To RCD protect or not to RCD protect (a hopefully simple question)?


S

Seri

My new boiler arrived today (feelings of happiness mixed with feelings of
emptiness in the wallet department).
As I was studying the wall that is to be its new home and making sure my
original designs would be accurate I realised I'd missed an area when
hatching my master plan.
I'm currently rewiring this house one room at a time.
In the kitchen I plan on having the only non RCD protected socket in the
property (for the freezer so if the RCD trips whilst on holiday the contents
won't spoil).

Questions:
Should the boiler be RCD protected or not (any pro's and con's?)
If the boiler shouldn't be RCD protected then is it okay to have it on the
same spur as the Freezer?
If the boiler can be on the same spur as the freezer then will I need to
convert that spur into a ring?
If the boiler should be on its own circuit, what rating MCB should generally
be fitted?

Thanks for any answers, as ever, it's all appreciated.

Seri
 
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L

Lurch

Questions:
Should the boiler be RCD protected or not (any pro's and con's?)
No, the only sockets\fittings that need RCD protection are ones that
are likely to supply portable equipment used outdoors. It has the same
pros and cons as the freezer, you don't lose heating or hat water if
the RCD trips.
If the boiler shouldn't be RCD protected then is it okay to have it on the
same spur as the Freezer?
Yes.

If the boiler can be on the same spur as the freezer then will I need to
convert that spur into a ring?
No, you can run two radials from one MCB. A 16A MCB with 2.5mm cables
is ample.
If the boiler should be on its own circuit, what rating MCB should generally
be fitted?
If it was on it's own circuit, then I would fit anything from a 3A MCB
upwards, and appropriate cabling to suit.
 
U

usenet

Seri said:
Should the boiler be RCD protected or not (any pro's and con's?)
There's no regulations requirement for it to be RCD protected and I
don't really see any good reason for doing so.

If the boiler shouldn't be RCD protected then is it okay to have it on the
same spur as the Freezer?
Yes, why not.

If the boiler can be on the same spur as the freezer then will I need to
convert that spur into a ring?
No, why on earth would you need/want to do that?

If the boiler should be on its own circuit, what rating MCB should generally
be fitted?
Probably needs only a very small current so a 6 amp would do, size
the wire to match.

However my feeling would be to use the same circuit as for the
freezer, wire it with 2.5sq mm and have a 20amp MCB. It's then a
'conventional' radial circuit as in the IEE On-Site Guide. The boiler
should have some means of isolating it, a double pole switch or use a
socket.
 
L

Lurch

However my feeling would be to use the same circuit as for the
freezer, wire it with 2.5sq mm and have a 20amp MCB.
16A is better as 20A needs calculating correctly and quite often needs
a smaller MCB or bigger cable.
It's then a
'conventional' radial circuit as in the IEE On-Site Guide. The boiler
should have some means of isolating it, a double pole switch
And a fuse, 3A usually. So a switched fused spur then.
or use a
socket.
Only if it's a switched socket, you shouldn't be able to remove the
socket while it's 'on-load'.
 
L

Lurch

And a DP switched socket at that!
No, a SP will do. The functional switching of the supply will be done
by the switch on the socket and the isolation is done when the plug is
removed from the socket.
Although a DP switched socket would be better.
 
L

Lurch

I was under the impression that SP switches weren't allowed for fixed
appliances in case someone mistakenly used the SP switch for isolation
rather than pulling the plug out. Possibly more of a best practice thing
than a specific regulation, though, I suppose.
That's why you usually use a DP switch for fixed appliances, and plugs
and sockets for portable appliances. Although you are right in a way.
 
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A

ARWadsworth

Lurch said:
That's why you usually use a DP switch for fixed appliances, and plugs
and sockets for portable appliances. Although you are right in a way.
I thought it was a choice of double pole switch (or DP FCU), double pole
switched socket or unswitched socket for fixed appliances. Many fixed
appliances such as cooker extractor hoods come with a moulded plug but they
do state double pole switched sockets or unswitched sockets must be used.

Lurch if I may ask a quick question, you said

Only if it's a switched socket, you shouldn't be able to remove the
socket while it's 'on-load'.

What do I do about my iron? I know it is a portable appliance but there is
no on off switch on it and if it was used on an unswitched socket I must
always insert and remove it under load. Are some appliances banned from
unswitched sockets.

