SIZING A SERVICE FOR MULTIPLE MOTOR LOADS RUNNING AT THE SAME TIME.

[Knox]

I AM IN THE PLANNING STAGE OF A GRAIN SETUP FOR A FARMER.
I AM WORKING ON SIZING THE SERVICE AND WOULD LIKE SOME SECOND OPINIONS.
HE CURRENTLY HAS A 208/120 3PH 600A SERVICE ON SITE. THE NEW SETUP WILL
CONTAIN THE FOLLOWING MOTOR LOADS THAT COULD POTENTIALY ALL BE RUNNING AT THE SAME TIME.
DRY GRAIN LEG: 1 - 75HP 3PH FLC 211A
WET GRAIN LEG: 1 - 30HP 3PH FLC 88A
LOAD CONVEYOR #1: 1 - 20HP 3PH FLC 59.4A
LOAD CONVEYOR #2: 1 - 20HP 3PH FLC 59.4A
DRYER BLOWER FAN #1: 1 - 20HP 3PH FLC 59.4
DRYER BLOWER FAN #2: 1 - 20HP 3PH FLC 59.4
DRYER BLOWER FAN #3: 1 - 20HP 3PH FLC 59.4
DRYER UNLOAD AUGER: 1 - 7 1/2HP 3PH FLC 24.2A
BIN FAN #1: 1 - 10HP 3PH FLC 30.8
BIN FAN #2: 1 - 7 1/2HP 3PH FLC 24.2A
BIN FAN #3: 1 - 7 1/2HP 3PH FLC 24.2A
BIN FAN #4: 1 - 7 1/2HP 3PH FLC 24.2A

CALCULATED FEEDERS USING (LARGEST MOTOR FLC X 1.25 + SUM OF REMAINING MOTOR LOADS FLC'S)
211 X 1.25 + 512.6 = 776.35

SIZE A MINIMUM OF AN 800A 3PH 208/120 SERVICE

I WILL MORE THAN LIKELY SIZE THE SERVICE TO 1,000A TO ALLOW FOR FUTURE EXPANSION AS THERE ARE ALREADY TALKS OF ADDING ANOTHER BIN OR 2 IN THE FUTURE AND MAY ALSO BE INSTALLING MOTORIZED SPREADERS AT THE TOP OF THEM.

AM I SIZING THIS CORRECTLY OR AM I MISSING SOMETHING.

THANK YOU ALL IN ADVANCE FOR YOUR COMMENTS/HELP.

 

[jumper]

Welcome to the forum!

Please note that typing in all caps makes a post hard to read and that some people consider all caps as a form of shouting or yelling.

Not a big deal as this is your first post, but please try and keep it in mind for future posting.

Good luck with your project.

 

[Smart $]

You appear to be sizing correctly. However, I did not check your math... nor can I account for any load which you may have omitted inadvertently :blink:

 

[augie47]

Your calculations look correct for sizing a multiple motor feeder, but I would look at Art 430 Part V
for motor feeder protection. If you are going to have a service or feeder Main, you will see those calculations will take you closer to a 1200 amp. Considering the possibility of future load I would be thinking more along those lines especially if your larger motors are across the line start.

SEE LATER POST

 

[m sleem]

Are these motors working simultaneously ?!!

 

[Smart $]

Your calculations look correct for sizing a multiple motor feeder, but I would look at Art 430 Part V
for motor feeder protection. If you are going to have a service or feeder Main, you will see those calculations will take you closer to a 1200 amp. Considering the possibility of future load I would be thinking more along those lines especially if your larger motors are across the line start.

You're talking about short circuit and ground fault protection (SC/GFP), whereas the OP only mentioned feeders. OP calculates minimum feeder ampacity. Once he starts implementing the maximum permitted protection device rating on the feeder (or service), that'll push the rating over 800A...

Here's where I am not clear. Does 240.4(C) kick in and and his feeder conductors will have to have an ampacity not less than the SC/GFP rating? Note 240.4(C) uses the terminology overcurrent devices, but Article 430 uses short-circuit and ground-fault protection. Are they considered one and the same for the purpose of 240.4(C) or not?

 

[petersonra]

I do not think there is any real difference in cost of service equipment between 1000A and 1200A. Does a service over 800A require GF protection as a feeder does?

The POCO will size their side of it according to their own criteria. They might well size it for 600A.

