolated TT earth at the pump end seems like the ultimate
goal. For the mo you will just have to risk the nuisance trip and try
and make sure stuff stays dry at the pump end.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

RCD discrimination - 10mA?
 

On 25/04/2019 18:11, John Rumm wrote:
On 25/04/2019 16:15, wrote:
On 25/04/2019 15:48, John Rumm wrote:
On 25/04/2019 13:46, wrote:
On 25/04/2019 11:04, John Rumm wrote:

Here I split the incoming supply after a stand-alone main switch,
and have two CUs - one for the house, and one for anything outside.
That way regardless of what happens on on the outside circuits,
problems can't com back to affect the house CU.

I've done that (with a split CU) at the other end of the house,
which feeds: the workshop, sheds, kitchen, car charger, utility area
and some other stuff. From there is a sub-main to a central CU with
radials, rings and light circuits for the main part of the house;
the well is

I take it the house CU is all RCD in one way or another?
It's on a journey in that direction. It will be a mix of RCDs and
RCBOs, plus a couple of non-RCD-protected buried SWA circuits to sheds
with their own CUs.

Any chance of introducing a non RCD split that you could then add a
RCBO to?
That would still need me to run a dedicated cable - it may be the
eventual solution but it's not viable at the moment.

(I did that for a kitchen circuit on my 16th edition style TT board,
when I was getting nuisance trips on the 30mA RCD side. Moved one
circuit to the 100mA time delayed side, and put in a single module
RCBO with 30mA trip just for the kitchen)

connected, via a switched FCU, to one of these radials. It would be
a pain to get a dedicated circuit to where the SWA starts, whereas
now it's just a cable through the wall from the FCU to an adaptable
box.
I think I'll have to live with it being on the one RCD for now (I
may change the MCB to be an RCBO to reduce the impact of any trip)
and when/if I next need to get the floorboards up I'll think about a
new circuit.

Now to confess my sins: as a short term solution I've exported the
earth about 45m to the well pump controller - an earth rod will be
my next purchase from SFix!

What earthing system is in use in the house currently?

TN-C-S

So non RCD head end of the circuit, exported earth just for the sub
main, and isolated TT earth at the pump end seems like the ultimate
goal. For the mo you will just have to risk the nuisance trip and try
and make sure stuff stays dry at theÂ* pump end.
Yes, we're in violent agreement ;-)
In practice, the pump supply may be used for other things in the future,
such as decorative lights, so I would either feed it from an RCBO at the
head end or add an RCD at the load end of the SWA (if I can find a
suitable weatherproof and lockable box at a sensible price).