Venue outlets have open ground. What does that mean?

[E2942]

When did we become so desperate to play that we risk our lives playing for a venue that doesn't even have a Ground on their electrical sockets?
I'd refuse to play there until they resolved that very serious issue.

 

[MVE]

Word of caution about outlet testers. Sometimes "grounded" isn't "grounded"

Let me give you a practical example. Bought an old house last year. A couple of circuits are old "BX" metal clad cable with only 2 conductors, no dedicated groundwire. 2 prong outlets. I replaced them with 3 prong outles but there is obviously nothing to hook the ground on the receptacle to. But they have metal outlet boxes and metal cladding all they way back to the breaker box so they read as "grounded" with an outlet testers, even the one that is only metal clad for about 10 feat to a metal junction box and then is "rag wire" back to the breaker

The “rag wire” is a problem and should be replaced with emt conduit or three wire romex if your local code allows.
The 2 wire in metal jacket bx is ok if all the screws are tight. The jacket is the ground.

 

[Old Garage-Bander]

ummm. I'm still on the first page but GfCI's do not require a ground to work. What they do is monitor the current between the hot and neutral wires and if there is a drop on the neutral (indicating a fault to ground) it trips. BTW, ground means ground not just the bare copper wire in the house.

How does a GFCI outlet work? | HowStuffWorks

Yup! There is a whole world of science and engineering and a major industry around just doing proper grounding.

 

[MidlifeBeginner]

I have traveled several times to Latin America for work.

In Guatemala I was told, "just don't touch both wires at once". People there often wire things with the wires still live.

I went to a job site in Bolivia that had 1 km of various wires patched together in a tunnel. We were standing in 3 inches of water, with the cables propped against the wall with sticks. Sadly, someone died in the lower powerhouse that week.

Point is, in the US we get used to safety laws that are mostly followed. My father in law's house had disconnected grounds and reverse hot wires all over the place. Bad wiring is less common in the US, but does happen. A customer had a 480VAC power supply blow up in an old part of LA. It was rated up to 600 VAC. That is how bad surges were in that part of town.

Solid state amps that can handle 110 VAC - 240 VAC tolerate a lot of bad 120 VAC lines. If I had a tube amp, I would protect it with something. Carry gear to protect yourself. Good UPS devices have a lot of protection in them.

 

[Old Garage-Bander]

Don't do that! Seriously... Leave it set to make the proper ground connection unless totally sure that it's only acting in the audio ground, and the electrical ground is hardwired and links to a properly grounded outlet too. 'Ground lift' is a Seriously Bad Idea, it should never have been invented.

There's a document by Rane called "Grounding and Shielding Audio Devices" that goes into this at length, but its an easy read, and has influenced the better habits of modern audio gear makers.

Just a minor tweak in terminology...

On old amps, the ones that originally came with two prong power cords, they some times also included a switch that was called GROUND. What these switches did was reverse the wires on the incoming two prong power cord. If it hummed, and the hum was reduced by switching, you left it there. This switch served the same purpose as just pulling the plug from the wall and turning it over. Back then those plugs were non-polarized. There was a capacitor associated with this that we now call The DEATH CAP. If the Death Cap became leaky or shorted, you had the potential for putting the full wall outlet line voltage on the chassis of the equipment which was a shock hazard.

On a more modern amp with a D.I., you may have a switch called GROUND LIFT. This switch has nothing to do with the power cord. It's purpose is to open the shield connection (pin 1) on the balanced audio of the cable going from the amp's D.I. to a mixer/PA system. This is perfectly safe to use as it does not involve the A.C. power coming from the wall. Nor does it disconnect the safety ground lead found on a three prong power cord. This is the safe way to deal with hum if it is caused by a ground loop. (Multiple ground paths.)

Many amp techs these days, as a matter of course will convert these two prong power cords to a three prong with the safety ground that comes from the outlet and that will be bonded to the chassis. They also remove or disconnect the death cap as it serves no purpose in a three prong power system. Likewise, if there is a GROUND switch (not GROUND LIFT) they will remove, disconnect, or repurpose it.

Some techs won't even work on an amp until they've first installed a grounded power connector.

But a Ground switch on an old amp is not the same thing as a Ground Lift switch associated with an audio cable.

 

[Paul New]

I was a staff electrician at a nuke power plant for 25 years, and personally wouldn’t worry about 120V, but that’s because I’ve been shocked so many times that I lost count around 1990. Or I wouldn’t have before my heart started screwing around.

