Resistance neutral to ground, amp tripping GFCI

[jdurango]

A friend of mine has an amp rack that will not play nicely with GFCI's. First thing I thought is, "Well, is there a ground fault?" I asked him to measure resistance of the AC leads coming out of the amp. He said he's getting 1 ohm between neutral and ground, which slowly drops to 0 ohms. It works fine on non-GFCI outlets.

I'm by no means and EE, but AFAIK there shouldn't be any path between hot or neutral and ground inside equipment itself (obviously different story at the panel).....and certain not 1 ohm??? Then again, I'm not up on how SMPS's work. Anyway, can any of ya'll advise what might be going on here? Thanks!

PS The amp in question is a CVR 4ch power amp.

 

[NOON]

Definitely shouldn't be any neutral to ground connection inside equipment! What happens when you plug it into a reverse wired socket? Potentially a failed X/Y filter cap.

 

[Khron]

I'm by no means and EE, but AFAIK there shouldn't be any path between hot or neutral and ground inside equipment itself (obviously different story at the panel).....and certain not 1 ohm??? Then again, I'm not up on how SMPS's work.

That's very correct indeed.

Y2 cap(s) between neutral and earth failed? And/or MOVs (metal oxide varistors) between neutral and earth failed / worn out?

https://diyaudioheaven.wordpress.com/tutorials/power-supplies/mains-filters/

 

[JohnRoberts]

In the professional sound reinforcement business there are a few (switching) amplifiers that are notorious for tripping GFCI protection outlet interrupters. The fault has been identified as mains filtering to suppress HF noise from getting conducted from the amp back out into the mains.

If there is more than one switching amp in the rack, can you get away with using different GFCI outlets for each amplifier?

Alternately maybe seek out a GFCI breaker with higher trip current. Consumer GFCI outlets trip around 6 mA.

This breaker I found on Amazon specs out at 30mA. https://www.amazon.com/CHTAIXI-Resi...-13-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9tdGY&th=1

Note: 30 mA can knock you off the ladder and cause a significant shock, muscle contraction can occur in the 10-20 mA range so 30mA is high for absolute human safety.

JR

 

[Philbo King]

Don't be stupid...
Fix the amp, before it kills you. The GFCI is doing its job.

 

[JohnRoberts]

Don't be stupid...

By all means let's not be "stupid" (ignorant) .

If this was a consumer amp rack (what consumers use amp racks?), I'd trust the consumer grade GFCI to indicate a faulty amplifier but with professional sound reinforcement amps a number of SKUs are known to routinely trip GFCI outlets.

A short list includes Crown I-Techs and Powersoft K series amps. Maybe we need to add CVR amps to that list? From a quick search they appear to be class D so candidates for EMI noise mains filtering.

Fix the amp, before it kills you. The GFCI is doing its job.

I have also seen false trips from consumer GFCI outlets, not the most reliable technology in my experience, but false trips are better than not tripping.

Of course ask CVR customer service about this. If there is a known design flaw(?) related to EMI interference filtering, CVR customer service should surely be aware of it and have suggestions about a remedy. Of course it might be a faulty EMI mains filter that is too aggressive about dumping HF noise into the safety ground instead of returning to neutral to keep things in balance.

JR

 

[radardoug]

1 ohm between neutral and ground is a fault. So find it and fix it.

 

[JohnRoberts]

1 ohm between neutral and ground is a fault. So find it and fix it.

Maybe there is some funny business going on in an EMI filter on the mains power coming in. I could imagine capacitance between neutral and safety ground but not 1 ohm.

JR

 

[Matt Syson]

One Ohm is definitely a faulty component somewhere.
potted EMI filters frequently used on mains inlets have a maximum of around half a milliamp of possible current (AC from either live or neutral conductor (the capacitance value and 'ohms law' ) but then mains is not VOLTAGE balanced but is and should be CURRENT balanced so GFCI trips do not normally trip but escessive numbers of filtered gear could get near the tripping current due to the inherent VOLTAGE imbalance. (possibly about 60 filters). Of course you would need a lot of filtered gear to cause this imbalance and you will need to consider exactly where it is flowing. Mains hum 'radiation' is CURRENT focussed and as mains cords are lightly twisted there is not much radiation due to CURRENT so normally balanced incoming mains is not necessary.