Amendment 2 BS7671 again

cliffed · May 1, 2022

Just watched a video by J Ward covering parts 1,2 & 3, any thoughts on the consumer unit, this being a Type Tested Assembly, where if non compatible Mcb’s are used it does not comply & does not remain a Consumer Type Tested Assembly.
No mention of what it becomes though, so what happens next, there’s thousands of Consumer Units out there with other brands of Mcb used in the CU.
The statement:An assembly of one or more protective devices, Proven during the TypeTest of the assembly as suitable for such use.

pc1966 · May 1, 2022

What it becomes is the electrician's design and they are then responsible for meeting all of the relevant safety directives and documentation responsibilities. That is a massively troublesome task so the simplest option is to install a CU that is all from one manufacturer's list of compatible products (i.e. that they certify as type-tested).

As for those CUs that have been repaired by others using different MCBs, etc, then the BPG#4 guidance is the sensible approach to determining the risks:

[C3 code for] Mixed branded switchgear components within a consumer unit or distribution board where:

there are no signs of thermal damage to component or associated connections
the enclosure/assembly hasn’t been modified to allow installation of the component
the component is securely fitted and all connections are adequate
correct manual operation of the component
direction of use of toggles/switches is the same as existing devices

Note:
If any of the above criteria is not met, this would warrant a code C2 classification to be recorded.

Points 1,3, and 4 in the above list are essentially saying the parts themselves (and related connections) are sound and functional. If you had same-brand parts you would expect exactly the same aspects to be met.

Point 2 is the one that prohibits bending/modifying of busbars to forcibly fit them to the devices (along with point 3) as well as prohibiting modifications of the enclosure. That is about maintaining the essential aspects of protection and current carrying (normal and fault) that would likely apply to the parts originally type-tested.

Point 5 is a basic safety aspect that the folk in the home, as well as some electricians, would assume operations are consistent and any inconsistency brought about by part substitution introduces a real additional risk for safe isolation.

Of course you see some cases where this looks odd (as someone pointed out the plug-in Wylex breakers operate in the opposite direction to the old rewirable Wylex CU main switch, but at least all plug-ins operate the same way, and the manufacturer is offering them as approved for use) and you get some SPD that are "universal fit", but they are not normally going on the busbar but a cable to main switch or via an approved MCB, etc.

cliffed · May 1, 2022

Thanks, we’ve all seen botched non branded replacements on CU.
Definitely a note on an EICR regarding the C3 code

Lister1987 · May 1, 2022

133.1.3 would come into play here so it'd be whoever altered its headache. 132.16 would come into play before doing anything of course and if ypu can't satisfy suitability for change thrn we shouldn't be touching it rotating on thr liability

LastManOnline · May 1, 2022

pc1966 said:
As for those CUs that have been repaired by others using different MCBs, etc, then the BPG#4 guidance is the sensible approach to determining the risks:

Can someone explain how using different makes of mcb,s can compromise the safety of a D.B ?

Dartlec · May 1, 2022

pc1966 said:
Points 1,3, and 4 in the above list are essentially saying the parts themselves (and related connections) are sound and functional. If you had same-brand parts you would expect exactly the same aspects to be met.

Agree with everything you've said, though it doesn't help when certain manufacturers change their design so that they look like they should fit but don't cough Wylex cough

Dartlec · May 1, 2022

LastManOnline said:
Can someone explain how using different makes of mcb,s can compromise the safety of a D.B ?

I doubt (mechanical fitting on the busbar aside) there is any safety compromise - the main practical issue is not being able to use the 16kA Type Testing limit - and if there was a consumer unit fire, the manufacturer's lawyers would absolutely deny all responsibility (maybe rightly).

Of course - an actual standard for busbars would solve the mechanical problem, but presumably be resisted by companies like Crabtree with their push in variant being so different.

It was nice recently to actually be able to retrofit into a very old Crabtree board with a shiny new off the shelf component. Hager and Crabtree deserve props for that.

With a move towards AFDDs being in effect separate little computers, it would be nice to just fit whatever was convenient, given that there should be no interaction between individual units.

westward10 · May 1, 2022

I've no idea why people think that using non-compatible devices is a new thing I have been noting this on periodics for over 25 years.

cliffed · May 2, 2022

westward10 said:
I've no idea why people think that using non-compatible devices is a new thing I have been noting this on periodics for over 25 years.

