Sizing A Service With 5 40HP Motors

[5 S electric]

Hello all,
Got another problem and all of you guys are great at helping me with them. We currently have a pump house with a 208 V 400 amp service. There are 5 30 HP pumps in there right now. The boss wants to upgrade these pumps to 40 HP pumps. They may all run at the same time but they do not all start at the same time. They start up in a sequence. The name plate on the motors he wants to buy is 90 amps at 230 v. I am almost positive they will not be pulling the nameplate. The pumps we currently have, have a nameplate of 70 amps at 230 V and they are only pulling 40 amps. My question is will the 400 amp service handle all 5 pumps and what article do i find this calculation?

Thanks in advance,
Scott

 

[petersonra]

Hello all,
Got another problem and all of you guys are great at helping me with them. We currently have a pump house with a 208 V 400 amp service. There are 5 30 HP pumps in there right now. The boss wants to upgrade these pumps to 40 HP pumps. They may all run at the same time but they do not all start at the same time. They start up in a sequence. The name plate on the motors he wants to buy is 90 amps at 230 v. I am almost positive they will not be pulling the nameplate. The pumps we currently have, have a nameplate of 70 amps at 230 V and they are only pulling 40 amps. My question is will the 400 amp service handle all 5 pumps and what article do i find this calculation?

Thanks in advance,
Scott

I don't think you can do that. See article 220 for how a service is required to be calculated.

I am not even sure you can use the motors that are rated for 230V on a 208V service, although many motors are dual rated for 208 and 230 V. If he is going to replace the motors, why not get the right ones?

According to my handy-dandy slide rule, a 208V 40 HP motor is calculated at 120 Amps.

I am curious why he wants to increase the size of motors that are not even running at full HP.

Just curious - what is a journeyman contractor that you have in your profile? Never heard that term before.

 

[augie47]

I agree with Petersonra

By Code, you should not be able to do what you are doing now with the 30HP much less 40s.

As always, the devil is in the details. The type motor, how they are loaded and how they are controlled (across the line start or drives) are all factors that will make a big difference.

Code in 220.14 refers you to 430.22 and 430.24 using the Table 430.250 values (unless you are using drives). A quick math check shows (5) 30 hp or 40 hp would be too great a load for a 400 amp service.

 

[Cow]

You should have at least a 600 amp service now, 800 if you go to 40hp motors.

 

[GoldDigger]

And if you have been getting good performance from your 200A service you have some load diversity factors that the NEC calculations do not recognize.
Even if you put in an 800A service, POCO may not change their existing transformers.
But the key point is that going to larger motors opens up the whole compliance issue.

 

[ActionDave]

I don't think you can do that. See article 220 for how a service is required to be calculated.

I'm not going to do that because I am so terrible at math and have found I can avoid it most of the time.

I am not even sure you can use the motors that are rated for 230V on a 208V service, although many motors are dual rated for 208 and 230 V.

You can. Don't try and use a 200V motor on 230V though.

If he is going to replace the motors, why not get the right ones?

Always the better choice.

 

[augie47]

(some related posts were moved to their own thread "Elevator Service")

 

[Tony S]

All could run, but it sounds highly unlikely considering the recorded loading on the installed pumps unless there are plans afoot to increase throughput considerably.
You have sequenced start up, therefore only one motor’s inrush needs to be accounted for above the existing load.
The existing feed is showing no signs of distress, at the moment. Have you taken peak and average current readings over a period of a week?

It all hangs on are plans afoot to increase throughput considerably?
Changing from 30 to 40HP motors without anticipated production increase seems a strange thing to do. Unless it means you can run with one less pump and lower losses.

Questions only the OP can answer.



Our hydraulic pump house had 12x150HP pumps on 2x1200A 433V feeders.
A maximum of 10 pumps could run (officially).
Load based sequenced start up and shut down.

In 13 years I’ve never known of an O/C trip on the feeders.

 

[mjmike]

I agree with COW above. At lease an 800A service. Think of the service as a feed for multiple motors. (2.5 x largest motor FLA, select breaker then + FLA of all remaining motors. Puts you at about 780A.

 

[kingpb]

a 40Hp 208V motor FLA is 120A, 120A x 5 = 600A, exactly how is that going to work on a 400A breaker?

That was the engineering answer.

If it's not being inspected, you can always try it, if the main trips, then you know it won't work. Far stranger things have been done.