Suggestions for best way to wire underground supply please

[Ian1981]

Needs to be 25.0 if your are burying it the ground on an 80A protective device.

What does?

Edit
You mean the swa

 

[Ian1981]

Yes, domestic, 10mm bond to gas/water - thanks for checking though!

As it's a new build I doubt you will need to provide a protective bonding conductor to the water as the incoming supply externally will be in plastic but you'll have to see

 

[telectrix]

Needs to be 25.0 if your are burying it the ground on an 80A protective device.

why?

 

[Ian1981]

16mm swa buried is only 78 amps ambient temperature 20 degrees and that's without applying the 0.9 correction factor as cable is buried for ambient temperature for 30 degrees plus any other factors like depth etc

 

[westward10]

I always opt for the three phase rating with a three core but that is another debate but yes either way it is undersized if you use 16.0

 

[Wilko]

16mm swa buried is only 78 amps ambient temperature 20 degrees and that's without applying the 0.9 correction factor as cable is buried for ambient temperature for 30 degrees plus any other factors like depth etc

Just trying understand - Table 4D4A for direct buried at 0.7m, ambient 30, ground ambient 20 and conductor 70 is 78A. So question is, why pick 30 ground temp to further derate to?

 

[Ian1981]

Just trying understand - Table 4D4A for direct buried at 0.7m, ambient 30, ground ambient 20 and conductor 70 is 78A. So question is, why pick 30 to derate to?

0.9 is applied where overload protection is required and prevents the cable going over temperature when overloaded.
The factor is used because cable ratings for cables in the ground are based on a ground temperature of 20 degrees compared with 30 degrees for other reference methods.
See regulation 433.1.203

 

[telectrix]

which is all wrong. rarely will the ambient temperature rise above 20dg. C. in this country. once you are down 2 ft. underground the temp. is down to around 10dg.C.

 

[Ian1981]

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

 

[telectrix]

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

fit a fan.

 

[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 ...