1mm cpc

[davetheglitz]

Just been reading OSG (God bless Eastenders and Holby!) appendix 2 pg 100.

Noticed that 1.0 mm2 cpc is not permitted on 30A BS3036 fuse.

Does this apply to a ring main? My gut feeling is that in that case the cpc is 2.0mm providing there is continuity so still OK - but would welcome a second (or third!) opinion.

Cheers

 

[Andy™]

Noticed that 1.0 mm2 cpc is not permitted on 30A BS3036 fuse.

Does this apply to a ring main?

i think so

 

[Evans Electric]

This may be to do with the early metric T/E .. 2.5 with a 1.00 earth wire. Still come across it, in situ. If its a ring main I think changing to a 20 A MCB complys but not sure.

Deke

 

[SPECIAL LOCATION]

approved doc P...

Page 38

top left hand corner of page..

1.0 CPC with 30a semi-enclose fuse will not always be properly protected against thermal effects...

so need to consult a competent electrician about upgrade CU or cable???

So..

don't go near the stuff in your thermal undies!!! :^O:^O:^O

 

[davetheglitz]

Thanks SL - good spot!

Can't really understand the logic however as if it's a ring surely there is a second earth path to split the current. I suppose if the fault was very close to one end of an extremely long ring and there was a very low Ze it might be feasible that there would be a problem - but highly unlikely!

Anyway - in black and white - upgrade the cables and or the consumer unit are the only options in part P. Obviously downgrading the fuse to 16A or fitting an MCB never enters into the equation

 

[cheggers]

just fit a retro fit 32a mcb, job done

 

[kme]

Agreed with cheggers here Dave. The fact that there is a ring would be expected for a 1mm cpc on a 32A - it ain`t going to be lighting cable, is it?

4 or 6 mm doesn`t come with 1mm cpc - therefore we must be on 2.5 T+E in a ring configuration - else it would fail to comply in lots of other respects.

KME

 

[Apache]

Isn't 2.5mm T&E's CPC 1.5mm anyways? What's the problem?

 

[kme]

The early stuff wasn`t mate. it was 2.5/1.0

bummer. I know

then they made it 2.5/1.5

Can sometimes be a ***** to tell the difference

 

[Apache]

The early stuff wasn`t mate. it was 2.5/1.0 bummer. I know

then they made it 2.5/1.5

Can sometimes be a ***** to tell the difference

I see

Thanks mate

 

[kme]

Dim problem.

 

[SPECIAL LOCATION]

Thanks SL - good spot!Can't really understand the logic however as if it's a ring surely there is a second earth path to split the current. I suppose if the fault was very close to one end of an extremely long ring and there was a very low Ze it might be feasible that there would be a problem - but highly unlikely!

Anyway - in black and white - upgrade the cables and or the consumer unit are the only options in part P. Obviously downgrading the fuse to 16A or fitting an MCB never enters into the equation

OR drop fuse size to 20a!

Its all down to complying with Reg 541.1.3

CSA of cpc... and doin the calc with the time-current graphs...

a 30A semi enclosed 3036 fuse needs a CPC greater than 1.0mm to meet the 0.4sec op time. (think it calcs top 1.15m? or thereabouts.)

BUT a 20A semi enclosed is fine...

I personally just always consider things in a more simplistic way..

ALL other circuits & cables have a CPC at least half the CSA of Line/Neutral conductors... but 2.5/1.0 T&E dont!!

 

[Evans Electric]

So ,as I said earlier, replace the rewirable 30a fuse with a 20a MCB

Deke

 

[kme]

Aye. That`ll work. Or change for plug-in 60898. Even better

 

[cheggers]

OR drop fuse size to 20a! Its all down to complying with Reg 541.1.3

CSA of cpc... and doin the calc with the time-current graphs...

a 30A semi enclosed 3036 fuse needs a CPC greater than 1.0mm to meet the 0.4sec op time. (think it calcs top 1.15m? or thereabouts.)

BUT a 20A semi enclosed is fine...

I personally just always consider things in a more simplistic way..

ALL other circuits & cables have a CPC at least half the CSA of Line/Neutral conductors... but 2.5/1.0 T&E dont!!

10mm 6242y 4mmcpc, 6mm 6242y 2.5cpc

 

[binky]

Its only an issue on a fuse due to thermal effects, its fine on an MCB at 32A, Now where I read that I'll be damned if I can remember, and I'm not planning to find out again tonight!!!

 

[SPECIAL LOCATION]

10mm 6242y 4mmcpc, 6mm 6242y 2.5cpc

ah!!! :^O :^O:^OApplaud SmileyApplaud Smiley

you spotted my go off into rambling mode at twenty to two in the morning

and lubricated!!!Guiness Drink

Guiness DrinkGuiness DrinkGuiness Drink

Blushing

 

[davetheglitz]

Just an interesting case. I accept the letter of the part P document as found by SL - but I don't think the ring has been considered in the implementation of the OSG. However if it's a Wylex - easy to fit an MCB. If it's an MEM - hope you can find some spares for an MCB or 16/20A fuse - otherwise it's down to part P

I'm just a bit annoyed that Part P only considers two options - replace the cables or replace the CU. Customers need to know why you do things and to my mind the only options given are to optimise profit rather than help someone over a problem!