Well whoever made that requirement was wrong then. As we all know the fuse is to protect the cable not what is on the end of it. That requirement should say all gas fed appliances should be protected internally at a max of 3 amp.
Boiler Supply Q
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I believe the requirement is to cover all circuitry connected to that of a gas appliance, so in the case of CH systems, pumps, valves, stats etc all need to be @ 3A max. So it can't be necessarily be satisfied by fitting a fuse in the boiler.
What does this 'magic' 3A prevent as far as a gas appliance - only in the UK - is concerned?
Don't forget - we are frequently told that the same is required for an extractor fan.
Don't forget - we are frequently told that the same is required for an extractor fan.
It will not surprise you to hear that all I can say is that your guess is as good as (maybe even better than
) mine!Kind Regards, John
That might be true but, if so, what has that got to do with 'gas regulations' (which is what I thought we were talking about)? There must be very few gas -powered pumps, valves, stats etc. around
Kind Regards, John
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No they are not, but the appliance they are all connected to is.
Yes, but as I presume you understand, my question related to why 'gas regulations' should be concerned about electrical 'protection' of items that were not 'gas appliances'.
Kind Regards, John
My guess would be something along the lines of : Boiler (gas appliance) is connected to various external devices, some of those devices can feed power into the boiler, we want a limit of a 3A fuse on such supplies.
Personally I think it's a bit bogus and the appliance should be "safe" whatever you feed into it's terminals (and noting that systems are starting to get more complicated these days). Relying on a user-replaceable fuse isn't safe as many people will work on the basis that a 13A fuse is the same size as a 3A fuse, therefore it must be an acceptable replacement for one - or they work on the basis that if a 3A fuse blows, then it's obviously too small and a 13A one should be substituted
Possibly the simplest example is an S-Plan setup with a boiler having both permanent and switched live inputs. The permanent live probably powers the boiler's internals (and typically has it's own internal fuse), the switched-live input probably just triggers the "fire up" circuits (and should be internally protected against faults as well). As a secondary thing, you don't really want the external controls applying power to the switched-live input when the permanent live isn't there - that's a recipe for someone seeing that the boiler is switched off and then finding out the hard way that bits of it are still live. Hence the BS7671 requirement for having a single means of isolation that turns off the entire system.
At the moment my CH system is on 2 13A plugs. One supplies the boiler which has just the volt-free contacts of a tank stat connected to it. The other powers the pump and zone valves. There's no electrical connection between them - the boiler simply fires when the thermal store needs more heat, and the CH runs from the store.
Personally I think it's a bit bogus and the appliance should be "safe" whatever you feed into it's terminals (and noting that systems are starting to get more complicated these days). Relying on a user-replaceable fuse isn't safe as many people will work on the basis that a 13A fuse is the same size as a 3A fuse, therefore it must be an acceptable replacement for one - or they work on the basis that if a 3A fuse blows, then it's obviously too small and a 13A one should be substituted
Possibly the simplest example is an S-Plan setup with a boiler having both permanent and switched live inputs. The permanent live probably powers the boiler's internals (and typically has it's own internal fuse), the switched-live input probably just triggers the "fire up" circuits (and should be internally protected against faults as well). As a secondary thing, you don't really want the external controls applying power to the switched-live input when the permanent live isn't there - that's a recipe for someone seeing that the boiler is switched off and then finding out the hard way that bits of it are still live. Hence the BS7671 requirement for having a single means of isolation that turns off the entire system.
At the moment my CH system is on 2 13A plugs. One supplies the boiler which has just the volt-free contacts of a tank stat connected to it. The other powers the pump and zone valves. There's no electrical connection between them - the boiler simply fires when the thermal store needs more heat, and the CH runs from the store.
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I believe it is because the non gas appliances are connected to the same supply as the gas appliance.
Because everything electrical associated with the boiler should be on the same supply as the boiler.
And the boiler is limited to 3A, therefore so is all the associated circuitry.
Why not ring Gas Safe and enquire?
Because everything electrical associated with the boiler should be on the same supply as the boiler.
And the boiler is limited to 3A, therefore so is all the associated circuitry.
Why not ring Gas Safe and enquire?
Which is an argument built on invalid assumptions.
It's only valid if you assume that the boiler needs the external 3A fuse to be safe. As in my previous post, that's an unsafe premise to start from since it's too easy for a non-skilled person to change the fuse and fit a larger value. So once you scratch the requirement for a 3A fuse to protect the boiler - then it comes down to "the fuse should protect the wiring", and noting that many devices such as stats are rated for more than 3A anyway.
It's a bit of an academic discussion anyway since in a domestic setting you are unlikely to need bigger than a 3A fuse for the whole system.
It's only valid if you assume that the boiler needs the external 3A fuse to be safe. As in my previous post, that's an unsafe premise to start from since it's too easy for a non-skilled person to change the fuse and fit a larger value. So once you scratch the requirement for a 3A fuse to protect the boiler - then it comes down to "the fuse should protect the wiring", and noting that many devices such as stats are rated for more than 3A anyway.
It's a bit of an academic discussion anyway since in a domestic setting you are unlikely to need bigger than a 3A fuse for the whole system.
I think we are probably talking about two different things here.
All of what you say above is a fairly good reason for requiring that all components of a CH system have a 'common el;ectricity supply', and I have no argument with that.
However, the discussion was about (3A) fuses, and I think we are agreed that if there are parts of the boiler which someone believes might benefit from 'protection' by a 3A fuse (I personally doubt that!), then such a fuse should exist internally in the boiler (not 'externally', as seemingly required by many MIs). However, it was suggested that, even if the boiler did have an internal 3A fuse, the requirement for an additional external one might be for the 'protection' of parts of the CH system other than the (internally protected) boiler - and that's the bit which I can't see should be any interest/concern to 'gas regulations'.
Kind Regards, John
Not "... it's provided internally" but, rather, "... it should be provided internally".
Kind Regards, John
The 3A fuse fits in with the 0.5mm² flex used on some heating systems for connections to the various components.
A 3a fuse will also limit the total energy to a low value in the event of a fault which will reduce or prevent damage to components.
A 3a fuse will also limit the total energy to a low value in the event of a fault which will reduce or prevent damage to components.
That's often been discussed, but I think it's nearly always going to be 'wishful thinking' (even though, probably being one of the greatest users of 1A BS1362 fuses, I don't necessarily practice what I preach/believe
)..In any event, as most people usually say/agree, if it is felt that a fuse of a particular rating may offer some useful protection to a particular piece of equipment, then there should be such a fuse within the equipment.
Kind Regards, John
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