reference method D

[ianphilip007]

hi everyone

quick question reguarding ref method D (cables in ground/or in ducting in ground)
i can find no figures or derating factor in the OSG. can anyone help me out with either the derating factor, or the current carrying capactity for 6mm 3core SWA installed using ref method D

many thanks

 

[telectrix]

SWA run underground, as long as it,s not more than about 2ft. deep needs no derating factor applied. IMO.

 

[ianphilip007]

thanks telectrix is that even when in ducting or buried direct ?

 

[telectrix]

both as far as i know. it's because the ground temp. is usually around 10-12 deg.C.

 

[pushrod]

single phase 46A, three phase 38A ref method D, table 4D4A of BS7671 would be my 2Ps worth

edit ; that is at 20C so at 15c the CCC could be x1.05

 

[scotsparky]

BRB app4 p267 table 4b2 shows rating factors for method d 4b3 is thermal for k facotr for underground conduit

 

[ianphilip007]

thanks push rod

 

[ian.settle1]

In the design book from the IET the de-rating factor if you bury the cable is 0.9.

 

[pushrod]

In the design book from the IET the de-rating factor if you bury the cable is 0.9.

True, but that wouldn't apply if you were using ref D, only derating for grouping, ambient temp and insulation if applicable would apply afaik.

 

[Engineer54]

The generally accepted depth for cables direct buried and cables buried in duct is 600mm to 650mm. Over 700mm then derating starts to rear it's ugly head... lol!!!