Control panel feeder cable sizing

[Indy]

We have a control panel that has a few fan motors (3phase) and two heaters ( 3 phase) and single phase loads to valve actuators. My question is regarding the sizing of the feeder cable to this control panel. Do we work out all the currents individually and then add them and treat this as a "lump sum" to size the feeder cable and its associated protection.

We are in the uk and voltages are 400v 3 phase and 230v single phase.

Thanks

 

[jraef]

Here in the US, our National Electric Code has a process that must be followed for this, most likely yours does as well, but it might be different. You should start there.

Here is how ours reads:
430.24 Several Motors or a Motor(s) and Other Load(s).
Conductors supplying several motors, or a motor(s) and other load(s), shall have an ampacity not less than the sum of each of the following:
(1) 125 percent of the full-load current rating of the highest rated motor, as determined by 430.6(A)
(2) Sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A)
(3) 100 percent of the noncontinuous non-motor load
(4) 125 percent of the continuous non-motor load.

There are several exceptions, allowances etc. pertinent to specific installation details, but this gives you an idea.




"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[7anoter4]

See IEC 61439-2 and IEC 61439-3.

http://www.schneider-electric.co.kr/documents/Catalogue/Okken_SpecifierGuide.pdf

 

[controlsdude]

I thought when i was involved in heat treating industry that any heater resistive loads were sized at 125% of rated load.

Everything else said above i agree with too.