Cable sizing for a 3 phase Chiller

I would expect that "386 amps" means 386 amps PER PHASE at full load.

Therefore a cable with a rating of at least 386 amps is required.

Confirm with the supplier if in doubt, but without wishing to sound patronising it think that it means what it says, without any need for furthur calculations, corrections, or assumptions.


I would be very cautious with cable sizing for large chillers for several reasons.

Firstly, most use is expected in hot weather, and cables might need to be de rated for UK summer ambient temperatures. If overseas in a hotter climate than the UK, then de ratting is almost certainly required.


Secondly, chillers tend to be very sensitive to voltage drop. A voltage below the nominal or expected voltage will tend to increase the current drawn, this will either trip the internal overload protection, or might result in the current exceeding the namplate by say 5%

In areas with a lot of air conditioning, utility voltage tends to drop on hot days.


And finally, chillers tend to be a long hour load in hot weather, and voltage drop represents money wasted in cable losses. This can be significant on such a large load.


Finally, double check if this chiller requires any other auxillary supply for controls. Some types need an additional single phase 230 volt supply for controls. If providing same is not easy, then the makers can generally supply a transformer in the control panel that derives the 230 volt control supply from the 400 volt main power circuit.

Be aware that any such transformer may be an extra cost, and that the input current to this control transformer will be a slight addition to the stated current, perhaps 5 or 10 amps.

I would expect that "386 amps" means 386 amps PER PHASE at full load.

Therefore a cable with a rating of at least 386 amps is required.

Confirm with the supplier if in doubt, but without wishing to sound patronising it think that it means what it says, without any need for furthur calculations, corrections, or assumptions.


I would be very cautious with cable sizing for large chillers for several reasons.

Firstly, most use is expected in hot weather, and cables might need to be de rated for UK summer ambient temperatures. If overseas in a hotter climate than the UK, then de ratting is almost certainly required.


Secondly, chillers tend to be very sensitive to voltage drop. A voltage below the nominal or expected voltage will tend to increase the current drawn, this will either trip the internal overload protection, or might result in the current exceeding the namplate by say 5%

In areas with a lot of air conditioning, utility voltage tends to drop on hot days.


And finally, chillers tend to be a long hour load in hot weather, and voltage drop represents money wasted in cable losses. This can be significant on such a large load.


Finally, double check if this chiller requires any other auxillary supply for controls. Some types need an additional single phase 230 volt supply for controls. If providing same is not easy, then the makers can generally supply a transformer in the control panel that derives the 230 volt control supply from the 400 volt main power circuit.

Be aware that any such transformer may be an extra cost, and that the input current to this control transformer will be a slight addition to the stated current, perhaps 5 or 10 amps.