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Message: <blockquote data-quote="Mike Sokol" data-source="post: 58656" data-attributes="member: 1989">Re: Why An Open Neutral Kills 120V DevicesThe more important thing to  observe when metering provided outlets or tie ins is voltage difference between  the safety ground and neutral (indicating poor panel bonding. Ideally, should  read zero volts) That's not exactly right, unless you're measuring in the service panel at the N-G and Ground Rod bonding point. The neutral wire will typically have a volt or two drop in any loaded branch circuit, unless it's feeding perfectly balanced 240-volt  loads like a stove or hot water heater. If there's any unbalanced load on a hot wire in a branch circuit, there will be a  corresponding and out-of-phase voltage drop on the neutral return wire. Since the  safety ground wire should not be part of the neutral current return path, it should  stick at earth potential. So if you meter between the ground and neutral in a wall  outlet you should see the voltage vary by up to several volts (and up to half of the total voltage drop on a loaded branch circuit) depending on the unbalanced load in that branch circuit, depending on length of run, wire gauge, etc.... If you  don't see at least some AC voltage (from a few tenths up to a volt or two) between the neutral and ground contacts, there's a good chance you  have a bootleg ground with N-G bonding close to the outlet. A 2 wire device such as a laptop power supply or lamp would not be  damaged, but a 3 wire device expecting a panel bonded safety ground  would get a nice voltage surprise. That's an old-wives tale and incorrect. I've done this experiment hundreds of times in my No~Shock~Zone seminars using every type of appliance with a grounded power plug such as guitar amps, active speakers, and toaster ovens. See attached picture below for my test bench. Modern devices with a safety ground really don't care about the  voltage difference between the safety ground and neutral and will operate normally. So a swapped Neutral and Hot really won't harm anything, but it's a serious code violation for many safety reasons. On the other hand a RPBG (Reverse Polarity Bootleg Ground) where the Neutral and Ground are at 120 volts and the Hot wire is at 0 volts is another story. These are often found in older renovated buildings where an old ungrounded wall outlet was "upgraded" to a grounded receptacle, and the ground screw was bonded to the neutral wire as a quick fix. If the hot and neutral wires were swapped in the walls (more common than you think), then the entire appliance can have a 120-volt hot-chassis, including your mixing console, guitar amps, microphones, and instruments. Interestingly, a RPBG outlet can't be found by a 3-light outlet tester, or even by simply metering from H-N, H-G and G-N. It will indicate as being wired correctly using any standard test procedure that doesn't have an earth reference, but this RPBG outlet will electrify the chassis anything with a grounded power plug. See <a href="http://www.youtube.com/watch?v=iLk-6pvSlWg&feature=plcp" target="_blank">Reverse Polarity Bootleg Ground Testing - YouTube</a> for a video of this failure. By adding a cheap NCVT (Non Contact Voltage Tester) to your tool kit, you can find and avoid this costly (and deadly) mistake. I can post circuit diagrams and pictures of destroyed gear as examples later.</blockquote>

Verification

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