Boiler Wiring Query

Danny30

Just an update. I just spoke with the installers.

I suggested the option of a second isolator switch on the wall near the pipes coming off the the current wire as suggested on this thread. He called the electrician who has agreed to do that so that seems like a good solution.
They will also apply a blanking plate on the current isolator switch.

I will now check if it is possible to get a chrome blanking plate. If not then I'll just have the white one.

Thank you all so much for the advice. Really helped me to find a suitable option away from what they suggested. 

Section62

Danny30 said:

I suggested the option of a second isolator switch on the wall near the pipes coming off the the current wire as suggested on this thread. He called the electrician who has agreed to do that so that seems like a good solution.
They will also apply a blanking plate on the current isolator switch.

I will now check if it is possible to get a chrome blanking plate. If not then I'll just have the white one.

Thank you all so much for the advice. Really helped me to find a suitable option away from what they suggested. 

The existing isolator also contains a fuse (so is technically a "fused connection unit" or FCU) - the fuse protects all the equipment and wiring downstream of that point.

Before removing the existing FCU the electrician should be confirming that all the wiring downstream is adequately protected by whatever fuse/MCB there is in the consumer unit for that circuit.  If not, they should either (i) change the MCB (ii) upgrade the wiring, or (iii) retain the existing FCU where it is.


Otherwise, you've got a good result.

Jeepers_Creepers

Good result, Danny.

Yes, you can get polished chrome blank socket covers, and even 'screwless' types - the face clips on to a plastic frame that's screwed in place first (check eBay if not a local electrical wholesaler/retailer.)

Now, the BG controller that's also up there! How is that wired to the boiler?! Since there's seemingly only a single cable going to the boiler, I wonder if it's a 5-core so's it also connects the boiler to that controller...

Anyhoo, I'm sure the sparky will be up to it And, if they remove that BG thingy, you can stick another chrome blank plate on that...

Jeepers_Creepers

Section62 said:

The existing isolator also contains a fuse (so is technically a "fused connection unit" or FCU) - the fuse protects all the equipment and wiring downstream of that point.

Before removing the existing FCU the electrician should be confirming that all the wiring downstream is adequately protected by whatever fuse/MCB there is in the consumer unit for that circuit.  If not, they should either (i) change the MCB (ii) upgrade the wiring, or (iii) retain the existing FCU where it is.


Otherwise, you've got a good result.

That's a very good point, since the BG controller next to that FCU will be supplied by it, and not just the boiler.

So, unless that controller is removed entirely, it would still - theoretically - need that FCU to provide fused protection for it.

Oooooh, it's sooo complicated :-)

Section62

Jeepers_Creepers said:

That's a very good point, since the BG controller next to that FCU will be supplied by it, and not just the boiler.

So, unless that controller is removed entirely, it would still - theoretically - need that FCU to provide fused protection for it.

Oooooh, it's sooo complicated :-)

More than theoretically, because even with the controller removed is possible any of the wiring used in a heating system (including that flex) could be 1.0mm2, 0.75mm2 or even 0.5mm2, and the MCB(/fuse) is what... 6A, 16A, 20A, 32A?

So all that downstream wiring needs to be checked out and the correct CU MCB(/fuse) confirmed, or keep the FCU having also checked the fuse in that is right.

I'd start on the basis the electrician who did the rewire had a reason to use the FCU there.....

Danny30

Section62 said:

Jeepers_Creepers said:

That's a very good point, since the BG controller next to that FCU will be supplied by it, and not just the boiler.

So, unless that controller is removed entirely, it would still - theoretically - need that FCU to provide fused protection for it.

Oooooh, it's sooo complicated :-)

More than theoretically, because even with the controller removed is possible any of the wiring used in a heating system (including that flex) could be 1.0mm2, 0.75mm2 or even 0.5mm2, and the MCB(/fuse) is what... 6A, 16A, 20A, 32A?

So all that downstream wiring needs to be checked out and the correct CU MCB(/fuse) confirmed, or keep the FCU having also checked the fuse in that is right.

I'd start on the basis the electrician who did the rewire had a reason to use the FCU there.....

Oh dear. What does this mean then. They can't use that wire from the fuse board to the boiler? 

Section62

Danny30 said:

Oh dear. What does this mean then. They can't use that wire from the fuse board to the boiler? 