Agree, the actual quote changed a couple of thoughts in my opinion though.
If non compatible mcb’s are fitted into an existing Consumer Unit, it cannot be deemed as a Consumer Unit….so what is it.
Once again the onus is on the electrician testing the install & responsibility if anything goes wrong.
There’s no chance of replacement, but that would be the safest option.

pc1966 · May 2, 2022

Dartlec said:
I doubt (mechanical fitting on the busbar aside) there is any safety compromise - the main practical issue is not being

My own view is the critical and fire-starting aspect is a poor connection, and if the busbar cannot be clamped properly than you have that problem.

Having said that, not all MCBs, etc, have terminal clamps that have the 'shutter' bit that is supposed to stop the bar ending up outside of the clamping "jaws" so you can get a fire hazard from matching parts but a tight-but-missed MCB, as well as some not correctly tightened.

Dartlec said:
Of course - an actual standard for busbars would solve the mechanical problem, but presumably be resisted by companies like Crabtree with their push in variant being so different.

It was nice recently to actually be able to retrofit into a very old Crabtree board with a shiny new off the shelf component. Hager and Crabtree deserve props for that.

Crabtree's push-in design is pretty unique and maybe more reliable than poorly checked MCBs on a pre-assembled board. But they are not the only one to have variations in busbar design, etc, that lead to incompatibilities with their own range of parts (Wylex FFS).

Dartlec said:
With a move towards AFDDs being in effect separate little computers, it would be nice to just fit whatever was convenient, given that there should be no interaction between individual units.

I doubt there is much risk of interaction really, at least at the 100A consumer level of DB. Really I think the main risk, as always, is a poor connection leading to overheating.

Lister1987 · May 2, 2022

LastManOnline said:
Can someone explain how using different makes of mcb,s can compromise the safety of a D.B ?

While the devices may be made to thr same standard (60898 say), how those devices form an approved type tested assembly will differ from manufacturer to manufacturer.

Take SBS for example with its dual busbar or (hopefully get this right) Crabtree Starbreaker and its busbar in the DIN Rail. 2 very different systems but made to the. same standards

Look at Crabteee, Wylex, Volex; same parent company but they will not state that devices are compatible across brandishing to micro differences in construction and implementation.

If components not mate just so, it can give rise to arcing, shorting and other thermal effects; all of which will affect the thr performance, lifespan and safety of the devices used.

Why we as a trade are so desperately trying to get thruseof mixed switchgear accepted as the norm is beyond me.

LastManOnline · May 2, 2022

pc1966 said:
My own view is the critical and fire-starting aspect is a poor connection, and if the busbar cannot be clamped properly than you have that problem...
...Really I think the main risk, as always, is a poor connection leading to overheating.

This is the bottom line.Even when installing a buzzbar for compatible units ultra care must be taken to ensure that each mcb is properly clamped to the buzzbar.I see no reason to use incompatible types except for situations where compatible ones are not available.
When incompatible ones have to be used the simple solution is to use compatible buzzbar and link to the existing buzzbar with a 10mm flexible loop.Problem solved.
(I,m getting dizzy from the number of times I,ve used the word "compatible" in just 2 sentences☺)

pc1966 · May 2, 2022

LastManOnline said:
This is the bottom line.Even when installing a buzzbar for compatible units ultra care must be taken to ensure that each mcb is properly clamped to the buzzbar.I see no reason to use incompatible types except for situations where compatible ones are not available.

Agreed.

LastManOnline said:
When incompatible ones have to be used the simple solution is to use compatible buzzbar and link to the existing buzzbar with a 10mm flexible loop.Problem solved.

Not sure I can agree with that. I think if you can't find one that is "close enough" to fit OK (given many obscure makes seem to be main one rebranded for large retail outlets) it really is time for a new CU.

pc1966 · May 2, 2022

Lister1987 said:
Why we as a trade are so desperately trying to get thruseof mixed switchgear accepted as the norm is beyond me.

