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Thread: Hot / Neutral reversed on outlet

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    Hot / Neutral reversed on outlet

    Because of the nice weather and because my band is doing an outdoor gig soon, my band practiced outdoors at my bandleader's house. I thought I would test the outlet with one of those cheap 3 light outlet testers. My concern would be a lack of ground. Well the tester indicated the hot and neutral reversed. Will using an outlet with this problem be detrimental to equipment?

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Axtman View Post
    Because of the nice weather and because my band is doing an outdoor gig soon, my band practiced outdoors at my bandleader's house. I thought I would test the outlet with one of those cheap 3 light outlet testers. My concern would be a lack of ground. Well the tester indicated the hot and neutral reversed. Will using an outlet with this problem be detrimental to equipment?
    If you test an outlet and it shows any incorrect wiring, do NOT use that outlet. Particularly if there is an open "ground" or if the polarity is reversed. This is especially cogent is situations where you are playing outside. There might be some risk to the equipment, but more importantly there could be significant risk to YOU. Electrical safety code is super important because it is almost always results from a forensic investigation.

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    Bent Member Chuck H's Avatar
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    This^^^^^^^^^^

    Consider the variables running gear on stage in different polarities and possible ground faults, or lifts, or some of the gear is old and has a hot chassis AND is plugged into that inverse polarity. You really don't want your lips touching the mic while you're holding your guitar strings.

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by Chuck H View Post
    This^^^^^^^^^^

    Consider the variables running gear on stage in different polarities and possible ground faults, or lifts, or some of the gear is old and has a hot chassis AND is plugged into that inverse polarity. You really don't want your lips touching the mic while you're holding your guitar strings.
    I remember years ago, when I first became a member I think, someone posted a really tragic account of a musician who suffered a severe shock during an outdoor show.

    edit* I think it might have been Fahey? I mention that, because think I remember someone translating the account for us.

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    Old Timer J M Fahey's Avatar
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    See for yourself what an extension cord with inverted hot-neutral can do:



    FWIW, the kid survived grabbing guitar strings with one hand, microphone with the other, but only because all of the following coincided in his favour:
    * he was a young strong heart athletic 27 y.o. guy
    * he was kicked away from the microphone stand (nobody dared touch it of course)
    * his Father in law who was present on first row was trained in CPR techniques and could assist him immediately

    * by sheer chance an Ambulance was already parked at the Theatre door to assist some elderly people in the next room Convention center.

    And even so he got a massive burn scar in his heart as if he had suffered a massive stroke, heīll have to live with that the next 40 or 50 years of his life.
    Of course, forget demanding Sports, etc.

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    Juan Manuel Fahey

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by SoulFetish View Post
    I remember years ago, when I first became a member I think, someone posted a really tragic account of a musician who suffered a severe shock during an outdoor show.

    edit* I think it might have been Fahey? I mention that, because think I remember someone translating the account for us.
    Scottish band Stone The Crows lost their guitarist when he took a shock onstage in 1972. And then there's the legend of the Yardbirds' Keith Relf who supposedly took a plugged-in microphone into the bath and didn't survive. I'm sure there's lots of other tales of woe besides.

    I see Juan already posted the video of Recife's Rocket Boy.

    One more for ya, goes back about 30 years. One of my old friends started up a blues jam at a local pub. He supplied a little PA, speakers on sticks, and a basic backline. This time he brought some ancient amp, with a 2 wire plug. This wasn't one of those supposed "widow makers," amps with AC line going directly to chassis. No it was a regular amp with a "death cap" connecting the AC line to chassis. But this death cap was - shorted! - so plug in one way no problem, other way the chassis is 120V hot. To test for safety he plugged in his guitar and pressed the strings onto the ball of his SM58 mic. Usually, if he saw a little blue spark, he would reverse the polarity switch on the amp, or lacking that, reverse the plug in its socket. But this time, none of that. Sparks shot off the guitar neck as if he was welding, five strings broke and the low E was stuck to some frets. Hmmm, better break out the spare amp! Spare guitar too. Well he made it thru the gig and lived on to get married to a terrific woman, have 3 kids & send 'em off to college. Saw him and his lovely missus last week at a friend's wedding. The stuff you can do, if you don't get killed...

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    Last edited by Leo_Gnardo; 07-21-2019 at 03:12 AM.
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    Bent Member Chuck H's Avatar
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    Jeez this is getting dark. But it's a VERY serious subject to be sure. I can personally attest to that because I'VE been hit. My band was playing a dive bar where (apparently) the owner fancied himself a handyman. Some plugs were inverse and some weren't even grounded (though they had the three prong outlets!). I've told this story in greater detail here in the past, but suffice to say it was very much like the video Juan posted and I earned the nickname "Sizzlin' Chuck". I suppose you could have a worse nickname as a guitar player, even though it wasn't for my playing.

