Ebtech HumX

Re: Ebtech HumX

Jay Barracato said:
I thought about testing with a meter but this time I did not have the house electrician present, and I did not want to be popping circuits on purpose without knowing what else is on them.
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What does testing with a meter have to do with having an electrician present -or- popping circuits? I don't plug a single thing in at a venue, without first metering the outlet. It sounds to me like you have gone all around the world with ISO's ... HumX products... Pin1 Ground Lifts... and swapping out your quad boxes.... all to fix a problem that you have yet to diagnose. I'm confused by your diagnostic process here.... seems like putting a meter to an outlet would be far simpler then much of what you have gone through (hoping) to stumble onto a potential fix.
 
Re: Ebtech HumX

Show 1- with hotel electrician present, I basically ran out of setup time. I was traveling light and did not have the box with my meter, and then burnt up all the preshow time before he had a chance to go get his meter.

Show 2 - 6 months later with no hotel electrician present.

What happens when I meter ground to hot and pop the breaker, not knowing where the panel is, not knowing what else in on the circuit, and not having the person responsible present? This is a good paying gig for the band and they would like to be asked back. Part of the management is not in favor of live music, and wants to limit the impact on hotel operations. I am not going to give them an excuse to shut down the show. I have the problem reduced to the point where it does not impact the show, nor do I believe any equipment is in danger (and that was without the humx being used). I am not sure why I would pursue it any farther.

So I meter the outlet (this is an edison in the wall) and find a potential on the ground. What can I do about that other than switch to a different outlet and see if that fixes it? My entire rig was run off of one plug. It is just as quick to drag an extension cord to a new outlet that you think is on a different circuit as it is to meter a different outlet.

As I said before, my job is to do a show, not to diagnose and fix their electrical problems. I did the show, someone who is knowledgable about systems might have noticed the slight background noise during a moment of absolute silence in the room, but no one in the audience did.
 
Re: Ebtech HumX

One of the reasons that you meter first every single time, is that YOU are now guessing as to what the problem is and you are making the call based on pure speculation as to what is safe and what is and isn't going to potentially harm gear or people. Dragging an extension cable from outlet to outlet might be easier, but it's also much more likely to end up in you plugging in and hurting your gear when you get something really out of whack going on.

I also have never tripped a breaker by metering between hot and ground with any of my meters... can you explain what you mean? (honestly.. I'm not being a smart ass, I'm curious as to what I don't know here and would like to understand your position better).

I understand that you just want to get on with the show... But I do believe when you are putting equipment at risk, and potentially people too, it very much IS your job to at least understand the situation with the electrics that you are planning to use. I wouldn't start doing any repairs.... but knowledge is awesome... and going to the venue to let them know what you have found is often very much appreciated. I have had numerous venues call out an electrician to sort simple problems, after I had metered and written down the wack results for them.

I certainly would not want a repeat client who had bad power and did not care enough to investigate further after being notified... thats a BAD client!
 
Re: Ebtech HumX

Next time I go in you can be sure I will meter, for my information. Most of my SOS shows I typically just use the circuit tester that shows the branches of the circuit are intact. I am still not sure what having that information will do because in the two shows there I have basically checked everything a meter could tell me. I am not sure what the difference between knowing there is a potential on the ground and knowing how much it is.

It appears that at least part of the noise is RF interference, and the meter isn't going to do much there either.

The use of some simple best practices including the use of quad cables and a couple of ground lifts on cables and DI's for all practical purposes eliminated the problem, without having to use the HumX or lifting the safety ground in anyway.

As for the popping, I am not sure if it was bad design but I had a low cost analog meter (sears special) that frequently would pop the breaker on ground to hot, so frequently that I would leave that test for last. That meter is long retired, but that possibility has always been in the back of my head.

I am back there in June, I will bring back meter readings and see what we can interpret from them then.
 
Re: Ebtech HumX

Jay Barracato said:
As for the popping, I am not sure if it was bad design but I had a low cost analog meter (sears special) that frequently would pop the breaker on ground to hot, so frequently that I would leave that test for last. That meter is long retired, but that possibility has always been in the back of my head
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That should never happen, ever. They only way it could happen is if a) your meter was a solid short as if you were sticking a solid wire between hot and ground or b) you were using the meter in ammeter mode and someone stuck a huge fuse in it that wouldn't blow before the breaker so that it 'looked' like a solid wire between ground and hot. In either case, you would never get a voltage reading at all, just some hot metal and a popped breaker.

