Wire Size, Breaker, and Three Phase Question

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  #1  
Old 05-03-07, 01:19 PM
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Arrow Wire Size, Breaker, and Three Phase Question

I am installing a 125 amp subpanel side by side off of an existing 125 amp subpanel. The existing subpanel only has 110 appliances drawing from it, with never more than 2000 watts being used at a time (but usually only 800-1000).

The subpanel I want to install will have 240 and 110 appliances drawing from it; drawing either 8800-9800 watts at 110v. or 10,000-12,000 watts at 240 but never at the same time.
My questions are:

A. What guage wire should I use for the 2 hot wires and the neutral wire? (It will only be running about 6-8 feet).
B. What size breaker should I use in the existing sub to feed the new one? (With the numbers given above taken into account.)
C. And lastly do I need (or should I buy) a three phase panel?

Thank You for all your feedback
 
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Old 05-03-07, 01:36 PM
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I would install nothing less than a 100 amp sub panel. You need FOUR wires to the sub panel.

You could use "mobile home feeder cable" which would be 2-2-4-6 aluminum cable, protected by a 100 amp circuit breaker. You could also use copper, 4 gage.

Three phase should not enter your mind for a residential application.
 
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Old 05-03-07, 03:32 PM
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Can I or should I use.....?

I forget the name of the wire, bout it comes as a harness (wrapped) as a four wire bundle? I heard this wire has much lower amp rating than copper wire of the same guage. Is this true? Also are there any advantages to this type of wire?

ALSO: I would REALLY like to know the largest breaker I can use in the existing sub to feed the hots of the new sub. (Taking into account the previously mentioned numbers.)

Thanks again
 
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Old 05-03-07, 04:07 PM
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> (wrapped) as a four wire bundle?

You're thinking of an aluminum quadplex style cable. You need to use thicker aluminum wires than copper, but it's one-third to one-half the price of copper. Aluminum wire requires a little more care to connect properly. For only 8', I would not bother with aluminum -- use THHN copper.

> largest

The largest subpanel you can install is 125A. If you choose that size, the wires must be at least #2 copper or #1/0 aluminum. However, you should determine if your service has enough spare capacity to support your proposed loads. This requires a "demand load calculation".
 
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Old 05-03-07, 09:03 PM
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What is the breaker size feeding the existing 125A subpanel?
 
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Old 05-03-07, 09:11 PM
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100 amp breaker feeding from main

100 amp breaker feeding sub from main (of which I am only using 10-20 at any given time, really only 5 if I am not using forced air heater).
 
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Old 05-03-07, 10:12 PM
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I read your posts, there are alot of nuts and bolts to your project.
Are you going to hard pipe or fish multicondonductor cable?
That is a huge 110v load and a real decent 240v load to get off a 125a subfeed.
Also need to know what actual load equip is for better idea.
If you do got zensco breakers, you could buy a ite panel and breakers for the price of one 125a zensco cb and yard that ranbow POS out of your walls.
 
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Old 05-03-07, 10:26 PM
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Narrowbackpride

I only have to run the wire about 6 feet thru the drywall, don't know if I am going to pipe or fish yet. (What do you think? Some say I have to go thru pipe at this load-with this wire.)

I am running every power tool in the shed, a pottery kiln (10,000 watts on low setting 12,000 on high) plus outdoor motion lights 400-3000 watts depending on how many have been tripped) plus the overhead lighting (500-1000 watts).
 
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Old 05-04-07, 07:11 AM
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Then the largest breaker you can use to feed the new subpanel should be no larger than the one feeding the existing subpanel, or you're just wasting it. So, use another 100A breaker for the new one. That will give you about 20000 watts of constantly usable power.
 
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