Adam
 
L

Lurch

I thought it was a choice of double pole switch (or DP FCU), double pole
switched socket or unswitched socket for fixed appliances. Many fixed
appliances such as cooker extractor hoods come with a moulded plug but they
do state double pole switched sockets or unswitched sockets must be used.
Can't say as I've ever read the instructions TBH, but see the response
below, I think that answers this question as well.
What do I do about my iron? I know it is a portable appliance but there is
no on off switch on it and if it was used on an unswitched socket I must
always insert and remove it under load. Are some appliances banned from
unswitched sockets.
That's why you're meant to have switched sockets. Unswitched sockets
are for where there are other means of switching, e.g. a switch fuse
above the worktop with an unswitched socket below.
 
A

ARWadsworth

Lurch said:
Can't say as I've ever read the instructions TBH, but see the response
below, I think that answers this question as well.

That's why you're meant to have switched sockets. Unswitched sockets
are for where there are other means of switching, e.g. a switch fuse
above the worktop with an unswitched socket below.
But there is no requirement AFAIK for switched sockets (but I always fit
them), only a requirement for DP switched sockets if an appliance is fixed
(or an unswitched socket or DP switch feed to an unswitched socket) as it is
the double dole isolation that is required.

It was the point you made about a loaded circuit not being allowed to be
unplugged that I was curious about as it would be impossible with some
appliances.

Adam
 
L

Lurch

But there is no requirement AFAIK for switched sockets
I seemed to think there was, maybe I'm mistaken but it sounds
sensible.
It was the point you made about a loaded circuit not being allowed to be
unplugged that I was curious about as it would be impossible with some
appliances.
I was referring to correctly wired installations, if there isn't a
switch to functionally turn of the supply to the socket then you're
right, you can't unplug an appliance 'off-load'. This is why you need
to have things done properly.
 
Z

Z

Seri said:
My new boiler arrived today (feelings of happiness mixed with feelings of
emptiness in the wallet department).
As I was studying the wall that is to be its new home and making sure my
original designs would be accurate I realised I'd missed an area when
hatching my master plan.
I'm currently rewiring this house one room at a time.
In the kitchen I plan on having the only non RCD protected socket in the
property (for the freezer so if the RCD trips whilst on holiday the contents
won't spoil).

Questions:
Should the boiler be RCD protected or not (any pro's and con's?)
If the boiler shouldn't be RCD protected then is it okay to have it on the
same spur as the Freezer?
If the boiler can be on the same spur as the freezer then will I need to
convert that spur into a ring?
If the boiler should be on its own circuit, what rating MCB should generally
be fitted?

Thanks for any answers, as ever, it's all appreciated.

Seri
If you can put the boiler on it's own circuit to minimise the disruption
caused by an interruption elsewhere. 16A breaker 2.5mm cable or 1.5
Pirelli terminating in a switched fused spur with /without neon as per
your preference.
No reason to RCD protect the central heating in fact one might get
nuisance tripping if RCD protected. I get pretty sick in winter of
calling out the the central heating contractors to look at GCH systems
which are tripping the RCD protected side of split load consumer units.
 
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U

usenet

Lurch said:
16A is better as 20A needs calculating correctly and quite often needs
a smaller MCB or bigger cable.
I'm unconvinced by this, a 2.5sq mm radial on a 20 amp MCB is no nearer to
'needing calculation' than a 2.5sq mm ring on a 32 amp MCB is it?

And a fuse, 3A usually. So a switched fused spur then.
Why the fuse? If the boiler installation instructions demand it then
yes but it's surely not a 'generic' requirement of any permanently
wired equipment is it?

Only if it's a switched socket, you shouldn't be able to remove the
socket while it's 'on-load'.
That's a new one on me, is there an IEE regulations requirement that
states this?
 
U

usenet

ARWadsworth said:
I thought it was a choice of double pole switch (or DP FCU), double pole
switched socket or unswitched socket for fixed appliances. Many fixed
appliances such as cooker extractor hoods come with a moulded plug but they
do state double pole switched sockets or unswitched sockets must be used.
Yes, surely this is to make sure that the person disconnecting the
device really does disconnect it and doesn't (by mistake) rely on a
single pole switch.
 
S

Seri

| >My new boiler arrived today
| >Should the boiler be RCD protected or not (any pro's and con's?)

Just wanted to say thanks to everyone for responding and I will be running
the boiler from a dedicated MCB on the non RCD protected side of the CU.

Really appreciated.

