Wire Size When Replacing Machine.

According to the NEC:

You can use the existing conductors provided you do not have to alter or modify the lugs/connectors on the new equipment or the existing conductors in any way to get them to land properly.

Same holds true for the new 60A CB and existing conductors at the panel board.

You should check your local codes though to be sure you are in compliance.

Thanks, there would not be any modifications of any kind necessary.

Circuit breakers protect wire. It's the other way around that you would be worried about. Your concern here though is that your old wire isn't too physically big for the lugs on the new breaker. Also, why are you replacing in the first place. A failure of some sort in the past could have damaged your wire. If you're not just strapped for cash, I,d go ahead and R+R the wire too.

Thanks for your comments. We moved into the building about 2 years ago and had new wire ran then. I am replacing a 1988 machining center with a new one, much faster and uses less electricity. There will not be any problems with the lugs. I was concerned about resistance in the larger wire, not sure why.

De-rate the breaker to suit the new equipment, attach the lines, and away you go. No issues that I can think of as long as nothing has been modified. The new wires will carry the load, and actually will have less resistance than a set designed for the new machine (considering the wires are in good operational condition and have not been overheated).

Sounds like you are good to go.

Enjoy the new equipment!

-R

thanks,

I apologize in advance for getting very picky. ;-)

I would not use the term "de-rate" the breaker. I'm trying to think of a good example when you'd realistically de-rate the breaker (or anything)--de-rate implies (to me) that you use the existing breaker but apply it (that is, consider the rating) less than what it really is.

Maybe (not a good example) you'd derate a breaker if it was in a much higher ambient temperature condition than it was originally designed / rated for--maybe at 50 degrees C a 100 amp breaker should be derated to 80 amps.

What needs to be done here is replace the breaker with one suitable for the new machine, which, iiuc, is 60 amps.

(I was going to respond to this thread earlier--some machines (e.g., home electric furnaces) (sometimes) come with suitable overcurrent protection built into the equipment. If that is the case here, I'm pretty sure the 100 amp breaker could be left in place at the panel (to protect the old wires), because the overcurrent protection built into the machine would be suitable for protection of the machine.)

Now, should I mark this OT, or count on someone else doing it soon (after RVZ717 has seen it)?

What I meant by De-rate (poor choice of wording) is "replace with one of lesser value".

You could also install a new breaker panel fed from the existing 100amp breaker and have additional circuits available for expansion.

Thanks ronseto, that is something to consider.

Sure you can - no detrimental effect.

Have you heard of Sir Isaac Newton.

He cut a big hole through main door for his(fat) cat to go out.

Later Sir Newton brought home a small cat . And NOW he cut a SMALL hole for small cat to go out!