Combi boiler to consumer unit

[preecy]

We had a new combi boiler installed a few years ago to replace an old conventional boiler. The plumber wired up the new combi using the fused spur/mains which feed the old boiler. The cable goes from a fused spur (mounted next to the boiler) to a switch in the kitchen, before going back to the consumer unit. We're looking to have the kitchen wall taken down and fit a new kitchen suite. The switch serves no purpose now as the combi is controlled by a wireless thermostat/programmer. The CU has a MCB for the boiler. Can i just run a new 1.5mm cable from the CU to the boiler fused spur or is there more to it than that? The boiler and CU are both located in the garage and only a few meters apart. I've not really touched a CU before but i cant imagine this being difficult. Is it just a case of isolating the power (ie: the switch in the outside switch electric meter cabinet, disconnecting the existing cable and wiring up the new one)?

 

[JohnW2]

The switch serves no purpose now as the combi is controlled by a wireless thermostat/programmer. The CU has a MCB for the boiler.

Those who work on boilers usually want to have (it may even be a regulation) a means close to the boiler of isolating it from the electrical supply (not the least because, if the CU is not within eyesight, they could not be certain that someone would not turn the boiler circuit's MCB back on if they turned it off - but a switched FCU also offers the advantage of 'double-pole isolation', which the MCB doesn't). Hence, if the FCU ('fused spur') is not a switched one, you probably should change it to a switched one if you are going to get rid of the other switch.

Can i just run a new 1.5mm cable from the CU to the boiler fused spur or is there more to it than that?

Yes, subject to the above, that's all that needs to be done.

I've not really touched a CU before but i cant imagine this being difficult. Is it just a case of isolating the power (ie: the switch in the outside switch electric meter cabinet, disconnecting the existing cable and wiring up the new one)?

Are you saying that there is an 'isolator' in the outside cabinet and that the CU is in the garage? If so, then switch off that isolator should make the CU totally safe, but you really should confirm that it is 'dead' (with some appropriate test instrument) before touching anything inside the CU As an added precaution, you could switch off the 'main switch' in the CU.

However, if you are not totally confident/comfortable about working in a CU, then you really should get an electrician to do the job - which would be very quick (and hopefully not too expensive).

Kind Regards, John

 

[preecy]

Ok cheers, yeah the FUC mounted on the wall near the boiler isnt switched, so makes sense to replace it with a switched one while doing this.
Correct, the CU and the boiler are both in the garage. The outside cabinet is on the other side (outside) of the garage wall. There probably is an isolator in the CU (not looked at it in ages) but there's definitely an isolating switch in the outside cabinet with the electric meter.
Think i'll have a quick look, then if im in any doubt ill ring a local sparky. As you say it should be a quick job.
Thanks for the help

 

[JohnW2]

There probably is an isolator in the CU (not looked at it in ages) but there's definitely an isolating switch in the outside cabinet with the electric meter.

It is ceryainly the isolator in the meter cabinet you should use. There will also be one in the CU (the "Main Switch"), but if you only used that, there would still be some live parts within the CU. As I said, even after usuing the isolator, you really should check that the CU is actually dead (everything in life, including isolators, have been known to 'not work properly!).

Think i'll have a quick look, then if im in any doubt ill ring a local sparky. As you say it should be a quick job.

Fair enough.

Kind Regards, John

 

[winston1]

As the boiler and CU are only a few metres apart there is no need for a FCU or switch. The MCB will do for both. Ignore any rubbish by the boiler manufacturer saying a FCU is required. Boilers are sold all over Europe where FCUs are not available or compliant. Boilers have internal fuses for protection.

 

[JohnW2]

As the boiler and CU are only a few metres apart there is no need for a FCU or switch. The MCB will do for both. Ignore any rubbish by the boiler manufacturer saying a FCU is required. Boilers are sold all over Europe where FCUs are not available or compliant. Boilers have internal fuses for protection.

As I said to the OP, many people will not work on boilers unless there is a means of DP isolation available in close proximity to the boiler. Even if the CU is within eyesight of the boiler, the MCB will provide only SP isolation. Whilst the fuse in an FCU is undoubtedly unnecessary, in the UK switched FCUs are often cheaper than DP switches, so might well be the more cost-effective solution.

