RCBO spacing

[martygturner]

Any definitive guidance out there on RCBO spacing, just going through some quotes for a flat referb, one has a note on it specifying that a 12 way board was needed to correctly space out the RCBO's to minimise " overheating and fire risk"... the two others spec a 8 way board ( its a tiny flat)

Is this something new ?

the last one we had done was installed with no spacing but the rcbo's were installed in a mix ie 32amp,6amp,32amp,16 ,,, as that electrician said they should not be ordered traditionally largest to smallest along the busbar to minimise heating but said that was to prevent unwanted tripping.

Any regs out there or is this just a case of I fink...

 

[Murdochcat]

Go back 40 years and it was recommended that they were arranged largest to smallest rating from the main switch but these things come down to best practice and personal choice of the spark.

What you don't want is a new board full up with no spacing. As for over heating - this is a questionable comment - unless you plan to have a hot tub circuit directly next to your EV point

These days I tend to "group" circuits - so radials like hob and oven, then gap, then socket circuits, gap, then radials, gap then lights, gap then outdoor circuits

How many circuits?

 

[AndyPRK]

No regulation on spaces.
You do require spare ways for expansion though.

 

[EFLImpudence]

What can we think up to bamboozle people with next year?

 

[JohnW2]

Go back 40 years and it was recommended that they were arranged largest to smallest rating from the main switch but these things come down to best practice and personal choice of the spark. ... What you don't want is a new board full up with no spacing. As for over heating - this is a questionable comment - unless you plan to have a hot tub circuit directly next to your EV point

No regulation on spaces. ... You do require spare ways for expansion though.

I agree with the above. However, some manufacturers have something to say about this, as per this relating to Wylex MCBs ...

In practice I doubt that many devices are "loaded at or approaching their nominal rates currents" for significant periods of time at all, whether adjacent or not.

 

[AndyPRK]

So what does that mean in practical terms?

1. A car charger circuit needs a gap both sides of the MCB ? (1 side could be next to a main switch which wouldn't be impacted by heat)
Alternatively.
2. If an MCB on circuit would normally pass around 32A, you would fit a 50A MCB ? (providing the cable allows)
If MCBs next to them aren't run near their rating, you would not implement changes

Are the instructions the same for mini RCBO's ?

 

[martygturner]

Ok thanks for that,, I was bit concerned at the over heating and fire risk and wondered if it was something that had come up recently, mind you I suppose if it was a thing the RCBO's would being pulled out of boards.

I should have been a bit clearer, 8 ways meant 8 free spaces for circuits not the total capacity of the board, I should have said 12 and 16 module boards. The flat has 5 circuits at present which will go up to 6 when the ring is split and de-rated. ( we split the socket ring in each rental as if something trips out or more commonly with renters the hairdryer goes bang then they have one set of sockets working to get them through until an electrician can get to them.)

 

[AndyPRK]

Come to think of it, I have 3 storage heaters (one small), on Wylex B16 mcbs, next to each other. They can be on for upto 2 hours at a time.
Current draw across all of them is about 30A.

I guess I am just about compliant. Though if the MCB for the small heater was in the middle that would be prefered.
Anyway, what is the worst that can happen here? A false trip?

 

[JohnW2]

So what does that mean in practical terms?

As I said, I would think very little, since adjacent devices loaded to near their nominal ratings for significant periods of time is probably pretty unusual in a domestic setting.

Are the instructions the same for mini RCBO's ?

The (fairly old) Wylex catalogue I'm looking at is fairly vague/confusing but, despite the wording of what I quoted (speaking only of MCBs), that wording appears in a section which seems to relate to RCBOs as well as MCBs.

 

[Murdochcat]

I agree with the above. However, some manufacturers have something to say about this, as per this relating to Wylex MCBs ...

View attachment 368908

In practice I doubt that many devices are "loaded at or approaching their nominal rates currents" for significant periods of time at all, whether adjacent or not.

Avoid Wylex is my advice

 

[JohnW2]

Avoid Wylex is my advice

Why? Is that perhaps the result of anecdotal personal experience.

For what 'personal anecdotes' are worth, I have 6 or so Wylex CUs in my house, which were very straightforward to install, and which have been trouble-free for over 20 years since I installed them. I have not had to replace a single device in any of them, and all the RCDs remain 'in spec'.

 

[flameport]

Is this something new ?

The concept isn't new, has been around for decades.
However like many things, some people only have recently been made aware of it.

For many domestic circuits it doesn't matter.
However for high load items which will be on for long periods the protective device should have space either side.

 

[Murdochcat]

Why? Is that perhaps the result of anecdotal personal experience.

For what 'personal anecdotes' are worth, I have 6 or so Wylex CUs in my house, which were very straightforward to install, and which have been trouble-free for over 20 years since I installed them. I have not had to replace a single device in any of them, and all the RCDs remain 'in spec'.

Experience based on having to replace more Wylex products than any other

 

[AndyPRK]

please give us some examples of wylex component failures