Sub-panel Wiring Problem

[Eric Porter]

Before purchasing my home, I had the builder install a sub-panel in the basement. The two hot feeder wires are #2 Al and the one neutral is #4 Al, its just a 3 wire feed. The feeder wire runs about 40 feet in pvc counduit from the main panel in the garage to the basement. The feed is protected by a 100amp breaker in the main panel. The sub-panel was only a 40 amp generator feeder with 8 slots (probably the cheapest thing the builder could buy). I have removed it and bought a 22 slot 100 amp panel.

After reading lots, and lots, and lots of posts about sub-panel installations I am concerned and confused with what the builder did, plus I know he did it after the electrical inspection. My questions are below.

1) From everything that I read, since the panel is in an attached building he should have run a 4 wire feed from the main panel to the sub-panel 2-hots, 1-ground, and 1-neutral, is this correct?

2) Even if a 3 wire feed is okay, I don't think a 100amp breaker in the main panel is up-to-code. I think it should be at max a 90amp breaker, is this correct?

3) If I do need to rewire the feed with 4 wire, what is the recommendation on size and type? Keep in mind that I bought the 100amp panel for the number of slots, not because I think I will ever need 100amps. I doubt I will ever exceed 60 amps.

4) The new 100amp panel has a green bonding screw to bond the neutral bus bar to the enclosure (the equipment ground is already bonded to the enclosure), I know if I had a 4 wire feed I don't install this because I will isolate the neutral and ground with separate wires, but if a 3 wire feed is okay, should I bond the neutral to the enclosure?



Thanks,
Eric

[Tom Godley]

You do need the 4 wires to the sub-panel - and you do keep the ground and neutral separate as you indicate.

If he ran individual wires and the conduit is large enough you may be able to pull another - but that will be difficult with that size wire unless it is a very large conduit. It also must be conduit that is made and designed for wire -- not plumbing PVC.

If it was cable that he used then you are out of luck as you can not add another wire and cable like NM is not to be installed in conduit. Conduit can be used to provide protection for cable like going through a wall or coming out of the ground.

As to the wire size you will need to check your local requirements -- and also to see if you need a main breaker in the sub panel. (in the basement you probably do not but they make it easier and safer IMO to work on the panel) Depending on the code version and the inspector -- the sizing can be a little different as to neutral size and ground.

[David G Baker]

This is what I would do.
1. Replace the aluminum wire with #2 copper wire using 4 wires as you described.
2. If the wire is copper the 100 amp breaker is fine. If it is going to remain aluminum I would try to find a smaller breaker. Depending on your shop requirements a 60 amp should be fine if the #2 wire will fit in the breaker.
3. I have a tendency to error on the plus side so I would stick with #2 wire. If you want to go to a 4 wire aluminum setup, you can try to run the 4th leg through the conduit. It is done all the time.
4. On a sub panel of any sort do not bond the neutral to the enclosure unless you are running a three wire setup to a detached building that has no other electrical contact with the mail building, (common water pipes, phone line, cable TV lines, etc.) then it can be set up like a main panel with ground rods and bonding in the panel. This varies from local code to local code.
The above is how I do my wiring. I am not a licensed electrician so the best advice I can give is collect all of your questions and contact a licensed electrician in your area. Many times you can get your answers from where you buy your electric supplies.

[Eric Porter]

Thanks for the replies. It looks like what I was afraid of was true, that I need a four wire feed. I am not sure what the difference is between all the different wire types are THHN, NM, etc. but the current wires are individual (not wrapped in a casing together), and all three including the neutral are insulated. They are all run in 1 1/4" pvc electrical conduit and there are pvc LB access fitting at each 90 degree turn.

Can I run a 4-wire #2 copper feed easily in this size conduit?

Eric

[Howard Norman]

How long ago did you purchase this house? Is it possible that you have recourse against the builder for not wiring the subpanel according to code? ie the lack of the fourth ground wire?

Just thoughts.

[Eric Porter]

How long ago did you purchase this house? Is it possible that you have recourse against the builder for not wiring the subpanel according to code? ie the lack of the fourth ground wire?

Just thoughts.