Kind Regards, John

 

[winston1]

Why do you need double pole isolation? Why isn't single pole enough as the neutral is virtually at earth potential?

 

[JohnW2]

Why do you need double pole isolation? Why isn't single pole enough as the neutral is virtually at earth potential?

Well, for a start, BS7671 requires isolation to be double-pole in TT installations - seemingly on the basis that the potential of CPCs in a TT installation (but not a TN one) can, under certain fault conditions, be nowhere near neutral potential.

I can see their point with TN-C-S (where neutral and CPCs are joined within the premises), but I'm less sure about TN-S which, given a couple of faults, could present a similar hazard to TT.

Kind Regards, John

 

[ban-all-sheds]

As the boiler and CU are only a few metres apart there is no need for a FCU or switch. The MCB will do for both. Ignore any rubbish by the boiler manufacturer saying a FCU is required. Boilers are sold all over Europe where FCUs are not available or compliant. Boilers have internal fuses for protection.

So have you established beyond doubt that there are no gas related regulations which require MI's to be followed?

For if not then the validity of the actual instruction is irrelevant, it may be mandatory to abide by it, in which case what you have written here is rubbish which should be ignored.

My understanding is that we do not know for sure that something other than BS 7671 doesn't make the use of an FCU compulsory if the maker says it should be used, and therefore you must stop telling people that they don't have to use one.

 

[winston1]

So have you established beyond doubt that there are no gas related regulations which require MI's to be followed?

For if not then the validity of the actual instruction is irrelevant, it may be mandatory to abide by it, in which case what you have written here is rubbish which should be ignored.

My understanding is that we do not know for sure that something other than BS 7671 doesn't make the use of an FCU compulsory if the maker says it should be used, and therefore you must stop telling people that they don't have to use one.

This has been suggested before. So far, no one has come up with any regulations (gas or otherwise) to this effect. Stop inventing regulations which don't exist. Consider that boilers have their own internal protection and are plugged straight into a 16 amp circuit in other countries.

 

[JohnW2]

This has been suggested before. So far, no one has come up with any regulations (gas or otherwise) to this effect. Stop inventing regulations which don't exist.

In terms of DP isolation, rather than the fuse itself, whether there are any regulations or not, there appear to be some (probably employer-imposed) 'codes of practice' which require there to be a means of DP isolation close to any boiler that is being worked on. On two occasions in the fairly recent past, folk I know have had people (one Worcester Bosch and the other BG) refuse to service/repair a boiler because of the absence of a nearby means of DP isolation.

Consider that boilers have their own internal protection and are plugged straight into a 16 amp circuit in other countries.

In relation to the above (not the fuse), if it is 'plugged in' then one obviously has the ultimate in all-pole isolation available.

Kind Regards, John

 

[EFLImpudence]

I suspect, as there is no electrical reason and no one can find a gas regulation, it is more likely something like Health and Safety - especially with large companies like Worcester and, even more especially, British Gas.

I have known a white goods company refuse to connect an oven because the circuit did NOT have a 45A MCB - just the normal 32A.

It only takes a rumour for these things to become gospel.

 

[JohnW2]

I suspect, as there is no electrical reason and no one can find a gas regulation, it is more likely something like Health and Safety - especially with large companies like Worcester and, even more especially, British Gas.

Indeed. I would say it's fairly clear that, at least for those two companies, the rules to which their employees appear to have to work exist in the name of "health and safety" (in the everyday sense) - and, for all I know, maybe even in H&S regulations/legislation.

Kind Regards, John

 

[John D v2.0]

Depends how worried you are about the possibility of reversed polarity. Depending on your opinion of the average standard of installation and testing of central heating installs, you may well be concerned about neutral being 240v from the boiler casing

 

[ban-all-sheds]

So far, no one has come up with any regulations (gas or otherwise) to this effect.

That does not mean there aren't any.

And crucially it does not mean that you KNOW there aren't any, therefore you cannot KNOW that your advice is not, in fact, advising the commission of criminal acts.

Stop inventing regulations which don't exist.

Consider that boilers have their own internal protection and are plugged straight into a 16 amp circuit in other countries.

Consider that if there was a relevant gas regulation, then a maker could insist that his products only be installed on the third Tuesday of each month by a left-handed red-haired technician, and it would be compulsory to abide by that.