It should never be "the norm" but often there will be an obsolete but otherwise perfectly good installation that needs just one MCB replaced for whatever reason. In a number of cases that can be done OK and, while not the best option, it might be better than either no repair or the householder getting Dodgy Dave to do something instead if the only legitimate answer is a £500-1000 CU change.

But in some cases it is simply not possible, for example you cite the SBS dual-busbar and the Crabtree plug-in cases when you simply have to use the original manufacturer's part as nothing else will fit (without serious bodgery). Also you get some busbar like the double-pronged Wylex ones (that are not compatible even with the newer Wylex MCB/RCBO/AFDD!) that can only really be used with their older parts, but often some still available.

And then you get the rest, where the busbar is basically a rod with prongs that will fit most MCB clamps, providing they are the same height, etc. In those cases you may know of an alternative make that is basically the same (as many come from the same factory with differing brands). Not perfect, but good enough in cases where the alternative outcomes could very well be worse.

EDIT: Of course, you might find obsolete parts on eBay or similar. That would get out of the "mixed brand" dilemma but I am not sure it really is much better if you have no easy means to verify the part is functioning correctly. RCD and RCBO at least can be tested by your MFT!

pc1966 · May 2, 2022

I don't think there is any simple answer. For a new install there is practically no reasons to mix equipment, certainly not busbar mounted stuff, timers/contactors in DIN box are rather different. Same applies to repairs where the compatible part is still available.

But in other cases it comes down to judgment, both engineering and business, as to what is the best approach to meet essential safety and to get the job done. There may be good reasons for a CU change outside of the one part to push that approach, or it might be the case the owner genuinely can't afford it.

LastManOnline · May 2, 2022

pc1966 said:
Not sure I can agree with that. I think if you can't find one that is "close enough" to fit OK (given many obscure makes seem to be main one rebranded for large retail outlets) it really is time for a new CU.

But instead of trying to make different types ""fit" , you simply loop a 10mm from the existing buzzbar to the new buzzbar housing the new type mcb,s.(allowing a physicall distance between both sets of mcb,s) How would any issues arise?

AJshep · May 2, 2022

We just have to do the best we can. And use our engineering judgement like PC1966 said.

To be honest there are so many issues arise now, by just adding a circuit to an existing installation especially if you follow BS7671. Whichever way you look at it, if a problem arises later your be prosecuted anyway.

1) Cant really add a circuit to a split load with a Type AC RCCB or RCD (unless its has no electronics)

2)since all manufacturers list RDF now. We have to allow for that in our design. So it might mean that even though there's space in an existing CU we can't install an additional OCPD in the CU as the circuits next to it are running at near full capacity.

3) if its a split load RCD board with a 63Amp RCD we may not be able add to it if the total sum of the OCPD exceeds the rating of the RCCB. (Unless there's protection upstream)

pc1966 · May 2, 2022

LastManOnline said:
But instead of trying to make different types ""fit" , you simply loop a 10mm from the existing buzzbar to the new buzzbar housing the new type mcb,s.(allowing a physicall distance between both sets of mcb,s) How would any issues arise?

It is a terrible bodge doing that!

If the MCB is fitting in the existing CU you would need it to be the end one so the current busbar could be cut short to fit. In some cases you can't fit cable under as it goes through a slot above the usual cage, so it would be run from the main switch/RCD.

If you are talking about a separate DIN enclosure you need space to fit it along side, and really want it linked by a bush/conduit so the supply cable (unprotected but for the DNO fuse in most cases) meets the requirement for being very unlikely to be shorted out.

Also it is very unusual, that presents further risk for the next spark attempting any work.

pc1966 · May 2, 2022

AJshep said:
1) Cant really add a circuit to a split load with a Type AC RCCB or RCD (unless its has no electronics)

I guess that will start to become an issue soon.

AJshep said:
2) since all manufacturers list RDF now. We have to allow for that in our design. So it might mean that even though there's space in an existing CU we can't install an additional OCPD in the CU as the circuits next to it are running at near full capacity.

This is often overlooked!

Only in a few cases have I seen dissipation limits for DIN rail boxes, which is something that ought to be considered if brewing your own stuff (yes, that is a BIG can of worms to open...)

