Fusing of fans to comply with manufacturers recommended instructions

[garaoke]

Manufacturers want there fans fused to 3a on the permanent feed but the switch wire is still on the 6a MCB doing an eicr is a c2 if there is no RCD protection

 

[SparkyAndGeorge]

c3 if no RCD on bathroom lights but check IP ratings & zones also. Seen several installs with a split load board where the bathroom light and fan were wired off the ring via a 3a fused spur, thus providing the RCD protection.

 

[Charlie_]

Just put the respective lighting circuit on a 3a MCB

 

[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.

 

[leebut]

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

Hence the reason why the manufacturers know best and stipulate the fuse for protection

 

[Marcus Vaughan]

Just put the respective lighting circuit on a 3a MCB

I’ve been through that thought process myself - but tend to use Hager or MK boards - neither of which have 3 amp MCB’s.

I am now just choosing fans where the manufacturer does not stipulate 3 amp...

 

[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