Sizing Conductors (Large motors)

[Jon456]

We have two large electric-powered pumps for evacuating a drainage pond; the pump motors are serviced by 3-phase delta 230VAC; each is on a magnetic starter with overcurrent protection, plus separate soft-start controllers for each motor.

Pump motor #2 is very old and no longer has a name plate; it draws 60A (measured) on each leg under load.

Pump motor #1 is just a few years old with the following specs: 40HP, Cont Duty, SF 1.15, 230VAC 60Hz, 100.0A, 117.0A (SF), PF 84.3, Max KVAR 10.2, Code F, Des B. This motor draws 114A (measured) on each leg under load.

Both pumps are automatically operated by a controller with on- & off-level float switch inputs. The controller alternates the activation of each pump to keep both exercised. There is also an alarm-level float that will energize both pumps if the water continues to rise after one pump is operating.

Ok, so on to the electric service. Here's where things get a bit "interesting"...

Outside on a pole, there's the meter base and a cutoff panel housing a 3-phase 100A (!) main OCPD. From there, four 2AWG copper CCC's and a 6AWG solid copper EGC pass through liquid-tight flex to the pump house where it enters a subpanel. The three hot legs from the outside cutoff panel are double-lugged on the subpanel bus with the three 2AWG copper CCC's that feed the branch circuit for pump motor #1. The branch circuit for Pump #2 (old) comes off a 3-phase 100A breaker in this subpanel.



The three 2AWG copper feeds for Pump #1 (new) goes from the double-lugged bus connectors in the subpanel to a fusible disconnect switch with 150A TD fuses.



From there, three 4AWG copper CCC's are routed to another wall in the pump house where they enter a second fusible disconnect switch with 125A TD fuses; this panel also contains the motor's mag starter.



Obviously, the service is insufficient for the load, even with the pump controller "alarm" condition disabled (so that both pump motors will never both be energized). Pump #2 (old) runs just fine on the existing service, but pump #1 (new) will sometimes trip the main 100A breaker in the outside cut-off panel. So we intend to upgrade the service to 200A. But it seems that the pump motor branch circuits probably need to be re-wired as well.

Also, it seems to me that the two fusible disconnect panels, wired in series for pump #1, are superfluous. I'm thinking, for pump #1, to run a new feeder from the soon-to-be-installed 200A main cut-off breaker directly to the second fusible disconnect (the panel with the mag starter for pump #1). I could then use the first fusible disconnect for pump #2 (not using the 100A breaker in the subpanel). Do you agree with this plan?

Also, it is my understanding that double-lugging is a violation (unless the lugs are specifically L&L for that). Would you recommend Polaris connectors inside the cut-off panel for the three feeder circuits (subpanel, pump motor #1, pump motor #2)?

So now for the conductor sizing questions (all copper THHN)...

1. If I do use one fusible disconnect panel for each pump motor, how should I size the feeder conductors from the 200A main cut-off breaker to the hot lugs in the fusible disconnect panels? Can the feeder conductors be sized for the loads on each branch circuit? Or do I need to size the feeder conductors to the 200A rating of the OCPD. If so, then I believe that would force the sizing to be 3/0 copper (and I'd probably have to put the taps for the feeders inside the wireway above the subpanel ).

2. Pump motor #2 has no name plate so I cannot calculate the FLC. But given that it draws 60A under load and it's currently wired using 4AWG copper THHN, should I just leave that as is?

3. By my calculations, the branch circuit conductors for pump motor #1 are undersized. From NEC Table 430.250, the FLC is 104A. Sizing it to 125% (430.22A) means a conductor ampacity of 130A. Thus 1AWG. Correct? Btw, wouldn't this also mean the TD fuses should be sized at 175% FLC = 183A (200A standard fuse)?

Thanks for your assistance!