No, it should be Ok to use, although it isn't possible to say definitely Ok without examining the whole length.

The issue is that the wire needs to be protected by a sufficiently low rated fuse (e.g. so the fuse blows before the wire melts)

At the moment the FCU above the toilet door probably has a 3 or 5 amp fuse in it. If the FCU is being removed the electrician needs to make sure the 'trip' for the boiler on the consumer unit (fuse board) has a low enough rating for the whole of that wire until it reaches the FCU in the new position.

It isn't really something for you to worry about, the electrician should take care of it, but I was surprised he had confirmed over the phone it could be done - it is the kind of thing you need to look at to really know whether it is Ok or not.

If you want further reassurance then have a look at the consumer unit trip for the boiler circuit. It should have a letter and number like 'B6', 'B16', 'B20' etc written on the front of it (the 'B' could be a 'C').  Let us know what it says.

Danny30

Section62 said:

Danny30 said:

Oh dear. What does this mean then. They can't use that wire from the fuse board to the boiler? 

No, it should be Ok to use, although it isn't possible to say definitely Ok without examining the whole length.

The issue is that the wire needs to be protected by a sufficiently low rated fuse (e.g. so the fuse blows before the wire melts)

At the moment the FCU above the toilet door probably has a 3 or 5 amp fuse in it. If the FCU is being removed the electrician needs to make sure the 'trip' for the boiler on the consumer unit (fuse board) has a low enough rating for the whole of that wire until it reaches the FCU in the new position.

It isn't really something for you to worry about, the electrician should take care of it, but I was surprised he had confirmed over the phone it could be done - it is the kind of thing you need to look at to really know whether it is Ok or not.

If you want further reassurance then have a look at the consumer unit trip for the boiler circuit. It should have a letter and number like 'B6', 'B16', 'B20' etc written on the front of it (the 'B' could be a 'C').  Let us know what it says.

Hi, the fuse for the boiler is B16. 

Jeepers_Creepers

Danny, I think you said earlier on that this circuit was put in by a sparky and it is solely for the use of the boiler - is that so? Ie, that 16A MCB has 'boiler' only written on it?

That would be ideal, but if it's the case, that MCB should preferably be the smallest, a 6A. That would offer the best - most sensitive - protection for the cable, especially if some of it is only 0.5mm as S62 says.

But, don't worry - this is a qualified sparky, and should figure out what's going on. Let's not worry

Section62

Jeepers_Creepers said:

But, don't worry - this is a qualified sparky, and should figure out what's going on. Let's not worry

Eh?  What's happened to the electrician whose workmanship was recently described as "poor, poor, poor"?  Has he been fired from the job now? 

The electrician is probably competent and knows what he's talking about.  But as I said in a previous post, it is a bit surprising that "we've got to do it this way" has turned into doing it exactly in the way you suggested Danny asks for it to be done, with a level of confidence you could only get after inspecting the installation.

Maybe my cynical side is thinking the situation might change back to the installer's preference once the job is started ("we've hit a snag")... or should my charitable side think the electrician will fund all the additional work needed out of their own pocket when they encounter problems?

There's no need for Danny to worry, but being informed is being prepared. 

Jeepers_Creepers said:

That would be ideal, but if it's the case, that MCB should preferably be the smallest, a 6A. That would offer the best - most sensitive - protection for the cable, especially if some of it is only 0.5mm as S62 says.

Again, for clarity, it isn't a case of 'preferably' - this is a MUST.  The protective device MUST have an appropriate rating for the load and the downstream wiring, up to the point where another protective device (if any) with a lower current rating takes over.  It isn't about sensitivity (that's a separate issue), it is about stopping the cable/flex being subjected to a current exceeding its design limit.


Danny, the 16 amp rating confirms what I suspected.  You don't need to worry about it, but the electrician should check the cable and if any of it is undersize for 16A then use one of the options I posted previously - i.e. changing the MCB to a lower rating, or retaining the FCU where it is, or upgrading the cable to a size suitable for use with the 16A MCB.

The electrician has probably got this covered, but as you want the work done a specific way which the installer initially rejected, you need to be prepared with the right responses if the installer again tells you it can't be done the way you want (once they have started work), because you may not have time to come back here and check. But it's up to you whether you want to now leave it in the installer's hands of course.