Several Motors on One Circuit

[Vi's_Dad]

I will try and be concise. I am moving a cord drop for a band saw which shares a circuit with another band saw and a hoist. Saw #1 has a FLA of 10.2 for the entire machine. Saw #2 is 9.7 FLA for the whole machine. These both have other components other than just the saw motors. The hoist is 1hp and has a nameplate of 3.5A @ 240V. They are all currently wired with #14s from a 240v 3 phase fuse panel with 15A fuses on that ckt. The saws branch (tap) off in a junction box to the individual cord drops and the hoist goes to a fused (15A) disconnect and then is hard wired. I believe 430.24 Exception #1 comes into play for sizing the conductors. I don't understand the last part "or the largest continuous..." They are never or very rarely running at the same time due to the lay out of the room (its very small) it just seems to me that #14 wire is too small. Does 430.28 come into play too? Sorry I wasn't concise. Take it easy on me this is my first post.

 

[augie47]

are the "cord drops" terminated in a 15 amp cord body or connected directly to the equipment ?
Is there any OCP internal with the equipment ?

 

[Vi's_Dad]

does this help?

does this help?

Only the saw I am wiring has a cord drop (its a 250v 20a 3ph body) the other saw is hardwired as well as the hoist. As for OCP yes the two saws each have fuses and motor starters with OLs to protect the motors. The hoist is wired from a fused disconnect. Keep in mind these are all on the same 3ph ckt from the fuse panel (15a fuses). Also I was told that it is common for both saws (but not the hoist) to be running at the same time but not for long periods of time (maybe 5 or 10 mins).

 

[kwired]

Your largest load you said is 10.2 amps. You said you have three different loads.

Lets assume for a moment that all three loads were 10.2 amps and they were balanced across the phases.

Each phase would be carrying 10.2 x 1.73 = 17.65 amps.

Now lets put 10.2 and 9.7 amp loads so they are sharing one phase.

9.7 x 1.73 = 16.78 + remainder of 10.2 amp load (.50) = 17.28

I am not going to figure the hoist 17.28 is the highest loaded phase.

14 AWG is good for 20 amps but the 17.28 probably does not take in account the fact that ampacity for conductors supplying motors needs to be 125% of the motor FLA. So I am guessing that the conductors likely need to be at least 12 AWG. The fact that they are on a 15 amp OCD kind of makes the installation acceptable but it should have originally been designed with 12 AWG conductors in the first place.

 

[Vi's_Dad]

quick reply

quick reply

thanks for the quick reply kwired! While you responded I was pulling in new #12 conductors.

 

[Jraef]

Your largest load you said is 10.2 amps. You said you have three different loads.

Lets assume for a moment that all three loads were 10.2 amps and they were balanced across the phases.

Each phase would be carrying 10.2 x 1.73 = 17.65 amps.

Now lets put 10.2 and 9.7 amp loads so they are sharing one phase.

9.7 x 1.73 = 16.78 + remainder of 10.2 amp load (.50) = 17.28

I am not going to figure the hoist 17.28 is the highest loaded phase.

14 AWG is good for 20 amps but the 17.28 probably does not take in account the fact that ampacity for conductors supplying motors needs to be 125% of the motor FLA. So I am guessing that the conductors likely need to be at least 12 AWG. The fact that they are on a 15 amp OCD kind of makes the installation acceptable but it should have originally been designed with 12 AWG conductors in the first place.

This is assuming the motors are single phase, he didn't actually say. If they are 3 phase he could potentially have almost 20A with both saws running.

 

[Vi's_Dad]

3 phase

3 phase

They are 3 phase loads I did mention that in my lengthy post.

 

[kwired]

They are 3 phase loads I did mention that in my lengthy post.

Somehow I missed that. So just add all of them together and add 25% of largest - that is your min conductor size. With numbers you gave in OP should need at least 23.4 amp conductor. You could easily have a 40 amp breaker on this if they are to all run at same time. The smallest motor especially likely needs individual overcurrent protection if there is a 40 amp breaker protecting it.

 

[Jraef]

Somehow I missed that. ...

Me too.

Vi's_Dad you didn't actually say that. You said they were wired from a 3 phase panel, but if they were single phase motors and a 3 phase service, that would be normal. I'm just being nit picky, I know.

Carry on, nothing to get excited about and no disrespect intended.

 

[Vi's_Dad]

thanks

thanks

I just want to thank everybody that responded to my question. This forum is an unbelievably helpful tool for any electrician. This was my first experience using it and it was certainly a good one.