Fused isolator switch for CH boiler

[Lucky Luke]

Hello. I don't know whether this is the correct forum for my enquiry, because it concerns the electrics for a gas central heating boiler. Well, here goes (excuse me if this seems a bit long-winded, but I need to get things across very clearly).

When our gas central heating boiler was installed (12 years ago), the electrician that the heating engineer brought in (a separate firm) fed the boiler power cable from a 32-amp supply fuseway in the consumer unit. Previously, this 32 amps supply went solely to the outside work-shed, but the electrician replaced the 32-amp RCB in the work-shed with a 20-amp one. The rest of the power potential from the consumer unit went to the boiler, and between the consumer unit and the boiler, he put a square, fused box that has no switch.

I should like to be able to quickly, easily and safely isolate the boiler (even if I never need to do this, it ought to be possible, at least). Therefore, I think there is a need for a switch as well as a fuse to this isolating point. Now, here is where my ignorance shows up (read on).

Unlike other fused switch-boxes that I have bought in the past, the entry and exit cables for the one next to the boiler do not merely have the 6mm2 cable (from the supply) going through a hole punched into the bottom of the plastic box — it has two nuts (also at the top, where the round, white cable emerges, one of these, top and bottom, is a lock-nut. So, it seems to be a special kind of fused switch-box, and I do not know its proper description so as to be able to order one. (I am unable to go to a store trade-counter, to tell them what I need, because of virus restrictions.)

So, will some knowledgeable person out there tell me what it is called, so I can order one on-line? (I have looked, without success, hoping to see this kind of switch, on various websites.) At present, my grandson is unemployed and he is an electrician. However, he is very difficult to reach, and I want to have the gear ready to fit, before asking him to do the job. (It would probably be a simple replacement of the existing box, by the other.)

With thanks for your patience and for any information you can give,
A.W .

 

[denso13]

Can you post a photo?

 

[oldbutnotdead]

Yep, pic would be handy. You probably only need to replace the FCU you have with a switched FCU. Unlikely the supply cable is 6mm, if it was then the electrician wouldn't have derated the circuit to 20A ( which is usual for a 2.5mm radial).

 

[muggles]

Wow, so many words where a single photo would have been much more helpful

 

[ianmcd]

cable wont be 6mm2 more likely 0.75mm2 or some use 1mm2

 

[Lucky Luke]

Yep, pic would be handy. You probably only need to replace the FCU you have with a switched FCU.

Thanks, obnd. As a result of your remark, it has dawned upon this thick-head that the pattress box itself could be retained. All that would be needed would be to replace the fused unit with a switched fused unit (as you have said), using the same mounting box — right? Also, what seemed to be a problem with buying the "same kind of" mounting box (patresss box) has disappeared, since I have found out that what seemed to make it a special kind of pattress box were, in fact, two (separately obtainable, if required) STUFFING GLANDS, which I thought were an integral part of the unit. That's why I could find nothing that was exactly the same, on-line! However, they are not integral, so I could keep the old ones, also the old mounting box. It's all been a series of misunderstandings, because of my ignorance of these matters.
Regards,
A.W.

 

[oldbutnotdead]

Perfect. Isolate power, swap that FCU for a switched FCU and job jobbed. That grey T & E cable looks like 1.5mm...

 

[Madrab]

It's just been installed properly by the electrician. The glands are used when the box needs sealed say within an outbuilding etc.

 

[Lucky Luke]

It's just been installed properly by the electrician. The glands are used when the box needs sealed say within an outbuilding etc.

Well, what you say seems to be perfectly reasonable, seeing that it was a proper electrician firm that installed the wiring etc. However, I can't help wondering why the isolator fuse does not have a switch, which would be much more convenient than taking the fuse out. Can you suggest a good reason for it not being switched? By the way, the boiler is in an outhouse (it's in a closet under the stairs, with an outside-only access door).
Regards,
A.W.

 

[denso13]

Can you suggest a good reason for it not being switched?

Hard to tell but if, as you say, it is in an "outhouse" it may have been done to stop any nuisance or accidental switching off.

 

[Harry Bloomfield]

I was under the impression that a boiler was required to have a DP means of isolation, adjacent to it?

OP - just buy a replacement DP switch fuse.

 

[Madrab]

Yeah, those types are usually used as an anti tamper fused unit, also where there may be damp conditions then a switch can be potentially dangerous if it were to be touched.

 

[Lucky Luke]

Yeah, those types are usually used as an anti tamper fused unit, also where there may be damp conditions then a switch can be potentially dangerous if it were to be touched.

That rings a bell with me, Madrab. It may have been intended that only an engineer was expected to isolate the boiler, and, being placed where it is (and in a confined little closet, at that), I suppose it COULD be accidentally switched off. It seems best to leave it as it is, after all. Anyway, I have learned something from these exchanges, and that's always worth something, to me!
Thanks to everyone that has replied.
Regards to all,
A.W.

 

[Madrab]

Ultimately that circuit may feed back to it's own MCB in the consumer unit so it can be isolated there if need be.

 

[Lucky Luke]

Ultimately that circuit may feed back to it's own MCB in the consumer unit so it can be isolated there if need be.

Yes, it does. However, the work-shed and the boiler both use the same fuseway (one fuse for the two circuits). That was the reason for my thinking that it would be more convenient to have a switch on the fused connector immediately next to the boiler. As it is, if the boiler needs to be isolated at the consumer unit, it would also isolate the work-shed, which might not be convenient at the time.
A.W.