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    Ok I have to ask. Why is polarity not an issue in Europe, where you can plug in anything both ways (the outlets are made like that on purpose ?!)

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    Old Timer J M Fahey's Avatar
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    Justb thinking aloud:

    1) death caps are never never ever used in Europe while they were all over the place in USA.
    Notice Peavey/Fender/Randall schematics where the 120V version has them, and exact same model but 220/240V version does not.
    I guess that alone says something.

    2) AFAIK UL compliance or registring is voluntary/optional in USA; while SEMKO/DIN/TÜV/etc. European ones were mandatory in their respective Countries so manufacturers were under confirmed pressure to meet or surpass insulation ratings.

    And some Countries such as Sweden had NO grounded outlets for general public use because "they have no easy access to Ground".
    The reason being that in great part of the Country they have permafrost: a frozen underground layer which never ever melts, not even in Summer, so itīs all but impossible to install grounding rods.

    I vaguely remember there was also a similar problem to bury people.

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    Juan Manuel Fahey

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    In the UK sockets are polarized. In many areas the house neutral is connected to ground at the distribution board where the mains enters the house. The whole issue of polarity-reversal not only concerns what happens in fault conditions, but increasingly with EMI supression components the equipment has to be connected with the correct polarity in order to prevent high leakage voltages appearing on the ground side of the equipment.

    A couple of examples - a customer complained of a shock from his lips touching the mic while holding the guitar and using a harmonizer off an SMPS wall-wart adapter. In the UK many devices do not need the ground connected but there's an assumption that in a correctly wired socket the neutral will be at or near ground potential. The wall wart had an integral plastic pin instead of the usual brass ground (earth) pin. This is to activate the shuttered sockets that we have and also ensures correct polarity. The plastic pin had broken off and this prevented the adapter being inserted. A band member spotted that if the adapter was flipped over a screwdriver could be used to open the shutter and allow the adapter to be used. This flipped the polarity and ensured that the singer got a shock. I opened up the adapter and saw that there was a capacitor from the output connected back to the mains neutral. Because the adaptor was flipped this now connected the output via the capacitor to mains live. OK, the impedance of the the capacitor reduced the shock but still not a good situation.

    The second example was an auto-transformer connected to a USA-made Bogner Shiva. The mains plug was the re-wireable type and the earth screw was loose. In addition, the extension cable was wired in reverse. I measured 80v between the guitar ground and actual ground.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by J M Fahey View Post
    I vaguely remember there was also a similar problem to bury people.
    They got the "Viking funeral" if ranked high enough, sail 'em off in a burning boat. The rest, left to the polar bears.

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    I must confess that it was only AFTER rehearsal that I noticed the problem. My bass amp rack has a Carvin power distribution / conditioner (think Furman). The unit shows voltage and indicates a presence of ground. While I was bending over to turn off the amp I noticed that the green ground LED was not showing. So dug through my gig bag for my trusty receptacle tester. That's when I noticed the problem. I let our band lead know and she is going to have an electrician look at it as well as other things in her house.

    We have another practice this Thursday. I am going to insist we use another outlet until the other outlet is rewired. Oh and I am bringing an GFCI extension cord just for added safety.

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    Old Timer tedmich's Avatar
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    Yikes this is some scary shit!

    from a US electricians web site:
    "AFCI protection for kitchen and laundry areas
    As of 2014, the NEC has added kitchen and laundry areas to the list of areas requiring AFCI protection. This includes all 120-volt, single-phase, 15- and 20-ampere branch circuits supplying not just outlets but also devices found in these rooms."

    Combo outlets are not terribly expensive
    https://www.homedepot.com/p/Leviton-...-0KW/206804820

    Now I've gotta buy one of these
    Click image for larger version. 

Name:	Extech CT70.JPG 
Views:	13 
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ID:	54408
    Extech CT70 $200 or
    Click image for larger version. 

Name:	Ideal Industries 61_164.JPG 
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    Ideal Industries 61-164 $300


    and test all of my Mom and Dad's hippy wired house...

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    Lifetime Member Enzo's Avatar
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    Not very dramatic, but we played a gig once and the guitarist raised the neck of the guitar, the high E-string touched the mic, and ZZZZZT, a flash of light and the string burnt in half.

