Adding ground wire to old 2-wire lighting circuit (Resid

[mhauer]

I am a new owner of a 1955 house who happens to be an electrical engineer, but by no means an electrician and I could use a little advice. I apologize in advance for the long post, but I want to be clear.

My house is a mixture of grounded and un-grounded branch circuits. The 15-Amp lighting circuit, which runs all through the attic, has 14-AWG two-wire NM cable (with no ground wire). I would like to add an equipment ground to some of the cases of the new fluorescent ceiling lights I have installed in the kitchen and laundry room.

I noticed that there is an uninsulated ground wire just freely running through my attic (it's not inside an NM cable; it looks like a fairly low-gauge copper ground wire made of two or three wires twisted together). It's looks pretty wimpy and all alone up there. This ground wire must somehow be connected to the ground wires from one of the circuits running in the walls or under the house, where there are grounded circuits. The prior owner must have done this when they remodeled the bathroom and needed to have a ground wire to connect to the new bathroom outlets (because that is where this ground wire is presently going).

So my question is, can (or should) I just connect another uninsulted copper "ground" wire to this existing one and run it over to my lighting fixtures in the attic? Ideally, I would like to just replace the entire lighting circuit with new NM cable all the way back to the service panel, but I am not certain how to "fish" the old NM cable going to the panel out and replace it with a new one. If I could just get a new NM cable from the panel to the attic, the rest would be easy to replace and clean up (the current cables are just strewn about through the attic without being properly stapled down and many of them are showing their age).

So,
1) Can I just connect the light cases to this existing ground wire from one of the other circuits in the house?
2) How difficult is it to add a new cable from the outside service panel running up through the wall and into the attick?

By the way, the urgency for wanting to ground the new fluorescent lighting cases is because it turns out that if you don't ground the cases, they emit some leakage radiation that produces about 60 volts AC between the case and ground (I see the 60 V if I connect one voltmeter probe to a screw on the light case and the other into the neutral or ground plug of an outlet that is on a separate grounded circuit). I talked to the ballast company and they said this is exactly what happens when you don't ground the case and that it is within the UL safety limits (i.e., if you touch the case and ground you will feel a buzz but you won't pass out). However, they told me I really need to ground the case because the ballast circuitry only functions properly when that ground is present.

Thanks in advance for any advice.

Michelle

 

[Ed MacLaren]

Re: Adding ground wire to old 2-wire lighting circuit (Resid

I would temporarily use the existing bare equipment grounding conductor to "ground" your new fixtures until you can get the new NM cables installed, and the sooner the better.

It is important from a safety aspect to get rid of that enclosure-to-ground voltage immediately, especially if it actually is 60 volts.

With regard to the problem of "fishing" the new cables in, an experienced electrician should be able to do that without great difficulty.

Ed

[ March 24, 2004, 05:04 PM: Message edited by: Ed MacLaren ]

 

[pierre]

Re: Adding ground wire to old 2-wire lighting circuit (Resid

Not to contradict Ed, without really knowing where that so called grounding conductor in your attic is going to I would not waste a nickel of my time with it. I would hire an electrician or try to install new circuit(s) pronto. If you can get one circuit up there, you can bring as many as you might deem necessary. To me it is even worth making holes (preferably in the closets) to help snake the NM cable to the attic. But I would really let the electrician make the connections.

Pierre

 

[hbiss]

Re: Adding ground wire to old 2-wire lighting circuit (Resid

...I see the 60 V if I connect one voltmeter probe to a screw on the light case and the other into the neutral or ground plug of an outlet that is on a separate grounded circuit.

As an EE you should realize that your DVM has a high impedance input and will give information that is misleading in cases like this. Though it may show 60VAC, add any resistance (like a human body) across your measurement points and it will drop to zero. There is just no current there. Wave your unconnected test leads around in the air so they will pick up some AC hum and you get the idea. I and many others in the electrical trade won't use such meters to check for wiring problems because the normal capacitance between conductors can cause abnormal readings. Anything we use will load the circuit.

As to the ballast manufacturer stating that "if you touch the (ungrounded) case and ground you will feel a buzz but you won't pass out", well, that's the stupidest thing I have heard in a long time and probably not the smartest thing he could have admitted from a company liability standpoint.

Keep in mind that there are a lot of flourescent fixtures sold with two- wire line cords and these obviously have no equipment ground. They use the same ballasts and operate just fine and are not a shock hazzard.

That said, (in an effort to lessen your immediate fears) yes, your fixtures should be grounded but it must be done properly. I would contact an electrician and get their advice about cleaning up and replacing your wiring and possibly your service. Sounds like nothing has been upgraded since 1955 and a DIYer has been messing around. I think your light fixtures are the least of your problems.

You sound like you are (rightly) concerned about the condition of your electrical system. For your own peace of mind and the safety of yourself and your family leave it to a qualified contractor, don't try to handle it yourself.

-Hal

 

[rhombus65]

Re: Adding ground wire to old 2-wire lighting circuit (Resid

I think you should consider as previously stated replacing some of the two wire circuits if you are really concerned.

There is no code reason to replace them other than perhaps the fluorescent light manufacturer installation instructions stating that the fixture must be grounded which most manufacturers do say.

If you choose to run a separate ground wire you need to consider the fact that the code requires the ground to originate at the loadcenter or at your water piping system within 5' of where it enters the dwelling.