Hello,

I have searched and read as much as I can on this subject, but I have not found the answer as yet... I know ground and neutral are so misunderstood, but I think I have a good grasp of the basics.

My problem is in a 50 year old house, which had no ground originally, but had it added sometime in the last 20 years. There is a ground rod driven below the meter, with a thick cable which terminates to the inside of the main disconnect box by means of a grounding lug. It is NOT bonded to the neutral bus bar in any way that I can see...

There are a lot of white and green wires terminated to both sides of the breakers on the neutral bus bars (alot of which were run by me using 12/2 0r 14/2 NM cable) My problem is this: when trying to tap off a little used circuit to feed exterior security lights I received a shock and some nice arcs when the bare copper ground wire from the NM cable touched the conduit. I checked with a voltmeter and there is about 45 volts between the two, and also between the neutral and the ground...

I hope that all makes sense; my questions are: Shouldn't the ground wire in the main disconnect be bonded to the neutral bus bar NOT the metal box? Do I have a short somewhere? Did older houses use the metal conduit as the ground?

There are more details (and weirdness) if anyone wants to try to help me out...

Thanks in advance!


Tom

Some additional info:

I have checked a bunch of the original outlets throughout the house - none of them are grounded via a separate ground wire, yet I get 120 volts across the ground hole on the plug and hot (the receptacles are all 3 prong)

Is this a problem since all new receptacles are grounded back to the main disconnect (which is not bonded to neutral)? Does this create multiple ground paths?

Any help with this would be greatly appreciated!


Tom

You may have a short of some type, Put a meter where you are getting a shock(ground and the conduit), turn breakers off 1 by 1 until that votage is gone, trace out that circuit(s).
Conduit and sround need to be at same potential. Find the problem first.
Ground and Neutral need to connect at the service.

I don't think anything is wrong, here's why:

1. I'll bet if you look really hard, you should find a green screw in the neutral bar. Look and report back.

2. You lifted the ground off a live circuit. Correct? What kind of devices were on that circuit? TV? Grounded devices with 3 prong plugs? Computers?

3. The metal box that the outlet is connected to is grounded, thus the third prong will be grounded by the screw. This typically is not a good idea. Ground should be made to the outlet and then pigtailed to the box. In a retrofit, it's sometimes tough to do.

Ok, some updates:

There is no green (or any other color screw) in either neutral bar. I removed the bar which bonds the two neutral/ground busses, and both the left and right side slide freely up and down in the box in a plastic "track"...

As for the ground the really weird thing is that is was new bare copper from the NM cable I ran for the lights. There are 3 ground wires connected together wit a wire nut, and on the other end they all terminate by being hooked up to typical motion sensitive security lights...

Any way to "test" if the neutral and ground are bonded in the box? Is it OK to continue to use the conduit as "ground" and pigtail a wire from the outlet to the box as suggested, OR is it better to pull a ground wire back to the box for each receptacle that needs it (not very practical, but probably a good idea wherever I have PCs or A/V equipment)

Lastly (for now) should I do anything with my ground? Test the rod, or have a new one put in? Someone suggested that it is probably inadequate due to the level or expertise demonstrated by the existing electrical work...

Thanks for your time!


Tom

It's time to post a couple of pictures. The inside of the disconnect and the inside of the fuse box.

Use Go advanced/Manage attachments

Quote:

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Originally Posted by jtn11

Ok, some updates:

There is no green (or any other color screw) in either neutral bar. I removed the bar which bonds the two neutral/ground busses, and both the left and right side slide freely up and down in the box in a plastic "track"...

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If this is the case, then all grounds shoud go to one bar and all neutrals to the other. If, indeed the ground/neutal bond is done at the disconnect. There should be a number of connections to the REFERENCE

1. a ground rod (mostly for ligtning protection
2. The neutral bond
3. The plumbing bond if copper plumbing (equipotential bonding)
4. The telco and cable ground for lightning protection

Quote:

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As for the ground the really weird thing is that is was new bare copper from the NM cable I ran for the lights. There are 3 ground wires connected together wit a wire nut, and on the other end they all terminate by being hooked up to typical motion sensitive security lights...

