1.5mm CPC on 6mm Cable

[briefcasedan]

Come across an old Installation with 1.5mm CPC on a 6mm Live conductors whilst doing an EICR. Not seen many of these, in everyones opinion perfectly acceptable if all R1 and R2, IR, Measured ZS test check out ok?

 

[Ian1981]

Are you sure it’s not 4mm as that has a 1.5 mm cpc?

 

[briefcasedan]

100% 6mm Cable, heard some really old installations used to do this

 

[Ian1981]

As long as the cpc is adequately sized for fault protection then I don’t see an issue with it.

 

[westward10]

Assuming this is T&E I have never seen a 6.0 with a 1.5 cpc. The only metric size I know of which doesn't comply to current UK sizing was 1.0 cpc in 2.5 cables in the early 70s.

 

[davesparks]

Come across an old Installation with 1.5mm CPC on a 6mm Live conductors whilst doing an EICR. Not seen many of these, in everyones opinion perfectly acceptable if all R1 and R2, IR, Measured ZS test check out ok?

It is acceptable if it meets the required size as calculated by the adiabatic equation and it passes testing.
You must ensure that the size is suitable not just rely on the test results, an undersized CPC could pass testing but melt under fault conditions before the OCPD operates.

 

[westward10]

I find it difficult to believe 6.0 T&E was produced with a 1.5 cpc, four times smaller than the csa of the line conductor.

 

[telectrix]

wondering if this was imperial cable ( 7/044 (6mm) or perhaps 7/036 (4mm) ).

 

[davesparks]

I find it difficult to believe 6.0 T&E was produced with a 1.5 cpc, four times smaller than the csa of the line conductor.

The OP hasn't confirmed what type of cable it is, I assume it is most likely singles.

 

[westward10]

The OP hasn't confirmed what type of cable it is, I assume it is most likely singles.

Yes I made the assumption T&E in #5 after he used the word cable in #3 but plenty of people refer to a single conductor as a cable so who knows.

 

[pc1966]

A quick check in OSG table B7 says it should be fine for typical modern MCBs up to 40A so long as the PFC is below 3kA (and circuits meet the disconnection Zs, of course).

Hopefully the OP can confirm the type of protection meets this sort of adiabatic limit?

 

[Mark Wright]

probably alot of the time you can go very small with the adiabatic equation but it's not great is it, if you have have such a small cpc for a large current carrying cable - before the protective device operates is it really going to be the path of least resistance compared to your body?

and if the protective device is slow or fails, it's going to burn up pretty. quick.

 

[davesparks]

probably alot of the time you can go very small with the adiabatic equation but it's not great is it, if you have have such a small cpc for a large current carrying cable - before the protective device operates is it really going to be the path of least resistance compared to your body?

and if the protective device is slow or fails, it's going to burn up pretty. quick.

Yes it will be a path of lower resistance than your body,

If the protective device fails then any CPC will melt, unless you size it bigger than the line conductor as then the line conductor will melt.