3 amp fuse in FCU for boiler

[winston1]

Agreed.

How DO they do in Europe though?

Is it possible they run a seperate radial with a 5 or 3 amp MCB?

Do FCUs or similar exist there?

FCUs do not exist in Europe (possibly with the exception of Malta and Gibraltar). I don't think you find 5 or 3 amp MCBs either. Boilers are normally plugged in to a Schuko socket protected by a 16 amp MCB in the CU.

 

[SUNRAY]

The internal fusing inside the load.

But as I mentioned before the responsibility to provide correct load protection is with the system manufacturer, in the case of a heating system with external components, such as valves etc, the manufacturer is the person bringing all the component parts together at the point of installation.

So I'll ask again, as the manufacturer (ie the electrician at the point of installation) what load protection do you, the electrician/engineer/designer/installer, add AFTER the isolator.

I'll bet that none of you consider adding any additional OCD and happily accept the protection offered by the device aimed at protecting the cable.

 

[SUNRAY]

FCUs do not exist in Europe (possibly with the exception of Malta and Gibraltar). I don't think you find 5 or 3 amp MCBs either.

Of course they do!!!!!!

Boilers are normally plugged in to a Schuko socket protected by a 16 amp MCB in the CU.

Not in my limited experience of working abroad.

 

[SUNRAY]

So would they run a seperate circuit for the boiler with a <3 amp mcb?

As you indicate, they do tend to run many seperate radials from what little I have seen over there.

In my experience, yes.

 

[SUNRAY]

Well, you are free to interpret it however you wish - but what it actually says that if the load is considered to be such that it is "not likely" to result in an overload current, then, provided there is adequate protection, the cable does not have to have any overload protection.

It is a different reg which allows from downstream overload protection.

So it is perfectly OK to install a complete house lighting system with 0.5mm² flex on a 50A MCB if the installer considers an overload is "not likely"... No I don't think so either

As I've just written, no - and I think that applies to most people, not just myself.

So while fitting some sort of connection device it makes total sense to incorporate a fuse of appropriate rating, which is also very likely to be one of the most economical devices to use.

The MI will usually call for both a 3A fuse and an isolator.

Kind Regards, John

And IF it does (my experience is different) then I will fit a 3A device, otherwise the house insurance will become null and void... oh you didn't think of that?

 

[JohnW2]

So it is perfectly OK to install a complete house lighting system with 0.5mm² flex on a 50A MCB if the installer considers an overload is "not likely"... No I don't think so either

You're trying to get silly. If you believed that the loads were such that overload was "unlikely" then it would probably be compliant with a 16A MCB (the regs do not allow lighting circuits >16A), provided you were satisfied that the load would not exceed the CCC of your flex.

And IF it does (my experience is different) then I will fit a 3A device, otherwise the house insurance will become null and void... oh you didn't think of that?

I think of all sorts of things, and am very happy to argue my case with anyone (insurer or whoever) who 'tries it on'! In any event, I'm not sure that I've ever heard of a house fire originating in a domestic extractor fan, no matter how externally fused. Don't forget that they have an internal thermal fuse/cutout which, as my experiments a while back indicated, operate at a current of well under 1A, and before the motor even gets too hot too touch and long before any wiring gets remotely warm.

Kind Regards, John

 

[SimonH2]

Has anyone experienced a situation where an internal fuse OR a 3 amp fuse in the FCU has blown?

Yes. Fixed No1 daughter's boiler last week - a connection had spring a leak and it just needed a new O ring. Putting it back together, the live terminal on the back of the main switch touched the case and it blew both of them. The terminal was supposed to be protected by an insulated cover - but the clip had broken and the hinge had opened enough to expose the terminal.
I had a replacement fuse for the FCU in my toolbox, but no spare 20mm fuses (of anything like the correct rating)

 

[JohnW2]

Yes. Fixed No1 daughter's boiler last week - a connection had spring a leak and it just needed a new O ring. Putting it back together, the live terminal on the back of the main switch touched the case and it blew both of them.

So I presume that the absence of the external 3A fuse would have made no difference?

