32A ring circuits wired in 1.5mm firetuf

[Natt]

I've been asked to inspect a shop and have found 4x 32 amp ring final circuits supplying socket outlets, all wired in firetuf 1.5mm twin and earth.
Actually all the circuits are wired in this stuff, there must have been a deal on at the wholesalers..
My concern is does this comply with 421.1.103 as it's not micc but from what I can find the current carrying capacity of the cable is not less than 20A?
Also the three phase GE board is filled with 6kA mcb's, I was told they should be 10kA but can't find a reg for this.
Measured Line to neutral Ipf is 2.62kA
If these are deviations then my next question would be about codes for the Periodoc form, but I should probably ask that in the Inspection& testing section

 

[GaryM]

It's 433.1.5

The ring finals are certainly non compliment circuits and as such require improvement. Without any more information I'd be opting for a code 2.

As for the 6kA MCB's, they seem fine, even after doubling the 2.62kA PSSC Line to Neutral figure for PSSC phase to phase.

This is from GN3:

Where a service cut-out containing a cartridge fuse to BS 1361 type 2 supplies a consumer unit which complies with BS 5486-13 or BS EN 60439-3, then the short circuit capacity of the overcurrent protective devices within consumer units may be taken to be 16 kA.

Fault currents up to 16kA
Except for London and some other major city centres, the maximum fault current for 230 V single-phase supplies up to 100 A is unlikely to exceed 16 kA.

The short-circuit capacity of overcurrent protective devices incorporated within consumer units may be taken to be 16 kA where:
-the current ratings of the devices do not exceed 50 A
-the consumer unit complies with BS 5486-13 or BS EN 60439-3
-the consumer unit is supplied through a type 2 fuse to BS 1361 :1971 rated at no more than 100 A.

 

[Deleted member 26818]

To my mind, if the current carrying-capacity of the 1.5mm² firetuff is greater than20A after all correction factors have been applied, then it is fine.
The 6kA MCBs are fine, it's usual in commercial/industrial installations to use 10kA, but if the PFC is less than 6kA, there's no need for 10kA.
As far as I'm aware, it is only Type tested Distribution Boards, refered to as Consumer Units, which are rated at 16kA. All other types are not rated, and the rating will be based on that of the lowest rated device which is installed.
In this case, most probably 6kA.

 

[migspat30]

i would stick in a 1.5 twin and earth to the outside light and wire the boiler accordingly

 

[Natt]

Thank you for the replies. The reg in the amended BS7671 is 433.1.103 my mistake.
There are no correction factors needed as far as I can tell, but I think I should list it on the Periodic as at least a code 3, as the next spark to inspect it will no doubt have a different opinion from whatever I say!

 

[IQ Electrical]

Thank you for the replies. The reg in the amended BS7671 is 433.1.103 my mistake.
There are no correction factors needed as far as I can tell, but I think I should list it on the Periodic as at least a code 3, as the next spark to inspect it will no doubt have a different opinion from whatever I say!

Don't list it as a 3, it doesn't need 'further investigation', list it something like 'ring final circuits A, B, C and D are wired in 1.5mm 'Firetuf' however there is still adequate current carrying capacity'.
In the defect code box, enter N/A.

Note, I'm assuming there is adequate CCC.

 

[Natt]

I think I will need to return to site and get more details of the cable used and find the manufacturers website, hopefully then I will be able to determine if the CCC is adequate.

 

[sparky3366]

And besides, lets face it...the cable won't burst into flames if the CCC is too low :chinese:

 

[Darkwood]

Just another angle to approach this problem from, due to higher operating temperatures the cable can run at - it may have a higher than expected ccc, say 90c operating temp for example; but this aspect may be affected by the equipment, mcb's etc connected to the wire which may have a 70c rating thus derate the handling temp and de-rating the ccc from manufacturers tables.
Consequently this could mean its a fire hazard at its termination points, what you need to do is derate the cable to 70c and recalculate the ccc from this.

 

[Simlec]

'firetuf 1.5mm twin & earth' ??Do you mean FP cable or low smoke t&E ?I get FP 1.5mm to a max of 19.5A !So the 32a MCB to big.

 

[Deleted member 26818]

'firetuf 1.5mm twin & earth' ??Do you mean FP cable or low smoke t&E ?I get FP 1.5mm to a max of 19.5A !So the 32a MCB to big.

It all depends on the reference method.
19.5A is reference method C, with a conductor operating temperature of 70ºC, and an ambient temperature of 30ºC.
With reference method E, the CCC is 22A.

 

[SPARTYKUS]

Simlec-its a ring , not radial.

 

[Simlec]

I know it's a ring, so there for on his 32a MCB he would need a cable capable of carrying 20amps would he not. Spinlondon you could be correct I would have to check, but I can bet that it's not all installed in ref E

 

[GaryM]

In any case, a ring circuit wired in 1.5mm2 conductors and protected by a 32A MCB is only permitted if MICC is used.