30 HP Pump Motor Feed

[FountainGuy]

Hello Guys! This is my first post.

I have a fountain system that will use a 30HP PACO pump (close couple end suction centrifugal type) with a 460V 3-phase ODP motor. I plan to use a Square-D motor starter and motor protector. The NEC FLA is 40.0, and I don't know what the nameplate amps are yet. I plan to use a 100A disconnect switch and request a 100A feed that originates from a building CB panel about 200 feet away. The pump will be within six feet from the control panel. I plan to use #8AWG THHN wire for the pump connection. The motor protector is protecting the #8AWG wire, not the circuit breaker. Can the wire from the 100A 3-pole CB source also be #8AWG or does it have to be size based on the the 100A circuit breaker size, #3AWG?

 

[iwire]

Can the wire from the 100A 3-pole CB source also be #8AWG or does it have to be size based on the the 100A circuit breaker size, #3AWG?

Likely code wise yes but at 200' away 8 AWG is likely undersized and will result in excessive voltage drop.

 

[infinity]

So you have a 100 amp CB feeding a 40 amp motor with the controller next to the motor and you want to use #8 AWG conductors? 40 amps at 200' will give you about a 2% VD.

 

[iwire]

So you have a 100 amp CB feeding a 40 amp motor with the controller next to the motor and you want to use #8 AWG conductors? 40 amps at 200' will give you about a 2% VD.

40 amps is not the start up current.

 

[ActionDave]

40 amps is not the start up current.

No, but on a centrifugal pump it's not such a critical thing. Limiting the start up current would act like a poor man's soft start.

 

[ActionDave]

Hello Guys! This is my first post.

I have a fountain system that will use a 30HP PACO pump (close couple end suction centrifugal type) with a 460V 3-phase ODP motor. I plan to use a Square-D motor starter and motor protector. The NEC FLA is 40.0, and I don't know what the nameplate amps are yet. I plan to use a 100A disconnect switch and request a 100A feed that originates from a building CB panel about 200 feet away. The pump will be within six feet from the control panel. I plan to use #8AWG THHN wire for the pump connection. The motor protector is protecting the #8AWG wire, not the circuit breaker. Can the wire from the 100A 3-pole CB source also be #8AWG or does it have to be size based on the the 100A circuit breaker size, #3AWG?

Welcome to the forum.

I'm unclear about where you want to run your #8, the entire 200' or just from the disconnect to the motor?

 

[iwire]

No, but on a centrifugal pump it's not such a critical thing. Limiting the start up current would act like a poor man's soft start.

I know Dave, I know.

But I feel the installer should be aware of it and not just go with the 'Dave's cool with it' method.

 

[kwired]

Have you looked into using a pump panel instead of separate disconnect and motor starter enclosures?

Nothing wrong with running 8 AWG on the 100 amp breaker if this supplies just the single motor. Square D slide chart I have suggests using an 80 amp breaker on a 30 HP motor but NEC says you can go with 250% FLA which would be 100, and if that won't let the motor start (which it should in your case) then you can go even higher - up to 400% in your situation. See 430.52 for information on max settings.

 

[ActionDave]

I know Dave, I know.

But I feel the installer should be aware of it and not just go with the 'Dave's cool with it' method.

If I am cool with it then it is very cool. VD is on my bottom five list of things to worry about.

You do have a valid point though. I get paid to fix things when they go wrong and don't really have much pressure to design something that will work out of the box.

 

[Besoeker]

40 amps is not the start up current.

I don't know what a ODP motor is but, if its a three phase cage induction motor, then six times FLA is likely to be the order on initially closing the supply.

 

[FountainGuy]

Welcome to the forum.

I'm unclear about where you want to run your #8, the entire 200' or just from the disconnect to the motor?

I want to run #8 through the entire 200' run, and originate from a 100A 3-pole breaker. An EE told me that the 200' run up to the motor protector needs to be #4 and originate from an 80A breaker. He says that #8 is ok from the motor protector to the pump, but that the motor protector only protects downsteam and not upstream. My thought is that when the motor protector does it's job, it protects the wire for the entire feed. This feed is just for one 30HP motor.

 

[FountainGuy]

Likely code wise yes but at 200' away 8 AWG is likely undersized and will result in excessive voltage drop.

Depending on what the original voltage actually is, the 200' long wire might need to be upsized to #6. But if the voltage drop was acceptable, does the wire need to be #4 on an 80A breaker or can it be #8 on a 100A breaker?

 

[FountainGuy]

So you have a 100 amp CB feeding a 40 amp motor with the controller next to the motor and you want to use #8 AWG conductors? 40 amps at 200' will give you about a 2% VD.

If originating from exactly 480V, a 2% loss gets you 470.4V for a 460V motor. I'm cool with that. On my control panel schematic/drawing though, I don't specify the feed size. 200 feet on a drawing could end up being +/- 80 feet, usually +, not -, so its typically up to the Site Electrician to select either #6 or #8 based on actual length. Usually, they'll stay on the conservative side and select #6 in this case.

 

[FountainGuy]

I don't know what a ODP motor is but, if its a three phase cage induction motor, then six times FLA is likely to be the order on initially closing the supply.

Open Drip-Proof motor, as opposed to a TEFC (Totally Enclosed Fan-Cooled) motor. Square-D has an Excel spreadsheet program on their site (free download) that says to use a 100A breaker and #8 wire.

