Max. amps and hp rating for electrical switch
Max. amps and hp rating for electrical switch
(OP)
Hi, everyone:
I need a switch to turn on/off a 2500W power supply(single phase) from wall outlet (220Vac). When I look at the specs of related product I get a little confusion: Why the manufactures give Max. amps at 240VAC/600VAC, but at the same time MAX. horse power. By just looking at the Amps spec, it's sufficient for my application, for example 30Amps @240VAC. But then the MAx hp is lower than my application,for example, 3hp. 3hp translated to 746Wx3=2238Watts which is lower than 2500W. Can somebody here help me to clarify this issue?
Thanks in advance
bj
I need a switch to turn on/off a 2500W power supply(single phase) from wall outlet (220Vac). When I look at the specs of related product I get a little confusion: Why the manufactures give Max. amps at 240VAC/600VAC, but at the same time MAX. horse power. By just looking at the Amps spec, it's sufficient for my application, for example 30Amps @240VAC. But then the MAx hp is lower than my application,for example, 3hp. 3hp translated to 746Wx3=2238Watts which is lower than 2500W. Can somebody here help me to clarify this issue?
Thanks in advance
bj





RE: Max. amps and hp rating for electrical switch
RE: Max. amps and hp rating for electrical switch
bj
RE: Max. amps and hp rating for electrical switch
As davidbeach was pointing out switches have different ratings for different types of loads. The standard value they provide, say, 10A @ 240V would be for a purely resistive load that has no inrush associated with it. It also means it would interrupt that 'easy' load perhaps 100,000 times before failing.
Now if you instead use it on tungsten filament light bulbs which have a high inrush the switch might work fine but only for 20,000 cycles.
Now use it on a motor that has a large inrush and a large inductance that defies easy interruption and that switch may provide only 20 cycles or may just explode. To avoid that the switch makers deal with that nasty motor load by derating the power allowed for motor starting.
Now with your device you have to think about how far from a straight forward resistive load it looks to a switch. I suggest that a typical supply might have a very large inrush thru rectifiers to initially charge a capacitor. This would impact the switch in a negative way. So if your supply is 2.5kW and demands a continuous 30A to operate you might want to go with a larger switch say a 40A switch or you will experience premature failure, maybe 300 switch cycles.
If your supply is a sophisticated supply with PF correction and softstart then you can likely use just a 30A switch with fine lifetime performance.
If not, you might want to consider instead switching a small inexpensive switch that switches a large relay or small contactor to provide what you need. You ca parallel relay contacts to boost lifetime and reduce cost.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Max. amps and hp rating for electrical switch
bj
RE: Max. amps and hp rating for electrical switch
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Max. amps and hp rating for electrical switch
UNLESS... there is a current limiting (a.k.a. soft start) circuit in the power supply, such as a pre-charge resistor. If that is the case, then the capacitor charging current and residual charge issue become less relevant. So in that case, just derate the thermal (resistive) current rating ( a.k.a AC-1) of the switch by 30%, which means your 30A switch would be fine.