Wire size

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jyohnyb

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wilmington nc
If i have a main panel with six throws of the hand but no main breaker what do i size the wire on? Say it has a 100 amp to a subpanel and a 125 amp to the heats. Do i use 125% of largest breaker?
 
Nah.

Nah.

They are using the 6 throws of the hand rule. Its a 3/0 copper from the meter to the lugs. Then it is a 125 amp breaker to a heat subpanel and a 100 amp breaker to the house subpanel.
 
The wire from the meter to the lugs is 3/0.

The wire from the meter to the lugs is 3/0.

3/0 copper is good for 200 amps. However you have a total of 225 with the 2 breakers. How do i size the feeder
 
jyohnyb said:
3/0 copper is good for 200 amps. However you have a total of 225 with the 2 breakers. How do i size the feeder
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You don't size it by adding the breakers, you size the main by doing a load calculation. I doubt you're other two panels will pull the rated load. You already have the 3/0 for the MLO panel. Just size the wire for each load/subpanel respectively, 125A for one and 100A for the other.
 
luckylerado said:
There is no OCP ahead of the MLO?
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In many residential services, especially in San Antonio, even in new construction, there is no OCPD ahead of the MLO panel. It seemed strange to me the first time I saw it, but now I have seen lots of them.
 
jyohnyb said:
3/0 copper is good for 200 amps. However you have a total of 225 with the 2 breakers. How do i size the feeder
Click to expand...


Terminology is important. The wire from the meter to the MLO panel is aa service entrance conductor and NOT a feeder. So if you have 3/0 copper then the wire size is fine in all probability.

If this is a residence then 3/0 is good for 225 amps. As stated above you don't add the breakers but you add the calculated loads of those feeders or branch circuits.
 
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