Question For The Gurus - Sub Panel

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  #1  
Old 10-16-07, 11:19 PM
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Question Question For The Gurus - Sub Panel

I know this subject has been beat to death, but I just want to get a nod from the experienced. I have been lurking around for some time and I think I know what I need to do.

I am installing a sub in my detached shop which is about a 150' run. My home has 200 amp service and I am going to feed a 70 amp 240v sub panel from the main. I plan to use 2-2-2-4 Al to feed the sub with 70 amp breakers at main and sub panels. I will drive two 8' copper clad rods (6' spacing) at the shop and connect to sub panel via #6 bare copper. As for the sub panel - I will remove the bond between the neutral and ground bus and then bond the ground bus to the panel. About 110' of the run will be through the attic and wall cavities inside of the home to a 40' run through 1 1/2" PVC conduit. The conduit will have and LB at the entrance/exit of the attic to a maze of 2 - 90 sweeps and 1 - 45 sweep.

Questions:

Im a little confused on what type of cable to purchase (I think I need SE-U or USE Al)

Is it safe/within NEC code to use two types of cable on the feeder run (example: SE in the attic and then switch to SE-U through the conduit with a splice just beforer the LB)


Your input and suggestions are greatly apprreciated. Please feel free to address anything that I did not.

Sorry for the long post. Thanks in advance.

Brooks
 
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  #2  
Old 10-17-07, 08:26 AM
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For the outdoor portion in conduit, use four individual conductors of THWN or XHHW. Heavy gauge cables are nearly impossible to pull through conduit as a consequence of their stiffness.

Inside the home, use 2-2-2-4 SER cable.

At the transition point in the attic, install a large junction box and use bolt connectors rated for #2 aluminum. Apply no-ox grease to all of the aluminum terminations (main panel, junction box and subpanel).

The rest of your subpanel plans sounds fine.
 
  #3  
Old 10-17-07, 08:43 AM
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Originally Posted by bhill2625 View Post

Questions:

Im a little confused on what type of cable to purchase (I think I need SE-U or USE Al)

Is it safe/within NEC code to use two types of cable on the feeder run (example: SE in the attic and then switch to SE-U through the conduit with a splice just beforer the LB)

Brooks
Your plan sounds good to me.

In my opinion....

#2 Aluminum is OK for the load and the voltage drop is OK.

I would use #2 SER Aluminum cable for the interior portion of the wiring.
This is 4 conductor cable (2-2-2-4) with a plastic outer covering.

For the underground portion, I would use #2 aluminum "mobile home feeder" cable.
This is 2-2-2-4... (4) conductor type USE cable that has a additional rating of RHH/RHW.

The RHH/RHW rating allows the cable to be used inside the garage.

This USE cable can be direct buried (24" minimum), or I could put it in (1 1/2" minimum) pvc conduit and bury it 18" deep.

Also, I could bury it 6" deep if I installed it in rigid or intermediate steel conduit. NEC Table 300.5

If I installed it under a driveway, I would increase the conduit burial depth to 18"

The cable is available at one of the big box stores.

Go to.... www.southwire.com ....to familiarize yourself with the different cable specifications.

Splicing the two cables together is perfectly OK.

I would be sure that the splicing connectors are rated for joining aluminum and also rated for the wire sizes.

As you mentioned, the splice needs to be made inside a junction box of sufficient size.

If using 1 1/2" conduit, I would use a box measuring at least 12" square on each side x at least 4" deep.
I may be able to use a smaller box by following NEC 314.28(A).

If I used a metal junction box, I would be sure to bond the enclosure to the (green) feeder grounding conductor using a listed lug.

My post is for informational purposes only.
I will accept no liability, nor will I be held responsible for the accuracy, use or misuse of the information that it contains.
Use it at your own risk.
You are responsible for your own work and the safety or correctness of the work that you perform.
My disclaimer for the day

Just my opinion
steve
 
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