4A fuse - how common are they ?

[Simon47]

Was looking at the manual for a Keston boiler and it specifies that the supply must be via a 4A fuse (P30). It strikes me as a rather odd instruction given it's not a standard BS1362 size and that's by far the most likely means of protection it would be connected to.
Presumably if you used a 5A fuse they'd say it invalidates the warranty, and it might blow a 3A fuse (no idea how much current it actually draws). If they answer my other queries I might ask them about this.
In case you're wondering, we have a rental flat that needs a new boiler, and so far this (at a price) seems like the only possibility that meets the regs for a flue.

 

[mainline]

Was looking at the manual for a Keston boiler and it specifies that the supply must be via a 4A fuse (P30). It strikes me as a rather odd instruction given it's not a standard BS1362 size and that's by far the most likely means of protection it would be connected to.
Presumably if you used a 5A fuse they'd say it invalidates the warranty, and it might blow a 3A fuse (no idea how much current it actually draws). If they answer my other queries I might ask them about this.
In case you're wondering, we have a rental flat that needs a new boiler, and so far this (at a price) seems like the only possibility that meets the regs for a flue.

Take the 4amp replace with a 5 and save it

 

[James]

BS1362 Fuses can be of any rating between 1 and 13A in 1A increments.
However the preferred sizes are 3 5 10 and 13

 

[Simon47]

Take the 4amp replace with a 5 and save it

I assume it's saying the installer has to provide the fuse. I can't say I've ever come across a 4A one before.

 

[Simon47]

BS1362 Fuses can be of any rating between 1 and 13A in 1A increments.
However the preferred sizes are 3 5 10 and 13

And many places have nothing but 3A and 13A.

 

[nicebutdim]

I've seen manufacturer's instructions specify odd fuse ratings and it's irksome given the relative lack of availability. I've also wondered if it was a means of denying warranty claims, but reckon that's unlikely unless it's an appliance likely to be assessed in situ.

 

[Avo Mk8]

If you look at the tolerance on fusing characteristics of (at least BS1362) fuses, they are fairly broad.
Only the 3A and 13A shown below, but a 3A fuse is allowed to take a sustained load between ~4.7A to ~5.6A without blowing.
I would suggest a 3A fuse would work, but not knowing the running current of the Keston boiler, I won't encourage you to do that as a 3A one might get the most microscopically bit warmer than a 4A one would!

 

[brianmoooore]

Running currents are given in the manual, and with the biggest boiler covered by it, plus the full load auxiliary current (pump?), it's not going to exceed 1.5A.
I'd be quite happy to feed this with a 3A fuse.

 

[Simon47]

Am I the only one who gets "irritated" when you ask a technical question, and get an answer from someone who ignores any engineering aspect and cites "because MIs" ?

The answer I got back basically said "4amp as per MI’s ... there is no way of working around this as it is a manufacturers requirement" As Brian says, not a huge load - 180W for the model I'm looking at, or under 1A. Add in one pump, still well within 3A.

I had another query which was also answered with "because MIs and we can't change it".

FFS, as the manufacturer, and I assume the design authority, in principle the engineers could change things if there was a business justification. But I suspect the real engineers never get to hear what people are asking for if the customer support team are efficient at blocking access.
I challenged the inadequate response of "because MIs" and was told "being the technical department of the manufacturers does not allow us to make alterations to a written document regarding the correct way to install the product". Interestingly, on P6 of the manual there's a note which says "... unless covered by these Installation and Servicing Instructions or as otherwise recommended by Keston in writing. If in doubt please enquire." So clearly whoever wrote the manual envisaged the possibility of there being authorised departures from the manual - pity the customer services people didn't get that message.

Oh well, I'll try again when I've figured out how to phrase it "in a constructive manner"

 

[brianmoooore]

Chapter 12 of BS7672 allows for deviations, as long as they're recorded, and you have sufficient knowledge to justify them.

 

[davesparks]

Don't worry about the 4A fuse, it's a Keston boiler, it'll be dead by the time you've found one and it's been delivered.