Subpanel feed Hots too large for main breaker

[Screwitharder]

Hi Everybody- I have a subpanel that is fed with 2/0 in a barn down the hill from my house. The feed is Aluminum. The problem I see is the feed hots are too large for the breaker screws. The previous owner snipped some Aluminum off, capped the hots to #4 tails and inserted the #4 in the breaker in order to get juice. Does this seem crazy to you? Seems dangerous to me to have the wire downsized right before the breaker. Should I uncap them and do something else?

Any help/ information is greatly appreciated-SIH

 

[2ManyProjects]

Hi Everybody- I have a subpanel that is fed with 2/0 in a barn down the hill from my house.

I take it that this "pole barn" is NOT the "Wood Shop" building that was under so much discussion in your other thread http://www.garagejournal.com/forum/showthread.php?t=216567?

The feed is Aluminum. The problem I see is the feed hots are too large for the breaker screws. The previous owner snipped some Aluminum off, capped the hots to #4 tails and inserted the #4 in the breaker in order to get juice.

We need more information.

First, what is the rating of this "Main" circuit breaker you're referring to, and where exactly is it installed? Based on your referring to it as a "Main" breaker, I am inferring that this is the "local disconnect" breaker in the sub-panel itself.

Second, what is the rating of the circuit breaker FEEDING this 2/0 cable at the main panel or meter box?

Third, what is the total run length of this cable, panel to panel?

Does this seem crazy to you?

Well, I certainly would not call it "kosher"; and I definitely don't care for the manner in which he joined the wires. But having said that, the situation MAY not be quite as bad as it would at first appear to be.

The fact that the breaker(s) in question are apparently intended for relatively small (relative to 2/0 anyway) wires implies that they are also rated for relatively low trip currents. From this, it follows that the LIKELY reason someone used a 2/0 feeder is because the run length was long enough that a smaller wire would have induced too much voltage drop. IF this is the case, the 2/0 wire is presumably not strictly needed from an "ampacity" standpoint; and so, a significantly smaller wire MIGHT actually be adequate for the maximum current the breaker(s) will allow anyway. Still, AWG 4 does strike me as a rather large difference from AWG 2/0 for this to be COMPLETELY plausible, unless that run length is insanely long (also, copper vs. aluminum could explain part of it; but that would raise still more issues with how the wires were joined). In any event, even at AWG 4, it certainly won't be imposing significant voltage drop over a run length of a few inches to a couple feet (but that's the least of the issues).

 

[malibu101]

This probably won't help you as you need a special press to install them
but
These are often used when running into a problem like yours.
http://www.tnb.com/ps/endeca/index.cgi?a=nav&N=1037+638+4294950927&Ntt=

 

[theoldwizard1]

This probably won't help you as you need a special press to install them but These are often used when running into a problem like yours.
http://www.tnb.com/ps/endeca/index.cgi?a=nav&N=1037+638+4294950927&Ntt=

Learned something new !

Generically they are called Bi-Metallic Pin Terminal Connectors. They appear to be designed specifically to solve your problem.

As stated, they require special crimpers.

 

[JakeKohl]

A new breaker may do the trick...breakers fittings are sized for the wire type and wire diameters normally associated with the load....so if the wire isn't fitting, either the breaker isn't meant for aluminum wire, the wire is oversized, or the breaker capacity too small. If the wire is too large for the rated load, and the breaker is designed to be used with aluminum, it's probably OK that it was trimmed down a little (although, probably not to "code").

Some breakers are not meant to be used with aluminum wire since aluminum has special expansion/contraction issues and is typically a larger diameter than copper for the same capacity. Check that your breaker is actually meant to be used with aluminum wire...if not, you should replace it because it could lead to an inconsistent connection and/or short.

 

[sberry]

As long as it has a solid crimp or connection is probably just fine.

 

[Aceman]

You have 3 options the way I see it, from best to worst in my opinion:

1. Use a larger breaker. Since you are using 2/0 AL I'd suggest looking into using a 2 pole 125A, the largest most panels take without getting into a HUGE 4 pole breaker. Make sure to verify it'll take 2/0.