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[quote]
I can't picture this and I'm not sure which end your talking about



Any way to "test" if the neutral and ground are bonded in the box? Is it OK to continue to use the conduit as "ground" and pigtail a wire from the outlet to the box as suggested, OR is it better to pull a ground wire back to the box for each receptacle that needs it (not very practical, but probably a good idea wherever I have PCs or A/V equipment)


The protective ground is usually the conduit. If you want to, you can purchase orange outlets which have an independent ground. The ground screw is NOT attached to the box. It's just attached to the ground prong on the outlet. Conduit is not used very much in residential applications.

Testing whether the ground is bonded to the box or disconnect is usully difficult. What can be done is the ground current can be measured and there should be very little. If it's not bonded, there will be appreciable ground current. There is a specific clamp on meter designed for this purpose.

Quote:

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Lastly (for now) should I do anything with my ground? Test the rod, or have a new one put in? Someone suggested that it is probably inadequate due to the level or expertise demonstrated by the existing electrical work...

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You might have an experienced electrican look at it. This is why I'm advocating posting a couple of pictures. Resizing pics can be done with the free program IrfanView - Official Homepage - one of the most popular viewers worldwide

Here is a picture of the ground bonded to the electrical box; also a picture of the entire box...

To clarify things a bit: The branch circuit from the box which I was trying to tap off has one white wire and one black wire in a metal box with metal conduit. I added three light switches to the box, and ran 3 red wires for hot for the lights. Four new romex lines were run to this box from outside the house and terminate outside with typical security lights; grounds were attached to the grounds on the lights. Back in the box the neutral wires were all wire nutted together, as were the ground wires. The hots were separate, and connected to their respective switch (red) wires.

Now everything worked fine, but when closing up the box I accidentally touched the bare copper ground wires from the romex cables to the metal box and got a shock plus some sparks. A voltmeter across the box and ground wires read 45 volts (steady) and also 45 volts across the ground and neutral. I separated the grounds and tested again two had around 16-17 volts; the other two had 4-5 volts. I also disconnected all the lights - same result.

What I have done is run a new branch circuit with ground to the box and disconnect the old line. I also replaced the breaker as it was an older twin 20 amp breaker and the line is only supposed to be 15 amp. I am still wondering what to do about my ground in the box though; should I move it onto one of the ground/neutral bus bars?

Any other questions or comments?


Thanks!


Tom

I would reinstall the Neutral Jumping bar, and with power off, Leave whites intact on both sides, then add a ground bar, and connect all of the Greens, and your big green to that as well.
Neutral and ground only connect at 1 spot, service or panel, not both.
Do you have a disconnect?

No, that is the main breaker box; on the wall outside the box is the meter.

Should I just put the ground wire (the one with green tape) onto the neutral bus bar? What about the breaker box then (and all of the conduit), should a short wire go from the neutral bus bar back to the metal breaker box?

I'm just as confused as you are right now.

The green wire goes to the ground rod, correct?
If the plumbing is copper, is there a ground to the plumbing system?

What is the model number of the panel?

Do you have a link to the manual?

Can you measure the voltage between the green taped wire and the neutral bus?

Turn on a heavy 120V load like on 1,5,9, 13 etc. Something that would be unbalanced and measure it again?

Your breaker numbers are strange.

I think something isn't right as well. I'm thinking on the lines of find the manual for the box and/or contact the manufacturer for suggestions on how to create the neutral to ground connection.

Meanwhile get back to us. I'm thinking like Strat and you at this point.

The breaker numbering can be corrected easy enough by relocating.
Try measuring voltage between the left neutral and right neutral bar. Or
Does it look like there is a hole in the end of the neutral bar that goes through the panel.
This may use the little copper piece that may screw in where you have the ground attached, then into the closes hole on neutral bar?

