I have 2no parallel 4-core 400mm2 XLPE SWA cables laid in pvc ducts directly in the ground. They run some 90m with a load which ranges between 780A to 1230A, the latter becoming more common for longer periods due to the addition of recently installed plant. I am not sure of the cable manufacturer, nor indeed if they are XLPE as the glands are made into the bottom of the switchboards. The installing sparks must have been super nimble contortionists! Anyway, I am seeking an approximate current carrying capacity for the method of installation. I believe the cables are under sized although not showing any signs of undue degradation. The Flir shows them around 100C at one end.
I'm rather hoping the switchgear is not buried, and the cores are separated out a few inches before they reach the contacts, so therefore the free ends of the cores are rather cooler for the same dissipation per unit length than the hottest parts of the cable run - just because the cable insulation is rated to stand 90 degrees for however many years make an operational life, does not preclude you running parts of the cable quite a bit cooler after all, it just lasts longer.
The real sticky question is how much better or worse a thermal conductor is the soil in this location compared to the example in BS7671- and that we probably do not know.
I'm rather hoping the switchgear is not buried, and the cores are separated out a few inches before they reach the contacts, so therefore the free ends of the cores are rather cooler for the same dissipation per unit length than the hottest parts of the cable run - just because the cable insulation is rated to stand 90 degrees for however many years make an operational life, does not preclude you running parts of the cable quite a bit cooler after all, it just lasts longer.
The real sticky question is how much better or worse a thermal conductor is the soil in this location compared to the example in BS7671- and that we probably do not know.
