Fuse rating in heating FCU

Is there anything to say that the BS1362 fuse in a central heating connection unit has to be 3A. Given that the smallest cable is a 0.75mm flex, is there any reason that the fuse could not be rated at 5A. This is purely hypothetical and results from a discussion with a colleague, we would just like some opinions on whether their is a specific regulation concerning domestic heating systems.

The one that usually applies is you have to follow manufacturers instructions.

If they say it's 3A, that is what you must fit.

If there's no specific mention of fusing in the boilers manual, then normal cable sizing and protection applies.

Have had discussions with heating engineers and they do not

like anything other than a 5A BS1362 or 1361 in an FCU for a

heating system. According to them, a larger fuse takes longer

to disconnect and sometimes, damage occurs to the control

circuit.

Others might comment on this.

Someone has said that it should be 3A for a gas boiler and 5A for oil. Never heard that one myself but...

Is there anything to say that the BS1362 fuse in a central heating connection unit has to be 3A. Given that the smallest cable is a 0.75mm flex, is there any reason that the fuse could not be rated at 5A. This is purely hypothetical and results from a discussion with a colleague, we would just like some opinions on whether their is a specific regulation concerning domestic heating systems.

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Welcome to the forum as a poster Stoff. As Provdave points out it is the regulation that says you must follow manufactures instructions that would define the rating of fuse fitted in any FCU to any fixed appliance. Some boilers have their own internal fuses protecting their internal PCB's, older non electronic traditional heating system probably rely on the FCU fuse for protection to the whole system. 3A or 5A are the sizes typically encountered to my understanding.

Doc H.

this is a good one,

as we dont install the boilers, (well Im not GAS SAFE), then manufacturers instructions are nothing to do with me,

I protect my cable, its down to the gasman to ensure he follows manufacturers instructions.

just for the record, I do fit 3amp fuses, but Im not obliged to.

It is also a poor design of "appliance" that relies on the supply circuit protection for its own internal protection!

Hi guys first post, it is standard practice to install a 3a fuse in a boiler swfcu/plugtop.

As said it is standard practice to fit 3 amp fuses on gas circuits and 5 amp on oil. I always do its going to take a lot of amps to blow a 13 amp fuse and printed circuits are quite delicate.

I beleive I have now found the difinitive answer to this.

A BS1362 5A fuse is not recognised in BS7671: 2008. Looking at Table 41.2, the only fuses to BS1362 are listed as 3A & 13A. Likewise in Table 41.4.

So there we have our answer.

Apparently a 3A is also stated as the required size in the GasSafe instructions for boilers, but we're sparks not heating engineers so we probably don't read that.

Thanks to all who responded to this question.

Stoff

Yes, there is. It's part of the gas regs. Gas boilers must be protected by a 3A fuse. Has been the case for many years.

Most oil boilers call for 5A - my understanding is because oil boilers also have an oil pump.