Question about reversed-polarity in an AC outlet

Most of the time, a bad or improper ground is the culprit. We were having numerous problems with the computers at our office. Somethings would work while others did not. Weird printer problems and reboots. We found a ground wire in the wall was spliced by twisting two bare copper ground wires together. They were loose. We retwisted and installed a wire nut on there and the problems have gone away.

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There is no obvious way for this to happen. Normally, modern equipment doesn't care about the polarity of the Hot and Neutral, even in terms of safety. (By regulation, it must NOT affect safety.) I would guess that if the problem was actually due to the reverse polarity, then it may have been the resulted from excessive hum/noise on the USB or whatever interface was used.

As noted, really shouldn't matter but each piece of equipment will be more or less susceptible to reverse polarity.

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The bare wires are safety ground, and should not be active under normal circumstances. I would be concerned. RF bypass capacitors with excessive leakage might be the culprit.

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This may be some kind of safety interlock.

For a 3-wire plug, a circuit can easily be created to detect whether the neutral line has a large potential with respect to the ground line, and to disable the appliance. That may be whats going on here.

The other possibility is that the appliance is using the ground wire as the current return, either through internal miswiring, or by design. In that case, if the hot and neutral wire is switched, there won't be a potential difference to run the appliance. Neutral is usually only a few volts away from ground.

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Best guess is that re-wiring the plug merely made good a poor contact. Household mains powered equipment does not have a 'polarity'.

If it does you have SERIOUS problems, and I would recommend finding a smart electrician to take a look.

N

On Saturday 09 October 2004 10:07 am, R.Lewis did deign to grace us with the following: ....

Oh, it most certainly does! It's just not "plus" and "minus," it's "hot" and "neutral." Reversing them is a safety issue.

Good Luck! Rich

Same in the UK but for slightly different reasons. Our Neutral connection is now bolted up to the incoming mains Earth, so it doesn't float above earth as it used to years ago.

The USA 120V is parts of a centre-tapped 240V if my memory serves me correctly?

Peter

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I think that might depend on which country you are in but I'm not 100% sure.

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Its 110V and 220V.

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I had a very weird one like this once, a cheap CMOS color video camera which was powered by a standard off the shelf magnetic transformer type 9v DC output wall wart. It would work fine plugged in normally, but plug the wall wart in upside down (reverse polarity) and the camera would power up but not produce an image, never did figure that one out.

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The bypass capacitors in the power supply usually connect to ground, so no ground, no bypass.

No ground -> chassis isn't necessarily at ground potential.

If another piece of equipment is closer to ground, and is connected via a cable carrying signals referenced to ground, you can induce noise.

Ground loops can be lots of fun to diagnose.

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These things don't always make good contact in the socket - Perhaps the weight of the adaptor on the pins one way up caused the problem?

Uhh this is definately not normal. I recently saw something like this. The guy who wired up the circuit didn't have a neutral available at the end of a 3way switch so he simply tied the light there to the ground wire. Tracing the ground wire back I discovered a place where it had just been touching the inside of an electrical box run with conduit. It had completely arced out and lost it's connection. If the conduit had ever become discontinuous all of the conduit (which was exposed work ) would have become hot.

On Monday 11 October 2004 12:13 am, CWatters did deign to grace us with the following:

No, it can actually make a difference. It's kind of surprising that a wall wart has that problem - it usually shows up in old equipment that didn't isolate neutral from ground properly, so if the hot/ neutral are reversed, you get all kinds of power line noise in the equipment and people get shocked.

You can get an outlet tester for about five bucks that will check all three wires and ground - I'd recommend that. Check the electrical dept. at your local home store.

Good Luck! Rich

The camera would power up and produce the video timing, but no picture, it was strange.

"R.Lewis" wrote in news:ck95rd$id6$ snipped-for-privacy@thorium.cix.co.uk:

First of all, I'm not sure what you mean by "the good old days". DC is very widely used today.

Secondly, AC does have a hot and a neutral. You can buy AC testers at Canadian Tire. It's looks sorta like a pen with a single plastic blade on the end. If you stick the blade into the hot side of a receptacle, the light will turn on, but if you put it on the neutral side, it will not.

This simple test proves that, even though there is no plus and minus with AC, there is still a polarity.

Not widely distributed in homes.

No, it proves that one side is grounded and the other is not.

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N