Rickresource Rickenbacker Forum

kennyhowes wrote:It's weird, you know...I'm old enough (born in 1970s) to have had to deal with microphones shocking me and being cautious of that - but it hasn't happened to me in years, in a club or otherwise. Is it because everything has a three prong plug now?

I used to think it was because I was using Vox/Thomas Organ amps. It seemed like no matter which way they were plugged in, it was the wrong way and you had to flip the polarity switch...

I decided a few days ago to purchase (what is referred to in this thread) the $5 life insurance policy (Electrical outlet tester). At a gig that I did yesterday evening I checked the outlet before plugging in and found that the ground and neutral were crossed in the outlet. It was good that all of the other outlets were OK. Who knows what could have happened and I'm glad not to find out. Like Kenny, I'm also old enough to remember getting shocked by microphones. The $5 tester is a great tool to have. I'm sure that these come in other voltage readings used in places other than the USA.

kennyhowes wrote:It's weird, you know...I'm old enough (born in 1970s) to have had to deal with microphones shocking me and being cautious of that - but it hasn't happened to me in years, in a club or otherwise. Is it because everything has a three prong plug now?

I used to think it was because I was using Vox/Thomas Organ amps. It seemed like no matter which way they were plugged in, it was the wrong way and you had to flip the polarity switch...

3-prong outlets have a lot to do with it. Also more modern wiring codes, though those only work when followed.

Two-prong outlets do not have "grounding problems". They simply aren't grounded. One 'prong' is "hot" and the other is a "Neutral". Historically, neutral was generally considered a ground, but it really isn't. Think more along the lines of a balanced microphone signal. There's 'hot' amd 'return'. The voltage on a balanced return isn't zero and the voltage on a neutral isn't neccesarily zero either - it's a return path to complete the circuit.

That also means many electrical devices don't care which way the plug is oriented and work fine either way. The problem generally comes from having more than one device plugged in opposite ways. If your guitar amp is in one polarity and the PA is in another, you'll get your lips shocked if they touch metal on the mic while you're touching guitar strings.

Another example is the case where I have a few old Fender 2-prong amps and I have a couple old 2-prong reverb units (one spring and one rotating disk). If the amp and reverb aren't both plugged in in the same orientation, I get a buzz when touching metal (e.g. faceplate) on either or exposed metal on the plug of the guitar cord or strings. If plugged in the same, no problem. I should just replace the cords on those, but I just bought 2-prong to 3-prong adapters, figured out the right direction, then taped the cord to the adapter - then they have to be the right way.

When dealing with modern 3-plug wiring, now there is an actual ground, so most of the amp chassis is actually grounded (no voltage) and the "hot" and neutral can't be plugged in incorrectly. Unless, as Scott and Steve have seen, the outlet is wired backwards. With more adherence to wiring codes, that gets less likely. Due to liabilities, most commercial places hire electricians instead of making it a DIY project. If you buy a house from a DIY-er, who knows what you'll find. I've found and fixed quite a few scary wiring things in my house.

Buying a $5 tester is certainly a good idea. If you decide not to, you should at least do what I do (though I'm not taking responsibility for anyone but myself). Tapping the microphone, guitar cord, or amp chassis with the back of your hand will let you know pretty quickly whether its "hot" or not. You get a bit of a buzz, but it hurts a whole lot less than on your lips. You use the back of your hand instead of the front of your hand because if you grab it, the electricity can cause your hand muscles to clamp down and might not be able to let go. Not a good thing.

Also make sure you're never touching metal with both hands. You don't want to set up a path going through your chest. There's actually a thing called "the hand in pocket rule" - usually more for dealing with high voltages (like tube voltages and higher), but not a bad idea for household voltages. Put one hand in your back pocket and make a fist. Then just touch with one hand. Making the fist in you back pocket should require you to relax your hand before it will come out - then you don't just accidentally pull the hand out and touch something.

Another option would be to have your drummer or bass player test it for you....

Yeah, that's mostly correct. The "neutral" wire is, in fact "grounded" (connected to the ground rod) at the service entrance. The big difference is that "neutral" carries the return current of the "hot" connection whilst "ground" carries no current except in a fault condition.

Now, modern 3 prong "grounded" connections connect the ground the the chassis, which makes the whole thing inherently safe since the main metallic structure of a device is "grounded", not intended to carry current. This makes the design a bit more costly since they have to use a transformer (which adds isolation and even MORE safety) since they can't tie everything to the chassis for the return current.

