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adm060306 07-07-2007 07:34 PM

Reverse Polarity at the Subpanel
 
Hello.
I have upgraded the electrical service in my home recently and have experienced no problems. I recently decided to complete the project by replacing the subpanel in the garage with a Cutler-Hammer 100 A subpanel. I did not replace the 12 gauge buried (hot and neutral) conductors, but opted instead to drive a 8' long copper rod into the ground near the garage. I was careful to separate the ground and neutral bus bars to eliminate the chance of touching. The problem started when i turned on the breaker at the Service Entrance Panel. I checked the receptacles with a plug (indicates with 3 lights whether i wired it correctly) and the lights indicated that the hot and neutral were reversed. I checked all the receptacles from the subpanel on and found no problems. I took a voltmeter and found that there was 120 VAC potential between the ground and the neutral, 0 VAC potential between the hot and ground, and 120 VAC potential between hot and neutral. I went back to the SEP and found no wire installation issues. I then changed the neutral wire from the neutral busbar to the hot lugs and the hot to the neutral wire and experienced the exact same thing. It appears that the hot stays on the neutral busbar no matter how i configure the 2 wires from the SEP. I believe i grounded everything correctly. I have not been able to find any reference to indicate anything i have done wrong. What could of caused this and how can i fix it? Also what is your opinions on installing a second ground at the subpanel to ensure that the subpanel and the branch circuits after the subpanel are grounded for safety. I appreciate your responses.

wiremeup 07-07-2007 08:45 PM

Questions:
1. Are you running 120 or 240 volts from the SEP to the sub?

2. Are you checking the voltage with all the breakers off in the sub?

3. What size breaker in the SEP is feeding the garage?

adm060306 07-07-2007 11:58 PM

Thank you for replying.

1. The wire from the house to the garage consists of two conductors; one hot and one neutral. Consequently, the voltage is 120 VAC and not 220 VAC.

2. Yes. I have checked with the subpanel breakers in a open and closed position. The odd thing regardless of the position of the subpanel breakers is that the neutral busbar in the subpanel remains "hot" while the "hot" at the lugs remains neutral no matter if i switch the wires around in the subpanel.

3. 20 Amp.

wiremeup 07-08-2007 10:45 AM

So there is no ground wire coming from the SEP? Any way you can take some pictures of the wiring in the sub?

adm060306 07-08-2007 01:08 PM

1 Attachment(s)
The picture of the subpanel is attached. The main power and neutral wires are not connected in this picture.

terrynistler 07-08-2007 01:31 PM

How are you testing that the Hot bus is nuetral? and the nuetral is hot?

adm060306 07-08-2007 03:01 PM

I initially tested in with a plug in circuit tester that alerted me to the hot and neutral being reversed. I then tested the wires at their initial configuration by using a volt meter. I measured between the neutral busbar and the ground and got 120 VAC. I measured between the neutral and the hot wire and got 120 VAC, but got 0 VAC between hot and ground. I then switched the configuration of the wires and got the same results. I then removed them from the lugs and tested them. I got 0 VAC between the hot and the neutral which may be a key.

dmaceld 07-08-2007 03:45 PM

Quote:

Originally Posted by adm060306 (Post 52132)
I initially tested in with a plug in circuit tester that alerted me to the hot and neutral being reversed. I then tested the wires at their initial configuration by using a volt meter. I measured between the neutral busbar and the ground and got 120 VAC. I measured between the neutral and the hot wire and got 120 VAC, but got 0 VAC between hot and ground. I then switched the configuration of the wires and got the same results. I then removed them from the lugs and tested them. I got 0 VAC between the hot and the neutral which may be a key.

I think your neutral is broken between the SEP and subpanel. Reverse the wires in the SEP for a test. If the white wire, when connected to the circuit breaker in the SEP, is not hot at the sub, then that would confirm it's broken. The way it is now, when you swap the wires just in the sub, any thing that is switched on in the garage will feed the 120v to the neutral so it, and the hot wire, will both show 120v to ground.

One of those yellow wires isn't the feed from the SEP is it? The reason I'm asking is those are NM and not UF, and the buried wire needs to be UF.

I would suggest you consider upgrading the feed from the SEP to the subpanel and bring 240v to the sub. If you are more than something like 50' from the SEP to the sub you can have voltage drop issues with 12 ga. I see you have 3 breakers in the sub. You really aren't gaining anything by having the sub with 3 breakers over having everything in the garage on just the one 20 amp circuit from the SEP.

Stubbie 07-08-2007 04:37 PM

Edited last reply on rereading your post......

One question you said that you had this sub-panel hooked up and powered up and this.......

Quote:

I checked the receptacles with a plug (indicates with 3 lights whether i wired it correctly) and the lights indicated that the hot and neutral were reversed. I checked all the receptacles from the subpanel on and found no problems
.

Where are the receptacles your checking that are showing hot neutral reversed?? This sounds like the receptacles your talking about have nothing to do with the sub-panel. If they are powered from the sub-panel then are we only talking about a couple receptacles that are showing hot neutral reversed and the rest are ok?
Are the receptacles on the same circuit?

Did anything work when plugged into these receptacles?

Could be we are spinning our wheels fooling with that sub-panel.

Stubbie

adm060306 07-08-2007 10:13 PM

I apologize on the mistake. I meant that every receptacle after the subpanel in the garage all showed the same problem. There are 3 branch circuits after the subpanel and each circuit has the same problem. For safe measure i checked some receptacles in the house to be sure that the problem is isolated at the subpanel. I switched on the lights and they worked and i also plugged in my old radio and it worked as well.

