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. :D

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?

[Eric Porter]

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. :D

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

Concerning replacing the Al with Cu simply to give me more flexibility (addition of a large welder) in the future. I know that if I truly want 100 amp service to the sub-panel then I will need the proper size conductor. I spoke with my neighbor, a licensed electrician, as well another friend who is also a licensed electrician but deals primarily in commercial work. They both agreed that the current #2 Al will not up to code for 100 amp service. My neighbor recommended #3 Cu for the 2-hots and neutral and #6 for the ground. My other friend agreed that this meets code but said that in the "real world" (i.e. commerical applications) he would use #2 copper for the hots and neutral.

[Eric Porter]

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.

Rollie,
Thanks for the advice. The panel that I bought does have a hold down for the backfed circuit breaker.

Eric

[Dan Friedrichs]

I agree w/ leave the Al wires and just pull a ground wire in the existing conduit. Easy and cheap.


The neutral from a feeder is usually smaller than the hots, because (as others mentioned) your larger loads are usually 240, meaning they don't return any current through the neutral.

Regular 12/2 Romex needs to have both the wires (except ground) the same size because all the current will flow on both. Certain 3-wire installations won't necessarily require that - for instance, a electric dryer might need 2 10ga hot conductors and 1 14ga neutral (for the light bulb), but selling 10/2+1/14+g wire probably wouldn't be worth the hassle, even with the current price of Cu.

[Matt Edwards]

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


In my experience the utility company is the only entity I've seen use a smaller size neutral, and that was on their service feeders. I haven't seen it done for branch circuits or distribution as a part of a buildings electrical system. Rick is correct that in a balanced situation, the neutral will carry the difference of the 2 phases. But since this is feeding a panel with 22 spaces it would be possible to for the imbalance load to be greater than what a #4 AL could handle. Either way, the OP needs to add a 4th wire to the conduit. If he chooses to add a 3rd #2 AL and use the #4 for a ground, he could very well end up having to pull all the wire out, add the new wire and pull it back in. I say this because he said the main panel was in the garage and the sub was 40' away in the basement, most likely with a couple of 90's and or other bends and fittings in the conduit run. Three #2 AL and one #4 AL conductors in an 1 1/4 conduit is leaning on the tight side so attempting push or fish a single #2 could be a real PITA. So, since Eric said he doubted a need for more than 60amps, I gave a recommendation based on the information, and what I would do at my house or out in the field.

As Rollie pointed out, if you do back feed a breaker and use it as a main, it does need a hold down as per the NEC (thanks Rollie)


I hope I haven't stepped on any toes or out of line here as my intentions are to be friendly and helpful.


Regards!
Matt

[Tom Godley]

Well, it is a shame it was not done correctly.

Only you can determine if it is worth the trouble to go after the contractor - or if the conduit layout will allow you to pull the additional wire or re-feed them with the forth included.

I see no reason to be concerned with the Al wire -- it is used all the time. The problem with Al wire in the 60's and 70's had to do with the connection points overheating.

It just may be that replacing them all with the proper sized CU wire will allow you to complete the job without too many difficulties - the CU wire is easier to work with when bending and making up the panel for those that do not do it every day.

I also agree that it is best to check locally on what wire size is required - as there are an unbelievable number of variables that can influence this.

I mentioned a main breaker in my previous post only because 100 amp panels with mains are so cheap that they make for good sub panels. I happen to like the regular main used as a disconnect rather that back-feeding. This is just my opinion -- but some not familiar with panels become confused with the back-feed breakers. In all the locations I have owned homes no restriction existed in using the 100-amp main breaker in the sub as a switch -- even with a lesser breaker in the main providing power through the correct wire size to the sub. I just like to be able to cut the power to the sub-panel without having to go to the main panel location

[Travis Lavallee]

Rick is correct that in a balanced situation, the neutral will carry the difference of the 2 phases.


Matt,

Actually, the only time the neutral will carry any current is in an unbalanced situation. Any of the "neutral" wires in the branch circuits are just providing a return path to the panel and require the rating to carry that load. Once the wire reaches the panel the loads from the opposite legs will combine to cancel each other out.

