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Two quick questions for you pros...


blazenut
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Hey there. I was over at a friends 65-75 year old home the other day and came accross a couple of questions that i wanted to ask you guys. I went around with my outlet tester and realized that many of their outlets had reversed polarity and several were un-grounded 3 prongers. I started to explain a bunch of these things to them and then just started fixing the reversed polarity ol's. Many, but not all were old fabric 2 wire. The one outlet was reversed and only two wire, but when i rewired it it showed up as a properly grounded outlet (no wire attached to the ground screw of the outlet). Is this pulling a ground from a different outlet on the same circuits neutral wire? I couldnt explain it so i figured i would ask you guys. Thanks in advance. The second question is this: They had a huge computer system/stereo system plugged into a surge protector plugged into an un-grounded three prong outlet. Can you properly surge protect without a ground? What is this installation doing if anything? Thanks in advance.

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The one outlet was reversed and only two wire, but when i rewired it it showed up as a properly grounded outlet (no wire attached to the ground screw of the outlet). Is this pulling a ground from a different outlet on the same circuits neutral wire? I couldnt explain it so i figured i would ask you guys.

If the grounding connection on a general purpose outlet device isn't connected and your tester says that it is grounded, you might try a different tester.

They had a huge computer system/stereo system plugged into a surge protector plugged into an un-grounded three prong outlet. Can you properly surge protect without a ground? What is this installation doing if anything?

The surge protectors that I know of employ a component called a varister to bleed high voltages to the ground connection. The resistance of a varister breaks down when the voltage across it reaches an approximate threshold, allowing current to pass but otherwise remaining high. The higher the dissipation value of the varister, the more joules of energy that it can absorb without damage and the more protection that it affords you. A surge protector without a grounding connection is only an illusion of protection and the power supply for any electronic equipment that is powered by it is at risk. Sometime, a voltage spike that's big enough will get thru the power supply itself and damage additional circuitry.

Marc

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The one outlet was reversed and only two wire, but when i rewired it it showed up as a properly grounded outlet (no wire attached to the ground screw of the outlet). Is this pulling a ground from a different outlet on the same circuits neutral wire?

Was the work box grounded? There has to be a conection to ground somewhere in order for your tester to show a ground, either an auxilary ground wire, conduit or armored cable. That still doesn't mean it's a grounded system, with the number of bootlegs you described it could be connected to one of them somewhere along the circuit.

The second question is this: They had a huge computer system/stereo system plugged into a surge protector plugged into an un-grounded three prong outlet. Can you properly surge protect without a ground? What is this installation doing if anything? Thanks in advance.

There may be some protection from low level surges, but there will be very little for a big surge, and nil for something like lightening. He should run a dedicated, grounded circuit for that equipment. A whole house lightening supressor couldn't hurt either.

Tom

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. . . The one outlet was reversed and only two wire, but when i rewired it it showed up as a properly grounded outlet (no wire attached to the ground screw of the outlet). Is this pulling a ground from a different outlet on the same circuits neutral wire? I couldnt explain it so i figured i would ask you guys. Thanks in advance.

First verify what you're reading with a real tester. I'd use a multi meter or, if I had one handy, a Wiggy. If it still shows grounded, then I'd look for a ground path. It's probably somethign attached to the box. I've heard of all kinds of strange ground paths to old metal boxes, including wire lath. Someone here, years ago, said that he found stone wire running from box to box during a remodel. It might be anything conductive.

The second question is this: They had a huge computer system/stereo system plugged into a surge protector plugged into an un-grounded three prong outlet. Can you properly surge protect without a ground? What is this installation doing if anything? Thanks in advance.

It's doing nothing. As Marc explained, these surge protectors work by shunting surges to ground. Without a path to ground, the surge will just travel over the regular circuit path and fry the electronics.

- Jim Katen, Oregon

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Your question #1 - could be BX cable, armoured cable connected to metal boxes. It could be armoured cable all the way from the panel or if upgrades were done, there could be a 3-wire grounded circuit feeding that branch.

Or it could be a false reading due to a bootleg ground, where the neutral is grounded to the box somewhere with a jumper.

Usually with a 2-wire circuit, the 3-light tester won't show reverse polarity even if it exists, because only the middle light comes on, showing power, no ground.

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