[SOLVED] Corsair RM850i trips circuit breaker during switch on surge ?

Mezoxin

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Nov 3, 2019
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I have noticed that my circuit breaker trips when i switch on the PSU after being turned off for a long time , this doesnt happen during load or normal operation or when i start up my pc when the PSU switch has been left on
I looked at the breaker and its rated at 10A , My PSU Inrush current at 220V is probably around 66.7A ( this is according to an HX850w review couldnt find one for my PSU)
https://www.tomshardware.com/reviews/corsair-hx850-psu,5257-4.html

Is this inrush current enough to trip the circuit breaker ?
 
Last edited:

Mezoxin

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Nov 3, 2019
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I found a Solution at the guru forums so I will post it here
A user made calculations and estimated that the duration on the inrush current would be about 4ms and could be enough to trip a 10A CB
Two 330µF capacitors charged to say 350V

I V Dt = 0.5 C V_c^2

where

I = 66.7 A
V = 220 V
C = 660 µF
V_c = 350 V

gives us a Dt of about 3 ms, which fits with the idea that things can charge up in the first ramp of the AC, which is a quarter cycle and so about 4 ms.

Now I recall about 30 years back there were special circuit breakers that were more tolerant to such inrush surge, I assume that they all are these days; how old are yours?

The attached tripping curve suggests it is quite possible as you are at about 7 times the rated current (for a few milliseconds)

I tried swapping the CB's with the same ratings to see if it was a faulty CB , but the problem was the same ,
finally I got the electrician to check the wires and changed the CB to 40A and the PSU stopped tripping the CB during inrush currents
 

Mezoxin

Upstanding
Nov 3, 2019
461
89
290
23
I found a Solution at the guru forums so I will post it here
A user made calculations and estimated that the duration on the inrush current would be about 4ms and could be enough to trip a 10A CB
Two 330µF capacitors charged to say 350V

I V Dt = 0.5 C V_c^2

where

I = 66.7 A
V = 220 V
C = 660 µF
V_c = 350 V

gives us a Dt of about 3 ms, which fits with the idea that things can charge up in the first ramp of the AC, which is a quarter cycle and so about 4 ms.

Now I recall about 30 years back there were special circuit breakers that were more tolerant to such inrush surge, I assume that they all are these days; how old are yours?

The attached tripping curve suggests it is quite possible as you are at about 7 times the rated current (for a few milliseconds)

I tried swapping the CB's with the same ratings to see if it was a faulty CB , but the problem was the same ,
finally I got the electrician to check the wires and changed the CB to 40A and the PSU stopped tripping the CB during inrush currents
 

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