There is also, of course, 433.3.1(ii) which is a regualation.
3 amp fuse in FCU for boiler
- Thread starter sparkwright
- Start date
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Indeed so - but it appears to be the view of bernard, Sunray and maybe others that a boiler, or some components thereof and/or associated components are "likely to result in an overload current".
I suppose that a pump, if jammed, could create an 'unusually high' current, but whether it would be high enough to qualify as an "overload current" and/or be high enough to blow a 3A BS1362 fuse, I don't know.
kind regards, John
Oh I can assure you a jammed pump will take out a 3A fuse and when it did one of my tenants decided to replace it with a 13A, the 0.5mm² cable then got hot and went s/c at the pumps cable clamp. Fortunately he reported it the second time the 13A blew.
But regardless of the potential overload current much of the average heating system is usually wired in 0.5 or 0.75mm flex so back to 3A FCU protecting the wiring.
I truly fail to understand why there is so much hesitation/discussion about installing such a basic device.
I thought it was a matter of course to fit an FCU with a 3 amp fuse for a boiler, and lighting from a socket circuit via an FCU with a 3 or 5 amp fuse, simply because that the way it was drummed into people, the fuse nearly matching the load, and a case of 'that's how everyone does it'.
But there's clearly different views.
Personally I like to follow MI, and I always like to fit fuses just above the required load, partly as (rightly or wrongly) every teacher has told me to, and also 'cos it just feels right and logical and that little bit safer perhaps. Superstition even.
But there's clearly different views.
Personally I like to follow MI, and I always like to fit fuses just above the required load, partly as (rightly or wrongly) every teacher has told me to, and also 'cos it just feels right and logical and that little bit safer perhaps. Superstition even.
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Maybe sometimes, but not always. When a pump in my system jammed a couple of years ago, it did not take out the 3A fuse (or anything else) and its cable only got slightly warm. In fact, the only reason I knew that anything was wrong was because it stopped pumping.
IF one believes that an overload current can arise, then I agree. EFLIs point was that there is a regulation which removes the requirement to provide overload protection for a cable if the load is "not likely" (whatever that means) to result in an overload current.
I personally think it is perfectly reasonable for people to hesitate/discuss if they feel that installation of the device in question is unnecessary.
Are you one of those who believes it is essential to supply a small extractor fan on a 6A lighting circuit via a 3A FCU?
Kind Regards, John
Since we're in the UK, I doubt that anyone is suggesting that either a boiler or lighting should be fed directly off a 32A circuit with no fusing down. Even in 'wider Europe' I doubt that people would do that with a >16A circuit (assuming they have some).
As you probably know, that is also my personal view/practice, but that's just me. However, I would rarely 'advise' anyone that they necessarily had to do the same, and certainly not tell them that they 'must', if the alternative they were contemplating was compliant and electrically 'reasonable'.
Kind Regards, John
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?
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?
It was always stated right from the start of rings that the fuse in the plug or FCU was to protect the cable. It is still legal to use 15 amp BS546 plugs in this country. They don't have fuses. If the boiler developes a fault its internal fusing should cut the power.
Fair enough, I fully understand and recognise the difference between devices and ratings etc.
My interpretation of that reg, and this is my personal interpretation and non negotiable, is if the cable is protected or otherwise current limited down stream in some way.
So do you advocate wiring the boilers factory fitted 0.5mm² flex directly into a 32A ring without any form of connexion device?
No unless the MI dictates otherwise, just a 3 pole isolator as a personal preference.
The internal fusing inside the load.
But again in Europe it would be the 16 amp MCB.
Now that someone else has raised this positive comment about foreign installations, I will comment.
In my limited experience European wiring does tend to be much better designed than ours and yes they do tend to have massive CU's with a plethora of correctly rated radials with MCB's right down to 0.5A.
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.
As I've just written, no - and I think that applies to most people, not just myself.
The MI will usually call for both a 3A fuse and an isolator.
Kind Regards, John
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.
As has been said, and although lower-current circuits certainly exist, I think that most standard loads (including boilers) are usually connected directly to 16A circuits.
Not as far as I am aware. That is the basis of many of the comments that have been made in this discussion.
Kind Regards, John
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