 

[FountainGuy]

Have you looked into using a pump panel instead of separate disconnect and motor starter enclosures?

Nothing wrong with running 8 AWG on the 100 amp breaker if this supplies just the single motor. Square D slide chart I have suggests using an 80 amp breaker on a 30 HP motor but NEC says you can go with 250% FLA which would be 100, and if that won't let the motor start (which it should in your case) then you can go even higher - up to 400% in your situation. See 430.52 for information on max settings.

There will be a control panel for the entire fountain system. There is also a 120/208V 3-phase feed for a filter pump, sump pump, pump vault ventilation and lighting, fountain LED lights, water level controls, wind compensation controls, and controls (time clocks and H-O-A switches for the pumps and lights). I have seen but don't have that Square D slide chart. On Square D's web site, you can download an Excel program/chart that says to use a 100A breaker and #8 wire for this 30 HP 460V motor.

 

[kwired]

I want to run #8 through the entire 200' run, and originate from a 100A 3-pole breaker. An EE told me that the 200' run up to the motor protector needs to be #4 and originate from an 80A breaker. He says that #8 is ok from the motor protector to the pump, but that the motor protector only protects downsteam and not upstream. My thought is that when the motor protector does it's job, it protects the wire for the entire feed. This feed is just for one 30HP motor.

For a single motor circuit, the breaker which could be up to 160 amps max if that is what is needed to hold on starting is what provides short circuit and ground fault protection. The motor overload inherently protects the conductors from overload as well. 8 AWG is fine the entire length as long as the voltage drop is deemed acceptable.

There will be a control panel for the entire fountain system. There is also a 120/208V 3-phase feed for a filter pump, sump pump, pump vault ventilation and lighting, fountain LED lights, water level controls, wind compensation controls, and controls (time clocks and H-O-A switches for the pumps and lights). I have seen but don't have that Square D slide chart. On Square D's web site, you can download an Excel program/chart that says to use a 100A breaker and #8 wire for this 30 HP 460V motor.

From past experiences I'd guess this motor would start on a 60 or 70 amp breaker and maybe even a 50, especially with some circuit length to choke the starting current, but unless using something already available just because it is available I am ordering the 80 amp breaker that is listed on my slide chart. Never had any issues starting a general purpose motor in good condition driving a load in good condition with the fuses or breaker settings on that chart.

 

[Besoeker]

Open Drip-Proof motor, as opposed to a TEFC (Totally Enclosed Fan-Cooled) motor. Square-D has an Excel spreadsheet program on their site (free download) that says to use a 100A breaker and #8 wire.

Most the thre-phase motor applications I dealt with were on variable speed drives. The relative small numbers of direct on line starter applications I got involved with had starting currents of between 5.5 and 6.5 times full load current.The breaker tripping characteristics had to accommodate that.

For something like a pump, the inertia would be quite low as a rule so loading beyond its declaared rating wouldn't last very long.

Here's one I made earlier...as they say on cooking shows.....
It's an application on a centrigugal gas compressor.

The initial starting current (top blue curve) is 6.5 times FLC and it doesn't drop much below 6% even by the the motor gets to about 90% of running speed. Sounds like a long period at high current but in real time it isn't. The motor is quite large relative to the driven machine.

 

[Jraef]

The real issue is whether that 100A breaker will be considered a Feeder or the Branch OCPD. Branch is defined as the last device before the load. In this case, your motor protector will technically be the Motor Branch Over Current Protective Device, so the 100A breaker could be considered the feeder, which means the conductors are sized for the feeder circuit. You also must check the UL listing of the motor protector to see if it is listed to be the Motor Branch Over Current Protective Device at all, some are not and require another OCPD in the circuit ahead of it anyway.

In your situation if there is NO other load on that circuit besides the motor, you could interpret that 100A CB as the branch device, and consider the motor protector as just the OL only. The problem with that though is the next guy that sees this long after you are gone. He sees a 100A breaker, then he sees another Branch device at the other end for your motor and decides, without checking the conductor size, that he can tap another load off of that 100A breaker circuit, which makes it a Feeder now. That's when your conductors are in trouble. Your Engineer may be wanting to err on the side of caution.

 

[david luchini]

The real issue is whether that 100A breaker will be considered a Feeder or the Branch OCPD. Branch is defined as the last device before the load. In this case, your motor protector will technically be the Motor Branch Over Current Protective Device, so the 100A breaker could be considered the feeder, which means the conductors are sized for the feeder circuit. You also must check the UL listing of the motor protector to see if it is listed to be the Motor Branch Over Current Protective Device at all, some are not and require another OCPD in the circuit ahead of it anyway.

#8 conductors would be properly sized feeder conductors for the 100A feeder breaker, per 430.24 and 430.62.

 

[zbang]

The real issue is whether that 100A breaker will be considered a Feeder or the Branch OCPD. [...]
In your situation if there is NO other load on that circuit besides the motor, you could interpret that 100A CB as the branch device, and consider the motor protector as just the OL only.

It sounds like there will be other equipment located with the pump, so unless the pump room is actually part of the building with the supply panel, there will be multiple supply circuits going to what's probably a separate structure, and that a problem.

Is this pump and the supporting equipment part of the main building or part of a separate shed or pump room? That'll make all the difference.