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Topic: Ground Lift/Third Prong Question |
Michael Pierce
From:
Madison, CT
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Posted 8 Feb 2008 4:16 am |
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I recently purchased an older Peavey amp head that arrived with the grounding prong removed from the 3 prong plug. My question is whether it's unsafe to use the unit until I get the cord replaced with a 3 prong? My house (the only place I play) has GFI circuits throughout, and there is no hum from the amp. I run the cord through a surge protector that does have 3 prongs. (By the way, it sounds great.)
The pots are also a bit scratchy, not unexpected in a 25 year old amp. Is there an easy fix for that (I seem to recall someone mentioning a spray available at Radio Shack)?
Thanks for your advice. |
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Randy Reeves
From:
LaCrosse, Wisconsin, USA
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Posted 8 Feb 2008 4:51 am
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| just be mindful not touch the amp while holding your guitar or mike. get that cord repaired. |
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Jack Stoner
From:
Kansas City, MO
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Posted 8 Feb 2008 5:06 am
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The ground connection is there for safety. Replace the power cord ASAP.
Pots can be cleaned with spray such as "De Oxit" cleaner. I don't know what Radio Shack has the keep getting less and less parts and supplies. But if they have a "control" cleaner it may work. When you spray a pot (and you have to do it with the chassis out of the cabine) rotate it from one end to the other several times so the cleaner works into all of the pot area. If spraying doesn't help then the pots will have to be replaced. After 25 years they could just be worn out. |
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Jerry Erickson
From:
Atlanta,IL 61723
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Posted 8 Feb 2008 6:37 am
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| I've used the Caig products for cleaning and lubricating pots with great success. I've also read that carburetor cleaner works very well. |
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Eric West
From:
Portland, Oregon, USA, R.I.P.
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Posted 8 Feb 2008 7:59 am
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Don't worry about it.
I always either remove them, or use an adapter. I don't sing however, and if I did, I'd just check the mike before I touched it with my lips.
Get a three prong plug when you can, and put it on, but since you are concened, get one of those couple dollar outlet checkers, and check the outlets you're plugging into.
Often three prong outlets are not really grounded or the ground ties into the neutral, giving you worse than a false sense of security.
Especially in clubs that are gerry-wired, which is most of them.
I run with sharp objects too.
EJL |
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Jeremy McCoy
From:
Washington, USA
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Posted 8 Feb 2008 8:39 am
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Seems like cleaning something that has the potential for sparking is a bad idea with carb cleaner. On top of being pretty flammable, that stuff always gives me a nasty chemical fume headache. I don't have any personal horror stories with electronics, though.
Seems like there wouldn't be any difference between removing the ground post and using the amp in an old building without one, which i've been doing for years. Never had any zapping issues. I seem to recall numberous people suggesting the ground tap to be removed in order to reduce noise in amps. Am I operating on false info? |
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Eric Jaeger
From:
Oakland, California, USA
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Posted 8 Feb 2008 11:58 am
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I'm paranoid. 99.999% of the time nothing will happen. But if you have an ungrounded component with an internal short to ground, that chassis is carrying full wall voltage on the outside. Now all you need it to compete the circuit to ground. If that path is your body, bad things happen.
What are the chances? Modern equipment is pretty good, so the above scenario isn't likely. But....
That's what the ground prong is for.
-eric |
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Eric Jaeger
From:
Oakland, California, USA
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Posted 8 Feb 2008 12:01 pm
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| Jeremy McCoy wrote: |
S
Seems like there wouldn't be any difference between removing the ground post and using the amp in an old building without one, which i've been doing for years. Never had any zapping issues. I seem to recall numberous people suggesting the ground tap to be removed in order to reduce noise in amps. Am I operating on false info? |
If the building doesn't have a ground but all the equipment shares a common ground, the fact that it's floating with respect to earth doesn't matter as much. Typically the problem doesn't come when your body completes a circuit to the actual earth beneath your feet, but between two pieces of equipment.