You could look at this much like a cheque book or bank account, where one leg acts like a deposit, and one as a withdrawl. At the end there will be a difference between the two, say 5 A, but it does not matter (to the neutral) if that was:

40 A on leg one and 35 A on leg two
or
5 A on leg one and 10 A on leg two

I hope this helps clear up the misconception about how the neutral from the supply works.

As for the reasons behind removing the Al wire at this point: If you can get the ground wire in easily and are only going to use 60 A, leave it in. You can always do the additional work later (and incurr the additional costs) if you find the need for the upgrade.

The only reason to pull out the wires at this point would be if I encountered trouble installing the ground, or knew that I would definately use the extra capacity and was trying to transfer part of the initial cost of say, setting up a welder, from someone who might not allow it with the extra cost. I'm just getting a welder could fly a lot better than a welder and a large electrical upgrade.

[David G Baker]

Eric,
I am a member of Hike Holt's code forum. Any time I have a question about electrical work I go there and always get the information I need. I signed up for the newsletter that has loads of ideas from electricians around the country. It is like the SMC of electrical work.

[ron hokenson]

Eric, I think your electrician neighbor and friend gave you good advice. It's been awhile since I have been in this game (electric work), but if it were mine, I would scrap the aluminum and go with copper wire, 3# 2's along with a #6 ground. Wiring is nothing you should guess at...That's why there is a National Electric Code. If in doubt, call your local inspector and ask him. Inspectors want you to get it right.

If I were doing the work, I would pull the old wire out and at the same time pull a small pulling rope in. I would measure the wire after it is out of the raceway. Make sure you add enough so you don't come up short. Once you get the new wire, tie it to the rope and pull it it. A little soap on the wire will make your pulling job easier. Make sure and identify your neutral when it's out on the ground and you can see both ends.

Good luck with your project, whatever you decide to do.

...ron

[Rick Christopherson]

Eric,
I am a member of Hike Holt's code forum. ... It is like the SMC of electrical work.Ummm, no it is not, because unless you are in the electrical field, your posting will either get yanked or you will get handily slapped about. :D Homeowner-type questions are not encouraged, and on most days, not even tolerated. Oh, I forgot, but the "selfhelpforum" is the best place to get this advice from many of the same people as Mike Holt's forum. I haven't been there in ages, but I assume it is as helpful as it was a year or two ago.


Wiring is nothing you should guess at...That's why there is a National Electric Code. If wiring is not something you should guess at, then why did you tell him to pull the aluminum for no electrical or NEC based reason? The only reason to pull the aluminum is if it is undersized for the load that he needs, and no one in this thread has asked him what the load will be.

[Rick Christopherson]

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.
This statement has been overlooked (I assume) by many people. Unless this expected demand is no longer true, there is no reason to pull the existing aluminum out. Reduce your breaker size in the main load center and pull a #8 ground wire. (#6 is more common, so you will probably have an easier time finding it at the home centers than #8.)

[Rick Christopherson]

By the way, here is a nice little trick for pulling a new ground wire through your existing conduit. Make sure you kill the power to the subpanel first.

Take some string (non-chalked chalk line) and tie a small knot in the end to prevent fraying and provide some air resistance. Connect a shop vac to the conduit entering your subpanel, and insert the string into the conduit at the main load center. The vacuum will pull the string through and you can jerk it back and forth (as needed) from the main load center if/when it gets hung up along the way. I think you already indicated that there were wire pulls at the corners, so you should be able to pull a #6 or #8 wire with this line even though it will stretch as you pull on it.

[Chris Padilla]

Rick,

I saw the "vacuum a pull rope through the conduit" trick on some episode of T.O.H. or maybe it was A.T.O.H. Pretty clever. They were pulling large multiple aught copper from the street and had pulley and winches and the sort. I guess you don't appreciate how hard it is to pull large gauge wire until you try it. Even #10 was tough on my arms and hands until I finally broke down and bought some pull lube--sure made a big difference!

[Rick Christopherson]

I saw the trick 20 years ago when I was schlepping my way through college in the maintenance department of a Caterpillar dealer. The company electrician asked me to help him pull wire through 1000 feet of buried conduit, and he used this just to get his fish tape through.

