3 amp fuse in FCU for boiler

[sparkwright]

Here's a new thread about fitting 3 amp fuses in FCUs for boilers, so we can carry on the discussion to find out if they are needed.

As I understand it, 3 amp fuses are required in the MI, and also some boilers do not have internal fusing. I also understand a blown circuit board or component in a boiler is something of a drama.

Discuss.

 

[winston1]

As I said in the other thread MI are for guidance only and DO NOT have to be followed especially if they are wrong. The fuse in the FCU is only to protect the cable not the boiler and controls on the end of it which should be internally protected. If the boiler does not have internal protection they are poorly designed, but the manufacturers cannot rely on an external FCU which is not available or compliant in the majority of the world. Boilers are not only sold in the UK, Ireland, and Malta. They are sold all over the EU and the only external protection is the 16 amp MCB feeding a Schuko plug.

 

[JohnW2]

As I understand it, 3 amp fuses are required in the MI, and also some boilers do not have internal fusing. I also understand a blown circuit board or component in a boiler is something of a drama. Discuss.

As I've just written in the other thread if, because of the lack of internal fusing, a boiler is deemed to require an external 3A fuse to protect its innards, one would expect that such a boiler would not be sold for use outside of the UK, and would carry warnings that it should not be used outside of the UK?

Is that really the case? Given the trivial cost of an internal fuse or two, I would have thought that manufacturers would have included them in order that the same product could be sold in all countries.

Kind Regards, John

 

[bernardgreen]

As I said in the other thread MI are for guidance only and DO NOT have to be followed especially if they are wrong.

And how would you determine that the manufacturer's instructions were wrong.

They are sold all over the EU and the only external protection is the 16 amp MCB feeding a Schuko plug.

Are you sure that the only external protection is always only the the 16 amp MCB ?

 

[JohnW2]

Are you sure that the only external protection is always only the the 16 amp MCB ?

Who knows - but, as far as I am aware, when appliances are sold in other European countries, manufacturers never impose a requirement for any external protection other than the circuit's OPD (usually 16A, except for dedicated high-load circuits), not the least because (in the absence of things like FCUs) there is no obvious way in which such additional external protection could be provided.

Kind Regards, John

 

[winston1]

And how would you determine that the manufacturer's instructions were wrong.

Using one's personal knowledge. e.g. If MI said a 3 amp fuse is needed to protect the boiler we know that is wrong because as I said above "The fuse in the FCU is only to protect the cable not the boiler and controls on the end of it which should be internally protected."

 

[bernardgreen]

Winston.

Have you considered that the fuse in th FCU could be performing two protective actions. (1) protecting the cable from FCU to boiler and (2) protecting the boiler by cutting power if the boiler develops a fault resulting in over current with the possibility of an electrical fire inside the boiler.

we know that is wrong because as I said above

You know it is wrong, please use I instead of we because you are speaking for yourself and not the general "we"

 

[sparkwright]

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

 

[JohnW2]

Have you considered that the fuse in th FCU could be performing two protective actions. (1) protecting the cable from FCU to boiler and (2) protecting the boiler by cutting power if the boiler develops a fault resulting in over current with the possibility of an electrical fire inside the boiler.

That's obviously what we're discussing.

However, as has been said by various people (including myself) countless times, if a manufacturer considers that (2) is an issue, because there is inadequate internal fusing, how can/could they sell it (without adequate internal fusing) in the rest of Europe (indeed, most of the rest of the world)?

Kind Regards, John

 

[JohnW2]

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

An internal fuse in my daughter's combi boiler once blew, but the 3A fuse in the FCU (yes, she has one) didn't, and nor did the circuit's OPD operate.

Kind Regards, John

 

[EFLImpudence]

Old Halstead/Wickes boiler

Are you sure that the only external protection is always only the the 16 amp MCB ?

If nothing else is required, why would anyone do anything else?


Here's a foreign installation manual

http://www.ajpinto.pt/downloads/file608_pt.pdf

It does state a minimum c.s.a. of 0.75mm² for the supply cable and through a double pole switch (or plug obviously).

I can't see any external fuse required. There is, of course, one on the PCB.

 

[JohnW2]

Old Halstead/Wickes boiler

Not all that 'old' (compared with mine!) - it's got electronics in it

Kind Regards, John

 

[SUNRAY]

I had not intended getting involved with this constant wittering on about the FCU only being there to protect the cable.

As far as I'm concerned that is a load of bowlocks. Any one with half a brain cells worth of common sense will recognise the futility of such a silly assumption. As is the stupid and ridiculous thought that an internal fuse is a requirement.

As I mentioned before - MY heating system consists of timeclock, thermostats, heating valves, pump and boiler. Pump, boiler and valves all come fitted with 0.5mm² flex and MI for a 3 or 5A OCD (timeclock 10A) maximum. The previous boiler had no internal fuse. These are all components and the manufacturer of the system (in this sort of case the installation engineer) is responsible for providing all the safety and not the manufacturer of the components.

So a simple question to all you saying the FCU is not to protect the load - what is the correct method of protecting the load?

And as to the rest of the world - this category is titled "ELECTRICS UK" please stop filling this thread with silly questions relating to parts of the world outside of the UK as there is a whole category within this forum dedicated for exactly those questions.

EDIT: The MI's are not wrong, they are part of the contractual agreement you enter into when you purchase the product and installing something contrary to MI's will negate any responsibility of the manufacturer or supplier, see sale of goods act for confirmation.

 

[JohnW2]

So a simple question to all you saying the FCU is not to protect the load - what is the correct method of protecting the load? .... And as to the rest of the world - this category is titled "ELECTRICS UK" please stop filling this thread with questions relating to parts of the world outside of the UK ...

The problem with that is the assertion (which, as far as i am aware, is correct) that many of the boilers (and many other things) sold in the UK are identical to those sold in other countries - countries in which there is no practical way to provide external fusing other than the circuit's OPD.

It would be different if you could convince us that the manufacturers, for some obscure reason, removed internal fuses from the boilers they sell elsewhere and then label them as UK-only products - but that would be daft in the extreme!

Kind Regards, John

 

[EFLImpudence]

As far as I'm concerned that is a load of bowlocks.

BUT -











what if you'm wrong?