2. Insulated taps. Use these on the ends of the 2/0 wire to pigtail a smaller PROPERLY SIZED wire to the breaker.

3. Pin adapters. Like mentioned above, these are one option. But, they do take a special press to crimp them right, not exactly a tool a diy'er will have. That's why I put this option last.

 

[Screwitharder]

Hi, Thanks for the advice. Let me describe it better. The barn sits just under 300 feet (I don't know if the wire curved underground) from the house. It has a 125 amp panel being used as a subpanel. The feed to the barn comes from the side of the house where there's an outside panel (200 amp). The outside panel has a 60 amp breaker that feeds the barn. I measured the wire and it's 2/0. That wire for the 2 hots and neutral (ground is smaller and fits) in both the subpanel and outside panel is too large for the main breaker in the subpanel and for the neutral bar. They spliced each wire with #2, capped them and ran the smaller wire into the breaker/neutral bar. The 2/0 is AL strand. I thought I'd buy some 2 screw connectors (the ALuminum ones), connect the feed wires with these on both ends
I though I'd take off the caps, connect the feed wires using the connections and Antioxidant, put #2 copper on and then run the copper into the breakers and neutral bars.
But, seems like the section of copper that is undersized is iffy to me and I'm worried about the connectors not being insulated. Thanks for the advice

 

[2ManyProjects]

Hi, Thanks for the advice. Let me describe it better. The barn sits just under 300 feet (I don't know if the wire curved underground) from the house. It has a 125 amp panel being used as a subpanel. The feed to the barn comes from the side of the house where there's an outside panel (200 amp). The outside panel has a 60 amp breaker that feeds the barn. I measured the wire and it's 2/0.

OK... That explains quite a lot -- in fact, almost everything.

Obviously, the sole reason you have AWG 2/0 cable is the length of the run, not the raw ampacity. Using the numbers you cited, you could theoretically have used AWG 1/0 aluminum for this; but that would be right on the ragged edge from the standpoint of allowable voltage drop (60A over a 600-foot round trip comes out to needing 106,000 CM using aluminum wire; AWG 1/0 is officially 105,531 CM, which gets rounded to 106K). If it were all copper, AWG 2 would suffice nicely; but apparently, that ship has sailed.

That wire for the 2 hots and neutral (ground is smaller and fits) in both the subpanel and outside panel is too large for the main breaker in the subpanel and for the neutral bar. They spliced each wire with #2, capped them and ran the smaller wire into the breaker/neutral bar. The 2/0 is AL strand. I thought I'd buy some 2 screw connectors (the ALuminum ones), connect the feed wires with these on both ends
I though I'd take off the caps, connect the feed wires using the connections and Antioxidant, put #2 copper on and then run the copper into the breakers and neutral bars.

Save for one possibly off-the-wall suggestion, I'll leave this part to those with more experience with these sorts of connections. That suggestion is: How large (in terms of trip current rating) a breaker would you need to use at each end in order to fit the AL 2/0 directly? If it is 125A or less (as I'm guessing it would be; but this depends somewhat on what make/model panels you have), that might be the simplest solution. Per the 2011 NEC, AL 2/0 is rated for anywhere from 115A to 150A, depending on the temperature rating of the conductors. So if that existing AWG 2/0 carries at least a 75°C rating, this would still be "legal". Note that this would NOT mean that you could really pull 125A through that cable; because if you did, the voltage drop would be downright gruesome. But as long as you still limited yourself to ~60A total load in the barn, it should work.

But, seems like the section of copper that is undersized is iffy to me

Actually, AWG 2 copper is rated for at least 75A; and as noted above, would even be just fine for the whole run, save for voltage drop effectively limiting you to about 60A.

 

[outbookinsis]

good,expansion/contraction issues and is typically a larger diameter than copper for the same capacity. Check that your breaker is actually meant to be used with aluminum wire...if not, you should replace it because it could lead to an inconsistent connection and/or short.