Amendment 2 BS7671 again

[cliffed]

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.

 

[LastManOnline]

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]

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]

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]

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.

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.

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]

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]

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]

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]

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]

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.

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]

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]

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]

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]

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]

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]

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