Cables heating up

[PURDY1888]

Installed a new 4 core 50mm swa to a 3 phase db to fed a heating panel.the length is 92metres. The underfloor elements had not been used in three years and the clients got us to rewire the circuits with 4mm tri rated single cores, after connecting them up at the elements and at the contactors which were fed from 20amp mcbs in the db thay started to heat up. Would like help with this problem

 

[SimpleSimon]

IR test the elements?

 

[mechelec]

how much current is being drawn? the MCB is not tripping so check with a current clamp if less than the rating of the cable it should not be a problem? is the connection to the element correct ie cold tails at the interface