In the "olden" days, with 2 wire circuits, they often skimped on the circuitry and connected the chassis to the "neutral" which is essentially (or eventually) grounded. Of course, if you got the wiring wrong, the chassis would be connected to the "hot" and have 120V (or 240V) directly connected to it. Touching something like a mic case that was "grounded" to the chassis would in fact connect you to the live 120V (or 240V) circuit and if you touched something else that was wired correctly, the current went through YOU with nasty effects. This is more prevalent in tube (or valve) amplifiers since they run on voltages in the range of "line" voltage. Solid state (transistor) stuff runs at generally lower voltages, which usually needs a transformer, which provides isolation and more safety as mentioned above...

Fair enough, CJ. Given that the neutral carries return current and is grounded 'remotely', there's always some voltage on it. How much depends upon current, wire gauge, and how far away the eventual ground is located - but yeah, there's rarely much voltage on it. That's why I don't necessarily consider a 2-wire system to be "grounded". (I'm a microwave/RF guy and generally think about grounding a little differently than most, anyway.)

Yeah, I've got a decade or so experience in the RF/microwave world as well.

The main point is that when everything is wired correctly, having the neutral connected to the chassis is generally safe (though not as safe as where the chassis (being really grounded) has no voltage because no current is carried on the wire connected to it. But, if it's connected wrong, either because the plug is inserted backwards or the outlet is wired wrong, you get the full line voltage on what's supposed to be "neutral/ground," which can be lethal...

I am starting up an amplifier company called LeTHaL Amplifiers®, should go over well with the doom/death metal guys!

Played with some guys once that used to laugh at me for bringing a small VOM to gigs. Until they took voltage to the mouth and I was able to show them 110v between their guitar strings and the mic. It was an old house, and who knows how it was wired. It gets really scary when you consider that if two improperly polarized amps (or outlets) are on two different legs of the building's power supply, it's even possible to have 220v between two pieces of equipment.

cjj wrote:Yeah, I've got a decade or so experience in the RF/microwave world as well.

The main point is that when everything is wired correctly, having the neutral connected to the chassis is generally safe (though not as safe as where the chassis (being really grounded) has no voltage because no current is carried on the wire connected to it. But, if it's connected wrong, either because the plug is inserted backwards or the outlet is wired wrong, you get the full line voltage on what's supposed to be "neutral/ground," which can be lethal...

Well, now I know that there are at least two fellow RF/Microwave types on this forum! I have enjoyed reading this thread. I earned a B.S. in Electrical Engineering after night classes over many years back in the late 90's, and one of my two senior year specialties was Power. I've forgotten most of that stuff being in the high frequency world before, during, and after, but at one time I could do 3-phase calculations with the best of them.

A story I will relate is from when I worked at defense contractor as a technician in the 80's. We used a device called a "Megger" (MegOhmMeter) to ring out missile cable bundles to make sure their insulation was good. We put something like 400-500 VDC across the center conductors. I accidentally got the tip of one thumb on the hot connection and it was sore the rest of the day.

The easiest way to make sure you are safe is to plug your equipment into a circuit breaker and then plug the circuit breaker into the supply. If the breaker senses anything that is not right it breaks the circuit immediately.

Wow!
So glad I happened upon this thread!
Looks like I’d better be more careful when I plug in my ‘65 Vox Pacemaker with the two-banger for a plug.
Bless ya, felas!

I know everybody will not re-wire their guitars. But...when I have to play an outdoor gig, or when I am playing an indoor gig where the wiring is substandard: I have a bass I have specifically wired with "goundless" EMG active pickups, and put LaBella "White Tapes" strings on it to insulate the bass from the mains as much as possible.

As much as I love my Rickenbacker guitars, I also want to live another day to play them.

If you've ever had your lips fried by non-matching polarities between guitar and microphone, you never forget it...

stringsncords wrote:If you've ever had your lips fried by non-matching polarities between guitar and microphone, you never forget it...

Indeed. That happened to me at a band camp gig in high school: old PA with non-polarized plug. I carefully checked everything. Between setup and performance someone knocked the plug out of the wall, and wanting to be helpful, plugged it back in, but didn't tell me so I could re-check the polarity. I walked up to the microphone with my electric guitar barely grazed it, saw a big white light in front of my face, the house lights dimmed, and everybody gasped. I calmly went over, flipped the plug on the PA, and resumed.