Cable magnetisation

[colt]

In installing single core non armoured cables from the x'mer to the LV Swgr (4 per phase plus 4 ea. as Neutral), I will get magnetisation on the cables? There is a way to avoid magnetisation installing the cables in the same path?
Any idea will be welcomed.
Colt

 

[redtrumpet]

I'm not sure what you mean by magnetisation of cables, but I believe you may be referring to one or both of two effects.

First, a single conductor cable will induce current in surrounding ferrous metal. If the cable is carrying enough current, this can cause substantial heating of the surrounding metal. This means the installer should use non-ferrous cable straps and non-ferrous entry plates at equipment.

Second, asymmetrical arrangement of parallel conductors causes differences in inductive reactance for each cable, with a resulting unequal division of load current. You don't say how you are running your cables, but if you were running them in two spaced layers in cable tray, or in a (non-ferrous) duct bank, a possible arrangement could be A1-B1-C1-C2-B2-A2 in the top layer and A3-B3-C3-C4-B4-A4 in the bottom layer. Alternatively you could run four (non-ferrous) ducts, each with an A-B-C arrangement. I'm from Canada and our Electrical Code illustrates various arrangements for parallel cables, so perhaps checking the Electrical Code for your area will be of help.

I'm not an expert on running the neutral as most of my work is on industrial systems with resistance-grounded system neutral and no single-phase loads, but I assume if it carries return currents there is no harm in treating it as another phase in grouping cables. On the other hand, since the return currents are zero sequence, you may be able to group all the neutral conductors together and run them separately. Anyone out there know more about this?

 

[jbartos]

Please, provide more info how you intend to install those conductors and subconductors, i.e. in conduit, what type of conduit, in tray, what type of tray, in the air, underground electrical banks, etc.
Generally, cables may have shields (single or double) and some electromagnetic field will propagate outside of those conductors/cables; especially, higher (harmonic) frequency caused emissions, if not installed in conductive metallic raceways.
Some of these phenomena can be modeled by software that is used for modeling of electromagnetic fields.