I re-arranged the breakers recently when tidying up the wires and have not re-numbered them as yet...

There is no hole or any metal that goes through the neutral bars into the panel... As I mentioned before if I remove the bar across the 2 neutral buses both of them move freely up and down in their plastic tracks, so it does not seem they are attached in any way to the box.

The green taped wire goes to a ground rod right outside the wall below the meter. There is a wire between the ground rod and water line also...

The voltage between the green taped wire and the neutral bus bar is 0. The voltage between the 2 neutral bars (with the connector removed) is also 0. The voltage between the ground wire and neutral under load (~35 amps) is still 0.

On the diagram for the box you can see on the left neutral bar the place where they show the ground should be bonded; this is a removable lug which I have taken off for now. I can just put that lug back on the neutral bar, and move the green taped wire to it; but what is your opinion of the question of my conduit and older outlets not being grounded anymore?

See the "Bond - when required"? There should be a machine scre in that hole bonding the bar to the case. That's the missing piece of info. At least that's how I read it.

Otherwise, it means it's suggested to use that hole when bonding to the box.

So, it's either:

1. There is a tapped hole there (Bond-when required)
2a. Connect green taped wire to left Bus Bar
2b. Connect lug where green taped wire was to (Bond-when required) hole.

But you said that both bars move. Confused. Checked for a tapped hole there, otherwise use method #2.

And the green taped wire should go to the lug on the left.

Zero volts can indicate that it's bonded or that it's open. Since you said it's zero, it's safe to do an ohms measurement, so do that.

2b. Answers the question about the conduit not being bonded anymore. They will be if you bond the bar to the box.

The bar is a better method because higher surges can be handled by the bar.


Unfortunately, we don't know what's going on in the meter socket, if anything.

I removed the neutral service wire and lug from the neutral bus bar, as you can hopefully see in the picture below there is no hole or screw to "bond" it to the metal case. Also they both move freely up and down so it is unlikely that they are attached to the box.

I think I will just do the following: attach the green taped ground wire to the bottom of the left neutral bus bar via the previously pictured lug. I will then jump a short wire between the ground lug bonded to the box and the right side neutral bus bar. Sound good?

As for the ohm measurement, I got mixed results, so I don't know if I was doing it correctly: with my meter set to 200 ohm limit, I received readings which varied from 80 ohms to as low as .3 ohms, is this normal? Main power was switched off, any other things to look for when testing ohms?

Thanks again for the help, there is still the mystery of the "phantom" voltage, but one problem at a time I guess...



Tom

1st two paragraphs sound OK.

3rd paragraph is probably OK, since zero doesn't really exist in this case.

4th paragraph. Phantom voltages. Here is a good example of one and probably not what happened in your case. Some electronics use switching power supplies and have "filter caps" going to ground. Capacitors are not perfect and the meter impedances are high, therefore if ground is lifted and you have a "filter" on one of the devices, you can see nearly 1/2 of the supply voltage on the ground leg. Typically, though this sort of voltage doesn't spark for as soon as you put an appriciable load on it, the voltage disappears.

Just to be clear, I put the neutral service wire back, I removed it just to see what was underneath.

I just finished "bonding my neutral and ground in the box" and WOW what a difference: my computer is faster, A/C is cooler...

Just kidding! I did buy an outlet tester and found 3 hot-neutral swapped outlets around the house...

I will follow up regarding the voltage after more testing.

You could measure the voltage at the panel, then go through house and look for those numbers between Hot and Neutral, and Hot and ground, should be about the same.

YES! The ground wire needs a path to the neutral/ground buss - instead of to the box it should be connected directly to the ground/neutral buss, which whould then be bonded to the service box with a green screw. YOU HAVE NO PROPER GROUND until that is done. Shut off the main power before you make the change. When you turn on the power touch the main breaker, then look away (for safety) and throw the breaker back into service. Another breaker may trip which will be the problem area.

With 45 volts between the conduit and any wire, you likely do have a short somewhere in your house so proceed carefully.