Kind Regards, John

 

[SUNRAY]

Ok so now we're nit picking different ideas to demonstrate our thoughts.

You're trying to get silly. If you believed that the loads were such that overload was "unlikely" then it would probably be compliant with a 16A MCB (the regs do not allow lighting circuits >16A), provided you were satisfied that the load would not exceed the CCC of your flex.

Admittedly choosing a lighting circuit as an example was a silly choice due to the 16A limit but it doesn't detract from the point in question namely your reference to a reg allowing a cable to not be protected by an OCD if an overload is unlikely.

I think of all sorts of things, and am very happy to argue my case with anyone (insurer or whoever) who 'tries it on'! In any event, I'm not sure that I've ever heard of a house fire originating in a domestic extractor fan, no matter how externally fused. Don't forget that they have an internal thermal fuse/cutout which, as my experiments a while back indicated, operate at a current of well under 1A, and before the motor even gets too hot too touch and long before any wiring gets remotely warm.

Kind Regards, John

Ah yes but if there was a fire (or other incident) due to an electrical issue of whatever cause and the installation was inspected as a result by the insurance company and indiscretions are found such as incorrectly protected devices and especially failure to adhere to MI's, then the fight with the insurance company is very long and protracted, and to put it bluntly they usually win.

Anyway AFAIC: an OCD will be installed for heating systems without question according to the MI's regardless of whether the regs demand it or not (some of the boilers I've worked on require protection other than a 3A fuse!) and missing it out is a fools errand.

At this point I'm done, whether my views right or wrong and as long as they are compliant or better I'm happy.

 

[SUNRAY]

Yes. Fixed No1 daughter's boiler last week - a connection had spring a leak and it just needed a new O ring. Putting it back together, the live terminal on the back of the main switch touched the case and it blew both of them. The terminal was supposed to be protected by an insulated cover - but the clip had broken and the hinge had opened enough to expose the terminal.
I had a replacement fuse for the FCU in my toolbox, but no spare 20mm fuses (of anything like the correct rating)

A short after the internal fuse usually does take out both, but better two than none!

 

[winston1]

Of course they do!!!!!!

In which European countries (with the exception of Malta and Gibraltar) do FCUs exist?

 

[JohnW2]

Admittedly choosing a lighting circuit as an example was a silly choice due to the 16A limit but it doesn't detract from the point in question namely your reference to a reg allowing a cable to not be protected by an OCD if an overload is unlikely.

Well the reference to it was by EFLI, not myself - but, whatever you, I or anyone else may think, that it what the regulation says.

Were it not for the 16A limit, the regulation would, indeed, allow any cable to be protected by a 50A OPD IF it were considered that overload was "unlikely", if the cable's CCC was adequate for the load, and if the cable had adequate fault protection. In practice, it's probably the last of those requirements that would catch you.

Kind Regards, John

 

[EFLImpudence]

A short after the internal fuse usually does take out both, but better two than none!

A short is not overload current which is being discussed.

ALL cables must be protected against fault current regardless of overload protection.



It's strange how we are being berated for questioning manufacturers' instructions yet you state you would ignore 433.3.1(ii) because you don't like it.

 

[JohnW2]

In which European countries (with the exception of Malta and Gibraltar) do FCUs exist?

I think his comment related to the "5A or 3A MCBs".

Kind Regards, John

 

[SUNRAY]

A short is not overload current which is being discussed..

In this instance I did mean short, the high current is usually enough to take out both fuses, I would like to think there is usually enough discrimination for an overload

ALL cables must be protected against fault current regardless of overload protection.

Indeed, the only situation I would expect to find unprotected cable is directly off a bussbar where it is terminated with some sort of OCD. I have encountered far too many overheated cables to want to introduce any unnecessary risk, example I refused to supply temp power for a food trailer using this cable.

and this panel which 'stopped working' on Christmas day a few years ago.

It's strange how we are being berated for questioning manufacturers' instructions yet you state you would ignore 433.3.1(ii) because you don't like it.

I take it this last comment is not aimed at me, there are number of MI's and regs I don't like or even don't agree with but I don't intentionally ignore them.