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I bought an electrical device a few months ago. A few weeks ago, it failed, complete with the release of magic smoke. I contacted the company, and they've had me mail it to them and have been investigating the failure.

Today they contacted me asking to have an electrician come to my house and take some measurements; they said that they've talked to experts and they "...have indicated that a grounded neutral in a house with wiring like yours may create a scenario that could cause something like this."

My house was built in 1959, and while some circuits are grounded, the room where the device was plugged in has two-prong outlets, and the cable going to the receptacles is ungrounded. The device used a two-prong plug.

I'm inclined to let them do the measurements, but before I do, I'd like to know:

What is a 'grounded neutral'? My main breaker panel only has two breakers, one 30-amp for the A/C and one 100-amp breaker for the subpanel that powers the rest of the house; I'm pretty sure that Neutral and Ground don't touch inside the subpanel, but I haven't looked inside it for a couple of years.

Is there anything else I should know?

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Check the voltage at the outlet. –  Brad Gilbert Mar 6 '13 at 16:21

2 Answers 2

That explanation doesn't really make any sense to me personally. The neutral bus bar in your main panel should be bonded to the ground bus bar so in effect, all neutral wires in your house are grounded.

The third prong in a typical three prong outlet is known as the equipment ground. This is a safety feature that should cause your breaker to trip if an electrical fault inside of an appliance causes the metal body of the appliance to become energized. The equipment ground protection however is a safety feature for YOU so that you won't be electrocuted in the case of an appliance fault. It doesn't and shouldn't make any difference at all do the proper functioning of an appliance.

If an appliance you (recently purchased, older appliances may not have the same quality standards!) purchased has only a two prong plug, then it is essentially assured to not be an electrocution hazard in the case of an electrical fault, or it is not capable of having such a fault.

So basically what I am saying, the appliance you are talking about would never have been grounded anyway if it has a two prong plug. Grounding has nothing to do with the failure of your appliance.

You must have misheard because perhaps the tech support person meant to say "Ungrounded Neutral" which potentially could be a problem for sensitive electronics. The neutral (connected to the center tap in the main panel) can and does carry an electrical charge, so the neutral bus bar should be grounded to the outside through the use of a grounding rod to bring Neutral to Earth Ground.

If your home was built in 1959 then it is possible that the grounding rod was never placed deep enough into the earth to provide proper grounding, or perhaps it rusted away over time. How far the grounding rod needs to go depends highly on the region you live in too. I used to live in a home built in 1958 and had a similar problem. A qualified electrician would be able to fix this for you, or an adventurous DIY'er.

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"Grounded neutral" was written in the email. But thanks for the info. My system is grounded to water pipes, I don't have a grounding rod. Though looking at the primary grounding point, it looks a bit corroded. (Replacing previous incorrect comment) –  Aric TenEyck Mar 6 '13 at 4:45
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@AricTenEyck Grounding your system to your water pipes is not the ideal way but it I do believe it was an acceptable way in the 50's. A corroded point doesn't make for good low resistance grounding. Try to replace the grounding point for a quick fix. –  maple_shaft Mar 6 '13 at 9:51
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The equipment grounding conductor (EGC) will not cause the breaker to trip if a fault energizes an appliances chassis, it will however, give the electricity a safe path to follow. –  Tester101 Mar 6 '13 at 12:00
    
@Tester101 If the ground is proper, has little resistance and shorts the circuit then enough current will flow to cause the breaker to trip. –  maple_shaft Mar 6 '13 at 12:47
    
@maple_shaft Maybe. It depends where the fault is. –  Tester101 Mar 6 '13 at 13:25

Was your main panel added afterwards, when A/C was added, making the original main panel a sub panel? If so, it must currently have separate and independant neutrals and ground buss bars.

A quickie (and safe) solution for 2 wire circuits without grounds is to add a GFCI at that outlet. Its slightly more difficult when there are continuation circuits. I would suggest adding them to the LOAD side and protect them as well. If you are not absolutely clear about proper installation, get a licensed electrician to install it.

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That's possible, though the main panel is right where electricity comes to the house, and the conduit leading from the main panel to the subpanel is installed in a way that it's obviously not original - It runs along the ceiling of a laundry room that used to have drywall on the ceiling and doesn't anymore. On the other hand, it seems odd that they'd install the subpanel, move the 2-wire circuits, and not upgrade them to grounded. Old houses can be an enigma... –  Aric TenEyck Mar 6 '13 at 16:15
    
Was thinking they did it that way to NOT disturb the 2 wires, in effect adding the new main panel UPstream from the old. –  HerrBag Mar 6 '13 at 16:44

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