Non-magnetic materials in TFo and cable's clamp

[MDom]

I need the advise.We have dry-type 2500 kVA transformer(TFo)
10/0.4 with the envelope (IP31).The manufacturer made the
non-magnetic(but conducting) rectangular part of the envelope near the place of 10 kV cable lead-in ( something like aluminium or duralumin),the same for LV lead-in,but I speak about HV.We have 3 one-core screened 10 kV cable between a/m TFo and upstream RMU( Ring Main Unit) The manifacturer uses magnetic ( steel)clamps for fixing the cable in RMU.The clamp constitutes curcuit.
I can't understand why does the manufacturer prevent the heating due to magnetic reversal in TFo envelope and doesn't prevent it in RMU,using steel clamps.Is it correct to use magnetic material in one-core cable clamps made curcuit ?
Best regards

 

[prc]

Unfortunately your question is not clear.Generally whenever single core cables are used nonmagnetic cable take out is provided to avoid heating from magnetic field of cable current.But magnetic material can be used if three phases are accomodated in 3 core cable as then the magnetic fields will get cancelled each other.

 

[MDom]

prc, I try to clarify.The manufacturer of single core cable
insists on using non-magnetic clamps and bolts for fixing
the single core cable to the steel enclosure of 10 kV RMU whereas the manufacturer of RMU ( ring main unit)uses steel for these details. My question is :do any documents regulate this point ? ( the current approx.150A and the cable is screened - I think it's important)

 

[gordonl]

A cable supplier I dealed with provided me with an installation guide which suggested that 200A was typically the cut-off where mitigation techniques had to be used with ferrous clamps, plates, etc. For a problem to exist the single conductor cable has to be totally surrounded.

 

[redtrumpet]

200 A is also the cut-off in the Canadian Electrical Code - Rule 12-106 (5).

"A single-conductor cable carrying a current over 200 A shall be run and supported in such a manner that the cable is not encircled by ferrous material."