Cable Current carrying capacity

[Tonkolili]

Why is it that the tables in the Regs for Cable current carrying capacities vary so much from that of a cable manufacturers data sheet, for example a table in the Regs book states a 240mm 4 core XLPE Armoured cable buried will carry 324 amps, but a data sheet for a leading manufacturer states 516 amps.

 

[Spoon]

Are you sure the temp ratings are the same?

 

[Darkwood]

The regs are British Standards and work on the worse case scenario as the tolerances of cables varies greatly dependent upon the make-up of the sheath/insulation.

You can use the manufacturers guide but caution that the tables they state are compliant to the UK regulation and not say reflecting a CCC for a country who's requirements are more relaxed this is where ambient ground and air temp's may give a different outcome.

The table you used is specifically for -

Air ambient at 30 degrees.
Ground ambient 20 degrees.
Conductor operating temp' 90 degrees.

The table you are using is not commonly used as most equipment you'll connect to will only have a 70c rating meaning you need to use table 4D4A instead.

Lastly the table you are referring from also has ducted swa which reduces the effective heat dissipation so its really ignoring direct buried cables for the worse case ducted ones.

 

[Spoon]

Just checked this out myself.
Eland cable XLPE/PVC/SWA/PVC 240mm Direct In Ground is 324A.
Anixter XLPE/PVC/SWA/PVC 240mm Direct Burial is 529A.

 

[Besoeker]

Why is it that the tables in the Regs for Cable current carrying capacities vary so much from that of a cable manufacturers data sheet, for example a table in the Regs book states a 240mm 4 core XLPE Armoured cable buried will carry 324 amps, but a data sheet for a leading manufacturer states 516 amps.

It depends on installation method which affects the ability of the cable to dissipate heat.
Direct burial is like thermal insulation compared to being mounted in free air or on perforated tray.