Greg
 
Re: Ebtech HumX

Greg,

You are correct about not getting a voltage reading. I am wondering if it didn't have some sort of shunt that basically passed current if the amount exceeded some value. I don't remember it having an ammeter, but I would not rule out operator error (trying to use it in the wrong mode). In those days I worked for a general contractor and did mostly carpentry, some plumbing, and some electrical work "under the guidance" of his electrician. I had nice carpentry tools of my own, but many of the specialty tools for the other trades were a hodge podge of patched together whatever. It could very well be that a fuse had been replaced with a wire. I know I saw him do that in a old style fuse box.
.
Actually thinking back some of what I know we did, now scares me because I now understand. This was one of those old timers who would check for hot with a wet fingertip and checked smoke alarms with unfiltered camels. He also had a 50's era Porter Cable worm drive saw that reeked of ozone when it was use, had no grounding on the case, and a blade that would spin for 10 minutes after you stopped using it.

Anyway, next show there I am going to make sure their electrician is on hand, that I have access to the panel, and can properly meter it.
 
Re: Ebtech HumX

Rob Timmerman said:
To trip a GFCI, the meter would need to have an impedance of lower than ~40kohms (for the most sensitive units, 20k is probably more realistic). Analog meters may have an input impedance this low, but a DMM will not.
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http://support.fluke.com/find-sales/Download/Asset/2793260_6116_ENG_A_W.PDF

The Fluke 110 series meters (113, 115, 117, etc.) have a LowZ mode that's about 3K - plenty to trip a GFCI. Obviously not enough to trip a breaker. They also have normal volts mode with an impedance of 5M which would be fine for circuit testing.

Hopefully the situations that Jay has encountered where breakers were tripped were GFCI breakers - If he really was tripping a regular breaker with a meter something is radically wrong.

Jay - I understand your concerns about being easy to work with in the eyes of the venue, but I've never been at a gig that was imporant enough to risk blowing up large chunks of my PA by not testing. Even if the gig were that important, it still wouldn't be worthwhile, because blown gear does not a successful gig make.

You test so that you have confidence the power is good. If it isn't, then you either find different power or you don't do the gig.
 
Re: Ebtech HumX

This is not all that mysterious. Some audio gear is less tolerant of environmental noise issues than others... This may vary from venue to venue but is not necessarily the venue's problem. The noise isn't bothering them, so as long as they don't shock their workers or patrons they are happy.

"Ground loop" is widely used as generic description for mains power related noise issues. Ground loops have a specific meaning which is mostly academic and unimportant for properly designed (wrt XLR pin 1) differential i/o gear.

A bass amp with an unterminated instrument cable plugged in, that is picking up hum, does not mean anything, other than the bass amp is turned on and working, and there is hum in the room,, normal for most rooms.

All gear will makes some hum and hiss, so it it is reasonably low and not massing with the performance your work is done.

JR
 
Re: Ebtech HumX

Test all your IEC-Edison (aka "computer cable") cables for correct wiring. About 1% of the ones we get here (new, from the factory) are miswired. Had that cause some very mysterious noises on occasion.

Also maybe ask if those outlets are somehow connected to dimmer circuits?
 
Re: Ebtech HumX

TJ Cornish said:
http://support.fluke.com/find-sales/Download/Asset/2793260_6116_ENG_A_W.PDF

The Fluke 110 series meters (113, 115, 117, etc.) have a LowZ mode that's about 3K - plenty to trip a GFCI. Obviously not enough to trip a breaker. They also have normal volts mode with an impedance of 5M which would be fine for circuit testing.

Hopefully the situations that Jay has encountered where breakers were tripped were GFCI breakers - If he really was tripping a regular breaker with a meter something is radically wrong.

Jay - I understand your concerns about being easy to work with in the eyes of the venue, but I've never been at a gig that was imporant enough to risk blowing up large chunks of my PA by not testing. Even if the gig were that important, it still wouldn't be worthwhile, because blown gear does not a successful gig make.

You test so that you have confidence the power is good. If it isn't, then you either find different power or you don't do the gig.
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The higher-end Fluke meters also have that LowZ mode, which is useful for catching floating connections. But since you have to manually select that mode, and you get the standard high input impedance if you simply select AC Volts, I didn't lump it in with the rest of the DMMs.
 
Return to the scene of the crime

With meter in hand.

This time the toolbox with the meter made the trip.

Hot to neutral- 120V
Hot to ground 120V
neutral to ground 0.5 to 2V depending on the position of light dimmers that are on a different circuit at the panel. The multiple circuits must be sharing a ground.

We did shows on both Friday and Saturday, and previously the RF interference was worse on Friday. At the last go around I thought the use of quad cables had made a difference, but it may also be something changing in the RF environment. I had no problems this time (still using quads), but I also could not get cell phone reception nor wifi, both of which were present in the past.
 
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