 

[Knox]

These motors will not all start simultaneously, but can all be running at the same time. For those unfamiliar with a grain setup I will explain, sometimes a better understanding of how these loads operate gives a better vision of the situation. Typically a farmer will park a grain trailer over the 2 load conveyors (20hp each) and dump. The 2 load conveyors transport the grain into the wet leg. The 110' wet leg (30hp) moves the grain vertically and then dumps the grain into the Grain Dryer. The grain then travels down through the grain dryer were 3 blower fans (20hp each) dry and cool the grain. once the grain reaches the bottom of the dryer, the dryer unload auger (7 1/2hp each) dumps the grain into the dry leg. The 130' dry leg (75hp) moves the grain vertically where it is then dumped into the grain bins. Each grain bin has a bin fan at the bottom of it that pushes the air through the grain in order to finish cooling it.

The load conveyors and the wet leg will only be running while a truck is dumping through out the harvest. the grain dryer blower fans, dryer unload auger and the dry leg run continuous during the harvest as long as grain is there to be dried. The bin fans are usually on the majority of the time during harvest. So yes the motors can and will run simultaneously but do not necessarily all start at the same time.

 

[Knox]

Sorry about the first post in caps. The estimating program I use recommends using caps at all times. My computer is usually set with the caps lock on. Didn't mean anything by it, just force of habit and didn't know the meaning behind it as it pertains to a post or message. Thanks for the info. it explains why my salesman usually get back to me quicker when emailing a question from my computer compared to sending it from my phone!

 

[kwired]

Unless too late or not possible, do yourself a favor and get a 480 volt service to that system. It will be well worth it in copper and equipment costs alone.

 

[augie47]

The OP sent me an IM which pointed out an error in my post #4.
When I applied 430.62 to his loads I came up with a SCGF requirement a bit over 1000 amps and went to "next larger" which is not allowed by 430.62,

 

[m sleem]

The OP sent me an IM which pointed out an error in my post #4.
When I applied 430.62 to his loads I came up with a SCGF requirement a bit over 1000 amps and went to "next larger" which is not allowed by 430.62,

430.52 Exception.2 (c) allowing you to apply 300 x flc, thereby the 1200 a is ok.

 

[Smart $]

430.52 Exception.2 (c) allowing you to apply 300 x flc, thereby the 1200 a is ok.

The exception only permits an increase to 300% when table sizing proves insufficient to start motor.

211 FLC ? 250% = 528A
211 FLC ? 300% = 633A

528A + 513 FLC_SUM = 1041A
633A + 513 FLC_SUM = 1146A

1200A exceeds both 1041A and 1146A, so not permitted.

Adjustable 1200A frame can be used with a compliant trip setting or module.

PS: As prompted in my earlier post, and still unanswered, does the ocpd rating affect required conductor ampacity under 240.4(C) over 800A....???

 

[ActionDave]

Unless too late or not possible, do yourself a favor and get a 480 volt service to that system. It will be well worth it in copper and equipment costs alone.

My first thought when I read the op.

 

[m sleem]

The exception only permits an increase to 300% when table sizing proves insufficient to start motor.

211 FLC ? 250% = 528A
211 FLC ? 300% = 633A

528A + 513 FLC_SUM = 1041A
633A + 513 FLC_SUM = 1146A

1200A exceeds both 1041A and 1146A, so not permitted.

Adjustable 1200A frame can be used with a compliant trip setting or module.

PS: As prompted in my earlier post, and still unanswered, does the ocpd rating affect required conductor ampacity under 240.4(C) over 800A....???

Where i can find the rule that you use "next size down"?

 

[augie47]

Where i can find the rule that you use "next size down"?

In this case, where can you find an exception that allows you to go to the "next size up" since 430.62 states "a device not larger than,....."
(Unlike 430.52 which has wording that allows next size up.)

 

[augie47]

PS: As prompted in my earlier post, and still unanswered, does the ocpd rating affect required conductor ampacity under 240.4(C) over 800A....???

IMO, the wording of 240.4, first section, which states "except as otherwise permitted in 240.4(A)thru (G), allowing "G" to stand on its own.

 

[Smart $]

IMO, the wording of 240.4, first section, which states "except as otherwise permitted in 240.4(A)thru (G), allowing "G" to stand on its own.

Well that works for me ... anyone else on the same page?

One caveat perhaps... 240.4 general states "unless otherwise permitted or required in 240.4(A) through (G)." 240.4(C) could be considered as required, regardless of (G).

Somehow I feel I will still have a problem with it in the future because Article 430 uses the term short-circuit and ground fault protection while Article 240 uses overcurrent protection.

 

[m sleem]

In this case, where can you find an exception that allows you to go to the "next size up" since 430.62 states "a device not larger than,....."
(Unlike 430.52 which has wording that allows next size up.)

In fact, I can not understand how to apply 430.52 exception.1 in the presence of 430.62.:?

 

[augie47]

In fact, I can not understand how to apply 430.52 exception.1 in the presence of 430.62.:?

430.52 is for Individual Motor Circuits, 430.62 for Feeders. Different circuits, different rules (other than 430.62 references 430.52 as a starting point)