-eric |
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Jim Sliff
From:
Lawndale California, USA
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Posted 8 Feb 2008 6:15 pm
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| Quote: |
| if the building doesn't have a ground but all the equipment shares a common ground, the fact that it's floating with respect to earth doesn't matter as much. |
The key word - "if".
Most buildings are grounded. And cut-off ground pins are deadly. Replace the cord now.
Guys cut those off because they have no idea how to deal with ground loops or bad house wiring, and it's a flat stupid thing to do. The same idiots are the ones that hear a hum on stage and lift the ground on someone's amp instead of solving the problem - I've been knocked 15 feet due to some dork pulling that amateur stunt.
Ground pins are installed for a reason. If the amp hums at some point, it's not because of the ground pin.
I must (even though I'm not an active tech any longer) replace a power cord every couple of weeks that has been clipped.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Eric West
From:
Portland, Oregon, USA, R.I.P.
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Posted 8 Feb 2008 10:17 pm
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Not to differ with my personal amplifier god
But...
If you play in bars, clubs, or most of the places we play, trusting that ANY outlet is REALLY grounded, instead of someone just putting a dummy 3 prong plug over a 2 wire hole for "code", or WORSE, just tied into the neutral or the neutral bus in the box is a lousy bet. You're really better off without a ground prong unless you know. Really.
Myself, being an 'electrician' albeit in the USAF '75-9 (as a 54250AFSC where I saw plenty of goobered wiring) I will usually poke around and see what the box looks like. If it's really nice with a nice inspection sticker on it, I figure it's OK. If not, I've been known to pull the cover off, and I can't tell you the number of double tapped breakers, bypassed breakers, and ground wires tied into the neutral bus.
Like I said, you won't get a shock that will hurt much more than your feelings, unless it's on your lips, or you happen to contact your winkie with some wet metal while you're playing. ( I hate when that happens..)
Harbor freight has them for 3$, and while you're there, get a good three prong plug AND an adapter for another couple bucks.
EJL |
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Jack Stoner
From:
Kansas City, MO
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Posted 9 Feb 2008 3:57 am
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| I carry a small circuit tester in my seat and check the ground/polarity everywhere we go. Out lead guitar player also has a plug in AC voltmeter to check the voltage. Between the two of us we are set for checking. |
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Michael Pierce
From:
Madison, CT
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Posted 9 Feb 2008 4:40 am Ground Lift/Third Prong Question
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| Gentlemen, thank you for your replies. Being hugely risk averse (particularly when it comes to my winkie and/or anything involving scissors), I'll look for an amp tech to undertake this seemingly simple job. Just out of curiosity, when I had my (very) old house rewired a couple of years ago, we had GFI circuits installed at the circuit box in the basement; my understanding at the time was that those would help prevent shocks... did I misunderstand? thanks again. mp |
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Jonathan Cullifer
From:
Gallatin, TN
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Posted 9 Feb 2008 6:31 am
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Yes...they will. They're a good thing to have.
I've been zapped too many times and I won't plug into a circuit that's ungrounded. Last night I had a rehearsal in a garage that was a little damp from the rain we've had this week, and initially plugged into an ungrounded outlet...I refused to turn my amp on until we remedied the situation. |
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Ken Fox
From:
Nashville GA USA
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Posted 9 Feb 2008 8:04 am
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| A GFI is your best friend! Be sure to test on a regular basis. NEC (National Electric Code) requires use of them to replace any ungrounded, two-wire outlet. In new construction they are required in bathrooms, basements, garages and other places where the potential for shock is high. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 9 Feb 2008 8:51 am
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EW - Your point are well taken, but not in disagreement with me. I always have the third prong in place - but I always test the house circuit before plugging in, use grund-fault interpters and a 30-pound line conditioner/voltage regulator/protection system (NOT a $10 power strip, which kicks the power off to prove you are already dead  )
A $7 circuit tester fits in you pocket, and EVERY giging guitarist should carry one and USE it every time. It identifies bad grounds, reversed polarity and open cicuits, and basically tells you what you need to hook up to be safe. Jonathan's example is a good one of a typical mistake - finding out about the problem AFTER pluging in. Again - test the power source first, before ANYTHING is plugged in. Digital equipment is especially suceptible to bad wiring, and you can cook a rack system in seconds just powering up. ALWAYS test first. I know, it sounds like a broken record, but when you've watched the Paramedics in action trying to restart a heart because a player "plugged and played" your attitude gets adusted...hopefully.
