Radial Circuits

[Jeremy Harris]

I couldn't agree more about the daft way that fire resistant domestic CUs have been mandated, when I'm near-certain the problem is really crap terminals.  Some of the single screw terminals are pretty rubbish, and, in my view, need to be re-tightened after they've sat for a while and compressed the wire a bit.  I wouldn't mind betting that crap connections were the true problem that caused this switch.

 

I came across a glass filled plastic box a few weeks ago that met the fire test requirement for a domestic CU.  Can't recall the make; not one of the big names; I was looking for a small waterproof enclosure to house a bit of kit and came across it by accident.  I don't quite understand why the manufacturers have all switched to metal CUs to meet the new regs, when I would have thought they could have just changed the type of plastic they use and carried on making the old designs.  I suppose it could be that their old moulds wouldn't work with a fire resistant plastic, but even so, I'd have thought it was worth the effort, given that they had to tool up to make new metal CUs anyway.

 

 

[Barney12]

OK, I've been doing some more reading and it all gets even more bonkers. If what I've read is correct then:

 

1. There is no requirement to protect openings in the metal cu with some form of intumescent seal. I.e. It's perfectly fine to use the great big cable opening on the back of the cu bolted to a wooden plinth and wooden stud wall. 

2. The use of plastic trunking, glands etc is perfectly acceptable. 

 

Its all madness!! Especially no.1. 

[Barney12]

4 hours ago, JSHarris said:

I couldn't agree more about the daft way that fire resistant domestic CUs have been mandated, when I'm near-certain the problem is really crap terminals.  Some of the single screw terminals are pretty rubbish, and, in my view, need to be re-tightened after they've sat for a while and compressed the wire a bit.  I wouldn't mind betting that crap connections were the true problem that caused this switch.

 

I came across a glass filled plastic box a few weeks ago that met the fire test requirement for a domestic CU.  Can't recall the make; not one of the big names; I was looking for a small waterproof enclosure to house a bit of kit and came across it by accident.  I don't quite understand why the manufacturers have all switched to metal CUs to meet the new regs, when I would have thought they could have just changed the type of plastic they use and carried on making the old designs.  I suppose it could be that their old moulds wouldn't work with a fire resistant plastic, but even so, I'd have thought it was worth the effort, given that they had to tool up to make new metal CUs anyway.

 

 

 

If this article is still current then the second paragraph seems to answer your question about using plastics?

 

http://electrical.theiet.org/wiring-matters/59/consumer-units/index.cfm

Edited August 30, 2017 by Barney12

[Onoff]

6 minutes ago, Barney12 said:

OK, I've been doing some more reading and it all gets even more bonkers. If what I've read is correct then:

 

1. There is no requirement to protect openings in the metal cu with some form of intumescent seal. I.e. It's perfectly fine to use the great big cable opening on the back of the cu bolted to a wooden plinth and wooden stud wall. 

2. The use of plastic trunking, glands etc is perfectly acceptable. 

 

Its all madness!! Especially no.1. 

 

The tails entry specifically must maintain the level of fire protection afforded by the metal cu "as far as reasonably practical".

 

One could argue that sealing the thing up cuts down on ventilation so could exacerbate the fire issue!

 

As I said, bolt a metal cu to a wall and you've got a wall mounted fire if it goes up! They haven't changed the design of say the incomers. It was MK, YES MK a little while back had a recall on their CUs as the incomers were I think going up.

 

"Not tonight dear, @Onoff's sent me a link!"

 

http://www.beama.org.uk/search-results.html?keyword=consumer+unit

[jack]

4 hours ago, JSHarris said:

I couldn't agree more about the daft way that fire resistant domestic CUs have been mandated, when I'm near-certain the problem is really crap terminals.  Some of the single screw terminals are pretty rubbish, and, in my view, need to be re-tightened after they've sat for a while and compressed the wire a bit.  I wouldn't mind betting that crap connections were the true problem that caused this switch.

 

According to my electrician, that was exactly the reason. He thinks most electricians are cowboys.

