Fusing of fans to comply with manufacturers recommended instructions

[Charlie_]

Manufacturers instructions are usually nonsensical, inappropriate and unattainable; a bit like the serving suggestions on food packaging

 

[leebut]

Manufacturers instructions are usually nonsensical, inappropriate and unattainable; a bit like the serving suggestions on food packaging

Might be nonsensical but as per The Wiring Regulations which in the UK we have to follow the manufacturers instructions supersede the Regulations and the greatest knowledge of all the electrician

 

[Wilko]

Hi - sorry to be a party pooper, but a BS1363 3A fuse is more sensitive to overload than a BS60898 6A mcb. For example, the 3A fuse will always melt at 6A but the mcb will never trip.

View attachment 48822

Ha - of course 1363 is one better than 1362 - oops

 

[Andy78]

Might be nonsensical but as per The Wiring Regulations which in the UK we have to follow the manufacturers instructions supersede the Regulations and the greatest knowledge of all the electrician

This is not the case. The regulations ask us to "take account of" manufacturer's instructions. This has recently been changed from the previous wording of "must be followed"

The reason for this is the proliferation of less than useful or appropriate info that is included in some products. Some would ask us to install to lesser standards than BS7671 asks.

 

[GeorgeCooke]

Might be nonsensical but as per The Wiring Regulations which in the UK we have to follow the manufacturers instructions supersede the Regulations and the greatest knowledge of all the electrician

Rubbish. Manufacturers instructions are for guidance only and yes we have to take account of them. But we do not have to follow them, especially when they are wrong.

In this case,
1. FCUs are not needed or used on lighting circuits which are already adequately protected.
2. A 3a FCU offers no discrimination against a 6a MCB in spite of 'Contacts' post above.
3. The fuse is to protect the cable, not the device on the end of it. It would be non compliant for a manufacturer to fit a cable so small it required 3a protection.
4. How would the manufacturers instructions be complied with in all the other countries where FCUs are neither available nor compliant?

 

[Marcus Vaughan]

2. A 3a FCU offers no discrimination against a 6a MCB in spite of 'Contacts' post above.

Why are so many people saying this? If you look at the time/current trip curves - then the 3amp fuse will trip first?

Am I missing something?

 

[GeorgeCooke]

I think you are missing the experience of what actually happens in practice.

 

[Charlie_]

3amp fuse blows (it won’t trip).. and then how many variants can that be replaced with?

 

[westward10]

The 3A fuse serves one purpose to hopefully rupture if the motor seizes and hence prevent fire from overheating windings.

 

[Charlie_]

PCB mounted fuse built into the fan would be the best solution

 

[Wilko]

Hi - Out of curiosity I have asked manufacturers what this is all about but they've been tight lipped. I have seen fans that don't spec 3A fuses and they seem to have a fuse on the control board and/or claim they've a thermal overload for the motor.

 

[Marcus Vaughan]

I think you are missing the experience of what actually happens in practice.

Sorry - that's not good enough for me to not follow Manufacturers Instructions. I still don't see why some people think the MCB will disconnect before the fuse.

 

[Marcus Vaughan]

I think you are missing the experience of what actually happens in practice.

Sorry - that's not good enough for me to not follow Manufacturers Instructions. I still don't see why some people think the MCB will disconnect before the fuse.

 

[Marcus Vaughan]

PCB mounted fuse built into the fan would be the best solution

Seems like a plan.

Another plan would be to use manufacturers that do not stipulate the 3amp fuse. I've stopped using Manrose, and am now using Envirovent. I see Greenwood don't ask for a 3 amp fuse either.

 

[GeorgeCooke]

Sorry - that's not good enough for me to not follow Manufacturers Instructions. I still don't see why some people think the MCB will disconnect before the fuse.

As I said what would you do if you were fitting the fan in a country where FCUs are not available nor compliant?

 

[Taylortwocities]

I’m not sure. Shall I ask Winston1 on diynot.com? He keeps banging on about exactly this, in the same way that you do.

He also has a thing about transformers, and not having 13A sockets on lighting circuits too.

Exactly the same bees that you have in your bonnet. Hmm, makes you wonder, do you have a long-lost identical twin?

 

[GeorgeCooke]

No I suggest you ask the manufacturer.

 

[freddo]

It would have to be a rather crappy fan for the motor not to have a thermal fuse embedded in the windings.

 

[Michaelwgroves]

Assuming you bring all wiring back to bathroom light, how about an inline fuse here, space permitting?
It wouldn't work in my bathroom as I have spots, but the vast majority of installs I do, I use Polo lights.

 

[sheppertonspark]

AFDD, soon this fuse problem will be irellavent (not sure if I've spelt that correctly).