For example, this one says 45W

48 Module Insulated Enclosure with Snap Closing Tinted Window and DIN Rails

Snap closing tinted window

www.cef.co.uk

But not all manufacturer's give to the dissipation at full load for MCBs, fuses, etc.

AJshep said:
3) if its a split load RCD board with a 63Amp RCD we may not be able add to it if the total sum of the OCPD exceeds the rating of the RCCB. (Unless there's protection upstream)

To be fair that should always have been the case!

Dartlec · May 2, 2022

cliffed said:
The statement:An assembly of one or more protective devices, Proven during the TypeTest of the assembly as suitable for such use.
View attachment 97139

Who's going to be the first to use the argument that if it's not a consumer unit when it's mixed brands, then it doesn't need to have its enclosure manufactured from non-combustible materials either? (taps forehead)

Simon47 · May 3, 2022

Dartlec said:
Who's going to be the first to use the argument that if it's not a consumer unit when it's mixed brands, then it doesn't need to have its enclosure manufactured from non-combustible materials either? (taps forehead)

Yeah, but then you add the bigger headache of complying with all the "accessible to ordinary persons" bits in BS7671. And as already mentioned, you become responsible for the design which may be trickier than you might think.

Example, if you use a "CU" then even if the devices aren't rated to break 16kA you aren't required to determine the prospective fault currents and verify that they are within the breaking capacity of the devices - because a type tested CU will be (or at least is deemed to be) capable of handling a 16kA fault current taking advantage of the breaking capacity fo the upstream protective device (a.k.a. main fuse in the service head). So if the PFC was say 7kA and your CU has 6kA rated devices : as a type tested CU it's acceptable because the manufacturer has determined that the upstream fuse will provide sufficient protection - but fit a different brand of MCB, it stops being a "CU", and you then become responsible for determining if those 6kA devices are OK for a 7kA PFC.
Luckily I think such high PFCs are rare.

But back to the question of what could go wrong. There is a, albeit a very slight, risk of interaction between adjacent devices. E.g. magnetic or electric fields from one device could interfere with an adjacent device from a different manufacturer. Where all devices are from the same manufacturer in a type tested CU, then the manufacturer should have considered that - and of course, will have knowledge of the internals so should be able to design the issue out. But a device could be sensitive to interference from a different manufacturer's device with a different internal layout.

cliffed · May 4, 2022

The regulations are forever changing covering their/our selves.
The frightening part is that the new regs partly condemn‘s what’s been done before & us being the installers are once again put in the firing line.
How can you possibly explain to a Client that the Consumer Unit fitted is now not a Consumer Unit, but it will be ok.
No signs of thermal damage etc….that’s just one issue there are many more

westward10 · May 4, 2022

cliffed said:
The regulations are forever changing covering their/our selves.
The frightening part is that the new regs partly condemn‘s what’s been done before & us being the installers are once again put in the firing line.
How can you possibly explain to a Client that the Consumer Unit fitted is now not a Consumer Unit, but it will be ok.
No signs of thermal damage etc….that’s just one issue there are many more

What do you mean is now not a consumer unit.

pc1966 · May 4, 2022

cliffed said:
How can you possibly explain to a Client that the Consumer Unit fitted is now not a Consumer Unit, but it will be ok.

It is still a consumer unit. If it has mixed-brand parts then it is not a type-tested CU.

cliffed said:
No signs of thermal damage etc….that’s just one issue there are many more

Mostly it is down to the question of acceptably good engineering practice. The BPG#4 just lays out the key concerns in a manner that allows a sane and uniform C3/C2 coding judgment.

You can have a same-brand CU butchered on installation that is a hazard, and you can have a mixed-brand CU that, while not certified by any of the manufacturers, is perfectly safe for continued use.

westward10 · May 4, 2022

pc1966 said:
It is still a consumer unit. If it has mixed-brand parts then it is not a type-tested CU.

Mostly it is down to the question of acceptably good engineering practice. The BPG#4 just lays out the key concerns in a manner that allows a sane and uniform C3/C2 coding judgment.

You can have a same-brand CU butchered on installation that is a hazard, and you can have a mixed-brand CU that, while not certified by any of the manufacturers, is perfectly safe for continued use.