No house wiring faults require removal of the ground plug (or a ground lift). Those methods are used (often) at clubs were the sound guy is some dude who owns a soldering iron and knows the owner...but has no working knowledge of electrical safety. I've encountered sound guys who had no idea AC power has polarity - the same doofuses that get confused when a polarity-correct two prong plug (with two different "blade" sizes) won't fit into their 20-year-old extension cord (that dosn't comply with code and needs to ethrown away...or cut into speaker cable).
As Ken said, a GFI (ground fault interruptor - wait, maybe h meant a GFI guitar! Heck, I like both....) and a simple circuit tester can keep you out of a lot of trouble. And I really recommend that gigging players use something beyond the cheaper Furman power systems or power strips - for the price of a decent effects box you can save you equipment and your life.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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John Billings
From:
Ohio, USA
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Posted 9 Feb 2008 9:42 am
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| Michael, I find a good source of new power cords to be the local "big box," like Home Depot. I buy a nice contractor sized extension cord. I like the 25 foot blue ones. 12 gauge. Then take your very, very, very sharp scissors, get winkie outa the way, and cut off the female end! |
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Michael Pierce
From:
Madison, CT
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Posted 9 Feb 2008 10:41 am amp
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This morning I took the Peavey head to a new music shop that just openend in my little town.. turns out they have an amp tech on staff who is going to install a new 3 prong power cord as well as clean up the pots. I love it when things work out!
Jim, I do have a GFI Ultra (as well as an old push-pull). Love 'em both. Love my winkie. It's all good. |
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Tucker Jackson
From:
Portland, Oregon, USA
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Posted 9 Feb 2008 12:19 pm
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| Not sure if this is the right place to post... but just wanted to go on record and say that I love my winkie too. |
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Eric West
From:
Portland, Oregon, USA, R.I.P.
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Posted 9 Feb 2008 1:02 pm
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No, Tucker, I'm sure it's fine.
I've had a kind of love/hate relationship with mine, but unlike other things in my life.
It's always right there.
EJL |
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Jim Sliff
From:
Lawndale California, USA
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Posted 9 Feb 2008 2:30 pm
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"winkie"?
...I don't wanna know...
Another cheap source for 3 prong power cords is the box of them most people seem to have in the garage fron old computers, printers, monitors etc. Just cut off the female end and voila - instant power cord.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Stephen Gambrell
From:
Over there
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Posted 9 Feb 2008 4:48 pm
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| I've been a maintenance electrician for thirty-odd years now, and all I can add is---If somebody cut the ground lug off a cord, that cord needs to be replaced. |
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Gareth Carthew
From:
West Sussex, UK
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Posted 16 Feb 2008 10:10 am
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I've never been able to understand why 3 pin grounded wiring seemed to be such a late starter in the U.S. and Europe.
Living in the UK of course I've grown up with it my whole life. Most sockets for many years now feature an interlock to prevent access to the live and neutral without an earth pin being inserted first. (our earth pins are longer that the circuit pins so it enters the socket first)
The style of plug also prevents it from being inserted backwards.
Of course this doesn't stop some wally from wiring the appliance plug incorrectly in the first place...
Anyway.
I figured that a basic explaination of what's going on from a safety point of view might be interesting and/or usefull for the non-technical types. I think it's always wise to understand what disconecting a safety ground actualy does.
So here you are... I hope it's understandable.
The idea of the ground wire is to provide a low resistance path to ground. In this way should a live connection touch the chassis a large current will flow in the ground wire - enough to blow the fuse or trip the breaker. Without that connection under the same circumstance the chassis would simply become live too. When you touch the case the current now finds a new path to ground - through you, just as if you had touched the live wire.
