service wire too thick for breaker

[fishman]

I've started on the wiring project for my tractor barn and my rv/boat barn. The electric coop sold me 4/0 aluminum service cable (direct burial) to carry the power from my meter to the barns. That cable is now in place, sleeved in 2" pvc. I purchased a 100 amp box for one barn and a 125 amp box for the other. Those have been installed and the service wire routed into them. Now to my problem: The "expert" at Lowe's insisted that 4/0 aluminum would work with the Cutler Hammer main breakers in the two boxes I bought. Of course I did not learn my lesson from previous misinformation I received at box stores and installed the boxes without checking. I found to my dismay that the breakers are sized for 2/0 cable, and there is no way to fit the 4/0 aluminum in there. Visits to two electric stores yielded the following facts:
1) There are no breakers that will fit in my boxes that will also accept 4/0 aluminum.
2) There is a device called a "aluminum to copper kearney" that will allow me to connect aluminum to copper. In looking at the device, it is essentially a double clamp, that connects the two metals without allowing them to touch.
3) 2/0 copper will carry 135 amps, enough for either box.

So my question is: Would it be acceptable to connect my 4/0 aluminum service wire to 2/0 copper wire using the above connector? Since the 2/0 copper wire ampacity exceeds the breaker I am using, it sounds like it should be o.k.

I am also using a paste that prevents oxidation on aluminum wire on all my connections, if that makes a difference.

The only other idea I have is to clip some of the aluminum strands until it fits. the wire has 20 strands and 9 must be clipped for it to fit. I don't like that idea at all.

Thanks for any input.

 

[podagrower]

Giving the wire a "hair cut" is not the proper way at all.
Using a kearney, split bolt, or other connector that has a barrier between the copper and aluminum wire (not all of them have a divider) is the proper way. Use Noalox or similar compound on the aluminum wire to prevent corrosion.
Aluminum and copper are dissimilar metals and direct contact should be avoided to prevent galvonic reactions (nasty corrosion)
For residential service feeders, the NEC allows 2/0 copper to be rated for 200 amps, the same as 4/0 aluminum.

Standard disclaimer applies, this is my opinion only

 

[randy41]

call the guy who will inspect it and ask him what you can do to pass.

 

[johnnylight]

Start off at a Electrical supply house.

Pick up:

E/L/B
4/0 stop connectors compression type
rubber tape
plastic vinyl tape or shrink sleeves -torch needed.
2/0 adapters for 4/0 copper connectors (compression)
crimping tool.

Install E/L/B end line box with 2" pvc connectors for your pipe feed your 4/0 with conn through the E/L/B tighten pipe to box, next install another 2" pipe to your breaker box.
install 2/0 copper wire though the E/L/B to breaker box.

use compression type connectors for your connections, use penetrox (fill the conn)for the side with the 4/0 alum cable.
for the copper you will need 2/0 adapters to fit in the 4/0 connectors they are thin wall looking. you need to compress them. rubber and plastic tape them
4 layers of rubber 2layers of plastic.

connect to breakers..

 

[fishman]

First off, I'm in the country, so no inspection is needed. Otherwise suggestion #2 would be a good one.

It sounds like connecting the aluminum to copper will be o.k. Is the end line box necessary? It sounds like it's purpose is to isolate the connection from the breaker box to prevent a bare wire. If the connector was properly sleeved, wouldn't that serve the same purpose? I'm not against using the e/l/b, I just want to make sure it is a significantly better approach.

Johnnylight, you are more specific than Podagrower on the use of connectors . . . recommending crimp style. I don't have a crimper so that would be additional cost. Is there some reason why the kearney is less satisfactory?

Thanks to all who have replied so far. Making progress. . .

 

[Sully2]

I've started on the wiring project for my tractor barn and my rv/boat barn. The electric coop sold me 4/0 aluminum service cable (direct burial) to carry the power from my meter to the barns. That cable is now in place, sleeved in 2" pvc. I purchased a 100 amp box for one barn and a 125 amp box for the other. Those have been installed and the service wire routed into them. Now to my problem: The "expert" at Lowe's insisted that 4/0 aluminum would work with the Cutler Hammer main breakers in the two boxes I bought. Of course I did not learn my lesson from previous misinformation I received at box stores and installed the boxes without checking. I found to my dismay that the breakers are sized for 2/0 cable, and there is no way to fit the 4/0 aluminum in there. Visits to two electric stores yielded the following facts:
1) There are no breakers that will fit in my boxes that will also accept 4/0 aluminum.
2) There is a device called a "aluminum to copper kearney" that will allow me to connect aluminum to copper. In looking at the device, it is essentially a double clamp, that connects the two metals without allowing them to touch.
3) 2/0 copper will carry 135 amps, enough for either box.

So my question is: Would it be acceptable to connect my 4/0 aluminum service wire to 2/0 copper wire using the above connector? Since the 2/0 copper wire ampacity exceeds the breaker I am using, it sounds like it should be o.k.

I am also using a paste that prevents oxidation on aluminum wire on all my connections, if that makes a difference.

The only other idea I have is to clip some of the aluminum strands until it fits. the wire has 20 strands and 9 must be clipped for it to fit. I don't like that idea at all.

Thanks for any input.

Take the box's back to Lowes. But put the blame on the coop...If you told them what sort of setup you had intended on doing...THEY should have never sold you 4/0 wire.

 

[johnnylight]

How long is the pull?
Can you remove the 4/0 and go back with the 2/0 on Lowes expense
What are the electrical demands?(welding)

I recommend compression overall it's what I use when I see bundy/clamp type connections.

If your using the clamp type make sure tighten good.

Def talk with a Manager from Lowes
either a new breaker box or replacement of cable --have them make it right.

 

[mrutkaus]

Clip off those 9 nasty strands; 1" of the fewer strand stuff will conduct more amps than a long length of the other!

Mike

 

[sandman2234]

I don't agree with cutting the wire down to fit, as decreasing the size of the wire reduces it's rated capacity. An inch or a couple of feet, it is still going to be a high resistance spot, and subject to making heat. Aluminum is bad enough as it is, about expanding and contracting, which is why when you use aluminum you have to check your connections on a regular basis.
David from jax

 

[johnnylight]

I don't agree with cutting the wire down to fit, as decreasing the size of the wire reduces it's rated capacity. An inch or a couple of feet, it is still going to be a high resistance spot, and subject to making heat. Aluminum is bad enough as it is, about expanding and contracting, which is why when you use aluminum you have to check your connections on a regular basis.
David from jax

I agree with sandman2234--don't break down aluminum...
True you will have to check these connections -depending on your use like welding it will make clamp down connections loosen over time.
This why I recommend compression connections.

If you can switch to copper being a short pull in and out I would swap.