Why is there a main switch as standard in a consumer unit? What is it for?

[JohnW2]

... when I fitted two RCD's feeding the two Wylex fuse boxes in my old house, ... I could not have fitted a twin RCD consumer unit as simply not made.

CUs (with as many 'ways' as you wanted), RCDs and busbars would have been available then so, even if not available 'off-the-shelf', you surely could have created a "twin RCD consumer unit" (or any other configuration of CU which you desired), couldn't you?

I suppose you are now going to talk about 'type-testing'?

Kind Regards, John

 

[ericmark]

I fitted RCD's back in 1992 or there about, may have been earlier, my son decided to follow my lead and become a radio ham, I was VP8XBHZ, then VP8BKM, then GW7MGW, and finally VR2ZEP, my son became GW7PVD. I am sure you can work out the year with the call sign, but I wanted to protect him, so RCD's were fitted.

Today roles reversed, he is looking after me, he fitted the all RCBO consumer unit, and yesterday was fitting extra lights for me. Sorry to say he did not renew his licence.

I now no longer work for money, I still work, but for no pay, I enjoy working on the local heritage railway, it is likely what keeps me alive, I enjoy working, even if not as an electrical engineer. Main job seems to be painting, if it moves wave to it, if it doesn't then paint it. Everything cream or brown, GWR colours.

But like to keep active, and it does not seem to make sense that you need two isolators for the same installation.

 

[sparkwright]

I can't answer Eric's question with any accuracy or reference to the regs.

But I suppose since the bog standard consumer units came out with things like 'switch off before handling fuses' it would be logical for every cu to have a main switch.

Also, most new houses from the last 60 years have tried to fit meter boxes on the outside, with the cu on the inside - so really need a main switch on these consumer units.

Can't really offer much more than that, only that several consumer units could be stacked on top of one another, and linked out so only one main switch is present - though in some cases it's just as easy to have several main switches if getting parts is tricky.

 

[JohnW2]

... Can't really offer much more than that, only that several consumer units could be stacked on top of one another, and linked out so only one main switch is present - though in some cases it's just as easy to have several main switches if getting parts is tricky.

Maybe 'just as easy' but, as I have been saying, not compliant with BS7671:2018 (even if, per eric, it was compliant with BS7671:2008!).

Kind Regards, John

 

[ericmark]

It was always preferred to have one single unit to switch off all power, so if there is any henley blocks then an isolator before the blocks so it turns off all, it seems to be a backwards step to say each consumer unit should have it's own master switch so no longer a single switch to isolate all.

I know with the old Wylex fuse box the isolator built in was only rated at 60 amp, where an external isolator could have a much higher rating.

 

[JohnW2]

It was always preferred to have one single unit to switch off all power, so if there is any henley blocks then an isolator before the blocks so it turns off all, it seems to be a backwards step to say each consumer unit should have it's own master switch so no longer a single switch to isolate all.

I'm not sure that there has been a (backwards) 'step' - since I don't think there ever was a 'standard' fuse box or CU which didn't have some sort of switch/isolator, has there.

If there is an upstream means of isolation (e.g. before an installation 'splits' at 'Henleys') then, at least with modular CUs, there has never been anything stopping people removing the Main Switch. However, I can see at least two downsides of that. Firstly it means that to work on one (of two or more) CUs requires killing the entire installation - which could be regarded as a definite ';inconvenience' in some situations.

However, I think there is also a safety issue, primarily for non-electricians, since having a 'big red switch' in each CU is a very obvious/visible indication/reminder that one needs to operate it before working within it.

If there is only one CU (and no upstream 'Henleys' etc.), whuich I presumed is the case for a very high proportion of domestic installations, then it would be silly to have 'the means of isolation' anywhere other than in the CU, wouldn't it?

Other than its taking up a couple of 'spaces' in the CU, can you think of any other downsides of having a Main switch in a CU?

Kind Regards, John