Visually it may seem fine but how can you be certain it is safe for continued use.

Simon47 · May 4, 2022

pc1966 said:
It is still a consumer unit. If it has mixed-brand parts then it is not a type-tested CU.

Actually, as it's no longer type tested, it's no longer a CU according to the definition in BS7671 : "Consumer unit (...). A particular type of distribution board intended for operation by ordinary persons, comprising a type-tested coordinated assembly for ..."
With mixed devices, it then becomes a distribution board : "Distribution board. An assembly containing switching or protective devices (e.g. fuses, circuit-breakers, residual current operated devices) associated with one or more outgoing circuits fed from one or more incoming circuits, together with terminals for the neutral and circuit protective conductors. ..."

I'm sure I remember there being some restrictions on the types of distribution board allowed for operation by "ordinary persons", which I vaguely recall mandated a "CU" for domestic environments. But I can't find that now.

pc1966 · May 4, 2022

westward10 said:
Visually it may seem fine but how can you be certain it is safe for continued use.

Well strictly speaking you can never know if anything is safe for continued use, unless you can see in to the future (in which case you are probably better off playing the lottery than being a spark). The best you can do is apply engineering judgment to what you are able to inspect and test.

Adding in mixed-brands of course adds to the uncertainty which I guess is why the BPG#4 has such specific notes on it.

Just to be clear on the matter I don't think mixing stuff is a good idea, but if it has been done for whatever reason it is not automatically a reason to fail something.

pc1966 · May 4, 2022

Simon47 said:
Actually, as it's no longer type tested, it's no longer a CU according to the definition in BS7671 : "Consumer unit (...). A particular type of distribution board intended for operation by ordinary persons, comprising a type-tested coordinated assembly for ..."

That is a good point to raise.

I am pretty sure there is more to the "domestic CU" aspect than just the type-testing (e.g. type of isolation switch, etc), but however it is done it is always the person who mixed thing's responsibility for safe operation as it no longer has that guarantee.

But then it is also the responsibility of the installer of a type-tested CU that it is safe with correct design of circuit protection, quality of workmanship, etc.

cliffed · May 4, 2022

pc1966 said:
That is a good point to raise.

I am pretty sure there is more to the "domestic CU" aspect than just the type-testing (e.g. type of isolation switch, etc), but however it is done it is always the person who mixed thing's responsibility for safe operation as it no longer has that guarantee.

But then it is also the responsibility of the installer of a type-tested CU that it is safe with correct design of circuit protection, quality of workmanship, etc.

That’s exactly how the Video described it, it’s not a Consumer Unit when non compatible Mcb’s are used, but didn’t actually say what it then becomes, maybe a Distribution Board….

Lister1987 · May 4, 2022

Most common thing that comes to my head is adaptable box with din rail mounted connectors

Simon47 · May 4, 2022

Something else to consider ...
What about a situation where one brand really is the same article as another but with different screen printing ?

Lister1987 · May 4, 2022

Simon47 said:
Something else to consider ...
What about a situation where one brand really is the same article as another but with different screen printing ?

Depends on your due diligence and how covered you want your arse as I'd want concrete certainty that the badge is the only difference before I start mixing switchgear

westward10 · May 4, 2022

Simon47 said:
Something else to consider ...
What about a situation where one brand really is the same article as another but with different screen printing ?

I would only use the scenario with Schneider for replacements in Merlin Gerin or Square D boards where the manufacturer confirms compatibility.

LastManOnline · May 4, 2022

westward10 said:
I would only use with scenario with Schneider for replacements in Merlin Gerin or Square D boards where the manufacturer confirms compatibility.

Are there documented cases of the dangers that using different makes pose?.

I ask as I have not had personal experience of this issue. From what I,ve read so far the 2 areas of concern appear to be....

1) possibility of overheating due to incompatible buzzbars
2) the electronics and magnetism of different mcb types interfering with operation of each other

I still can,t figure out how both issues can,t be addressed by physical distancing of the different types in the same CU.Over here we use a 2 row D.B. Having one make on the top row and another on the bottom row has never led to any issues in my experience.
The situation I describe would be unusual ( and unprofessional in my view).
But occasionally circumstances require it.