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    Quote Originally Posted by Mick Bailey View Post
    A band member spotted that if the adapter was flipped over a screwdriver could be used to open the shutter and allow the adapter to be used. This flipped the polarity and ensured that the singer got a shock. I opened up the adapter and saw that there was a capacitor from the output connected back to the mains neutral. Because the adaptor was flipped this now connected the output via the capacitor to mains live. OK, the impedance of the the capacitor reduced the shock but still not a good situation.
    That's exactly what I was wondering - how come this doesn't happen with EU-type plugs? There is a great deal of equipment that has no ground connection (including wall warts) and they can be plugged in both ways, but no shock. Is it somehow designed differently? Mr Fahey mentioned insulation certification, but is there anything else?

    For instance, this cap you mention sounds a lot like a "death cap". I presume it is of type that can't short, but are they used at all in Europe then?

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    There's plenty of domestic equipment in the UK with 'figure of 8' type IEC connections which can be inserted either way, but I can't say if there's a European equivalent of the wall wart I mentioned or whether it's constructed differently to account for non-polarized countries. Quite a lot of equipment has the modern-day equivalent of death caps, but it comes down to the class of cap that's used.

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    Bent Member Chuck H's Avatar
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    Lots of older gear had "polarity" switches and what we call death caps. That doesn't mean it's a good idea. Well, it was for getting quietest operation on the fly under less regular conditions. But certainly with higher danger risks relative to that "isolation" Juan was talking about. And lots of things can go wrong. There's a reason changes were made to grounded, polarity specific AC plugs. Of the nine posters on this thread three have reported experiences where something went dangerously wrong because of polarity and ground issues with AC outlets. I'm sure such stories are still happening in places where polarity and grounding haven't been standardized. We just don't hear much about it because it's common, and/or electronics regulations in those regions stipulate greater isolation in electronic designs. It can't be for any other reasons because, of course, electricity has no idea what country it's in.

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    Senior Member nevetslab's Avatar
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    Quote Originally Posted by Chuck H View Post
    Lots of older gear had "polarity" switches and what we call death caps. That doesn't mean it's a good idea. Well, it was for getting quietest operation on the fly under less regular conditions. But certainly with higher danger risks relative to that "isolation" Juan was talking about. And lots of things can go wrong. There's a reason changes were made to grounded, polarity specific AC plugs. Of the nine posters on this thread three have reported experiences where something went dangerously wrong because of polarity and ground issues with AC outlets. I'm sure such stories are still happening in places where polarity and grounding haven't been standardized. We just don't hear much about it because it's common, and/or electronics regulations in those regions stipulate greater isolation in electronic designs. It can't be for any other reasons because, of course, electricity has no idea what country it's in.
    I've always been puzzled by a generation of Fender amps having a 3-wire grounded AC Mains cord, WITH the 3-position Grounding Switch, coupled to the Death Cap. I think I've eliminated all of those from our inventory, but, there may be some still lurking about, with so many of them not going out on rentals that often. I know I've nailed all of the Twin Reverbs and Deluxe Reverbs, though they did that on so many models in that era.

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    Old Timer Leo_Gnardo's Avatar
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    Quote Originally Posted by nevetslab View Post
    I've always been puzzled by a generation of Fender amps having a 3-wire grounded AC Mains cord, WITH the 3-position Grounding Switch, coupled to the Death Cap. I think I've eliminated all of those from our inventory, but, there may be some still lurking about, with so many of them not going out on rentals that often. I know I've nailed all of the Twin Reverbs and Deluxe Reverbs, though they did that on so many models in that era.
    I think engineers call that the "belt and suspenders" approach. If you want the old fashioned Fender shock hazard, just stick on a 3-to-2 prong adapter - or tear off the ground pin with pliers - then flick the switch until sparks fly. For that authentic Fender feeling! BZZZZZZZT ! ! ! It's not a rock show until somebody gets shocked at least once.


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    Don't forget the joker g1's Avatar
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    Quote Originally Posted by nevetslab View Post
    I've always been puzzled by a generation of Fender amps having a 3-wire grounded AC Mains cord, WITH the 3-position Grounding Switch, coupled to the Death Cap. I think I've eliminated all of those from our inventory, but, there may be some still lurking about, with so many of them not going out on rentals that often. I know I've nailed all of the Twin Reverbs and Deluxe Reverbs, though they did that on so many models in that era.
    You'll find a lot of current production gear with caps across the AC line. Whether switched or not is kind of moot.
    To try and eliminate them all would be a never ending battle.
    The caps are there for a reason, and the modern ones are a type considered safe and acceptable. (look at switch mode supplies and line filters)

    I think if we get rid of the troublesome (non-safety rated) ones in vintage gear, and install 3 prong if not present, then we have done our part.

