Vertical consumer unit

[Jeremy Harris]

I've long been convinced that the major cause of overheating in CUs is loose or poorly designed terminals.  The switch to fire resistant enclosures seems to be a secondary way of overcoming poor installation and design practices to me.  If someone isn't competent enough to check that all terminations are tight and secure, then there seems a very good chance that they won't be competent enough to ensure all the fire seals are doing their job in the case.

[ProDave]

I think most electricians were disappointed that the "solution" to CU fires was to put them inside a tin box.  Just about any other situation where there are a worrying number of fires, you look at what is causing them and design out bad engineering.  Instead the electrical industry just designed a fire barrier.

 

My pet hates are cage clamp terminals with no shield to stop the busbar going in behind the clamp and thus not being clamped at all, and heavy duty terminals on things like main switches that only have one screw.

 

We didn't have this problem on wooden backed 3036 Wylex fuse boxes were every termination had two screws.

 

 

[Jeremy Harris]

35 minutes ago, ProDave said:

I think most electricians were disappointed that the "solution" to CU fires was to put them inside a tin box.  Just about any other situation where there are a worrying number of fires, you look at what is causing them and design out bad engineering.  Instead the electrical industry just designed a fire barrier.

 

My pet hates are cage clamp terminals with no shield to stop the busbar going in behind the clamp and thus not being clamped at all, and heavy duty terminals on things like main switches that only have one screw.

 

We didn't have this problem on wooden backed 3036 Wylex fuse boxes were every termination had two screws.

 

 

 

 

I fitted a new isolator switch the other day that had really well-designed terminations.  Not only did it have two socket head screws per terminal, but the design of the brass and copper terminal body was such that the tails were very securely held, with cable grips in the case far enough away from the terminals to get rid of the "sideways wobble loosening effect".  The latter is my pet hate with cage clamps.  You can do them up to the specified torque, then if you move the wire slightly you find that the thing has loosened a bit, especially with thick wires.

[Pocster]

10 hours ago, MrMagic said:

I'd be tempted to move the Qubino units out in to a seperate DIN rail enclosure - it looks like they have different wiring rather than standard 'bus bar' style connections. This could also help with sign off as there is some debate at the moment as to what constitutes 'designed and built for compatibility', i.e. you shouldn't be mixing different manufacturers gear together in one CU ... (although this is a weird reg but I can understand it a little with different manufacturers using different offsets for their bus bars).

 

May also help with serviceability since when you want to put those Qubinos in association mode you won't have to be poking around in the main CU - plus should you ever replace the Qubinos with another technology you only have to rip and replace the 'lighting board' as such.

 

As an alternative to the double height boards you can simply stack smaller units together. Even with your 30cm width that's still going to be tight, especially once you factor in space for the tails and perhaps some vertical trunking to run carrying all the cables in and out.

 

See what your sparky says as they'll be the one putting pen to paper for you.

I have already purchased a seperate Din rail box - can take 48 Qubinos - that should be enough ?

[epsilonGreedy]

1 hour ago, ProDave said:

I think most electricians were disappointed that the "solution" to CU fires was to put them inside a tin box.  Just about any other situation where there are a worrying number of fires, you look at what is causing them and design out bad engineering.  Instead the electrical industry just designed a fire barrier.

 

 

Are we sure that fire risk was the only driver of the change?

 

When I heard that mobility regs required a CU be fitted in an accessible location about 4 feet off the ground my immediate that was "how long before someone dies after the metal ladder or bicycle being carried through the house swings into the wall, crunches through the plastic cover of the CU and contacts something live".

Edited February 18, 2020 by epsilonGreedy

[epsilonGreedy]

In a new build is it possible that a vertical column of circuit breaker switches would result in some switches at the top or bottom being outside the permissible height range?

[Jeremy Harris]

13 minutes ago, epsilonGreedy said:

 

Are we sure that fire risk was the only driver of the change?

 

When I heard that mobility regs required a CU be fitted in an accessible location about 4 feet off the ground my immediate that was "how long before someone dies after the metal ladder or bicycle being carried through the house swings into the wall, crunches through the plastic cover of the CU and contacts something live".

 

 

Yes, it was solely due to fire risk.  The driver behind it was a series of CU fires, and the one that forced the change was a fire that started in a CU fitted under the stairs of a house, which trapped the occupants upstairs.  Fitting CUs in the cupboard under the stairs is pretty commonplace.

 

The regs don't say that the CU case needs to be metal, just fire resistant, although manufacturers have interpreted that as being metal.  30 odd years ago many CUs used to be metal cased.  The Wylex board in our old house was metal, for example. 

 

 

[MJNewton]

1 hour ago, Jeremy Harris said:

I've long been convinced that the major cause of overheating in CUs is loose or poorly designed terminals.

 

And on that point why don't MCBs etc have spring loaded connectors (Wago style) in order to avoid the issue of undertightening, overtightening, vibration, copper creep etc altogether? 

[epsilonGreedy]

1 hour ago, Jeremy Harris said:

Fitting CUs in the cupboard under the stairs is pretty commonplace.

 

 

Yes though no one is mandating a wholescale replacement of such plastic CUs under stairs. However for a period of time plastic CUs were being fitted in new builds in accessible locations exposed to impact damage.

 

I am happy to fit a metal CU in my new build in view of this risk.

Edited February 18, 2020 by epsilonGreedy

[Jeremy Harris]

6 minutes ago, epsilonGreedy said:

 

Yes thought no one is mandating a wholescale replacement of such plastic CUs under stairs. However for a period of time plastic CUs were being fitted in new builds in accessible locations exposed to impact damage.

 

I am happy to fit a metal CU in my new build in view of this risk.

