Suggestions for best way to wire underground supply please

[telectrix]

IET Forums - Underground SWA Current Rating? - http://www.------.org/forums/forum/messageview.cfm?catid=205&threadid=27920

 

[telectrix]

as an experiment, try shoving 100A down some 16mm for an hour. then measure the temp. of the cable. if you read >40deg.C. then your temp gauge is wrong.

 

[Wilko]

What about the part of the cable that comes out of the ground?

That part would be ok - 89A clipped direct or 97A in free air ?

 

[Ian1981]

That part would be ok - 89A clipped direct or 97A in free air ?

Based on 30 degrees tho yes?

 

[Ian1981]

as an experiment, try shoving 100A down some 16mm for an hour. then measure the temp. of the cable. if you read >40deg.C. then your temp gauge is wrong.

Only if you pay my electric bill

 

[Wilko]

Deleted while thinking a bit more ... might be a while ...

 

[telectrix]

we not in the sahara . not even spain. 30deg. my arse. we'd all be like essex boys at that temp. but with real tans.

 

[Ian1981]

we not in the sahara . not even spain. 30deg. my arse. we'd all be like essex boys at that temp.

Well it errs on the side of safety but I didn't write the regs , send any complaints to jpel/64 ha

 

[telectrix]

haha, trouble is that the regs. are so pessimistic. written to cover arses. as a famous person once said." rules are for the strict adherence of fools, and for the guidance of wise men"

 

[Wilko]

Based on 30 degrees tho yes?

Yes, 4D4A is for ambient air temp of 30. Still thinking ...

 

[Ian1981]

Yes, 4D4A is for ambient air temp of 30. So for cable in free air Ref E - well the cable isn't buried any more - so 433.1.203 doesn't apply and that part of the cable doesn't need derating from what's listed in the table ?

The overall ccc of the cable needs to be the lowest rating if installed using different reference methods using the most onerous method

 

[Wilko]

Got it - thanks Ian

 

[Ian1981]

haha, trouble is that the regs. are so pessimistic. written to cover arses. as a famous person once said." rules are for the strict adherence of fools, and for the guidance of wise men"

I would assume tests would have been performed and the appropriate ccc recorded as we see them today.
Perhaps cables buried in walls and installed in trunking etc are more like at an ambient temperature of 30 as there's no free air?

 

[Ian1981]

Got it - thanks Ian

Don't thank me yet wilko as someone might come along and shoot me down in flames.
It's how I understand it and it's written in be 7671 so got to go with that don't we?

 

[Wilko]

Don't thank me yet wilko as someone might come along and shoot me down in flames.
It's how I understand it and it's written in be 7671 so got to go with that don't we?

Ha ha, always on the cards !
I needed to re read 433.1.203 a few times. Using an 80A fuse for overcurrent protection of a buried cable then the cable needs to be rated >=89A and clearly 16mm isn't when it's buried