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    Old Timer J M Fahey's Avatar
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    Typical death cap rating was 600V DC

    Hey!!!! mains is 115/117V !!! (way back then) ... I have a HUGE safety margin!!!

    Think again.

    To begin with, that mains voltage means 150V peak.

    And that IF everything is as in the textbook ... but let lightning hit a transmission line, even hundreds of miles away, and all Hell breaks loose.

    Yes, there are spark gaps to deal with that ... but they trigger with scary high voltages ... or they would trigger all the time.

    I checked "250 VAC" caps meant for line filtering duty , just quoting from memory they had to stand 3000V DC for 1 hour and 5000V DC for 1 minute, or similar specs.
    Or 2000 and 3000 ; in any case the point being that old standard 600V DC is absolutely inadequate by modern standards.

    Didnīt check X and Y rated caps, but I bet they at least meet or surpass these specs, adding fail safe failure modes.

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    Old Timer olddawg's Avatar
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    I play a lot of venues, but mostly dive bars nowadays. I always ASSUME that ALL outlets are suspect. A brand new recepticale in an old building means nothing. Usually I will run the whole band with a breakout box off of one outlet so everything at least has the same reference and hope for a sturdy breaker. I ALWAYS use a wireless.... only a total cork sniffer will say they can tell a huge difference live. The absolute worst is an outdoor gig with generators. I loath to even plug in. I played a big gig in LV a couple of years ago, I saw the whole back line fried TWICE in one day. Luckily it was all rented by the event. 2 JCM800s, a JCM900, 2 vintage SVTs, and a bunch of other stuff fried.

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    Senior Member SoulFetish's Avatar
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    Quote Originally Posted by olddawg View Post
    I play a lot of venues, but mostly dive bars nowadays. I always ASSUME that ALL outlets are suspect. A brand new recepticale in an old building means nothing. Usually I will run the whole band with a breakout box off of one outlet so everything at least has the same reference and hope for a sturdy breaker. I ALWAYS use a wireless.... only a total cork sniffer will say they can tell a huge difference live. The absolute worst is an outdoor gig with generators. I loath to even plug in. I played a big gig in LV a couple of years ago, I saw the whole back line fried TWICE in one day. Luckily it was all rented by the event. 2 JCM800s, a JCM900, 2 vintage SVTs, and a bunch of other stuff fried.
    The guitar player in the last band I ran sound for recently used a wireless setup. The particular unit he used was pretty noisy on this night. But, I've used some wireless systems in playing a couple of large auditoriums and outdoor venues, and if you factor in all the acoustic effects from the physical distance between the mains sound reflections, monitor sound, and location of the amp, I don't know if I could tell any difference at all between a RF and direct cable connection. If there was a "live chassis" fault situation, there is still risk of physical contact with the amp, through an effects loop or controls adjustment. But, it does offer a really attractive margin of safety.

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by SoulFetish View Post
    The guitar player in the last band I ran sound for recently used a wireless setup. The particular unit he used was pretty noisy on this night. But, I've used some wireless systems in playing a couple of large auditoriums and outdoor venues, and if you factor in all the acoustic effects from the physical distance between the mains sound reflections, monitor sound, and location of the amp, I don't know if I could tell any difference at all between a RF and direct cable connection. If there was a "live chassis" fault situation, there is still risk of physical contact with the amp, through an effects loop or controls adjustment. But, it does offer a really attractive margin of safety.
    The only time I took a hit was when holding my (cable connected) guitar and touching the mic. Which raises the question... Why the hell is the average mic screen grounded to the case?!? Anyway, yes a wireless does provide a good safety margin. Believe it or not I was always careful not to touch potentially grounded or hot parts on other systems whenever hooking things up for gigs. But that was setting up. Put a guitar in my hands and a mic in front of me and it changes because I'm trying to perform an art, not execute a logical function. So my lips touched the mic screen and I got knocked to my knees. It started with HUMMMMMMM!!! And then arms slack and guitar feeding back acoustically while I tried to reconcile if I was actually hurt. We took a break and finished the show

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    Old Timer J M Fahey's Avatar
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    Why the hell is the average mic screen grounded to the case?!?
    Shielding.

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    Juan Manuel Fahey

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Shielding.
    Since the shielding is for the electric field I would have thought a suitably rated low inductance capacitor no bigger than 10nf ( approx 1mA at 240V 60Hz) instead of the wire to the case would be almost as effective and would eliminate the possibility of electrocution by touching the mic case. The inductance of the leads would have to be kept as low as possible so think really short.