 

 

It's always been the case the regulation shall not be applied retrospectively.  For example, the regs now state that tails have to be 25mm², yet if I do an EICR on a house where the installation has older 16mm² tails that's not a cause for anything other than a C3 observation now.  That changed a few years ago, as there used to be a category that specifically covered items that were compliant with an older edition of the regs.  Forcing the use of C3 means having to explain to someone worried by it that it isn't really a problem, even though the definition of C3 is "improvement recommended but not required".

[Onoff]

3 hours ago, Jeremy Harris said:

The regs don't say that the CU case needs to be metal, just fire resistant, although manufacturers have interpreted that as being metal.  30 odd years ago many CUs used to be metal cased.  The Wylex board in our old house was metal, for example.

 

You can put a good old insulated ("plastic") consumer unit in a fire resistant enclosure I think.

 

It also applies to domestic only. Hager for instance do some lovely IP55 "plastic" cus with see through plastic doors for use say in humid environments like swimming pools.

[Onoff]

3 hours ago, epsilonGreedy said:

In a new build is it possible that a vertical column of circuit breaker switches would result in some switches at the top or bottom being outside the permissible height range?

 

Sure there's something about the "height" being taken as mid point of the switchgear. Something in Part M on it...I think.

[Jeremy Harris]

1 minute ago, Onoff said:

 

You can put a good old insulated ("plastic") consumer unit in a fire resistant enclosure I think.

 

 

I've done this in the garage/workshop.  Fitted the plastic CU etc inside a steel industrial-type enclosure.  I did it as much to keep dust and muck out as anything else.  I just have runs of conduit coming out of the steel enclosure and running around the walls to the outlets etc.  I also fitted a 4 pole 20 A contactor in there, to switch the two radial power circuits.  I have that hooked up to emergency stop switches, so the power can be easily isolated.

 

[Onoff]

1 hour ago, Jeremy Harris said:

runs of conduit

 

Aka chimneys! ?

 

I've wondered on this myself, whether to put a good squidge of intumescent mastic around the t&e, singles etc where they come up out of cu into the steel conduit. Or maybe some removeable fire stopping would be better. 

 

You might recall any mods/runs I make now are run in galv steel conduit that pokes up into the loft. Eventually it'll all be run back to the (new) cu in lovely vermin proof steel!

[Jeremy Harris]

7 minutes ago, Onoff said:

 

Aka chimneys! ?

 

I've wondered on this myself, whether to put a good squidge of intumescent mastic around the t&e, singles etc where they come up out of cu into the steel conduit. Or maybe some removeable fire stopping would be better. 

 

You might recall any mods/runs I make now are run in galv steel conduit that pokes up into the loft. Eventually it'll all be run back to the (new) cu in lovely vermin proof steel!

 

 

All mine exit out the bottom of the enclosure (where all the knockouts are) and then most run horizontally around the garage walls, with just the SWA feed and a bit of conduit over the earth electrode wire coming vertically up from under the thing.

 

I'm not sure that there's much of a risk of spread of fire along inside 20mm conduit, TBH.  My guess is that the wires would turn into a twisted molten mess and block any gap up pretty well, stopping air getting in and allowing any fire to spread.  Probably more of an issue with larger trunking, perhaps, but it's easy enough to just stick those intumescent fire stop pads inside trunking.

[epsilonGreedy]

1 hour ago, Onoff said:

Sure there's something about the "height" being taken as mid point of the switchgear. Something in Part M on it...I think.

 

 

That makes more sense.

 

I was watching a Hager CU installation video on YouTube and that claimed the regulation height was 1400 from FFL to the row of CU switches + or - 50mm. However another Hager video demonstrated the fitting of a flush mounted CU in hole in a 100mm inner block wall. They pushed the metal recess box of the CU into the recess to the point it was backed up to the insulation cavity batts, the same video showed cables running down the cavity sandwiched between the inner blocks and cavity blocks which got me wondering is they were doing things correctly?

[Onoff]

32 minutes ago, epsilonGreedy said:

 

That makes more sense.

 

I was watching a Hager CU installation video on YouTube and that claimed the regulation height was 1400 from FFL to the row of CU switches + or - 50mm. However another Hager video demonstrated the fitting of a flush mounted CU in hole in a 100mm inner block wall. They pushed the metal recess box of the CU into the recess to the point it was backed up to the insulation cavity batts, the same video showed cables running down the cavity sandwiched between the inner blocks and cavity blocks which got me wondering is they were doing things correctly?

 

Not quite sure of the wall section you refer to but there's various good reasons for not running cables in traditional cavity walls. To name but a few of the top of my head:

 

- if the cable touches the outer leaf it can allow moisture to wick from there to the inner leaf under gravity.

 

- assist vermin traversing the cavity

 

-be later affected by existing or subsequent cavity wall insulation

 

-be subject to thermal effects from said insulation

 

-be subject to inadequate support and or sharp edges like ties

 

Which is all well and good but there's loads of council built places around here with flush, steel CUs in the inner leaf and the cavities chock full of cable!

[epsilonGreedy]

46 minutes ago, Onoff said:

Not quite sure of the wall section you refer to but there's various good reasons for not running cables in traditional cavity walls. To name but a few of the top of my head:

 

 

Any one of your points would persuade me, now I am utterly convinced not to follow that Hager video!

 

My current thinking, to excuse the pun, is to create a partial 35mm recess in the inner wall block masonry with 65mm coursing bricks on their edge within the blockwork hole, then batten out the inner wall by another 30 to 40mm to create sufficient depth for the recess mounted CU.

 

Schneider have the most attractive CU faces but I think I will go with a Hager because their recess box and mounting system looks the most thought through design.