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I have several old, ungrounded outlets in my house which are protected with GFCI, which is allowed per code as the GFCI will protect a person in the event of a ground-fault.

These outlets are supposed to be labeled "No equipment ground" but the previous owner neglected to do this. I assume that if I plug electronic equipment into this outlet there could be problems, but it is not clear what those problems would be.

Is "No equipment ground" a hazard to either people or equipment? What problems could happen if I plugged something like a 3-prong laptop power supply into this outlet? What about a device which uses a 2-prong power cable (no ground) such as some space heater or televisions?

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See here for what the ground wire is for, and here for a GFCI is does. –  BlueRaja - Danny Pflughoeft Sep 17 '13 at 2:27
    
In theory, nothing bad should happen. The equipment grounding conductor is there as a safety device, and should only be used in the event of a fault. If you are truly installing sensitive equipment, you should follow the wiring methods described in Article 647 Sensitive Electronic Equipment of the National Electrical Code (NEC). –  Tester101 Sep 17 '13 at 11:40
    
I solemnly swear that no medical equipment is plugged into this receptacle, and if it were I would install an isolated ground. –  Stefan Lasiewski Sep 17 '13 at 16:10

2 Answers 2

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Any equipment that uses a two prong plug will be as safe being plugged into this setup as they would be if they were plugged into a properly grounded three prong outlet. Two prong plugs (obviously) do not use the ground pin. As for three prong plugs, this depends on what is being plugged in. If the item is a laptop power supply that is sealed in a plastic shell, the ground pin is pretty much ISO-proforma [meaning, that is the standard cord- whether the equipment needs a ground or not.] I would be hesitant to plug in something with a metal shell, like a full size desk top tower, because the power supply is enclosed in a metal shell and attached directly to the frame of the case, this could present a shock hazard if the power supply were to malfunction.

A GFCI is a good start. If they are functioning properly, they will guard against lethal shocks, but you may still get a tingle if the electric is not quite right.

A possible suggestion: Use a 2->3 pin converter and attach a ground wire to the grounding tab. Attach the other end of the wire to a radiator if you have steam heat or possibly a metal water pipe. (no gas pipes.) This will get you a ground and you can use those items safely.

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Normally, the grounding wire on a piece of equipment is intended to ensure that if a fault develops which would cause the chassis to become live, it will shunt away any as much current from the chassis as the main could supply to it, typically popping a breaker. A GFCI will ensure that if a conductive path would take current from the mains without feeding an equal and opposite amount of current through the neutral wire, it will disconnect power fast enough to minimize risk of personal injury.

If a piece of equipment were to develop a fault which would energize the chassis and normally result in current flowing through the grounding wire, such a fault would not trip the breaker but would persist until there was some other path for current to flow from the chassis. As soon as that other current path appeared, the GFCI would pop; it is entirely possible, however, that before the GFCI popped the chassis would deliver a significant (but hopefully not injurious) shock to the person touching it, or could deliver sufficient current into part of a device that wasn't ready to accept it and consequently damage or destroy the device. Although the GFCI will generally protect against injury, it won't provide as good protection against shocks or equipment damage as would a properly-grounded receptacle.

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