Dmaceld,
I don't clearly understand how i could be getting 120 VAC potential at the neutral busbar no matter the configuration of the two UF wires coming from the SEP. It does make sense that when i switch on the lights and plug in the radio it appears that i have no problem. The three breakers was just a means to get the branch circuits isolated, so if i can shut off a breaker (i.e. a branch circuit that goes to a gazebo) to work on a circuit.

Thanks for the responses.

dmaceld 07-08-2007 11:24 PM

Quote:

Originally Posted by adm060306 (Post 52132)
I then removed them from the lugs and tested them. I got 0 VAC between the hot and the neutral which may be a key.

What do you get between each one and ground? If both are showing 120v to ground then that would be why you show 0v between them. That would indicate pretty strongly the wires are shorted somewhere between the 2 panels with a high resistance short. Regardless of how high the resistance of the short is, 120 volts will be impressed on both wires if there is no other current flow path available. How old is the UF wire? Does it have a ground wire in it? The UF cable might be leaking between the two conductors. Both wires of the UF are connected correctly in the SEP and in good condition at that end, right?

For good measure, double check to make sure you have 0v between neutral and ground back in the SEP. Of course you will if both neutrals and grounds are on the same bar.

Stubbie 07-09-2007 04:17 AM

I take it that before you installed this new panel that everything worked in the garage from the old panel? I'm going to assume that is a yes.

I don't see any uf just yellow nm-b. So where in the picture is the feeder entering?

One thing I would check and thats the clamp coming into the new box that has the feeder from the main panel. Is that clamp sharing a branch circuit cable with the feeder?

Make sure you haven't tightened that clamp to where it has damaged the cables and is causing the white in that branch circuit to be energized by the feeder hot. Look at the cables very closely sometimes it is not obvious.

That is about the only thing you could have done that would have caused any wild strange kind of wiring problem. Not likely but check it. Normally when this happens the breaker back in the main trips but maybe you have a really odd set of circumstances like cutting the feeder neutral and feeder hot shorting to the branch circuit neutral. This would backfeed the neutral bar and all the branch circuits.

See what you find then we will go from there.

One last thing what are you using for your ground path when you test? The equipment ground wire in the feeder or are you not connecting the feeder ground wire and just testing to the ground bar and using the earth ground provided by the ground rod and gec you installed?


Stubbie

adm060306 07-09-2007 08:41 AM

Both wires are connected correctly at the SEP. The UF cable comes in from the bottom of the subpanel. It has 2 wires and no ground. I installed an 8' rod ground at the garage and grounded the subpanel to the 8' rod at the garage. If the feeder from the SEP had a ground i would use that rather then adding a second ground at the subpanel. I test the neutral busbar to this ground. When it was terminated at the SEP the readings i expressed earlier is what i continue to get. I still don't understand why the neutral busbar keeps showing potential no matter how i configure the two feeder conductors.

HouseHelper 07-09-2007 09:06 AM

First off, grounding the subpanel the way you did does NOT provide an effective ground path back to the SEP. You must have a third wire (grounding wire) or bond the panel and the neutral (only if it is a detached building and there are no other metallic paths between the two).

Is it possible you drove the new ground rod in the same area the old UF cable runs? Everything I see from your description points to a hot grounding conductor. If you run an extension cord from a receptacle in the house that checks good and use that ground as a reference when checking the hot, neutral and ground at the subpanel, it should tell us (and you) a lot.

Stubbie 07-09-2007 01:58 PM

Thanks Househelper

You saved me some typing. I looked closer and thought I could see the uf coming in at the bottom but I couldn't make out the ground wire in the feeder. Also by the way the op was describing his understanding of grounded got me wondering about what he was actually measuring for his ground reference. So I asked and you verified it. As you I'm trying to figure out what he could have done that is causing his problem. Good catch on the ground rod possibly penetrating the buried UF.

Way back in the thread ...wiremeup actually discovered there was no feeder ground and the op replies verified it. I suspect you caught that. So should have caught this but I just read over it. Sometimes we miss things skim reading. Bad habit. Anyway credit where credit is due.

adm:

Now that we know you have no equipment ground in the feeder you have no choice but to run a new UF cable with ground. Abandon your existing uf and run a 120/240 4 wire feeder to the panel so that you have an effective ground fault path. You need 2 hots, a neutral and a equipment ground wire in the feeder. What you have now is not going to allow a breaker to trip in the sub-panel nor will the feeder breaker trip in the main in a ground fault condition. The ground rod is not needed if this is an attached garage but Househelper has already touched on this.

You are confusing the grounding electrode system with the equipment ground, these are completely different systems that serve different purposes. We can explain if you like, so ask if you need clarification on the differences.

Until you get a new feeder your losing energy chasing your existing problem. If this is an attached garage forget the ground rod and disconnect it from the panel. If you don't have a ground rod at the service panel then you can add one there if you like. You cannot keep what you have now. What was existing is no longer existing when you installed that new panel and you must run a feeder that is up to present code.

As for the problem feeder you have now a pretty good way to see whats going on with it would be to do a continuity check and this would get you away from all the confusing voltage readings. However I think what househelper suggested would straighten these readings out to where they made more sense. And I agree with him that you have a problem with the hot wire in the feeder. May not tell you 100% where the problem is but will satisfy your curiousity.

Please do not use a digital volt meter these are not the best for house wiring, use a analog multimeter or wiggy or a simple two wire light tester.

When you get the new feeder ran you will still keep the neutral and ground seperate in the sub-panel.

I've been reading this as an attached garage so that would be nice for us to know. I still won't change what I suggested though about the new feeder.

Things are never as simple as they seem in this electrical trade so when you start the new feeder open a thread and tell us if you are going to direct bury again or wires in conduit. There are things your going to have to know to be compliant with code.

Stubbie


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