 

[RUWired]

Jon, you obviously have some problems for sure. Just looking at the pictures you have 6 nec violations. 1 is (230.42)the service is not rated for the load, 2 is (250.32B)the grounds and neutrals should be seperated in the pump house panel, 3 is (250.32)i don't see a grounding electrode conductor installed, 4 is (110.14A)the tap on the lugs, 5 is (408.3E)the higher voltage to ground should be on the "B" phase,and 6 is (225.33A)when you do actually put in the required breaker for the 1st pump you will have more than 6 disconnecting means in the panel and a disconnect will be required.

Running a seperate feeder from the new 200 amp panel to pump 1 will be a problem with 225.30, and using the existing 100 amp panel with a 200 amp feed will be a problem with 408.36,

I would suggest upgrading the service and feeder to the pump house, install a panel with a main breaker or install a disconnect before the new panel in the pump house and correct all the problems.

Rick

 

[Jon456]

Thanks Rick for your reply.

Jon, you obviously have some problems for sure. Just looking at the pictures you have 6 nec violations.

Yup... it's a mess. And I was told this was installed by a Master Electrician (although to be fair to him, he had wanted to upgrade the service to 200A). Actually, there's even more violations not pictured or discussed. I didn't mention all the violations because was trying to focus the topic on my questions at hand. But I'd like to address and clarify some of the points you've raised.

4 is (110.14A)the tap on the lugs

I am curious about this. If a termination point is L&L for double lugging, is that typically marked conspicuously on the equipment? I've seen a lot of diagrams and book photos showing double lugging in panels such as this. In fact, here is a nice diagram from our forum's host that implies a double-lugged connection:



So how do I know when a double-lugged termination is in violation? Do I have to contact the manufacturer of each panel to inquire if it's permitted?

6 is (225.33A)when you do actually put in the required breaker for the 1st pump you will have more than 6 disconnecting means in the panel and a disconnect will be required.

I wasn't planning on putting in a breaker for pump #1 (new). I want to use one of the existing fusible disconnect panels for pump #1. In fact, I want to take pump #2 (old) off the 100A breaker in the subpanel, and use the other existing pusible disconnect panel for pump #2. [After this post, I'll draw and post some diagrams to illustrate what we have and what I want to do.]

So after I remove the 100A breaker from the subpanel, there will be 6 or less disconnecting means in that subpanel, all for single-phase branch circuits (one or two of the breakers in that panel are unused and I will remove them).

Running a seperate feeder from the new 200 amp panel to pump 1 will be a problem with 225.30, and using the existing 100 amp panel with a 200 amp feed will be a problem with 408.36

I'm not clear from 225.30 why there is a problem running three seperate feeders from the 200A main cut-off (one feeder to each of the fusible disconnect panels for each pump, and one feeder for the subpanel). Would it help if the new meter base and 200A cut-off are going to be located on the exterior wall of the pump house (on the backside of the wall the subpanel is mounted on) as opposed to being on a pole detached from the pump house (as the 100A service is now)?

I forgot to make note of the subpanel specs when I was last out there, but it does look like a 100A panel from the size of the lugs and bus bars; I'll check next time I go out there. So according to 408.36, when the service is upgraded to 200A, then the subpanel must also be upgraded to 200A, even if the load in the subpanel is far less than 200A. Correct? If so, then each of the fusible disconnect panels would also need to be rated to 200A?

I would suggest upgrading the service and feeder to the pump house, install a panel with a main breaker or install a disconnect before the new panel in the pump house and correct all the problems

The service will be upgraded with a new SECs and combination 200A meter base/breaker which will be mounted on the exterior wall of the pump house. I'm still not clear about the sizing requirements for the feeders to the pump motor fusible disconnect panels and to the subpanel.

You suggest installing a panel with main breaker or a disconnect before the new panel in the pump house. Isn't that what the new cut-off panel is doing? :-?

