Replace MCB with RCBO's

Joined
2 Oct 2010
Messages
116
Reaction score
4
Location
Surrey
Country
United Kingdom
Maybe I’ve got that wrong, but I’m sure I read on here somewhere that there needed to be a means of providing local isolation (e.g. via an FCU) to a thermostat that could otherwise only be isolated at the consumer unit. Thinking about it, the thread I’m thinking of probably relates to underfloor heating so I assumed it would relate to wall mounted electric rads too. As it stands, the circuit runs consumer unit -> thermostat -> FCU -> Electric heater.

I’ll see if I can track down the thread I’m thinking of.

tbh makes my life much easier if I can leave things as they are.
 
Joined
28 Jan 2011
Messages
50,154
Reaction score
3,354
Location
Buckinghamshire
Country
United Kingdom
Maybe I’ve got that wrong, but I’m sure I read on here somewhere that there needed to be a means of providing local isolation (e.g. via an FCU) to a thermostat that could otherwise only be isolated at the consumer unit.
As you probably realise from my question, I'm unaware of any such regulation. In fact, as far as I am aware, there are extremely few (if any) requirements in the Wiring Regulations for anything to have a 'local' means of isolation in domestic premises.

Having said that, it often makes sense to have such means of isolation, in order to avoid having to disable too many things (at the CU) when something 'goes wrong' or needs attention. However, that's different from a 'regulatory requirement'.

Kind Regards, John
 
Joined
2 Oct 2010
Messages
116
Reaction score
4
Location
Surrey
Country
United Kingdom
If there’s no requirement then I don’t see the need to do it and I’m all the happier for it. One less thing to do.

My installation has three independent heating circuits covering the bedrooms, the hall & kitchen, and the lounge which in my mind offers enough discrimination and local(ish) isolation given the CU is just outside my front door in an adjacent utility cupboard.
 
Joined
28 Jan 2011
Messages
50,154
Reaction score
3,354
Location
Buckinghamshire
Country
United Kingdom
If there’s no requirement then I don’t see the need to do it and I’m all the happier for it. One less thing to do. ... My installation has three independent heating circuits covering the bedrooms, the hall & kitchen, and the lounge which in my mind offers enough discrimination and local(ish) isolation given the CU is just outside my front door in an adjacent utility cupboard.
Fair enough - as you say, that doesn't sound unreasonable ('convenience'-wise).

As for whether there is a 'requirement', you'd better wait to make sure that no-one comes up with one - but I doubt that they will!

Kind Regards, John
 
Joined
2 Oct 2010
Messages
116
Reaction score
4
Location
Surrey
Country
United Kingdom
As for whether there is a 'requirement', you'd better wait to make sure that no-one comes up with one - but I doubt that they will!

Kind Regards, John

indeed. If someone knows of it I’m sure they’ll be forthcoming.
 
Joined
2 Oct 2010
Messages
116
Reaction score
4
Location
Surrey
Country
United Kingdom
Well, it took me most of an afternoon and into the early evening, but i got it done. Surprisingly hardwork getting it all to fit. Not helped by the CU being quite shallow in depth, and there not being a lot of space behind the RCBO's once fitted - hence having to run the functional earths over the top. Not ideal, but it works. I know theres some debate about using bootlate crimps, but i love them - makes terminating multi core wires so much easier. Aesthetically, i like the yellow on blue too.

upload_2021-7-10_22-51-1.jpeg
 
Joined
2 Oct 2010
Messages
116
Reaction score
4
Location
Surrey
Country
United Kingdom
Whilst i was doing it i thought i might as well put in another couple of 32A's whilst i can get hold of them - gives me the option of running in a second cooker line and a kitchen ring when i replace the kitchen. Taking out the double width RCD means i could always potentially add more later too - though tbh its getting so busy in there that at that point i think it will be new CU time
 

bsr

Joined
5 Aug 2008
Messages
679
Reaction score
61
Location
Gloucestershire
Country
United Kingdom
Have you noticed the CU getting warmer? I was looking into RCBOs but one of the concerns I noted was that the parasitic current draw is much higher - up to 5W per RCBO.
 
Joined
2 Oct 2010
Messages
116
Reaction score
4
Location
Surrey
Country
United Kingdom
Have you noticed the CU getting warmer? I was looking into RCBOs but one of the concerns I noted was that the parasitic current draw is much higher - up to 5W per RCBO.

when i took the cover off yesterday to do some more testing / tidying up i did notice some of the 32A RCBO's felt warm. Don't really have any sense of what the MCB's were like so i can't say if this is warmer or not. When i get a moment I'll take the lid off again and grab a thermal image - got one of those thermal camera add ons for my phone a while back. Can't say that my electrical monitoring system has picked up an increase in the base load of my flat - certainly nothing in the region of 50W (5W per RCBO). If anything, my base load seems to have dropped - but that's probably because i didn't plug something back in...
 

bsr

Joined
5 Aug 2008
Messages
679
Reaction score
61
Location
Gloucestershire
Country
United Kingdom
Interestingly though, this spec sheet from Wylex says the current draw is comparable to the MCBs.

Although the RCBOs are switching both poles so could have twice the draw in real service?
 

Attachments

  • 20171130143632_0_224019 Wylex SNC RCBO (Web).pdf
    1.5 MB · Views: 15
Sponsored Links
Top