[Eric Porter]

Thanks again to all for the good information. I made a copy of the NEC 310.16 table and thanks to Rollie know that I should be referencing the 70 degree column in that table.

As Rick and a couple of others noted I did make the statement that doubt I will ever need more than 60 amps. The only two reasons to upgrade the conductors to carry 100 amps are just so I can say I have it, and because my FIL has a monster welder that I hope to inherit at some point in the future.:)

The most reasonable options as I see them are below:

1) 90 AMP SERVICE - Run another 2 AWG Al conductor - only problem is that I am having trouble finding this. Big boxes don't have it, and the couple of local electrical supply houses that I called don't carry Al except in much larger gauges. I plan to check with a couple of other places tomorrow. I have know idea how much 55' of this will cost, but I know it will be chaper than copper. In addition, I will also need a 90 amp breaker about $32.

2) 70 AMP SERVICE - Pull out the Al and run 6 AWG copper w/ 8 AWG copper ground. This is readily available and would be extremely easy to pull through 1 1/4" conduit. Rounding up 65 to 70 amps. Cost would be about $100 for the wire and $20 for a 70 amp breaker.

3) 100 AMP SERVICE - Pull out the Al and run 3 AWG copper w/ 6 AWG copper ground. This is not available at the big box stores, but I have found it online and I am still checking with some of the local electrical supply houses. This is going to be somewhat expensive best price on the 3 AWG is .99/ft. and 6 AWG about .49/ft. so about $190.

4) 100 AMP SERVICE - Pull out the Al and replace with 1 AWG Al. I am sure it would be cheaper than option 3, but I haven't been able to find a source.

I am going to pursue option 1 to see if I can find a local source for the 2 AWG Al. If this proves difficult I will look at option 3 and try to find the best price for 3 AWG copper.

Thanks again everyone,
Eric

[Chris Padilla]

Eric,

Maybe track down the electrician who ran your sub-panel to see where he got his #2 Al?

Have you looked into your conduit? Do you feel like you could pull another #2 through it? Pulling big wire is tough, tough work....

[Eric Porter]

Eric,

Maybe track down the electrician who ran your sub-panel to see where he got his #2 Al?

Have you looked into your conduit? Do you feel like you could pull another #2 through it? Pulling big wire is tough, tough work....


Chris,
The "electrician" was my builder, I choose not to call him an electrician because I have much more respect for true men of the trade. That being said I checked with several local electrical supply houses during lunch and found one that was really friendly and had great prices on wire. The strange thing I found is that at the few places that carried 1 AWG Al wire it was priced nearly 30% higher than 3 AWG Cu, my two 100 amp service options. Below are my updated prices

1) 90 AMP SERVICE - Run another 55' 2 AWG Al conductor, cost $30 plus I will also need a 90 amp breaker about $32 - total $62

2) 70 AMP SERVICE - Replace Al with 6 AWG copper w/ 8 AWG copper ground, cost $65 for the wire and $20 for a 70 amp breaker - total $85

3) 100 AMP SERVICE - Replace Al with 3 AWG copper w/ 6 AWG copper ground, found a great price at local supply house 3 AWG at .50/ft. and 6 AWG about .25/ft., $83 and $14 respectively - total $97

4) 100 AMP SERVICE - Replace 2 AWG Al with 1 AWG Al - off the table because 1 AWG Al is more expensive than 3 AWG Cu.


WINNER - Option 3 - 100 AMP Service with 3 AWG Cu! - with a cost differential of only $35 over the cheapest option, plus the added amperage, plus the ease of pulling the smaller wire through an empty conduit.

Thanks again for all the information,
Eric

[Chris Padilla]

Eric,

Nice job on the research and I think you've got a good plan. Now take that Al wire and put yourself in a 50-A breaker for your future welder. It'll have TONS of overhead but no biggie.

Is your #3 THHN?

[Eric Porter]

Eric,

Nice job on the research and I think you've got a good plan. Now take that Al wire and put yourself in a 50-A breaker for your future welder. It'll have TONS of overhead but no biggie.

Is your #3 THHN?


My thoughts exactly on the welder circuit! :)

Yes, the #3 is THHN.

Eric