feeder to breaker question

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gance

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For some reason I am drawing a blank on this question, maybe im over worked or just plain stupid, regardless


If an existing 100 amp panel was changed to a 200 amp panel, "but no power upgrade done" is it illegal to overamp a main panel when incoming feeder is less amps then the main


thanks for the help
 
Re: feeder to breaker question

If the overcurrent device on the supply side of the "now 200 amp panel" is properly sized for the conductors supplying the secondary panel, it would be permitted.
408.36


Now that I took a closer look at your post, I see the panel in question is a main panel - which I take to mean the first point of disconnect (service).

You cannot just upsize the panel overcurrent protection without taking into consideration the size of the service entrance conductors supplying the main panel.

[ September 20, 2005, 05:14 PM: Message edited by: pierre ]
 
Re: feeder to breaker question

If you are feeding a 200 amp main breaker where the wire was rated for 100 amps for the old panel, the new main breaker will allow 200 amps through a service wire that can only safely handle 100 amps. FIRE :eek:
 
Re: feeder to breaker question

Strictly speaking, there is the risk of fire only if the actual current exceeds what the wire is rated for. Just because someone puts a 200A breaker on a service that can only handle 100A doesn't mean bad things will happen. But it could, which is why it's illegal to overamp this way.

Then again, sometimes it has to be done on a temporary basis. I just did one like that today. I upgraded a service from 60A to 150A, but the utility's lines are not capable of handling the 150A. Also, I tapped the existing utility lines with some #4 Cu between their lines and the new service drop I put in. Theoretically, the utility's lines and the temp #4 Cu lines are at risk of overcurrent, but based on what I saw in the house, I think it's very unlikely.

When I did a 200A upgrade once, the utility lineman told me that the triplex they use is only capable of about 170A. He said they realize it's possible someone could overamp their lines, but the risk is low enough that they are going to leave the triplex in place.
 
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