Verify that the receptacles are indeed ungrounded, and then talk to the venue or do whatever it takes to get it corrected. Very small currents CAN cause injury or death.

 

[Old Garage-Bander]

Yeah, you're right. Sorry for the bad info.

OP, does your amp have a ground lift? Flip that if it's humming.

The ground lift switch is only effective with audio connections between your amp and a mixer/PA.

 

[Lostgallifreyan]

Just a minor tweak in terminology...

On old amps, the ones that originally came with two prong power cords, they some times also included a switch that was called GROUND. What these switches did was reverse the wires on the incoming two prong power cord. If it hummed, and the hum was reduced by switching, you left it there. This switch served the same purpose as just pulling the plug from the wall and turning it over. Back then those plugs were non-polarized. There was a capacitor associated with this that we now call The DEATH CAP. If the Death Cap became leaky or shorted, you had the potential for putting the full wall outlet line voltage on the chassis of the equipment which was a shock hazard.

I had some fun earlier with that Death Cap terminology but I agree, the non-polarised thing could leave either line being referenced to ground in some unexpected place. Very nasty risk of harm.

Someone else posted about using an isolation transformer, which can help, though I have heard tales of builders trusting them on sites, only to have nasty surprises. Even an isolated current has to flow somewhere when a fault arises, so it's always best to define that cleanly well in advance of using any system, no matter how temporary it is.. I'd want a 5mA trip residual current breaker for a case like that because at least it will detect a leak lower than could kill me, and open both lines to cut all flow.

I think the risk of the audio ground lift is that when it's NOT there people have opened the mains ground as the only easy recourse! I think this was the risk Rane had in mind. It's better to have the right audio cabling grounds, that way all mains grounds can exist, and no signal 'ground lifts' need exist, so no-one has to worry or wonder about it, let alone take these risks when trying to cure noise. It also makes people think more about their choice of cables, which is never a bad thing.

 

[Old Garage-Bander]

I use an isolation transformer for my rig. Cuts down ground noise, and allows me to avoid getting shocks off of others, and their mics. NOT a replacement for a good PE (protective earth) connection, but eliminates voltage differentials with others.

Be careful that the isolation transformer is the type that breaks the ground connection in addition to the isolation. If not, it may not be protecting YOU as well as you think. The purpose of most isolation transformers is to protect other equipment. And since people use that equipment, the ground, by law/code needs to carry through.

 

[12BitSlab]

I am all for calling the authorities about bad wiring.

I played the Beverly Hills Supper Club the night before it burned to the ground because of bad wiring. 158 people died. Hundreds more were injured.

NEVER take a chance on bad wiring. You are absolutely betting your life on it.

Beverly Hills Supper Club fire - Wikipedia

 

[E2942]

I’ve been shocked so many times that I lost count around 1990.

I would have probably lost count at 999.

 

[groovaholic]

I played the Beverly Hills Supper Club the night before it burned to the ground because of bad wiring. 158 people died. Hundreds more were injured.

Horrible, and preventable.
IMO @12BitSlab shared what should be the final word on the topic.

 

[Old Garage-Bander]

I had some fun earlier with that Death Cap terminology but I agree, the non-polarised thing could leave either line being referenced to ground in some unexpected place. Very nasty risk of harm.

Someone else posted about using an isolation transformer, which can help, though I have heard tales of builders trusting them on sites, only to have nasty surprises. Even an isolated current has to flow somewhere when a fault arises, so it's always best to define that cleanly well in advance of using any system, no matter how temporary it is..

I think the risk of the audio ground lift is that when it's NOT there people have opened the mains ground as the only easy recourse! I think this was the risk Rane had in mind. It's better to have the right audio cabling grounds, that way all mains grounds can exist, and no signal 'ground lifts' need exist, so no-one has to worry or wonder about it, let alone take these risks when trying to cure noise. It also makes people think more about their choice of cables, which is never a bad thing.

In Death Cap amps there is no reference to ground. That's problem #1. Problem #2 is you have a 50/50 chance of the reference being hot or neutral.
Do ya feel lucky? Well do ya?

Ground lifting of the audio shield is perfectly acceptable safe and easy. It's virtually impossible to ensure that the shield on cable A and the power cord ground will have the same impedance as the shield on audio cable B and it's power cord. The more of these you have, the more likely to get ground loop hum. It's the difference in ground wire impedances that allow a small voltage potential. And in an amp it doesn't take much of a difference to be noticed.
Imagine all the possible combinations with just a couple of guitars, bass, a mixer, powered monitors, mic cables and who knows what else. Ground lift switches are the cheap solution. The expensive one is audio isolation transformers.
And those often come with a ground lift switch on them as well.

