100 AMP Sub Panel?

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  #1  
Old 09-24-11, 01:50 PM
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100 AMP Sub Panel?

I am having an electric in floor heat boiler installed and I am trying to do as much wiring as I can. The boiler is rated at 75 amps, but has two breakers on the panel, a 50 amp and a 60 amp. I would like to install a sub panel off the main panel to power the boiler, both main and sub are in the basement, about 60 feet apart.

Looking at the boiler I would assume 110 amps would be required, but the documentation says the rating is only 75 amps.

My question is, can I get by with a 100 amp sub panel with a 90 amp main breaker? In other words, do I go by the boiler specifications or the physical breakers in place to size this thing?
 
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Old 09-24-11, 06:24 PM
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Originally Posted by extex View Post
I am having an electric in floor heat boiler installed and I am trying to do as much wiring as I can. The boiler is rated at 75 amps, but has two breakers on the panel, a 50 amp and a 60 amp. I would like to install a sub panel off the main panel to power the boiler, both main and sub are in the basement, about 60 feet apart.

Looking at the boiler I would assume 110 amps would be required, but the documentation says the rating is only 75 amps.

My question is, can I get by with a 100 amp sub panel with a 90 amp main breaker? In other words, do I go by the boiler specifications or the physical breakers in place to size this thing?
My opinion is you need a 100 amp subpanel fed from a 100 amp breaker in the main service panel.
 
  #3  
Old 09-26-11, 10:09 AM
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The circuit for a load like a boiler is usually sized for 125%, so 75A * 125% = 94A. You should do a 100A panel with full 100A feeder. That means #3 copper in conduit, #2 copper cable NM or SER, #1 aluminum in conduit, or #1/0 aluminum SER cable.
 
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