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    Quote Originally Posted by nickb View Post
    Since the shielding is for the electric field I would have thought a suitably rated low inductance capacitor no bigger than 10nf ( approx 1mA at 240V 60Hz) instead of the wire to the case would be almost as effective and would eliminate the possibility of electrocution by touching the mic case. The inductance of the leads would have to be kept as low as possible so think really short.
    Still... enough of a shock for a person to feel, especially on the lips.

    I remember a couple decades ago, local farmers were complaining after a new 745 kV power line was installed, their cows would not eat grass on fields under the line. There was enough of a field to deliver a mild buzz but that's all it took to set 'em off. The shock was enough to "train" the cows to avoid grass on other fields too. How to convince 'em "it's OK Bossy, no shock here..." Same goes for some vocalists - once you catch a good buzzer it's hard to approach the mic again. Put a big foam "sock" on it !?!

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    Bent Member Chuck H's Avatar
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    My thinking was that since "touching the mic" has been a common denominator in the problem often enough that (maybe) some clever manufacturer could have started coating the screen with insulative material or use a secondary plastic guard or some such. I hate spit guards, but I use them. I bought a big, fat bag of them after my shock and changed them every so often when they got smelly or whenever someone of questionable oral hygiene used my mic

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    Quote Originally Posted by Chuck H View Post
    use a secondary plastic guard or some such.
    Is the metal screen on an SM57 actually grounded? I had a friend in college (where all the houses and bars had terrible wiring) who would only sing with 57's because he got shocked less than 58 style mics.

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    Quote Originally Posted by glebert View Post
    Is the metal screen on an SM57 actually grounded? I had a friend in college (where all the houses and bars had terrible wiring) who would only sing with 57's because he got shocked less than 58 style mics.
    Having dissected several SM57's, the screen is not grounded but held in a groove in the plastic end cap. Same for the similar PE54 series that look like silver body SM57's. Likely the same for the rarely seen SM77. Can't speak for SM57B or any other variant.

    Yes those college facilities had some very dodgy situations. I remember playing gigs in the basement of an off campus fraternity, crammed into a corner of the room with a steel lolly column in the middle of the stage. Touching the lolly pretty well guaranteed a painful shock no matter where one's "ground" switch was set. Of course that was back in the day when grounded AC outlets were rare, same for grounded AC cables on amps. BZZZZZT - - -OW OW OW !!!

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    Bent Member Chuck H's Avatar
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    Quote Originally Posted by glebert View Post
    Is the metal screen on an SM57 actually grounded? I had a friend in college (where all the houses and bars had terrible wiring) who would only sing with 57's because he got shocked less than 58 style mics.
    That mirrors my experience. I never had any of the 57 or 58 variants. Just the basic SM57 and SM58 mics. Tried and true. My personal vocal mic was a 58 because I was playing a guitar and singing backup while dodging around on stage. Less directional than the 57. I used the 57's for recording and mic-ing cabinets and instruments. If I were only singing and had the mic in my hand I suppose I could have used the 57. I know Robert Plant used one and (of course) he did well with it.

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    Quote Originally Posted by nickb View Post
    Since the shielding is for the electric field I would have thought a suitably rated low inductance capacitor no bigger than 10nf ( approx 1mA at 240V 60Hz) instead of the wire to the case would be almost as effective and would eliminate the possibility of electrocution by touching the mic case. The inductance of the leads would have to be kept as low as possible so think really short.
    I like the idea with galvanic isolation of the mic case which should include the shell of the connector as well.
    But do you really think a series inductance of maybe 50nH matters?

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    How come nobody just throws some heat shrink or something similar on their mic bodies?

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    "Thermionic Apocalypse" -JT nickb's Avatar
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    Quote Originally Posted by Helmholtz View Post
    I like the idea with galvanic isolation of the mic case which should include the shell of the connector as well.
    But do you really think a series inductance of maybe 50nH matters?
    Sure! At 1GHz that's over 300 ohms. Think WiFi 5.4GHz, radio mics 0.8GHz, cell phones 0.8-1.8Ghz. It's dirty out there.

    I also like the insulting coating / covering ideas

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    Sure! At 1GHz that's over 300 ohms. Think WiFi 5.4GHz, radio mics 0.8GHz, cell phones 0.8-1.8Ghz. It's dirty out there.
    But the inductance of the cap leads would be in series with/just add to the hundred times higher inductance of the mic cable's shield.
    Mic and instrument cables act as low pass filters at high frequencies.

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    Last edited by Helmholtz; 07-25-2019 at 05:33 PM.
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