Control Voltage 480VAC for PB Start-Stop Station fm antiquated Combo-Starter.

Status
Not open for further replies.
I

Isaiah

Senior Member
Location
Baton Rouge
Occupation
Electrical Inspector
I have a very old combination starter, oil filled, installed sometime back in the 50's. The control voltage to Start-Stop PB station is tapped directly off L1 and L2 at 480V with NO CPT in between. I've never seen this before but cant see anything NEC wise that would prevent it, as long as the PB station has contacts rated for 480VAC.
Am I missing something?

Thanks in advance
Isaiah
 
Isaiah said:
I have a very old combination starter, oil filled, installed sometime back in the 50's. The control voltage to Start-Stop PB station is tapped directly off L1 and L2 at 480V with NO CPT in between. I've never seen this before but cant see anything NEC wise that would prevent it, as long as the PB station has contacts rated for 480VAC.
Am I missing something?

Thanks in advance
Isaiah
Click to expand...

pretty common on older larger starters. otherwise the coil current would become an issue.
 
ptonsparky said:
480 control is very common in what we call a Pump Panel. Fused sometimes, but often enough, not.[/QUOTE

Good point. The two wire control circuit is tapped within the starter L1 and L2, and run nearly 300 feet to the PB station —- no fuses on tap...conductors are number 14AWG. This can’t be good
Click to expand...
 
Isaiah said:
ptonsparky said:
480 control is very common in what we call a Pump Panel. Fused sometimes, but often enough, not.[/QUOTE

Good point. The two wire control circuit is tapped within the starter L1 and L2, and run nearly 300 feet to the PB station —- no fuses on tap...conductors are number 14AWG. This can’t be good
Click to expand...
Now that's a Big No, and has been for some time.
Click to expand...
 
430.72 covers the overcurrent protection for those conductors. The 14 AWG control conductors are permitted as long a the rating of the motor branch circuit OCPD does not exceed 45 amps.
 
The good thing with that is you don't have to need auxiliary contacts to make your starter work!

It was like "wow", when the gray-haired electrician taught me how to wire the 480V start/stop PB--> no auxiliary contacts!
 
don_resqcapt19 said:
430.72 covers the overcurrent protection for those conductors. The 14 AWG control conductors are permitted as long a the rating of the motor branch circuit OCPD does not exceed 45 amps.
Click to expand...
I have taken advantage of this rule a few times before. Then you can also increase control circuit conductor size in some situations and have even higher motor branch OCPD protecting it.

Only load is your contactor coil, maybe an indicator light in some cases, it has no real need for overload protection, just short circuit and ground fault protection.
 
topgone said:
The good thing with that is you don't have to need auxiliary contacts to make your starter work!

It was like "wow", when the gray-haired electrician taught me how to wire the 480V start/stop PB--> no auxiliary contacts!
Click to expand...

What do you mean by not needing any aux. contacts to make your starter work?


Jap>
 
kwired said:
I have taken advantage of this rule a few times before. Then you can also increase control circuit conductor size in some situations and have even higher motor branch OCPD protecting it.

Only load is your contactor coil, maybe an indicator light in some cases, it has no real need for overload protection, just short circuit and ground fault protection.
Click to expand...

I have to admit, I was surprised to see this is allowed...but when you consider, "Only load is your contactor coil"...it makes sense.

thanks to all

Isaiah
 
topgone said:
The good thing with that is you don't have to need auxiliary contacts to make your starter work!

It was like "wow", when the gray-haired electrician taught me how to wire the 480V start/stop PB--> no auxiliary contacts![/QUOTE]


Without a set of auxiliary contacts somewhere in the control circuit, activated by the overloads, you wouldn't actually have a starter at all.

If a 2 wire control, you would simply have a contactor who's coil is being controlled by a maintained on off switch.


JAP>
Click to expand...
 
When I worked at a steel mill, all of our starters used common control (which is what that is called). Up to 45A, no control fuse required, but we used a 10A fuse because contacts on PBs and relays were all rated for 10A max..

The thing is though that was in the days before any electronics in the systems; no PLCs, no VFDs, no Soft Starters anywhere. There were some DC drives of course, but those were all on their own isolation transformers. The reason I bring this up is that using common control means that when coils open and close on the line voltage, it creates transients that can affect power electronics. When there were no power electronics, there was nothing to affect. But now this is a really bad idea. If you have to do it, you should be adding coil suppressors on all equipment and by the time you do all of that, you could ahve bought a control power transformer.
 
Last edited:
Jraef said:
When I worked at a steel mill, all of our starters used common control (which is what that is called). Up to 45A, no control fuse required, but we used a 10A fuse because contacts on PBs and relays were all rated for 10A max..
Click to expand...
And depending on available fault current and current limiting abilities of your fuse, one might weld a switch closed anyway after closing it into a fault.
 
Isaiah said:
I have a very old combination starter, oil filled, installed sometime back in the 50's. The control voltage to Start-Stop PB station is tapped directly off L1 and L2 at 480V with NO CPT in between. I've never seen this before but cant see anything NEC wise that would prevent it, as long as the PB station has contacts rated for 480VAC.
Am I missing something?

Thanks in advance
Isaiah
Click to expand...

This was typical in the refinery i used to work at.
 
Status
Not open for further replies.
Top