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

#### Mezoxin

##### Upstanding
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

##### Upstanding
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
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