Question House breaker tripping when a new USB device is connected while the computer is completely turned off and then turned back on.

[Athsara]

So today i built a PC , When the computer is powered on normally without any USB connected the computer turns on and works , but when u turn the system completely off (from the psu and pull the cable out) and then connect a USB device from the rear and the turn the PSU switch on the House breaker will trip , but once u turn the switch off , turn the trip back on and then turn the PSU switch on without removing the attached USB then it will turn on normally , this doesnt happen consistently but happens from time to when a New USB is introduced while the power is cut off and the PSU is turned off and then power is given back from the PSU.



What could be the issue?

 

[MoroMoro]

Im no electrician, but that sounds like a problem with resistance.

 

[Athsara]

Im no electrician, but that sounds like a problem with resistance.

are u suggesting that it cud be an issue with the PSU?

 

[mmp09]

If I correctly understand, you just turn on the PSU switch. Not the Power ON Switch or button on the cabinet.

So the PSU when switched on from mains enters a Stand-By state, where it supplies minimum voltage and current required to run certain systems like LAN, RTC etc etc. Only after you press the PowerOn button on cabinet, then full voltage is supplied and system boots.

So try the same config without any cabinet and re-test with min parts. What are the USB devices in question? Does it happen with USB Keyboard/Mouse?

Some shorting somewhere is likely the cause and looks like it's strong enough to override the Over Current Protection deployed in ATX PSU.

 

[Ralston18]

@Athsara

Update your post to include full system hardware specs and OS information.

Include PSU: make, model, wattage, age, condition (original to build, new, refurbished, used)?

Disk drive(s): make, model, capacity, how full?

Very likely that there is some misconnection and/or a short.

Refer to the motherboard's User Guide/Manual and the Case Manual to double check all connections and wiring.

With power off and the build unplugged use a bright flashlight to carefully inspect the I/O panel - common location for shorts to occur. Inside and out. Also check all stand-offs.

You should not be and should not need to turn of the computer using the PSU's power switch. The computer should be shut down by using the Windows power shutdown menu. (Right click the window icon usually located in the lower left screen corner.)

 

[Athsara]

If I correctly understand, you just turn on the PSU switch. Not the Power ON Switch or button on the cabinet.

So the PSU when switched on from mains enters a Stand-By state, where it supplies minimum voltage and current required to run certain systems like LAN, RTC etc etc. Only after you press the PowerOn button on cabinet, then full voltage is supplied and system boots.

So try the same config without any cabinet and re-test with min parts. What are the USB devices in question? Does it happen with USB Keyboard/Mouse?

Some shorting somewhere is likely the cause and looks like it's strong enough to override the Over Current Protection deployed in ATX PSU.

Yeah its the PSU switch

so i swapped the PSU to my old CV450 from corsair and so far the issue doesnt seem to come up, it could be a faulty PSU but im looking further trying to replicate it incase its something else.

Yes it can happen with any device connected via usb in the back (i didnt test the front however)

@Athsara

Update your post to include full system hardware specs and OS information.

Include PSU: make, model, wattage, age, condition (original to build, new, refurbished, used)?

Disk drive(s): make, model, capacity, how full?

Very likely that there is some misconnection and/or a short.

Refer to the motherboard's User Guide/Manual and the Case Manual to double check all connections and wiring.

With power off and the build unplugged use a bright flashlight to carefully inspect the I/O panel - common location for shorts to occur. Inside and out. Also check all stand-offs.

You should not be and should not need to turn of the computer using the PSU's power switch. The computer should be shut down by using the Windows power shutdown menu. (Right click the window icon usually located in the lower left screen corner.)

I used the PSU switch to turn off since i was moving some componenents and i noticed it happenning, i swapped my PSU to an old one from my other system and this stopped happening on my new system , i connected the new PSU to the old system and i was able to replicate the issue on that.

 

[helper800]

Yeah its the PSU switch

so i swapped the PSU to my old CV450 from corsair and so far the issue doesnt seem to come up, it could be a faulty PSU but im looking further trying to replicate it incase its something else.

Yes it can happen with any device connected via usb in the back (i didnt test the front however)

I used the PSU switch to turn off since i was moving some componenents and i noticed it happenning, i swapped my PSU to an old one from my other system and this stopped happening on my new system , i connected the new PSU to the old system and i was able to replicate the issue on that.

Definitely a faulty PSU then. Make sure you get a quality PSU as a replacement. Anything from tier A for a computer with a graphics card or anything from tier B or above for a PC with no graphics card.

 

[Misgar]

then connect a USB device from the rear and the turn the PSU switch on the House breaker will trip

Two questions:

1). What USB device causes the fault? Is it a mains powered device, e.g. a USB printer with its own mains lead or an external 3.5" USB hard disk with a 12V DC mains brick?

2). Does your house breaker incorporate an ELCB or RCB trip function (Earth Leakage or Residual Current breaker)?

What I'm theorising is your breaker may be tripping on 20mA+ leakage current (20mA difference between current flowing in through breaker on Line input and current flowing back through breaker on Neutral wire).

I doubt very much your house breaker is tripping on the normal overcurrent (thermal/magnetic components) of a breaker, because it takes a fault current of tens of Amps to trip a house breaker, if there is a major fault in your PSU which seems otherwise OK.

ATX PSUs include a number of Y-class capacitors (typically 2 or 4) from Line to PSU chassis and Neutral to PSU chassis. If you check PSUs reviews by Aris on Tom's, you'll see he often measures PSU leakage currents. These are normally only a few mA, not enough to trip an RCB individually.

However, if the mains earth to your ATX PSU becomes disconnected, the computer chassis will no longer be grounded. The class-Y capacitors inside the PSU then become a capacitive divider and the computer metalwork will float at an elevated AC voltage (and high impedance) above ground. If you touch an ungrounded chassis, you may feel a "tingle" or "buzz".

Class-Y capacitor leakage currents on an ungrounded chassis will look for an alternative route to ground, e.g. through your USB device, provided it too has its own mains lead. If other devices in the house have their own leagage currents of a few mA each, when added together, they might exceed the 20mA rating of an RCD. Leakage currents flowing through your USB connection may be enough to exceed the RCB's 20mA limit.

This is all conjecture on my part, but might explain why an otherwise "working" PSU trips out your house breaker via USB. If your USB device is entirely isolated from the mains, e.g. a USB memory stick, then bang goes my theory.

Get a professional engineer in to check your house/computer wiring and run a Portable Appliance Test on the PSU(s).
https://en.wikipedia.org/wiki/Portable_appliance_testing