 

[RUWired]

I am curious about this. If a termination point is L&L for double lugging, is that typically marked conspicuously on the equipment? I've seen a lot of diagrams and book photos showing double lugging in panels such as this. In fact, here is a nice diagram from our forum's host that implies a double-lugged connection:



So how do I know when a double-lugged termination is in violation? Do I have to contact the manufacturer of each panel to inquire if it's permitted?

In the diagram the lugs are 2-hole mechanical. Mechanical lugs whether single or double have the conductor size stamped on them and in parenthesis, the number of conductors allowed in the lug.The single lugs that are rated for more than one conductor look elongated front to back typically.

. [After this post, I'll draw and post some diagrams to illustrate what we have and what I want to do.]

pictures are great

I'm not clear from 225.30 why there is a problem running three seperate feeders from the 200A main cut-off (one feeder to each of the fusible disconnect panels for each pump, and one feeder for the subpanel). Would it help if the new meter base and 200A cut-off are going to be located on the exterior wall of the pump house (on the backside of the wall the subpanel is mounted on) as opposed to being on a pole detached from the pump house (as the 100A service is now)?

Is the cut off panel outside a disconnect, breaker enclosure or main panel? My quote about 225.30 was a broad statement. The feeder disconnect for a building can be located outside and doesn't have to be attached to the building. It can be remote, but needs to be at a readily accessible location. I'm not sure how far away the meter and cutoff panel is from the building. If its close, it would qualify but could be a judgement call.

I forgot to make note of the subpanel specs when I was last out there, but it does look like a 100A panel from the size of the lugs and bus bars; I'll check next time I go out there. So according to 408.36, when the service is upgraded to 200A, then the subpanel must also be upgraded to 200A, even if the load in the subpanel is far less than 200A. Correct? If so, then each of the fusible disconnect panels would also need to be rated to 200A?

Should the outdoor panel qualify as the required disconnect for the building and you run the three seperate feeders in to the building for the sub and two disconnects, then the drawing would help for location of OCP and size conductors for each of the feeders or if their taps from the new 200 amp.

You suggest installing a panel with main breaker or a disconnect before the new panel in the pump house. Isn't that what the new cut-off panel is doing? :-?

If the location of the cutoff panel is readily accessible the new cutoff panel could be used. If the new cutoff panel is an enclosed breaker or disconnect, then you'll have to deal with the tap rules for each of the three feeders. Seeing the one line drawing will clarify a lot more.

Rick

 

[Jon456]

In the diagram the lugs are 2-hole mechanical. Mechanical lugs whether single or double have the conductor size stamped on them and in parenthesis, the number of conductors allowed in the lug.The single lugs that are rated for more than one conductor look elongated front to back typically.

Ahhh... I didn't notice the 2-hole lugs in that diagram. (I have a large monitor that I run at hi-res, so the diagram is really small. Without zooming, it's easy to overlook those two screws.) Thanks for the additional info... very helpful!

pictures are great. Seeing the one line drawing will clarify a lot more.

Sorry, I'm still working on those.

Is the cut off panel outside a disconnect, breaker enclosure or main panel? My quote about 225.30 was a broad statement. The feeder disconnect for a building can be located outside and doesn't have to be attached to the building. It can be remote, but needs to be at a readily accessible location.

The existing 100A service entrance is on a pole no more than 3 ft from the pump house door. The new 200A service will be mounted on an exterior wall of the pump house (back side of the interior wall with the subpanel and one disconnect). The new service will be just around the corner from outside the pump house door... about 3 ft walking distance.

The new 200A service/cut-off panel is listed as a "Commercial Meter Socket With Main Circuit Breaker". It encloses a single 200A 3-phase breaker.

Should the outdoor panel qualify as the required disconnect for the building and you run the three separate feeders in to the building for the sub and two disconnects, then the drawing would help for location of OCP and size conductors for each of the feeders or if their taps from the new 200 amp.

I think the new cut-off will qualify as the disconnect. But I'm still unsure about how to size the feeders (and where to make the connections for them).

I'll post more info soon.