B3 MCBs in domestic installation

[Dartlec]

Going to fit an 'boiling' tap for a plumber next week so asked for a pic of the CU and got this:



which is all rather odd. Doesn't affect what I want to do, but the first time I've been B3 MCBs being used and can't think of any reason why someone would choose them over the standard B6

The label appears to have been custom printed, which suggests this wasn't a DIY bodge up - not to mention that the sheds never sold B3 as an option as far as I'm aware, so seems like someone went out of their way to spec this from scratch.

Are there any benefits that I'm missing? Or could this just be someone using up old stock they happened to have. Seems like it would just be more likely to trip if a lamp blows, and unless it's wired in bellwire, 6A really shouldn't ever be an issue in terms of protecting cabling.

And yes I'll check out the "micro wave" on a 6A breaker when I'm there - my suspicion is that it may have become the boiler feed at some point...

Or maybe this was a very early example of April Fools joke perpetrated by eFixx??

 

[Dustydazzler]

I am going back possibly 10 years but I would always get my MK split boards from Eddies near me and they accidently stocked up on 3amp MCBs back then and chucked me a few boxes of free ones.
So from time to time I would use them up for boiler circuits , door bells and smoke circuits etc even garage lighting

 

[DPG]

At least the fans won't need fusing down.

 

[Dustydazzler]

At least the fans won't need fusing down.

I have never fused a fan down in my life on a 6a circuit ( but don't tell anyone )

 

[telectrix]

I have never fused a fan down in my life on a 6a circuit ( but don't tell anyone )

me neither. 6A MCB will trip before a 3A fuse anyway or if really unlucky, like I had once on a vivarium, 2 x 5A fuses and the 6A MCB all tripped on a heat lamp failure.

 

[ipf]

Nowt up with 'em, if appropriate.

 

[pc1966]

I would argue that we should be using C3 RCBOs for most light circuits, etc, these days, if only anyone made them...

 

[James]

I would argue that we should be using C3 RCBOs for most light circuits, etc, these days, if only anyone made them...

why?
they are there to protect the circuit from overload, if we used 0.5mm cable then maybe but with even as small as 1mm it really is not necessary and will just lead to more people falling down the stairs when the lamp fails in the upstairs bedroom and the top floor lights go out.

I may agree with you if houses were wired with a lighting circuit for each room individually but if you are covering a whole floor then just no, keeping the power on through a minor and short lived fault is important.

remember, a 1mm cable is not going to get overtemperature if you pull 16A for 30 seconds.

 

[pc1966]

why?

Because we could drop the charade about bathroom fans needing a 3A fuse.

 

[ipf]

I find the most frequent use for such low current rated breakers is for control circuits in control panels. Can't see the benefits in consumer units.

 

[pc1966]

1mm it really is not necessary and will just lead to more people falling down the stairs when the lamp fails in the upstairs bedroom and the top floor lights go out.

A C3 MCB would have roughly the same surge trip point as a B6 (5-10 * 3 versus 3-5 * 6)

 

[James]

A C3 MCB would have roughly the same surge trip point as a B6 (5-10 * 3 versus 3-5 * 6)

Sorry, didn’t notice the C type in your post.
However, I can’t stand B type breakers personally I see them as a hair trigger. There are few cases that a C type won’t meet disconnection times.

 

[freddo]

We used to use them for things like door chime transformers and smoke detector circuits when we used to install MK consumer units. MK consumer units got a bit crappy so we moved to a different brand.