Seri
 
L

Lurch

I'm unconvinced by this, a 2.5sq mm radial on a 20 amp MCB is no nearer to
'needing calculation' than a 2.5sq mm ring on a 32 amp MCB is it?
Well, I don't generally fit any 2.5mm radials with 20A MCB's unless
they're relatively short\exposed runs. I'll look into that though,
it's just the way I've always done it and I seem to think I did have
some theory behind it once!
Why the fuse? If the boiler installation instructions demand it then
yes but it's surely not a 'generic' requirement of any permanently
wired equipment is it?
So you'd fit a boiler to a DP switch with only a 16\20A MCB as
protection would you? I haven't come across a domestic boiler yet that
doesn't state "use a 3A fuse". However, I was only referring to this
particular appliance, it wasn't a generic requirement. If the CPD is
sized correctly to be able to offer overload protection to the
appliance then a DP switch is all that is required.
That's a new one on me, is there an IEE regulations requirement that
states this?
I seem to think there is, buggered if I can find it though! It's
probably written in such a way that it's doesn't mean that until
you've read it half a dozen times.
 
U

usenet

Lurch said:
Well, I don't generally fit any 2.5mm radials with 20A MCB's unless
they're relatively short\exposed runs. I'll look into that though,
it's just the way I've always done it and I seem to think I did have
some theory behind it once!
Who are 'they'? A radial wired in 2.5sq mm protected by a 20 amp MCB
is one of the 'conventional circuits' for BS1363 sockets listed in the
appendices of the IEE "On-site guide". It's only the wierd insistence
on ring circuits in this country that means radials are not so widely
used, in some situations a radial makes much more sense than a ring.

particular appliance, it wasn't a generic requirement. If the CPD is
sized correctly to be able to offer overload protection to the
appliance then a DP switch is all that is required.
Which is basically what I was saying, I think.

I seem to think there is, buggered if I can find it though! It's
probably written in such a way that it's doesn't mean that until
you've read it half a dozen times.
Anyone else any ideas?
 
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L

Lurch

Who are 'they'?
You know, them, they're everywhere and know our every move!
A radial wired in 2.5sq mm protected by a 20 amp MCB
is one of the 'conventional circuits' for BS1363 sockets listed in the
appendices of the IEE "On-site guide". It's only the wierd insistence
on ring circuits in this country that means radials are not so widely
used, in some situations a radial makes much more sense than a ring.
I'll concede that one then as I never said you can't do it, put as
many 20A radials in as you want, I'm not going to stop anyone.
Which is basically what I was saying, I think.
Sort of, depending on which way you read the question.
 
G

G&M

Yes, surely this is to make sure that the person disconnecting the
device really does disconnect it and doesn't (by mistake) rely on a
single pole switch.
What exactly is wrong with a single pole switch ? The earth is hard
connected to the neutral back at the consumer unit anyway and so the casing
is still connected. Either the regs should demand a 3P switch/removable
plug or allow single pole switches for fixed appliances.
 
M

Martin Angove

In message <[email protected]>,
On 20 May 2004 10:06:02 GMT, in uk.d-i-y (e-mail address removed) strung
together this: [...]
A radial wired in 2.5sq mm protected by a 20 amp MCB
is one of the 'conventional circuits' for BS1363 sockets listed in the
appendices of the IEE "On-site guide". It's only the wierd insistence
on ring circuits in this country that means radials are not so widely
used, in some situations a radial makes much more sense than a ring.
I'll concede that one then as I never said you can't do it, put as
many 20A radials in as you want, I'm not going to stop anyone.
[...]

Just to confirm that - note table 6F (OSG) or 4D5A. Even under
installation method 6 (in conduit in insulation) 2.5mm cable is rated at
20A. Of course, if you're going to stuff it into the conduit with half
a dozen other circuits, or run it next to the heating pipes then you
might need to think again :)

Oh yes, and don't forget the derating for rewireable fuses... in this
case according to my calculations even a 15A fuse is pushing it, but
we're talking about MCBs here presumably.

Hwyl!

M.
 
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L

Lurch

What exactly is wrong with a single pole switch ?
The regs say DP.
The earth is hard
connected to the neutral back at the consumer unit anyway and so the casing
is still connected. Either the regs should demand a 3P switch/removable
plug or allow single pole switches for fixed appliances.
You should never ever under any circumstances even contemplate placing
a switch in the earth\cpc cable.
 

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