Cable Size

don_resqcapt19 said:
240.4(B) permits you to use 4AWG copper on a 100 amp breaker for that load.
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Now I'm really confused and were getting ready to start work ..lol. again it's AL SER cable.

Breakers is 100a and calculated load is 80a. How would #4 be ok?

Doesn't the breaker need to protect wire so the wire ampacity should be equal or above breaker size ?
 
If I did my math correctly using the 4/0 to a splice and then 1/o would exceed your 5% limit,
You are better off with 4/0 all the way.
and, as infinity noted, the cost of material and labor with the splice would not be worth the effort.
 
infinity said:
Yes you do two separate calculations as if there are two separate runs.
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So ..because I really need to know.lol. if the run is 490' and the calculated load is 79 amps( not taking into account the ocpd feeding the load..for now) and the splice box is located at the 290' mark of a 490' total run.

1. I can do a voltage drop calc using the calculated load to the splice box(290'). Then do my second voltage drop calc using the same calculated load from the splice box to the load?

Thanks
 
augie47 said:
If I did my math correctly using the 4/0 to a splice and then 1/o would exceed your 5% limit,
You are better off with 4/0 all the way.
and, as infinity noted, the cost of material and labor with the splice would not be worth the effort.
Click to expand...
We figured 3/0 for a portion of the run( to the splice box)and 1/0 for the remaining. I'm really hoping this works. We HAVE to install a splice box per the customer
 
don_resqcapt19 said:
Or the fact that Southwire is in the business of selling product.
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This is what I believe Southwire's calculator is doing behind the scenes.
1754098091434.png

What we'd calculate with the NEC's effecitve resistance values in Chapter 9/Table 9, would be (|green| - |blue|)/|green|
What Southwire's tool is calculating, is |red|/|green|. While technically a form of voltage drop, it's not the voltage drop we most commonly care about.
 
This is what southwi1000000064.pngre vd calculator is bringing back
 

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Alwayslearningelec said:
1. I can do a voltage drop calc using the calculated load to the splice box(290'). Then do my second voltage drop calc using the same calculated load from the splice box to the load?
Click to expand...
Yes the total load is the same per post #16, 79.52 amps. You stated no more than 5% VD, 208*5%=10.4 volts maximum for both sections of the run combined.
 
Carultch said:
This is what I believe Southwire's calculator is doing behind the scenes.
View attachment 2578920

What we'd calculate with the NEC's effecitve resistance values in Chapter 9/Table 9, would be (|green| - |blue|)/|green|
What Southwire's tool is calculating, is |red|/|green|. While technically a form of voltage drop, it's not the voltage drop we most commonly care about.
Click to expand...
Note the south wire "commercial mode" calculator allows power factor to be entered and defaults to .9
 
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