General Inrush calculation inquiry

[El Papa]

Hi. I would like to know about inrush calculations in regard to disconnects. I am designing a small control cabinet and have three power sources to feed. One DC power supply for valves and instrumentation(T1), one PLC power supply(T2), and one 230VAC/24VAC power supply(T3). Simple stuff. The question I have is that if I calculate switch-on current and inrush for these, I get 83A inrush/switch-on current. We will use a 40A disconnect, but the inrush is 83A..

Should the disconnect be sized for 83A or is it just to check the short circuit rating of the disconnect?
(I am interested in calculation/real life physics here)

Thanks in advance!

 

[Ingenieur]

look at the HP rating
that will give you an idea of the inrush it can handle

 

[Besoeker]

Hi. I would like to know about inrush calculations in regard to disconnects. I am designing a small control cabinet and have three power sources to feed. One DC power supply for valves and instrumentation(T1), one PLC power supply(T2), and one 230VAC/24VAC power supply(T3). Simple stuff. The question I have is that if I calculate switch-on current and inrush for these, I get 83A inrush/switch-on current. We will use a 40A disconnect, but the inrush is 83A..

How did you calculate it?

 

[El Papa]

Thanks

Thanks

look at the HP rating
that will give you an idea of the inrush it can handle

The kW rating(I'm in Europe) isn't enough, but that is helpful. I also saw the Icw, which is fine. Thanks!

 

[El Papa]

Thanks

Thanks

How did you calculate it?

Took the inrush current from a transfomer(10x rated current) and then added the 'switch-on' current for the PLC power and power units.. 20A seems like an awful lot for that, but I guess it is flooding the circuitry in an almost insignificant amount of time... Maybe another question that can be of value is for low-voltage equipment, at what rating do switch-on, inrush current ratings become significant? I have a friend who makes installations and constantly is baffled by engineers, since he knows much more 'real-life' of how the equipment is affected, working. I guess on my side I want long-term safety and liability covered along of course with correct functionality and general safety.

 

[Ingenieur]

The kW rating(I'm in Europe) isn't enough, but that is helpful. I also saw the Icw, which is fine. Thanks!

my point is if the disconnect is rated for say a HP rating of 30 A equivalent, it should handle at least 5-6 times that for inrush