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# MV Cable ampacity in concrete trenchs

## MV Cable ampacity in concrete trenchs

(OP)
I need to calculate current carrying capacity for 20 kV cables, cables are laid in concrete trenches with traffic rated tile covers, it is not sealed and does allow some air circulation but not fully ventilated, just sun protected mostly.

The approach as I remember is to calculate the temperature rise inside the trench due to cable losses and sun exposure (not straight forward) and get the corresponding temperature derating factor accordingly.

Do you guys have similar experiences or useful reference to go with?

### RE: MV Cable ampacity in concrete trenchs

See:
IEC 60287-2-1 2.2.6.2 Unfilled troughs of any type, with the top flush with the soil surface and
exposed to free air. An empirical formula is used which gives the temperature rise of the air in the trough above the air ambient as:
tr=WTOT/3/p where:
WTOT is the total power dissipated in the trough per metre length (W/m)
p is that part of the trough perimeter which is effective for heat dissipation (m)
Also, for covered trench:
Power cables and their applications by Lothar Heinhold

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