hi, i recently had a new mains board installed by a friend. i have a TT
system so in the new board i have a 100mA and 30mA RCD. Every night when the
boiler comes on, in trips out the 30mA RCD. Ive been told its the element on
my old boiler. is this true? if so, is there anything i can do apart from
getting a new boiler?


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In article , paddy
writes
hi, i recently had a new mains board installed by a friend. i have a TT
system so in the new board i have a 100mA and 30mA RCD. Every night when the
boiler comes on, in trips out the 30mA RCD. Ive been told its the element on
my old boiler. is this true? if so, is there anything i can do apart from
getting a new boiler?
If it's a gas boiler that would be quite a trick.

Does it only trip on central heating or does it trip when just heating water
too? If only on CH demand, the motorised valve may have come leakage.
--
fred

paddy wrote:

hi, i recently had a new mains board installed by a friend. i have a TT
system so in the new board i have a 100mA and 30mA RCD. Every night when the
boiler comes on, in trips out the 30mA RCD. Ive been told its the element on
my old boiler. is this true? if so, is there anything i can do apart from
getting a new boiler?

Element? Are you sure you are not talking about an immersion heater? If
so then yes they can be prone to causing unwanted RCD trips when they
start getting on a bit. Replacement is the only real cure in these cases.

If you are talking about a boiler (as in gas or oil), then the trip
would indicate a fault. You will need to start investigate further as to
what is causing the trip. Checking there are no leaks inside would be a
good start - a damp PCB or wiring loom would cause the problem you are
seeing.

Note that there is no reason to have either a boiler or an immersion on
the 30mA RCD anyway. They would be better of protected by just the 100mA
trip RCD.

--
Cheers,

John.

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

In message , John
Rumm writes
paddy wrote:

hi, i recently had a new mains board installed by a friend. i have a
TT system so in the new board i have a 100mA and 30mA RCD. Every
night when the boiler comes on, in trips out the 30mA RCD. Ive been
told its the element on my old boiler. is this true? if so, is there
anything i can do apart from getting a new boiler?

Element? Are you sure you are not talking about an immersion heater? If
so then yes they can be prone to causing unwanted RCD trips when they
start getting on a bit. Replacement is the only real cure in these cases.

If you are talking about a boiler (as in gas or oil), then the trip
would indicate a fault. You will need to start investigate further as
to what is causing the trip. Checking there are no leaks inside would
be a good start - a damp PCB or wiring loom would cause the problem you
are seeing.

Or pump


Note that there is no reason to have either a boiler or an immersion on
the 30mA RCD anyway. They would be better of protected by just the
100mA trip RCD.


--
geoff

In article ,
wrote:
hi, i recently had a new mains board installed by a friend. i have a TT
system so in the new board i have a 100mA and 30mA RCD. Every night when
the boiler comes on, in trips out the 30mA RCD. Ive been told its the
element on my old boiler. is this true? if so, is there anything i can
do apart from getting a new boiler?


What make and model? Modern electronic ones might possibly have a fault
that could trip an RCD, but on an older one my money would be on the pump.

--
*I finally got my head together, now my body is falling apart.

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

wrote:

Note that there is no reason to have either a boiler or an immersion on
the 30mA RCD anyway. They would be better of protected by just the 100mA
trip RCD.


If the whole installation is on the 100ma trip (likely) and a part further
protected by the 30ma trip, then transferring to the 100ma trip will plunge
the whole house into darkness when the boiler comes on. Better to fix the
fault,

Fixing the fault is indeed the first priority....

/and/ leave it 30ma protected.

Definitely not.... ;-)

There is no beneficial reason to have either a boiler or an immersion
heater on 30mA protection. They are not portable appliances, you wont be
using them outside, and they don't pose a high risk of causing a shock
to an operator.

There are however undesirable consequences of having them on the 30mA
protected side of the CU:

Immersion heaters are often made with mineral insulated elements that
will unavoidably have some leakage current. Powering one from a 30mA RCD
may unacceptably eat into the available leakage budget, and result in
sensitising the whole system which in turn could allow unwanted trips
that are not in response to a fault conditions.

Having a boiler on 30mA protection only increases the risk that the
heating may be disabled at a time where this would be undesirable (i.e.
mid winter when there is not one home for a few days any you need the
frost protection)

--
Cheers,

John.

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

John Rumm wrote:
wrote:

Note that there is no reason to have either a boiler or an immersion
on the 30mA RCD anyway. They would be better of protected by just the
100mA trip RCD.


If the whole installation is on the 100ma trip (likely) and a part
further
protected by the 30ma trip, then transferring to the 100ma trip will
plunge
the whole house into darkness when the boiler comes on. Better to fix the
fault,


Fixing the fault is indeed the first priority....

/and/ leave it 30ma protected.

