[Simon]

I will shortly be replacing a central heating controller clock. The entire
house is covered by a single RCD at the consumer unit, so I guess good
practice is to shut down the entire house rather than rely on the single
pole MCB feeding the clock, and try not to touch neutral to anything
earthed. What would a professional electrician do in this case?

I plan to do this job in daylight, as the lighting will either be off from
the start (if I switch off the entire house) or may go off suddenly (if I
only switch off the MCB and get careless with the wires). How would a proper
electrician handle this situation? Do they carry powerful torches for use in
the winter months? Is limiting myself to daylight hours the sign of a
ill-prepared bogder?

Thanks

[Rumble[_3_]]

Simon wrote:
I will shortly be replacing a central heating controller clock. The entire
house is covered by a single RCD at the consumer unit, so I guess good
practice is to shut down the entire house rather than rely on the single
pole MCB feeding the clock, and try not to touch neutral to anything
earthed. What would a professional electrician do in this case?

I plan to do this job in daylight, as the lighting will either be off from
the start (if I switch off the entire house) or may go off suddenly (if I
only switch off the MCB and get careless with the wires). How would a proper
electrician handle this situation? Do they carry powerful torches for use in
the winter months? Is limiting myself to daylight hours the sign of a
ill-prepared bogder?

Thanks


Well, the central heating should either have a 13A plug or be connected
to a Fused Spur. If it's a plug, unplug it.

If the fused spur has got double pole switching, turn it off and tape it
off with some insulating tape whilst you rewire the timer.

If the fused spur does not have double pole switching, change it for one
that does, then turn it off and tape it off with some insulating tape
whilst you rewire the timer.

A pro would turn the fused spur off and then grumble when the RCD
tripped. He would then remove the neutral wire from the input side of
the spur and tape it up whilst he rewired the timer.

[John Rumm]

Rumble wrote:

A pro would turn the fused spur off and then grumble when the RCD
tripped. He would then remove the neutral wire from the input side of
the spur and tape it up whilst he rewired the timer.

Switched FCUs will usually have double pole switches since this is what
is required for isolation.


--
Cheers,

John.

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

[David Hansen]

On Thu, 08 Nov 2007 23:14:21 +0000 someone who may be Rumble
wrote this:-

Well, the central heating should either have a 13A plug or be connected
to a Fused Spur.

If it is fed from a power circuit.

Alternatively it may be fed by a dedicated circuit, though even then
a local fuse may be necessary if some equipment is designed to be
protected by a 3A fuse.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

[Rumble[_3_]]

John Rumm wrote:
Rumble wrote:

A pro would turn the fused spur off and then grumble when the RCD
tripped. He would then remove the neutral wire from the input side of
the spur and tape it up whilst he rewired the timer.

Switched FCUs will usually have double pole switches since this is what
is required for isolation.



I'm pretty sure that the switch in an FCU is for functional switching
not isolation. See chapter 537 of the regs.

[Ed Sirett]

On Thu, 08 Nov 2007 20:34:39 +0000, Simon wrote:

I will shortly be replacing a central heating controller clock. The entire
house is covered by a single RCD at the consumer unit, so I guess good
practice is to shut down the entire house rather than rely on the single
pole MCB feeding the clock, and try not to touch neutral to anything
earthed. What would a professional electrician do in this case?

Switch the CH off at its (double pole) switch or remove its plug.
After that the lights stay, the kettle is working and you only have the
job to consider. Read the FAQs.

All time switches do the same job that is to provide connect the mains to
certain wires at certain times of the day.


--
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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

[Ed Sirett]

On Fri, 09 Nov 2007 13:12:14 +0000, Rumble wrote:

John Rumm wrote:
Rumble wrote:

A pro would turn the fused spur off and then grumble when the RCD
tripped. He would then remove the neutral wire from the input side of
the spur and tape it up whilst he rewired the timer.

Switched FCUs will usually have double pole switches since this is what
is required for isolation.



I'm pretty sure that the switch in an FCU is for functional switching
not isolation. See chapter 537 of the regs.

I have just looked up 537 and I don't see anything about the use of a FCU
being unacceptable. The FCU has a double pole switch. In my book an
unswitched socket or switched FCU is entirely acceptable as the
maintenance (and emergency isolator) for a domestic CH system.



--
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
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

[Rumble[_3_]]

Ed Sirett wrote:
On Fri, 09 Nov 2007 13:12:14 +0000, Rumble wrote:

John Rumm wrote:
Rumble wrote:

A pro would turn the fused spur off and then grumble when the RCD
tripped. He would then remove the neutral wire from the input side of
the spur and tape it up whilst he rewired the timer.
Switched FCUs will usually have double pole switches since this is what
is required for isolation.


I'm pretty sure that the switch in an FCU is for functional switching
not isolation. See chapter 537 of the regs.

I have just looked up 537 and I don't see anything about the use of a FCU
being unacceptable. The FCU has a double pole switch. In my book an
unswitched socket or switched FCU is entirely acceptable as the
maintenance (and emergency isolator) for a domestic CH system.



I wasn't suggesting that FCU's were unacceptable. I was observing that
it is inappropriate to refer to a switched FCU as an isolator.

Isolation has a specific meaning within the Regulations.

Double pole switching is *not* required (on a single phase supply) for
isolation and FCUs do not comply with the majority of the other
requirements of 537-02, viz:

FCU doesn't have minimum 3mm contact gap.

FCU doesn't have positive indication of contact position.

FCU doesn't have provision against unintentional reclosure.

FCU doesn't have a provision for locking off.

[John Rumm]

Rumble wrote:

Double pole switching is *not* required (on a single phase supply) for
isolation and FCUs do not comply with the majority of the other
requirements of 537-02, viz:

FCU doesn't have minimum 3mm contact gap.

Does not have to have, but many do anyway (the DP ones at least).

FCU doesn't have positive indication of contact position.

They have a readily observable switch position, and possibly a neon.

FCU doesn't have provision against unintentional reclosure.
FCU doesn't have a provision for locking off.

That depends a bit, on many you can also open the fuse tray and put a
padlock through it (by design), although obviously that does not
guarantee someone will not close the switch and make the neutral
connection.

See pdf page 7 for example (also note the comment on contact separation
on page 2):

http://www.mkelectric.co.uk/PDF/tech..._PLUS_prod.pdf


--
Cheers,

John.

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