[Nickfromwales]

 

15 hours ago, JSHarris said:

Some of the single screw terminals are pretty rubbish, and, in my view, need to be re-tightened after they've sat for a while and compressed the wire a bit.

 

11 hours ago, jack said:

 

According to my electrician, that was exactly the reason. He thinks most electricians are cowboys.

 

You only have to make off one CU to realise that this is almost always the case. I've been to loads of call outs where people are complaining of circuits not working, most with heavy loads like the kitchen ring, and I've found loose terminals on MCB's, and most where it's a relatively new CU / retire and they can't get hold of the original electrician to rectify. 

Make off the CU, go off and do a bit of second fixing for an hour or so, and then you'll be shocked at just how much more you can turn those terminal screws again, the ones just now that wouldn't budge any further. Plumbers fitting electric showers and 45a pull-cords are the best, lost count of how many of those I've been called out to and they're charcoal by then. 

Went to one not so long back where there was power ( live ) in all the sockets, so some hero with a volt-stick had said its not a problem with the CU, only for me to find the neutrals all lifted where they'd arc'd themselves dry. 

If trades folk had to do the kind of apprenticeship I had to do then there would be enough wankers scared off in the first year to sieve through this problem, but the market is flooded with college heros who can't drill a hole in a straight line. I'm constantly getting calls from mates who can't get something to work, can't fault find, or simply don't know what they're looking at.

The garage which carries out my class 7 mot had a big compressor sat in the corner with the wires hanging out of it. I asked why they're hiring a small compressor whilst that's there and they said its been there for 2 years whilst they've asked every Tom, Dick and Harry to get the big one going, and none of them returned. 10 mins on the phone to Alan ( Magnum Compressors, very helpful guy if anyone is stuck ) and a new star / delta starter box and associated controls was posted out. A Saturday morning fine tuning the start over-current trip ( pita ) and jobs done. If you don't know, ask someone who does . Simple. 

[ProDave]

Another common CU fault is the busbar finger missing the cage clamp terminal.

 

Most mcb's have a terminal arrangement where if the clamp is closed you can insert the busbar finger into empty space. Then you can "tighten" the terminal and "job's a good un" except it's not.

 

A few makes of mcb have solved this for a few pence, by adding an extra tang onto the cage clamp that blocks the hole into the space behind the clamp, so the only place the busbar can go is into the correct place.

 

It iritates me that we "solve" the problems by putting it all in a tin box, rather than mandating engineering solutions like a very simple modification to the terminal design to design out the possibility of faults.

[Barney12]

OK, so I've decided to rationalise the circuits slightly to reduce the number of runs. Any comments?

 

[Nickfromwales]

Do 1 and 5 really need segregation? Normally all under the title of kitchen ring. 

[Barney12]

3 minutes ago, Nickfromwales said:

Do 1 and 5 really need segregation? Normally all under the title of kitchen ring. 

 

I guess not. I just liked the idea of separating them off to prevent defrosting of fridge/freezer in the event of a trip. Overkill?

[Nickfromwales]

8 minutes ago, Barney12 said:

 

I guess not. I just liked the idea of separating them off to prevent defrosting of fridge/freezer in the event of a trip. Overkill?

IMO yes. Think how many houses you've lived in that didn't have that and you'll see it's not really necessary. The only thing I'd go for is a single un-switched socket on the kitchen circuit that has a power fail alarm plugged into it, somewhere where it's inaccessible, say above the larder unit where it can't get taken out. 

Iirc, @Temp posted a thread with one that had a GSM dialler ( text ) to say the power has gone off. My expensive Hotpoint freezer is a bag of shit. Instead of a loud wailing alarm to say the doors been left ajar by one of my lolly-loving kids, AGAIN, a bloody red light just comes on. Thanks to the total and utter PENIS at Hotpoint who thought that the light would be of any other help than to show you that you need to go food shopping in the morning and chuck everything out. Must be on the 4th or 5th child related freezer bail-out now in 10 years. Not once was it to do with a power cut. 

Tbh, if the door is kept shut and it's reasonably full, the freezer will go at least half a day without losing a crumb.