Definitely not.... ;-)

There is no beneficial reason to have either a boiler or an immersion
heater on 30mA protection. They are not portable appliances, you wont be
using them outside, and they don't pose a high risk of causing a shock
to an operator.

There are however undesirable consequences of having them on the 30mA
protected side of the CU:

Immersion heaters are often made with mineral insulated elements that
will unavoidably have some leakage current. Powering one from a 30mA RCD
may unacceptably eat into the available leakage budget, and result in
sensitising the whole system which in turn could allow unwanted trips
that are not in response to a fault conditions.

Having a boiler on 30mA protection only increases the risk that the
heating may be disabled at a time where this would be undesirable (i.e.
mid winter when there is not one home for a few days any you need the
frost protection)

I aggree with that. If the guy who fitted the consumer unit really put
an immersion heater on a RCD circuit then he needs his arse kicking.

"OldBill" wrote in message
...
John Rumm wrote:
wrote:

Note that there is no reason to have either a boiler or an immersion on
the 30mA RCD anyway. They would be better of protected by just the
100mA trip RCD.


If the whole installation is on the 100ma trip (likely) and a part
further
protected by the 30ma trip, then transferring to the 100ma trip will
plunge
the whole house into darkness when the boiler comes on. Better to fix
the
fault,


I'd pass a comment here that simply shifting the immersion heater load to
the non 30mA part of the split board will result in any immersion earth
fault taking out the whole supply via the 100mA time delayed "main" RCD
breaker. Supplying it from a 30mA (or even a non time delayed 100 mA) x 16A
RCBO downstream of the 100mA time delayed RCD would be a better solution all
round as this way an immersion earth fault will clear by operating the
dedicated RCBO without loss of the whole supply. A Hager RCBO will cost
around £35 as opposed to the cost of a simple 16A MCB.
You pays your money and you takes your choice

John wrote:

I'd pass a comment here that simply shifting the immersion heater load to
the non 30mA part of the split board will result in any immersion earth
fault taking out the whole supply via the 100mA time delayed "main" RCD
breaker. Supplying it from a 30mA (or even a non time delayed 100 mA) x 16A

Indeed. I was not suggesting this as a solution to the problem. That
needs addressing first.

However it is usually considered poor practice to put even a correctly
functioning fixed load heating device like an immersion on a low trip
threshold RCD for the reasons I gave. Still the bottom line is it should
not be causing a trip in the first place.

RCBO downstream of the 100mA time delayed RCD would be a better solution all
round as this way an immersion earth fault will clear by operating the
dedicated RCBO without loss of the whole supply.

Yup, RCBOs are the "Rolls Royce" solution. In fact a plain incomer
switch followed by a RCBO on every circuit would be the ultimate in
ensuring discrimination. Bit pricey though! ;-)

A Hager RCBO will cost
around ï½£35 as opposed to the cost of a simple 16A MCB.
You pays your money and you takes your choice

One thing to bear in mind is that the Hager one is typically two modules
wide - which may be a problem in some cases. Contactum, MK, and MEM
(plus others probably) all do some single module RCBOs at the moment
which can be better as long as the CU has enough height

(BTW if you order a hager RCD from TLC at the moment they have them
listed at about 18 quid, but only seem to charge 12 odd when the bill
turns up)

--
Cheers,

John.

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

"John Rumm" wrote in message
...
John wrote:


SNIP


However it is usually considered poor practice to put even a correctly
functioning fixed load heating device like an immersion on a low trip
threshold RCD for the reasons I gave. Still the bottom line is it should
not be causing a trip in the first place.

I totally agree.


RCBO downstream of the 100mA time delayed RCD would be a better solution
all round as this way an immersion earth fault will clear by operating
the dedicated RCBO without loss of the whole supply.

Yup, RCBOs are the "Rolls Royce" solution. In fact a plain incomer switch
followed by a RCBO on every circuit would be the ultimate in ensuring
discrimination. Bit pricey though! ;-)

A Hager RCBO will cost
around ?35 as opposed to the cost of a simple 16A MCB.
You pays your money and you takes your choice

One thing to bear in mind is that the Hager one is typically two modules
wide - which may be a problem in some cases. Contactum, MK, and MEM (plus
others probably) all do some single module RCBOs at the moment which can
be better as long as the CU has enough height

The newer version are only one unit wide but have a "higher" casing which
might restrict their use to boards which have the appropriate space in them.


(BTW if you order a hager RCD from TLC at the moment they have them listed
at about 18 quid, but only seem to charge 12 odd when the bill turns up)


Compared with MCBs from other sources thats a bloody good dealg

On Sat, 9 Jul 2005 09:18:42 +0000 (UTC),it is alleged that "John"
spake thusly in uk.d-i-y:

[snip]


(BTW if you order a hager RCD from TLC at the moment they have them listed
at about 18 quid, but only seem to charge 12 odd when the bill turns up)


Compared with MCBs from other sources thats a bloody good dealg

http://www.tlc-direct.co.uk/Products/HGCD263U.html I assume we're
talking about?

