Power Light - depends on location

[lowell]

My custom amp has a 120v power light in it. I wired it from the 120vac to ground and it's connected to the 120vac when the power switch is turned on. One club I play at the light does not work... I have to look at the tubes to see if the amp is on. Also, someone just bought one and took it home only to have the power light backwards from the switches. IE when the amp is off, the light is on and vice versa. Shoudl the light go between the mains hot and neutral instead?

[greekie]

Shoudl the light go between the mains hot and neutral instead?

YES! And don't look back.

[DIY_Guy]

Yeah sounds like the club has the hot/neutral flipped. That's why it won't light there but works for you at home. Going from hot/neutral it would work at home and at the club.

[lowell]

Right on I just fixed it. Thanks guys!

[R.G.]

Right on I just fixed it. Thanks guys!

Even more importantly, a miswired club can have bad effects on equipment and your own personal health.

I urge everyone who plays in a variety of different places of older construction to go get a mains outlet tester plug. These look like the plug-in end of a heavy extension cord without the cord attached, and have three lights on them. Plugging them into the outlet tells you whether the plug is wired correctly according to the electrical wiring codes, at least as regards line/neutral/ground. Knowing this may save your amp, or your life.

[riz]

What R.G. says. I swear I've been meaning to pack one of those testers in my gig bag. My studio may have a backwards-wired outlet--gotta check that when I get back to town. The more I work on amps, the more I think about this stuff.

[Tom Phillips]

And when (or if) you find an outlet that is wired correctly it's a good idea to plug a power strip into that outlet and then run all the band's equipment from that power strip. In testing stage outlets I have often found 50% of the outlets with hot & neutral swapped even if the earth ground was hooked up correctly.

[riz]

No doubt, and that's a big "IF" regarding the earth ground even being connected. Most of the 3-prong outlets in my old house don't really have it, I ran a dedicated circuit up from the garage when I rewired the shop down there, for my home studio room! Wouldn't surprise me at all if our rehearsal room was wired wrong (different location...). I don't sing much, but some new guys are reporting getting shocked by the p.a., but I can't look into it till I get back. It's on a different outlet than the guitar amps, I know the one for the amps is good. Told 'em to try the power strip thing... If you think about it, the guys wiring bars and clubs, who we trust with our lives nightly, are often working for a BAR TAB... Duh. I've BEEN THAT GUY!!

[Gaz]

Here's a hypothetical: What if you bring your tester to a gig, and the wiring is screwy? Do you refuse to play?

I carry a tester with me, and have not yet been so unlucky to be confronted with that situation, but something tells me that I'd say f#ck it, cross my fingers and play the set. That's sad isn't it?!

[riz]

I suppose you could carry a little handyman rig, either dedicated "conversion" leads, or a little box you could re-wire quickly to deal with the situation. Assuming the bar has plumbing (!) be prepared to run a quick and dirty ground wire... Seeing as I've never done that, I've always said "f-it" too...

[J M Fahey]

My custom amp has a 120v power light in it. I wired it from the 120vac to ground

You are crazy.
No, it's not a compliment.
Say hello to Jimi and Elvis when you meet them.

[R.G.]

Here's a hypothetical: What if you bring your tester to a gig, and the wiring is screwy? Do you refuse to play?

I carry a tester with me, and have not yet been so unlucky to be confronted with that situation, but something tells me that I'd say f#ck it, cross my fingers and play the set. That's sad isn't it?!

Actually, there is a difference.

If you *know* you may be dying for your music (or the bar owner's cheapness) at least YOU are making the choice, not the owner or electrician 40 years ago.

And you may be really, really careful about grabbing that mike stand. You might even use the back-knuckles test on your amp, mike stand, bass player's strings, whatever you may touch in performance to see if it's an electrocution hazard.

You might even pull out your $5.00 Harbor Freight multimeter and test for AC between things you're likely to touch and see if it's deadly, or just benignly hum-my.

And then play the set, after donning your full-body condom.

[Pat Burke]

You might even use the back-knuckles test on your amp, mike stand, bass player's strings, whatever you may touch in performance to see if it's an electrocution hazard.

Do you mean "feel the electricity"? Many years ago I discovered that I could very lightly rub a finger along the front panel of my 2-wire Ampeg and if I felt a sort of vibration I knew the ground switch was set wrong. I've never heard anyone else make reference to the phenomenon.

You might even pull out your $5.00 Harbor Freight multimeter and test for AC between things you're likely to touch and see if it's deadly, or just benignly hum-my.

You can get a false positive that way due to the high input impedence of the meter (but better a false positive than a false negative ). You can make a poor man's leakage tester by bridging the meter with a 1500 ohm resistor parallelled with a (I think) .15 uf cap. 0.75V = 500uA leakage.

Regards,
Pat Burke

[Steve Conner]

"Feel the electricity" is a known phenomenon. I've seen it discussed by one of the hi-fi guys, maybe Doug Self or Rod Elliott. In this age of Class 2 equipment and EMI filters, the "death cap" is back with a vengeance, and so most Class 2 equipment is live to some extent. My personal "favourite" is the standard cheap Chinese SMPS wall wart, which having no ground pin, connects an EMI suppression cap between the DC output and one of the AC input prongs. Some of these downright nip and can be quite startling. I have tried to specify ones with ground pins for equipment I've designed, but it's almost impossible to find them.

The resulting current that flows through your body is called "touch current" and IEC 60950 specifies how much designers of equipment are allowed to inflict on their customers. Even with completely legal amounts, metal parts of the equipment can feel as if they are furry or vibrating.

I found that if I rub the offending apparatus against my ear, I can hear a buzz, but only when it's moving, as if the electricity affected the coefficient of friction somehow. Please don't ask how I found this out. I was bored one day.

[Pat Burke]

I found that if I rub the offending apparatus against my ear, I can hear a buzz, but only when it's moving, as if the electricity affected the coefficient of friction somehow. Please don't ask how I found this out. I was bored one day.

Exactly! The "vibration" I felt had an element of friction to it, and only happened when my finger was moving. I've often wondered if I'm particularly sensitive to it, because I absolutely HATE getting shocked (funny, for someone in the electronic repair business ).