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Discussion Starter · #1 ·
I have a sub-panel in my barn that is currently fed by a 60 amp breaker and the appropriate wiring. I would like to upgrade this to larger wire and 100 amp breaker, but I don't know the amperage of the sub-panel. How can I figure out how many amps the sub-panel will handle, and is it OK to use a 100 amp breaker with the appropriate size wire, to go to a lesser amperage sub-panel?
 

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Discussion Starter · #4 ·
You need to provide a manufacturer and model number for your panel. No one can give you an answer without that info.

FW
OK, it is a Zinsco, but I don't know how to find the model #. There is a UL numberA-4017. I am aware of the issues with Zinsco panels, but I do want to find out the amperage of this one, it is fed with #2 aluminum wire. Here are photos:

By yellowdog5, shot with Canon PowerShot A620 at 2009-05-04


By yellowdog5, shot with Canon PowerShot A620 at 2009-05-04
 

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Discussion Starter · #5 ·
I forgot to say, I figured out that the sub panel is 125 amp, but the one in the above post is what feeds the 125 amp panel. I want to know if I can put more than a 60 amp breaker on the main panel.
 

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You can use whatever size panel you want.

The 60 amp breaker protects the 60 amp wire feeding the sub.

You cannot put a larger breaker on the 60 amp feeder wire.

Edit. I'm confused. Is the main panel pictured?
 

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Discussion Starter · #7 ·
Yes, the main panel is pictured. Can you tell me anything about it? It is fed by #2 aluminum wire and it has a 60 amp breaker. Can I use a larger breaker, or 2 breakers (a double pole 30 amp for the well and a double pole 60 amp for the sub panel?
 

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IF YOU CAN TURN OFF THE POWER, you can easily replace the panel. Change it to one with a few more spaces.

And tape those neutrals white.


And tighten that locknut when you reinstall the conduit.


As far as running a bigger circuit to the barn sub (the conduit exiting the lower left?), you will need to increase wire size to get more amperage out there. To increase wire size, you will need to increase conduit size.
 

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Discussion Starter · #12 · (Edited)
IF YOU CAN TURN OFF THE POWER, you can easily replace the panel. Change it to one with a few more spaces.

I can't turn off the power, that's why I'm asking all these questions. I think the #2 aluminum wire is the limiting factor. What is the maximum ampacity of #2 aluminum (type THW)? And my other question is how can I determine the ampacity of the panel pictured?
 

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Once again, to clarify, you can put a larger breaker in to feed your sub panel but you have to upsize the wire and conduit also.

The breaker protects the wire.

Since you "can't" turn off the power, be very careful when removing/replacing the breaker. In fact, don't do it. Even I would hesitate doing it and I have decades of expeience, Things happen....like phase to phase explosions from old equipment.

I would say that (although illegal) you would be safer...more safe... by pulling the meter to kill power. That's what I would do.
 

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Discussion Starter · #16 ·
I really appreciate everyone's advice. I already have #4 copper going to the subpanel. Is this adequate for 90 amps?
 

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I really appreciate everyone's advice. I already have #4 copper going to the subpanel. Is this adequate for 90 amps?
According to the ampacity chart link I posted, 85A is the max for #4 copper THW.
 
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