Bought one ~2 weeks ago to convert an older split load board (which
for some reason best known to the installer had 2 main switches and no
RCD, maybe they intended to come back and conveniently forgot).

I was pleasantly shocked at the invoice total, and so was the
customer:-)

And yes, 63 amp was enough in this case, 2x32amp ring circuits is all
that's on the load side of it, the shower has its own RCBO installed
by the plumbing contractor or his electrical subcontractor, so that
made the choice easier.

Kind of back on topic, the BG installer was the reason for me getting
called in the first place, he *insisted* that the boiler was on an RCD
before he'd make the final connection to the FCU. I have no idea if
that's some kind of rule BG have, or if he was just being paranoid,
but after discussing with the customer the advantages in general of an
RCD, we went for one.

--
I have left orders to be awakened at any time in case of national emergency,
even if I'm in a cabinet meeting.
- Ronald Reagan

Chip wrote:

(BTW if you order a hager RCD from TLC at the moment they have them listed
at about 18 quid, but only seem to charge 12 odd when the bill turns up)


Compared with MCBs from other sources thats a bloody good dealg

http://www.tlc-direct.co.uk/Products/HGCD263U.html I assume we're
talking about?

yup, that is the one.... looks like they have updated the web site to
match what they charge rather than the other way round, which is nice ;-)

Kind of back on topic, the BG installer was the reason for me getting
called in the first place, he *insisted* that the boiler was on an RCD
before he'd make the final connection to the FCU. I have no idea if
that's some kind of rule BG have, or if he was just being paranoid,
but after discussing with the customer the advantages in general of an
RCD, we went for one.

The only advantage I can think of for having a boiler on an RCD would be
from a servicing perspective. If you are planning to work on it while
live and with the case off it would lower the risk to the operative if
there were any exposed live conductors touchable.

--
Cheers,

John.

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

On Sat, 09 Jul 2005 16:14:35 +0100,it is alleged that John Rumm
spake thusly in uk.d-i-y:

Chip wrote:

(BTW if you order a hager RCD from TLC at the moment they have them listed
at about 18 quid, but only seem to charge 12 odd when the bill turns up)


Compared with MCBs from other sources thats a bloody good dealg

http://www.tlc-direct.co.uk/Products/HGCD263U.html I assume we're
talking about?

yup, that is the one.... looks like they have updated the web site to
match what they charge rather than the other way round, which is nice ;-)

Kind of back on topic, the BG installer was the reason for me getting
called in the first place, he *insisted* that the boiler was on an RCD
before he'd make the final connection to the FCU. I have no idea if
that's some kind of rule BG have, or if he was just being paranoid,
but after discussing with the customer the advantages in general of an
RCD, we went for one.

The only advantage I can think of for having a boiler on an RCD would be
from a servicing perspective. If you are planning to work on it while
live and with the case off it would lower the risk to the operative if
there were any exposed live conductors touchable.

This might very well be the reason then, it may be a directive from on
high to reduce BG's chances of having to pay out to a grieving family
of an engineer.

In any case, it made sense:-)

--
I have left orders to be awakened at any time in case of national emergency,
even if I'm in a cabinet meeting.
- Ronald Reagan

Chip wrote:

This might very well be the reason then, it may be a directive from on
high to reduce BG's chances of having to pay out to a grieving family
of an engineer.

In any case, it made sense:-)

For them anyway ;-)

--
Cheers,

John.

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

On Sat, 09 Jul 2005 15:25:45 +0000, Chip wrote:

On Sat, 09 Jul 2005 16:14:35 +0100,it is alleged that John Rumm
spake thusly in uk.d-i-y:

Chip wrote:

(BTW if you order a hager RCD from TLC at the moment they have them listed
at about 18 quid, but only seem to charge 12 odd when the bill turns up)


Compared with MCBs from other sources thats a bloody good dealg

http://www.tlc-direct.co.uk/Products/HGCD263U.html I assume we're
talking about?

yup, that is the one.... looks like they have updated the web site to
match what they charge rather than the other way round, which is nice ;-)

Kind of back on topic, the BG installer was the reason for me getting
called in the first place, he *insisted* that the boiler was on an RCD
before he'd make the final connection to the FCU. I have no idea if
that's some kind of rule BG have, or if he was just being paranoid,
but after discussing with the customer the advantages in general of an
RCD, we went for one.

The only advantage I can think of for having a boiler on an RCD would be
from a servicing perspective. If you are planning to work on it while
live and with the case off it would lower the risk to the operative if
there were any exposed live conductors touchable.

This might very well be the reason then, it may be a directive from on
high to reduce BG's chances of having to pay out to a grieving family
of an engineer.

Any lawyer working for BG would simply state that the appliance
instructions state that maintenance must done with the appliance isolated
from gas and electric supplies. Year Right.

--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html