I thought about that as the house in not quite two years old, but the "home warranty" ran out after 12 months. Not to mention that the builder is a complete jerk. I am just not sure it is worth it. I do however know that he wired the sub panel after the electrical inspection so I could call the inspector's office to see what he thinks about it. If there is a problem, and I think there is, then I could contact the builder and let him know that I will tell the inspector unless he fixes it. But as I said the builder is a real jerk and I am not sure it is worth the hassle. I don't really trust him anyway so the most I would want him to do is buy the wire and drop it by my house. I would want to pull it myself to know it is done correctly.

[Matt Edwards]

Eric,

If you are sure that 60 amps will meet your needs what I would do is remove the #2 AL and #4AL neutral. and replace it with #6 copper, 4wires (2 hots 1 neutral 1 ground). Put a 60 amp 2p breaker on the feed end. If your new sub panel has a 100amp main beaker you can use it as your service disconnect and land your new feeders there. If it is a Main Lug panel and you are going you have more than 6 breakers in use, I would install another 2pole 60 breaker and back feed it, thus giving you a service disconnect. Your neutral does need to to be isolated at the sub, and not bonded to the case or equipment ground. The equipment ground does, obviously, need to be bonded to the case.

If you don't think 60 amps is going to do it for you, do the above, but substitute #3 copper, for the 2 hots and the neutral, the ground can stay #6. All of which will easily fit in 1 1/4 pvc conduit. And use a 100amp breaker on the feed end, and at the sub.

HTH
Regards!
Matt

[Charlie Knauer]

If you have seperate conductors in the conduit you can pull them out and install a #8 ground. If you choose not to use the existing conductors pull 3 # 3 copper thhn/thwn a the #8. You will still be good for 100 amps.


Charlie

[Rollie Meyers]

If a circuit breaker is installed in a panel to be used as a main breaker (backfed) it is required to have a hold down see 408.36(F) 2005 NEC.

Edit: That only applies to plug-in type circuit breakers but bolt-on is not found most home shops.

[Chris Padilla]

I don't understand why folks are advocating replacement of the Al wire. Just pull another #2 Al and I think you are done. The #4 *might be* adequate size for the ground so you should check this but I'm fairly certain the ground can be sized smaller than the other "normally carrying current" wires.

[Rick Christopherson]

You need to replace the breaker with a smaller one, and you need to pull a new ground wire. However, replacing the aluminum is kind of silly, and throwing away money for no reason.

[Rick Christopherson]

I don't understand why folks are advocating replacement of the Al wire. Just pull another #2 Al and I think you are done. The #4 *might be* adequate size for the ground so you should check this but I'm fairly certain the ground can be sized smaller than the other "normally carrying current" wires.

I sat blindly staring at my computer trying to think of a polite way to say what you just asked. I gave up and just went with a short answer.

However, I believe that he needs only a #8 ground wire for this size feeder, but #6 is definitely fine.

[Chris Padilla]

You need to replace the breaker with a smaller one, and you need to pull a new ground wire. However, replacing the aluminum is kind of silly, and throwing away money for no reason.

Forgive me if I'm reading too much into this but shouldn't the 2 hots and neutral be the same size?

[Rick Christopherson]

Forgive me if I'm reading too much into this but shouldn't the 2 hots and neutral be the same size?

I stay away from conductor size questions because there are too many variables to keep up with, so I don't even try. However, it is typical for a neutral to be smaller than the non-grounded conductors, because the neutral only carries the imbalance of the other two. If you had a 20 amp load between phase-A and neutral, and a 30 amp load between phase-B and neutral, then the total current flowing through the neutral would be only 10 amps. The currents cancel.

[Chris Padilla]

I stay away from conductor size questions because there are too many variables to keep up with, so I don't even try. However, it is typical for a neutral to be smaller than the non-grounded conductors, because the neutral only carries the imbalance of the other two. If you had a 20 amp load between phase-A and neutral, and a 30 amp load between phase-B and neutral, then the total current flowing through the neutral would be only 10 amps. The currents cancel.

Yes, agreed. I guess I'm just used to thinking about the phase-A and phase-B somewhat independent of each other in regards to 120 V instead of 240 V. When you buy good old 12/2 or 12/3 Romex, the conductors are all the same size (although the ground might not be). For wires feeding a sub-panel, perhaps things are different?