what size disconnect

Status
Not open for further replies.
Sierrasparky

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I have just been asked to install a new machine in a machine shop.
Name plate tag say's 208v 3ph 96 amps
What size disconnect can I use?
Can I get away with a 100a
 
Sierrasparky said:
I have just been asked to install a new machine in a machine shop.
Name plate tag say's 208v 3ph 96 amps
What size disconnect can I use?
Can I get away with a 100a
Click to expand...
Perhaps 100A-rated disconnect would work... but don't have enough information to determine for certain.

The first question here is going to be how much of the 96A is continuous load. Additionally, is the disconnect also going to incorporate overcurrent protection. Is the machine comprised of one or several loads? What kind? How many? If multiple, what currents do the individual loads present to the overall, and are they continuous or non-continuous? Any motors? Combination motor, non-motor loads?

Does the machine's nameplate have any other electrical information on it? ...if so, what is it???
 
Smart $ said:
Perhaps 100A-rated disconnect would work... but don't have enough information to determine for certain.

The first question here is going to be how much of the 96A is continuous load. Additionally, is the disconnect also going to incorporate overcurrent protection. Is the machine comprised of one or several loads? What kind? How many? If multiple, what currents do the individual loads present to the overall, and are they continuous or non-continuous? Any motors? Combination motor, non-motor loads?

Does the machine's nameplate have any other electrical information on it? ...if so, what is it???
Click to expand...

how about the 80% rule does that not come into play:confused:
 
There are several motors and other loads, Primarily motors , The device will operate all day.
THe name plate says 208 3 ph 96 amps . This is an older machine I have

no additional information.

what percentage is continuous I don't know?

I am asking both overcurrent and size of disconnect. I am primarily looking at disconnect size because to go from up from 100 would be a 200 amp switch.

I hope this helps.
 
Sierrasparky said:
There are several motors and other loads, Primarily motors , The device will operate all day.
THe name plate says 208 3 ph 96 amps . This is an older machine I have

no additional information.

what percentage is continuous I don't know?

I am asking both overcurrent and size of disconnect. I am primarily looking at disconnect size because to go from up from 100 would be a 200 amp switch.

I hope this helps.
Click to expand...
This machine is multi-motor and combination load equipment. While it may have been factory wired, if it does not include all the information required under 430.7(D)(1), I believe you will have to consider it as a "Not Factory-Wired" unit under 430.7(D)(2) and perform your own determination for the minimum supply circuit conductor ampacity and the maximum ampere rating of the circuit short-circuit and ground-fault protective device.

Sorry, but can't get any more specific than this without all the necessary info.
 
I would do a load calc.

Does your new machine have a main in it? fusses or breaker?

If it does, I would size the feeders at least one breaker size bigger.
So the machines main trips before my feeder circuit.
avoids confusion of who's problem it is. :grin:
 
I thought you had to use the HP rating of the motor and then go to 430.250 and I also thought you have to size the disconnect at 115% of the fla.
 
Status
Not open for further replies.
Top