What is a 'grounded neutral' and how bad is it?

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

Is it possible that the polarity is reversed at your outlet? Are the hot and neutral switched in the service panel (neutral connected to the breaker, hot connected to the neutral bus). If so, maybe their reference to "grounded neutral" was an unclear reference to the grounded conductor being connected to the wrong end of the circuit inside your device?

If the device had a two-prong outlet, as @maple_shart said, then grounding is not your issue, presuming that's the correct plug for the circuitry in the device (is it UL listed?).

If the plug is polarized (one prong is wider than the other), then the device is sensitive to the polarity of the electrical supply in some way, possibly because it only has a single-pole switch making it unsafe for humans if the neutral is switched instead of the "hot" conductor.

If the plug is not polarized (both prongs are the same width), then the device should not be sensitive to polarity.

Every correctly-wired neutral is a grounded neutral. The neutral is the grounded conductor. Even if you're talking about a subpanel with the grounded (neutral) and grounding buses unbonded, the neutral and grounding buses are (supposed to be) bonded in the main panel, and the grounding bus in that panel is supposed to be bonded to grounding rods and/or water pipes (as appropriate, for anything new it should be a couple of grounding rods, and also your water pipes if they are metal, so that they don't end up accidentally energized with no safe current path). But even if the neutral isn't grounded at your main panel, it's grounded at the power company's transformer (that bare copper wire running down the pole from the transformer to a ground rod at the base of the pole).