 

[Lostgallifreyan]

I went to a job site in Bolivia that had 1 km of various wires patched together in a tunnel. We were standing in 3 inches of water, with the cables propped against the wall with sticks.

That reminds me of a 6-floor office building in the early 1980's, it was a squat in Islington, London, and I went from Bristol to look at it, someone hoped I might be able to get some more electricity on than they'd already got (they only had power on two floors). There were huge metal boxes all over the walls in a little concrete room, with old blue milk crates standing (and even swimming) in a pond that sat on the recessed floor from some water leak high up in the building. I walked away from that. I wouldn't touch it, and it's not the only time in a squatted building where this was the only signal to send. Fortunately people respected the decision each time and left it well alone.

I think that little concrete room was the single scariest room I have ever seen. It looked like a small substation, and just getting in there would have felt like walking the plank.

 

[Lostgallifreyan]

In Death Cap amps there is no reference to ground. That's problem #1. Problem #2 is you have a 50/50 chance of the reference being hot or neutral.
Do ya feel lucky? Well do ya?

Nice.

About signal ground lifts, I take the point, but I always prefer to hardwire such arrangments in the cabling, outside the gear. That's another thing I like about the Rane docs, they explain that detail well, for easy building of DIY cables that are safe as well as curing noise in most possible arrangements.

 

[Old Garage-Bander]

I have traveled several times to Latin America for work.

In Guatemala I was told, "just don't touch both wires at once". People there often wire things with the wires still live.

I went to a job site in Bolivia that had 1 km of various wires patched together in a tunnel. We were standing in 3 inches of water, with the cables propped against the wall with sticks. Sadly, someone died in the lower powerhouse that week.

Point is, in the US we get used to safety laws that are mostly followed. My father in law's house had disconnected grounds and reverse hot wires all over the place. Bad wiring is less common in the US, but does happen. A customer had a 480VAC power supply blow up in an old part of LA. It was rated up to 600 VAC. That is how bad surges were in that part of town.

Solid state amps that can handle 110 VAC - 240 VAC tolerate a lot of bad 120 VAC lines. If I had a tube amp, I would protect it with something. Carry gear to protect yourself. Good UPS devices have a lot of protection in them.

It depends on how you define good. Like many other things, UPS devices are there to protect equipment, not people. Some will warn you of a wiring area, some may even refuse to work if they don't have a proper ground at the input. But ya gotta do your homework. It's not enough to assume that protecting equipment from spikes, noise and power outages offers any protection for the user beyond what he gets at the wall outlet.

 

[crazyBassClown]

Ever wonder why you normally only see GFCI's in wet locations; bathrooms, kitchens, garages, swimming pools/ hot tubes?

Because the US is extremely relaxed about Electrical safety

All outlets(and i think actually all circuits) must be protected here in australia , and AFAIK a deathcap amp would never have been approved here, even back in the day.

 

[Old Garage-Bander]

Nice.

About signal ground lifts, I take the point, but I always prefer to hardwire such arrangments in the cabling, outside the gear. That's another thing I like about the Rane docs, they explain that detail well, for easy building of DIY cables that are safe as well as curing noise in most possible arrangements.

That's a personal choice and you know it's done the way you want. Good for you.
I've made up all manner of those things along the line as well.
Some times life doesn't always give us a "lift." In a pinch I've even opened up a cable and snipped the shield
Now when it comes to Joe Average guitar player... not so many options as you and I have. They just wanna shred!

 

[Spidey2112]

And if you sing stay away from the mics!

It's not the initial shock that kills you, it's the bad falsetto out of key.

 

[fdeck]

Amusing story: Long ago I played through a totally homemade combo amp. At one gig, it tripped a GFCI outlet on stage. The sound guy said to me: "Don't worry, guitar amps trip that GFCI all the time." He showed me an unprotected outlet. My amp was in fact safe, as I had checked it out pretty carefully.

At home, I told my wife about it.

Wife: Why are you still playing through a homemade amp?

Me: Well, it's worked up until now.

Wife: Don't they make bass amps that you can buy?

Me: Yeah, there's a nice little GK combo at the music store down the street...

Wife: Well, just go and buy it.

Me: