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Author Topic: Dangerous AC situation in reception hall - PLEASE READ  (Read 184362 times)

Jonathan Johnson

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Re: freak accident? help!
« Reply #90 on: May 11, 2012, 02:32:10 AM »

The house I now own with my wife had an interesting issue in the laundry room. We had a brand new Kenmore washer and dryer set put in there. One day whilst doing laundry my wife was reaching into the dryer while resting her hand on the locking nub of the front loading washer right next to the dryer. She got a good jolt. I whipped out the DMM and check between the dryer drum and washer enclosure. a bit over 100V. I checked the outlet the dryer was plugged into, it had a hot neutral swap. Now even so, it should not have been an issue. For some reason, the drum of the dryer was tied to neutral instead of ground. The ground wiring on both receptacles was correct. AFAIK, any metal parts that a person could come into contact with should only be tied to ground. I replaced both outlets with GFCIs when correcting the wiring issue and sent a message to Sears that I believe they might have a design or assembly issue. They didn't seem very concerned, which of course concerned me since it's a potentially fatal issue. Not good policy.

This is not Sears' (the corporation) fault and not necessarily the manufacturer's fault. It is the fault of the installer (which may be an employee of the local Sears store). It may be the fault of the local Sears store for failing to properly train the installer.

Dryers and ranges do not ship with cords. The cordset is attached by the installer. Because 3-prong 120/240V receptacles (hot-hot-neutral) are common in older homes while newer homes have 4-prong 120/140V receptacles (hot-hot-neutral-ground), the manufacturer leaves it up to the installer to choose and install the cordset that matches the existing receptacle.

However, the manufacturer ships the appliance with the neutral and ground bonded in the appliance. The installer must unbond these when connecting a 4-prong cordset, or leave them bonded when connecting a 3-prong cordset (essentially creating a bootleg ground).

In your case, it appears the installer left it bonded and probably left the ground lead in the cordset disconnected in the appliance.

As for myself, when I install such an appliance I will change the receptacle (rewiring if necessary) to provide a properly connected 4-prong 120/240V receptacle rather than installing a 3-prong 120/140V cordset with a bootleg ground. Of course, I can't expect appliance installers to do this, but for liability reasons, I would suggest that appliance installers should refuse to install an appliance using a 3-prong cord with bootleg ground. The homeowner then has two choices: call an electrician to rewire the receptacle, or install the cordset themselves.
« Last Edit: May 11, 2012, 02:42:53 AM by Jonathan Johnson »
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Stop confusing the issue with facts and logic!

Mike Sokol

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Re: freak accident? help!
« Reply #91 on: May 11, 2012, 08:10:02 AM »


Point is, no ground is a much more common occurrence then a hot ground pin. And arguing with someone who is certain that the way hes been doing it for years is just fine is nearly futile.
Very true.... and most of you know that an "ungrounded" sound system can go instantly hot at any time if a single piece of gear develops a short or leakage to actual earth ground. The best you can do is protect yourself from getting shocked and hope that nobody in the band kills themselves on your watch.

I really think that bringing and using your own power distro is the safest thing to do. I built my first distro for my band back in the late 70's after a particularly nasty shock from a club. We were all plugged into what appeared to be grounded stage outlets, but I later discovered that while all the outlet grounds were connected together, NONE of these "grounds" were connected back to the ground buss in the main panel. So EVERYTHING was floating together. I built a simple circuit breaker box with Edison outlets on a piece of plywood and had a pair of vice-grips on a 100 ft piece of 10 gauge wire I could clamp onto a cold water pipe in the basement.  Not exactly code, but it worked perfectly. That's also when I bought my first Ground Loop Impedance Tester (GLIT) since I really don't like getting shocked on stage (or anywhere else for that matter).

Mike

John Livings

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Re: freak accident? help!
« Reply #92 on: May 12, 2012, 02:52:47 AM »

However, the manufacturer ships the appliance with the neutral and ground bonded in the appliance. The installer must unbond these when connecting a 4-prong cordset, or leave them bonded when connecting a 3-prong cordset (essentially creating a bootleg ground).

+1,  The actual cord set may also have the ground nico pressed (swaged) to the neutral when you purchase it.

Also common is have installers run out of space in the neutral bar in a sub panel and run the neutral to the grounding bar.
Then installing a jumper between N and G. (or vice versa)

Some have been told not to add more than one wire to the same connecting screw hole in the neutral or ground buss connection.

The solution would be to install another (or more spaces) neural bar.

One other thing is very common; Correction of a "Dropped Neutral," (or loose connection upstream) In a box all the neutral are tied together and the neutral going to your receptacle is "Open" (Dead). Many times the installer can get his 120 Volts by testing P to G = 120 V,  P to N = 0 V.

So he connects the ground to the neutral screw of the of the plug,There by energizing (when something is running)  all the Grounds and all metal connected to them.

In the older systems (2 wire) the N is dead and the installer jumps the Neutral screw of the receptacle  to the metal box as to complete the circuit (120 V)

Now all the metal conduit and grounds could be connected to neutrals.

Also common, is on the Duplex Receptacle is to break off the brass tab connecting the two plugs so each can be used as a separate circuit (no problem), Then on the neutral side of the plug, that tab is broken off, opening the N run to the next plug.
Now the "Jumping" starts again resulting in the grounds being connected to the Neutrals.

Use the screws for wire connections on receptacles not "Back Stabbing". Some folks are lucky, however with lots of noise and movement, back stabbing is a bad idea.

Another issue is an installer Jumping the neutral and ground bar or engaging a bonding screw. This is done sometimes when the installers looks at the Main Panel set up and then copies it.

Just my opinions

Also Mike and others , thanks for posting all this information, Most useful.

Regards,  John
« Last Edit: May 12, 2012, 03:12:03 AM by John Livings »
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Mike Sokol

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Re: freak accident? help!
« Reply #93 on: May 12, 2012, 08:25:28 AM »

However, the manufacturer ships the appliance with the neutral and ground bonded in the appliance. The installer must unbond these when connecting a 4-prong cordset, or leave them bonded when connecting a 3-prong cordset (essentially creating a bootleg ground).

+1,  The actual cord set may also have the ground nico pressed (swaged) to the neutral when you purchase it.

Also common is have installers run out of space in the neutral bar in a sub panel and run the neutral to the grounding bar.
Then installing a jumper between N and G. (or vice versa)

Some have been told not to add more than one wire to the same connecting screw hole in the neutral or ground buss connection.

The solution would be to install another (or more spaces) neural bar.

One other thing is very common; Correction of a "Dropped Neutral," (or loose connection upstream) In a box all the neutral are tied together and the neutral going to your receptacle is "Open" (Dead). Many times the installer can get his 120 Volts by testing P to G = 120 V,  P to N = 0 V.

So he connects the ground to the neutral screw of the of the plug,There by energizing (when something is running)  all the Grounds and all metal connected to them.

In the older systems (2 wire) the N is dead and the installer jumps the Neutral screw of the receptacle  to the metal box as to complete the circuit (120 V)

Now all the metal conduit and grounds could be connected to neutrals.

Also common, is on the Duplex Receptacle is to break off the brass tab connecting the two plugs so each can be used as a separate circuit (no problem), Then on the neutral side of the plug, that tab is broken off, opening the N run to the next plug.
Now the "Jumping" starts again resulting in the grounds being connected to the Neutrals.

Use the screws for wire connections on receptacles not "Back Stabbing". Some folks are lucky, however with lots of noise and movement, back stabbing is a bad idea.

Another issue is an installer Jumping the neutral and ground bar or engaging a bonding screw. This is done sometimes when the installers looks at the Main Panel set up and then copies it.

Just my opinions

Also Mike and others , thanks for posting all this information, Most useful.

Regards,  John

All seem like real life scenarios to me. The problem is that sound gear manufacturers and sound technicians ASSUME that perfect wiring practices will always be used in buildings. And this is simply not the case. I've been on enough house wiring jobs to know that the electricians and inspectors often have a "good old boy" relationship where the inspectors stops by the job site for coffee and donuts, then signs-off on the job without even pulling out a meter.

The problem with all this extra N-G bonding is that any voltage drop in a hot wire(s) will be matched by an equal (and inverted phase) drop in the neutral wire(s). If a ground wire is bonded at a secondary neutral point, then it too will move around electrically. Power two pieces of audio gear (a mixer and a powered speaker) on these different outlets with "dirty" grounds then cross connect them with an XLR cable. Ta da.... now you have a ground loop current flowing in the shield of the XLR cable which is trying to equalize the voltage between the two pieces of gear. My tests show about 1 ampere of current per volt of ground loop differential will flow through the XLR shield, and you can see why there can be several amps of current flowing in an XLR shield between your mixing console and amp racks. I won't go into the pin 1 problem here, but depending on the audio gear manufacturer you'll either get a tiny bit of hum (rejected by the CMRR) or a lot of hum (due to a pin-1 XLR trace on the circuit board). These ground loop hums can seem to come and go at random times, but in actuality are being modulated by electrical loads changing in other rooms. So when somebody starts a coffee maker in the kitchen, you get a large current draw on the neutral line in that box, which causes a corresponding voltage differential between the two different grounds that your gear is plugged into, which causes ground loop currents and hum.

This crazy coming and going of hum often causes sound technicians to break off the ground pins or use a ground lift adapter on the power plug in a futile attempt to stop the hum. Of course, bypassing the safety ground on sound gear can be dangerous since you have the possibility of a piece of gear's chassis "floating" above ground and possibly at 120 volts. Now touching that piece of gear (your guitar stings or mic) while leaning on the grounded metal rail around the stage can cause your heart to be in the current path, with the result being electrocution. Yikes.....

Getting the power right is the first step in running a great sounding and safe sound system. Incorrectly connected power can make the best sound system sonically challenged and dangerous to be around.

Mike

Scott Wagner

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Re: freak accident? help!
« Reply #94 on: May 12, 2012, 11:07:32 AM »

This topic should become a "sticky" before it becomes a "shocky".

Scott Wagner
Big Nickel Audio
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Big Nickel Audio

Tim McCulloch

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Re: freak accident? help!
« Reply #95 on: May 12, 2012, 11:57:10 AM »

This topic should become a "sticky" before it becomes a "shocky".

Scott Wagner
Big Nickel Audio

I have suggested that to the mods.  With some editing it could also become a Study Hall article.
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Bob Charest

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Re: freak accident? help!
« Reply #96 on: May 12, 2012, 06:42:23 PM »

I have suggested that to the mods.  With some editing it could also become a Study Hall article.
Good ideas, Scott & Tim. After reading the thread and getting the Fluke Volt-Alert I found that the outlet in our kitchen island is a bad actor. The outlet must be tapped off the electric oven. I'll check it out later, but that one raised my awareness. All the other outlets were by the numbers.

Best regards,
Bob
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Mike Sokol

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Re: freak accident? help!
« Reply #97 on: May 12, 2012, 07:14:11 PM »

Good ideas, Scott & Tim. After reading the thread and getting the Fluke Volt-Alert I found that the outlet in our kitchen island is a bad actor. The outlet must be tapped off the electric oven. I'll check it out later, but that one raised my awareness. All the other outlets were by the numbers.

Best regards,
Bob
Once you start looking around, you can find all sorts of mis-wired outlets using a VoltAlert or other non-contact AC tester. Most aren't dangerous, but all of them should be repaired by a properly trained electrician.

Bob Charest

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Re: freak accident? help!
« Reply #98 on: May 12, 2012, 08:28:18 PM »

Once you start looking around, you can find all sorts of mis-wired outlets using a VoltAlert or other non-contact AC tester. Most aren't dangerous, but all of them should be repaired by a properly trained electrician.
Hi Mike,
Agreed. It goes to the point of expectations that things have been done correctly. The other outlets on the main floor were all good. When I got up the next day I wanted to check the various power distribution sources we use for the band, and was also trying to get used to either turning it on to beep or just flash. So strong was my expectation that all was well when I tested the rogue outlet (nearest to where I was standing when I turned the Fluke on and hadn't been tested yet) that at first I thought I had turned on the unit incorrectly! To me, aside from a proper repeatable method, my mind-set needs to be changed.... Maybe there's a tester for my brain - Nah, no market for that!
Best regards,
Bob
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Mike Sokol

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Re: freak accident? help!
« Reply #99 on: May 13, 2012, 08:36:37 AM »

Agreed. It goes to the point of expectations that things have been done correctly.

Exactly right. How many times have you fired up a big genny on an outside gig, and the first thing you do is check the line voltage and frequency. Why? Because we don't trust generators.

But how many wall outlets have you plugged into without thinking about it? Thousands? Tens of Thousands? While most wall outlets have been wired correctly, and some are wired incorrectly but not dangerously, some will be wired so wrong as to present a shock hazard. And as others have note on this thread, manufacturers don't think about gear being cross-connected between multiple power outlets. That's mostly reserved for the A/V industry with mixers, amps, lights and projectors positioned around the room, all interconnected by signal cables, each with their own shields.

I don't mean to scare everybody with my postings, just to make you aware of electrical situations that can put your gear and your life in jeopardy. I've been studying this a lot lately and have figured out all sorts of wiring situations that make sound systems sick.
« Last Edit: May 13, 2012, 10:02:36 AM by Mike Sokol »
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Re: freak accident? help!
« Reply #99 on: May 13, 2012, 08:36:37 AM »


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