The ground needs to be bonded to earth at multiple intervals (common in the UK is to connect it to the mains water pipe. I'd assume the same in the US) but it also needs to be connected to the Neutral at the main service pannel. The reasons are technical and not that important for a non-tech. Suffice to say that without that connection it is possible for current to flow in the ground wire and not trip the breaker.
The ground also has another function - to hold a steady reference at ground potential (commonly zero volts or as close as).
If grounds are left floating (not connected) then it is very possible for dangerous voltage differences to exist between two chassis.
I measured 115 volts between cases on my 240v hi-fi equipment once when a ground connection become broken. This resulted in me getting a startling shock if I accidently touched two cases at the same time.
I did suffer a particularly painful shock between my left hand (via my guitar strings and amp to ground) and my nose through a microphone once... that was interesting! lol
GFI's are also also known as: GFCI - Ground Fault Circuit Interrupter; ALCI - Appliance Leakage Current Interrupter; and in the U.K. as: RCD - Residual Current Device; RCCB - Residual Current Circuit Breaker.
These are required in electrical installation in the UK and by the sound of it in new installations in the US too.
The concept here is that the current flowing into a circuit should always be the same as the current flowing out. That's a standard.
So the RCCB measures the current flowing through the "live" (read "Hot" in the US) into the curcuit and the current flowing through the "neutral" returning from the circuit. They should always be the same.
If they are not then then it means that the current is taking another path somewhere in the ciruit e.g. through the chassis to ground, or through a human body to ground or to anywhere with a lower potential (perhaphs that floating chassis I mentioned earlier...)
The RCCB detects the variation and disconnects both the Live and the Neutral connections, shutting off the power and hopefully saving you from a nasty shock or even death.
It's easy to become blasé about electric shock having recieved a number of startling but ultimatly harmless shocks in the past.
The sensible tech/electrician/engineer however will always remember that electricity can and does kill.
Only a fool removes a safety ground to solve a hum problem. Why take the chance? |
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c c johnson
From:
killeen,tx usa * R.I.P.
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Posted 16 Feb 2008 2:00 pm
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| remember way back when the 3 prong first came out? None of the clubs etc had a receptical for three prongs and all us poor boys needed to play the gig so we had to pull out the third prong. Lo and behold some bright fella brung out the adapter that you could plug the three prong deal into and plug the adapter into the two prong wall recepticle. Should have got a medal. cc |
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Keith DeLong
From:
Dartmouth NS Canada
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Posted 20 Feb 2008 5:58 am
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Definitely carry a circuit tester--I played in a fire hall one time where one of the wall outlets was not grounded, the other was, if I hadn't checked it my wife who was playing bass and would have had her amp plugged into that outlet would have ended up with Julia Roberts' lips when she touched her microphone.
A lot of plugs now have one blade wider than the other which makes it easier to get the polarity right, but I still think the 3rd prong is the best way to go. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 20 Feb 2008 6:11 am
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| Quote: |
| Lo and behold some bright fella brung out the adapter that you could plug the three prong deal into and plug the adapter into the two prong wall recepticle. Should have got a medal. |
Actually, he should have been strangled with an extension cord. Those adapters, when used correctly on a grounded receptacle (with the wire or tab screwed in - AFTER it's checked to ensure the receptacle box IS grounded AND the polarity is correct) are fine.
The problem is, most people who use them 1) never check the wall plug box for ground or the outlet for polarity, and 2) NEVER attach the ground wire (or tab).
Just plugging one in to get around the 3-vs-2 plug issue is life threatening...it's also a code violation in most places, but most people don't care.
You'd think they'd care just a tad about staying alive, though.
I always carry one. I think I have used it once in 30+ years.
Postscript - if you live in a house, apartment, whatever, that has two-prong plugs - GET RID OF THEM. Have grounded outlets installed by a licensed electrician (many do-it-yourself'ers install the things but either hook the ground wire to nothing or attach it to the box without checking to see if the box is actually GROUNDED, which many older ones are NOT...and often hook up the black and white wires reversed, which will result in hum if you have a mix of right and wrong outlets used for your gear). And if you're going to upgrade outlets, you might as well install the ground-fault type. For a few extra bucks you get a lot of safety.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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