Singles in ducts

[Uncle gaz]

We have to install 3 x 240mm singles and 1 neutral to a panel in a LV room.the ducts aren't large enought.What happens if the singles are split through 2 ducts.IE, 2phases in 1 duct and the other phase and neutral in another duct.Where might i find a contradictory regulation.

 

[pc1966]

This would appear to go against regulation 521.8.1

However, if you could fit 4*120mm in one duct, and 4*120mm in another so you have a parallel arrangement but each duct has all live conductors of that parallel set, it would appear to be OK.

 

[pc1966]

Obviously you have added requirements for protection of parallel circuits, but if that can also be met then probably a whole lot easier to install as well.

 

[Rockingit]

This would appear to go against regulation 521.8.1

However, if you could fit 4*120mm in one duct, and 4*120mm in another so you have a parallel arrangement but each duct has all live conductors of that parallel set, it would appear to be OK.

Absolutely this. But only if the ducts are the same length!

 

[pc1966]

Yes, a good point!

Still, as long as the length of cable in either route is sensibly similar than it ought to be fine. Not sure what that actually translates in to but I would guess 5-10% max difference might be reasonable (so long as a similar level of current imbalance is not pushing one set above its CCC rating)?

 

[DefyG]

Whilst I agree its non-compliant as far as regs go but, does the line within the NICEIC test certifcate EIC) which ends -
"2018+A2:2022 except for the departures, if any (Regulations 120.3, 133.1.3 and 133.5), detailed as follows:"

provide some sort of caveat for non-compliant but equally safe work?

May not necessarily apply in this instance?

Opinions?

 

[westward10]

This would appear to go against regulation 521.8.1

However, if you could fit 4*120mm in one duct, and 4*120mm in another so you have a parallel arrangement but each duct has all live conductors of that parallel set, it would appear to be OK.

Wouldn't necessarily need to be 120.0 a basic calculation gives 95.0 which may in parallel fit the duct. Other factors would need to be calculated however.

 

[pc1966]

Whilst I agree its non-compliant as far as regs go but, does the line within the NICEIC test certifcate EIC) which ends -
"2018+A2:2022 except for the departures, if any (Regulations 120.3, 133.1.3 and 133.5), detailed as follows:"

provide some sort of caveat for non-compliant but equally safe work?

To some degree it would depend very much on the nature of the ducting and routes they take. My concern with this is you could get a significant magnetic field between the two runs due to the lack of current balance (cancellation) on each pair of conductors and so if they are separated by far, or ducts form some sort of a magnetic path, it might cause trouble.

 

[pc1966]

Wouldn't necessarily need to be 120.0 a basic calculation gives 95.0 which may in parallel fit the duct. Other factors would need to be calculated however.

True, cooling is generally better with parallel split. I just halved the OP's value as should be more or less the same VD, etc, and at least as good CCC.

 

[Rockingit]

The rules on parallel conductors are very clear: same length, same OCPD, same terminations. That’s why there’s no other derate factors applicable - doesn’t matter how many cables there are (we always assume two sets but no reason for three or more), it’s the same circuit.