Universal MCBs

[JohnW2]

The conductor size will depend on the upstream protective device and the adiabatic equation, you wouldn't want to be too close to a piece of 1.5mm in a direct short circuit with a 100A fuse protecting it.

I suppose that's theoretically true in the case of a (I would have said exceedingly unlikely) short to N or E from the input side of the device (or the cable itself) - but in all other circumstances (i.e. faults on the output side of the device), the device itself would protect the input cable, just as it protects the rest of the conductors in the circuit.

However, maybe (probably!) fear of 'the exceedingly unlikely' would prevail. Mind you, I doubt that calcs would reveal the need for a particularly hefty cable with an upstream 80/100A fuse (and it could, again, be flexible) - let's face it, we're only talking of a fuse rated at 2 or 3 times the continuous current carrying capacity of 4mm² conductor in free air.

Kind Regards, John

 

[EFLImpudence]

The conductor size will depend on the upstream protective device and the adiabatic equation, you wouldn't want to be too close to a piece of 1.5mm in a direct short circuit with a 100A fuse protecting it.

Would not 434.2 apply?

Bonsoir

 

[JohnW2]

The conductor size will depend on the upstream protective device and the adiabatic equation, you wouldn't want to be too close to a piece of 1.5mm in a direct short circuit with a 100A fuse protecting it.

Would not 434.2 apply?

As I implied in my response to Spark123, I was wondering whether the 'exceedingly unlikley' might come within the terms of 434.2.1. Maybe not - but, as I said, I doubt that calcs would reveal the need for tree trunks connecting MCBs/RCBOs to the 'L-bar'.

Interesting though this discussion may be , it relates to something that is almost certainly not going to happen (as 'the norm') in the UK during many of our lifetimes, if ever - the die has been cast!

Kind Regards, John

 

[EFLImpudence]

I doubt that calcs would reveal the need for tree trunks connecting MCBs/RCBOs to the 'L-bar'.

I did not have an 'L-bar' in mind, just wires.

Interesting though this discussion may be , it relates to something that is almost certainly not going to happen (as 'the norm')

No, I didn't expect busbars to be abolished and I don't see any advantage, but if I wanted to do it (all wires) I can't see any reason why not.

Also, in relation to the OP, should you want to fit a 'foreign' mcb which did not align with the busbar what would be wrong with connecting it by a wire as, indeed, are any RCCBs.

 

[Spark123]

The conductor size will depend on the upstream protective device and the adiabatic equation, you wouldn't want to be too close to a piece of 1.5mm in a direct short circuit with a 100A fuse protecting it.

Would not 434.2 apply?

Not sure, don't really want to find out the hard way with a face full of molten metal either, reg or no reg!! I don't think the IEE regs will cover internals of accessories, they will come under their own standard.

 

[Spark123]

I suppose that's theoretically true in the case of a (I would have said exceedingly unlikely) short to N or E from the input side of the device (or the cable itself) - but in all other circumstances

I don't think it is that unlikely, having a L-E short in a metalic consumer unit where people are tinkering about inside it

 

[JohnW2]

I did not have an 'L-bar' in mind, just wires.

Fair enough, but I think that attempting to satisfactorilty terminate up to half a dozen conductors in a RCD or Main Switch terminal might be difficult/iffy - particularly if, per recent dicsussion here, it were decided that fairly large CSA wires were needed.

No, I didn't expect busbars to be abolished and I don't see any advantage, but if I wanted to do it (all wires) I can't see any reason why not.

I agree - apart from the issues we've been discussing, none of which (apart from loss of 'type tested') are insuperable.

Also, in relation to the OP, should you want to fit a 'foreign' mcb which did not align with the busbar what would be wrong with connecting it by a wire as, indeed, are any RCCBs.

Again, nothing apart from the issues we've been discussing.

Kind Regards, John

 

[JohnW2]

Would not 434.2 apply?

Not sure, don't really want to find out the hard way with a face full of molten metal either, reg or no reg!!

Pending doing the sums, I think one can say with confidence that one definitely would not need >10mm² (which would not be a major problem if flexible), at the very most, in normal domestic circumstances. 10mm² is normally deemed adequate for the main earthing conductor of such an installation - and that conductor might, under some fault conditions, have to carry the ful fault current (without turning into 'flying molten metal'!) until the cutout fuse operated.

Kind Regards, John.

 

[kai]

A similar situation occurs where a thin 4mm street lighting cable is tapped straight off a street main fused at say 800amps, when a short circuit occurs, the 4mm is often destroyed along its entire length, because the heat from the short circuit vaporises all the insulation around it.

 

[ban-all-sheds]

not to say it isn't possible with a normal busbar, it just takes a bigger idiot.

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