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rdag · Jul 22, 2007, 01:19 PM

I am doing minor rehab in my loft that requires some wiring changes, and I discovered an odd (to me) wiring condition for the air conditioner. Here is what I found. At the panel, I found a 30amp 240 breaker with a blue wire and red wire and with a white wire neutral. This is delivered in metal conduit so there is no ground wire. At a junction box between the panel and the AC, I found the red and blue and white wires from the metal conduit but they are connected to two NM cables - one is a # 10 and the other is a #12. The black and white #10 wires are connected to the red and blue (also #10). The #12 neutral is connected to the #10 neutral. And the NM ground wire is not connected to anything. Question: is this OK (if the ground wire is connected to the metal junction box)? Or do I need to have the two NM cables replaced with a #10 3 wire NM cable with ground. This will require going through the roof membrane, which would I would rather not do if not absolutely needed. Help!
Thanks

tkrussell · Jul 22, 2007, 01:37 PM

So the 2 wire # 12 is only using the neutral? This goes to the end with the #10 cable?

Conduit is allowed by code as an equipment ground. Not saying that is how I do new conduit, but it was popular in older buildings. Any bare or green grounds should be connected to any junction box. Best to use machine threads into the threaded hole in any metal box.

I would rather see a hot in the #12 than the neutral, if these two cables must remain. Would be better to have a 3 wire with ground cable, but if the neutral can be swapped with a hot in the other cable, and keep both cables closely wrapped together the entire length, then you may be able to get away from replacing the cables.

Any cable through a rubber roof should use a raceway to pull wires through. Flexible Liquid Tite or PVC is popular. Allows for easy replacing of wires if needed.

rdag · Jul 22, 2007, 01:54 PM

Originally Posted by rdag

I am doing minor rehab in my loft that requires some wiring changes, and I discovered an odd (to me) wiring condition for the air conditioner. Here is what I found. At the panel, I found a 30amp 240 breaker with a blue wire and red wire and with a white wire neutral. This is delivered in metal conduit so there is no ground wire. At a junction box between the panel and the AC, I found the red and blue and white wires from the metal conduit but they are connected to two NM cables - one is a # 10 and the other is a #12. The black and white #10 wires are connected to the red and blue (also #10). The #12 neutral is connected to the #10 neutral. And the NM ground wire is not connected to anything. Question: is this ok (if the ground wire is connected to the metal junction box)? Or do I need to have the two NM cables replaced with a #10 3 wire NM cable with ground. This will require going through the roof membrane, which would I would rather not do if not absolutely needed. Help!!
Thanks

Thanks for the quick reply. I will replace the NM cables with three wire cable with ground. I assume that I can still connect at the existing junction box without any problem. Correct?
Thanks

tkrussell · Jul 22, 2007, 02:48 PM

Correct.

labman · Jul 22, 2007, 03:01 PM

Before I rewired, I would check to see if the neutral is actually being used. Most condenser units are all 230 volt.

acetc · Jul 22, 2007, 03:31 PM

At what point of amp draw or horse power do you have to use a ground wire in lu of metal conduit as the ground?

Stratmando · Jul 22, 2007, 05:23 PM

Many don't need Neutral to Compressor Unit. Cap off. Both ends. Pull a ground for everything, keeps it from becoming live.

Update, Identify white wire with green tape, and use that for ground, at both ends. You are not using it anyway.

thumbs · Jul 24, 2007, 12:23 AM

Originally Posted by rdag

I am doing minor rehab in my loft that requires some wiring changes, and I discovered an odd (to me) wiring condition for the air conditioner. Here is what I found. At the panel, I found a 30amp 240 breaker with a blue wire and red wire and with a white wire neutral. This is delivered in metal conduit so there is no ground wire. At a junction box between the panel and the AC, I found the red and blue and white wires from the metal conduit but they are connected to two NM cables - one is a # 10 and the other is a #12. The black and white #10 wires are connected to the red and blue (also #10). The #12 neutral is connected to the #10 neutral. And the NM ground wire is not connected to anything. Question: is this ok (if the ground wire is connected to the metal junction box)? Or do I need to have the two NM cables replaced with a #10 3 wire NM cable with ground. This will require going through the roof membrane, which would I would rather not do if not absolutely needed. Help!!
Thanks

Maybe, if it ain't broke, don't fix it.

The by the book method would be to run a 10/3 with ground from the JB to the AC.

But if you want to avoid going to the roof... I would leave both of the blue and red hot wires connected as is through the #10 bk & wh wires since they are properly rated for the load.

Originally Posted by tkrussel

I would rather see a hot in the #12 than the neutral, if these two cables must remain.

That would seem to be dangerous and non-code afaik. Running one of the 30A service wires in the conduit to a single #12 in the NM isn't right, as the #12 is only rated for 20A.

If the AC is purely 230 v without any 115v taps then I suppose the existing neutral is needed. But if it is, doubling up on the #12 wires would be safe, since 2 #12 can carry a 30a load without a problem. But it may be that the white neutral isn't carrying anyload anyway. This might not be strict code, but it would be safer than using a single #12 if there is any significant amperage flowing on the neutral.

To do it this way, wrap white tape on both ends of the #12 bk NM at JB and AC. Then double up the #12 wh and now wh(bk) wires and in the junction box connect them both with a wirenut to the #10 wh from the conduit to the panel. Connect both of the NM ground wires to the conduit-grounded JB.

At the AC, either connect both wh and wh(bk) to the neutral buss or perhaps better yet, add a #10 wh pigtail and connect 1 end to both of the #12 wh and wh(bk) with a wirenut. Connect the other end of this #10 pigtail to the AC neutral. Also at the AC, connect both NM ground wires to the AC ground.

labman · Jul 24, 2007, 04:40 AM

Originally Posted by rdag

Thanks for the quick reply. I will replace the NM cables with three wire cable with ground. I assume that I can still connect at the existing junction box without any problem. Correct?
Thanks

If you need the neutral, I hope you did go ahead with the 10-3 as tkrussel said. Going by what he has said before, it is the only way to meet code. The twined 12 likely is neither needed or acceptable.

Along with Stratmando, I still think you shouldn't need a neutral unless somebody has substituted a 115 volt component for the original 230 one. It is common for ranges and driers to need neutrals, but not common for outside A/C compressor units.

Stratmando · Jul 24, 2007, 05:29 AM

Double up the #12 wh?
You can Parallel Conductors less than 50 volts, or Larger than 1/0.
If a #12 anywhere in there needs to be on 20 Amps, #10 will can be 30 amps.

rdag · Jul 24, 2007, 05:42 AM

Thanks to all of you for suggestions. I went to the roof, check the wiring, and found that the ac condenser does not have a neutral - the white #12 was capped as was the black #12. Who knows what the person who did the wiring was thinking. So, I am all set - I keep the #10 from the condenser, properly mark the neutral black at both ends, connect it to the #10 red and blue at the JB and I am set. All is fine with the grounding.
Thanks.