3 amp fuse in FCU for boiler

[ericmark]

I suppose the difference between what I have done in commercial premises and domestic is it is under the control of an ordinary person. So it must have a consumer unit not a distribution unit for example. Not allowed repairable fuses, and so the question is if it needs protecting at less than 13A then can you really use a FCU as these have no way to stop some one fitting a 13A instead of 3A this is why we are no longer allowed rewireable fuses in a house distribution unit.

So if it needs a 3A supply then it would need to be a MCB at the consumer unit and a dedicated supply, otherwise the incorrect fuse could be fitted. Yes that is going silly but if you can't have rewireable fuses in domestic in case the wrong size is fitted, then neither can you expect the ordanary person to fit 3A not 13A.

I have seen where the pumps, valves and other control gear have exceed 3A and a 5A was fitted, however 3 and 13 amp are the two preferred sizes however this is where the fuse protects the cable, you can get 1, 2, 3, 5, 7, 10 and 13 amp and the manufacturer could stipulate any of those sizes, however getting other than 3 and 13 is not so easy, most electricians will have 3 and 13 in their tool bag but a 2A is unlikely to be carried, so if called to a system with a blown 2A or 1A fuse unless the longer or shorter fuses not used in a plug, it will likely be replaced with a 3A.

 

[SimonH2]

Well that's a different discussion altogether. I can only assume that when the "13A plug" was being designed, they decided that the convenience of having all the fuses the same size outweighed the risk of the wrong one being fitted. They could have done different sizes (like the old cartridge fuse fuseboards) so that (say) a 13A fuse wouldn't physically fit in a "3A plug" - but I imagine that had they done that, we'd be having loads of moans about how inconvenient it is having different plugs for different fuse ratings
At the end of the day, there's a limit to how far you can protect people from themselves. The logical next step is to do away with fuses - because I think we all know that a piece of 1/4" (or 6mm) bolt fits nicely in place of a BS1362 fuse and solves problems of the fuse blowing* So when do we start seeing plugs with integral MCBs

* c.f. a farm I've worked on many years ago with one of those Pickhill 180A oil filled welders that like to eat 13A fuses. One day the rubber plug exploded - the casing peeled back like a banana skin, and the fuseholder was reduced to a blob of copper on the end of what was left of the live core

 

[JohnW2]

Bzzzt - wrong. In SOME installations other components are wired (get their power from) the boiler, but especially in older systems, the boilers tend to just have L&N supply and a switched live to make it run - some very old ones are even simpler and the boiler runs when power is applied to it. .... Before it got replaced recently, the system at my parents house had all the stats and zone valves supplied from the FCU - with the switches on the zone valves controlling the pump and boiler.....

Indeed, and mine is one of those 'very old' boilers to which you refer.

However, whilst I can't speak for anyone else, I have been thinking/talking of an FCU/Plug which, like mine and your parents old arrangements, is supplying/'protecting' all components of the CH system, not necessarily just the boiler. That does not, however, make much difference to what we've been discussing - since if a boiler manufacture 'requires' 3A fusing, that presumably must relate to the boiler alone (together with all components it contains or is designed to 'power'), since they can't know what else might be connected to the circuit.

Even on systems where external stuff is powered from an output terminal on the boiler, without something in the manual to say so or examining the internals, it would be dangerous to assume that the output terminal went through the fuse on the control board - it's quite possible that the output is switched but the fuse only protects the control board.

That's quite possible - but, again, since it relates to components other than the boiler, I'm not sure it makes much sense for the boiler manufacturer to impose 'requirements' to protect ('unknown') things other than the boiler. Indeed, I suppose it's theoretical possible that (if they did not have adequate internal protection) some of those 'other things' might need a degree of 'protection' that was not adequately provided by a 3A fuse!

Kind Regards, John

 

[mwatsonxx]

My boiler doesn't have a fuse, should I be worried

 

[JohnW2]

My boiler doesn't have a fuse, should I be worried

Do you mean no internal fuse (like mine) or no fuse at all? If the latter, what is the OPD protecting the circuit?

Kind Regards, John

 

[SimonH2]

There are other ways of protecting a circuit - a resistor used as a fuse, small transformers where the winding will fail before it could blow a fuse, ....

 

[JohnW2]

There are other ways of protecting a circuit - a resistor used as a fuse, small transformers where the winding will fail before it could blow a fuse, ....

I would think they would count as 'ad hoc fuses' - but since they aren't designed for such a purpose, their performance/characteristics as fuses would presumably not be known.

Kind Regards, John

 

[mwatsonxx]

There are other ways of protecting a circuit - a resistor used as a fuse, small transformers where the winding will fail before it could blow a fuse, ....

Ha ha ha, been waiting for someone to mention that fact. That will keep these numpties going for another month. hahaha

 

[mwatsonxx]

Do you mean no internal fuse (like mine) or no fuse at all? If the latter, what is the OPD protecting the circuit?

Kind Regards, John

What is an OPD?

 

[JohnW2]

What is an OPD?

If you don't know that, I doubt that you should be attempting to contribute to this forum.

Mind you, I suppose that since your contributions seem to major on comments about "waffling", that does not require any particular knowledge about matters electrical.

Kind Regards, John

 

[SimonH2]

I would think they would count as 'ad hoc fuses' - but since they aren't designed for such a purpose, their performance/characteristics as fuses would presumably not be known.

Yes, a fuse of a type - but someone looking at the device wouldn't normally "see a fuse". I believe that some components do have parameters stated for such uses - but if you have (say) an 1/8W metal film resistor, then you can be sure that it won't take much to fuse it. If you look inside most "wall wart" power supplies with a main transformer, I doubt you'll find a fuse - the connecting leads to the transformer will do the job and can be "designed" (ie CSA selected) for their fusing characteristics.

 

[JohnW2]

Yes, a fuse of a type - but someone looking at the device wouldn't normally "see a fuse". I believe that some components do have parameters stated for such uses - but if you have (say) an 1/8W metal film resistor, then you can be sure that it won't take much to fuse it.

Well, that obviously depends upon the value of the resistor! However, the point is that you won't know the exact 'fusing characteristics', nor how safely it would 'blow'. One can, of course, get 'fusible links', designed for the job and with known characteristics, which look much like a small resistor.

Kind Regards, John

 

[mwatsonxx]

Have any of you considered why the WIRING regulations are called the WIRING regulations, it would provide all the answers to this unbelievable nonsense.

 

[JohnW2]

Have any of you considered why the WIRING regulations are called the WIRING regulations, it would provide all the answers to this unbelievable nonsense.

Does that mean that, provided the cable connecting it is adequately protected by some over-current device, you do not think that a boiler needs to be protected by a 3A fuse, even if the manufacturer (but not the WIRING regulations) say that it does?

Kind Regards, John

 

[mwatsonxx]

The WIRING regulations are not applicable to ANY connected equipment, because they are the WIRING regulations. They are not the equipment connection regulations.

Any premise in this country can be completely inspected and tested and certified as 100% compliant with the WIRING regulations without ANY equipment being connected.