Several motors and other loads on conductors

[Jpflex]

Hi I’m trying to get a general idea on feeder size for ball mill building.

The largest motor has two ampere ratings on nameplate for 3 phase 380 volt source one at 225 amperes and another for rotor current at 150 amperes. Since this is a low RPM motor under 1200 rpm code 430.6A says to use nameplate current rather than FLC based on Horsepower and NEC tables. I assume I go off of 225i ampere rating?

I’m not sure when you would go off of field current vs rotor current. Rotor current is merely induced voltage current from field.

When trying to figure out feeder I’m following NEC 430.24 for multiple motors and loads on a circuit

So far I have two identical large at 225 amperes with one being rated at 125% and the remaining motors at 100%

225i x 1.25 + 225 = 506.25 amperes so far
Plus

2 vat motors 7.5 of 3 phase with 11 FLC amperes each 2 x 11 = 22 amperes

6 more motors at 25 horsepower each or 34 FLC amperes each x 6 = 204 amperes

Ball mill general lighting VA based on outside dimensions 2485.02 sq ft x 1.7VA (workshop?) x 125% continuous load = 5281.28 VA

5281.28 va / 480v x 1.73(3 phase) = 6.35i amperes (Or do I go off of 120 v single phase voltage divider for lighting?)

Total all up = 738.6i amperes BUT table 310.16 only goes up to 665 amperes at 70 degree rating with 2000 kcmils

And there may be more motors being added

What do you do? Does this seem right so far?

 

[infinity]

Total all up = 738.6i amperes BUT table 310.16 only goes up to 665 amperes at 70 degree rating with 2000 kcmils

I'll leave the load calculating for someone else to comment on but if your load is 665 amps then you would typically use parallel conductors. For example 2 sets of 500 kcmil copper would give you 760 amps.

 

[Jpflex]

480 volts 3 phase not 380 volts shown above

 

[Jpflex]

I’m not familiar with the parallel method you mention. I’m used to a single conductor per phase

 

[ptonsparky]

Your life will be easier with parallel conductors.

 

[infinity]

I’m not familiar with the parallel method you mention. I’m used to a single conductor per phase

Have you ever worked with feeders or SEC's that exceed 400 amps? For the most part parallel conductors (connected at both ends) are used in "sets" to achieve the desired ampacity once you get above a certain size conductor. For us it's 750 kcmil. If I remember correctly here's 6 sets of 750 Kcmil Cu for a 2500 amp circuit.

 

[tom baker]

As the size of a wire increases, the ampacity is not proportional. So it’s less expensive to use multiple conductors in parallel.

 

[rambojoe]

Have you ever worked with feeders or SEC's that exceed 400 amps? For the most part parallel conductors (connected at both ends) are used in "sets" to achieve the desired ampacity once you get above a certain size conductor. For us it's 750 kcmil. If I remember correctly here's 6 sets of 750 Kcmil Cu for a 2500 amp circuit.
View attachment 2562560

Beautiful. Great crimps sir.

 

[Jpflex]

I have not worked with such high amperes before. I have Noticed today as you

As the size of a wire increases, the ampacity is not proportional. So it’s less expensive to use multiple conductors in parallel.

Ii have not had to work with s

Have you ever worked with feeders or SEC's that exceed 400 amps? For the most part parallel conductors (connected at both ends) are used in "sets" to achieve the desired ampacity once you get above a certain size conductor. For us it's 750 kcmil. If I remember correctly here's 6 sets of 750 Kcmil Cu for a 2500 amp circuit.
View attachment 2562560

uch high current before

Have you ever worked with feeders or SEC's that exceed 400 amps? For the most part parallel conductors (connected at both ends) are used in "sets" to achieve the desired ampacity once you get above a certain size conductor. For us it's 750 kcmil. If I remember correctly here's 6 sets of 750 Kcmil Cu for a 2500 amp circuit.
View attachment 2562560

 

[infinity]

I have not worked with such high amperes before.
I have not had to work with such high current before

No problem, there are many here who can answer your questions and make it easier to navigate an area that you may not be very familiar with.

 

[Jpflex]

Phone is acting up on my text but No I’ve worked mostly residential before this job at a mine, I now have. I’ve had to teach myself and become familiar with 3 phase 480 v systems.

We did decide to parallel circuits to split 1200 ampere load into 3 panel disconnects at 400 amperes each similar to your post

Although most likely backwards and incorrect the owner is having me size feeders based on transformer output rating rather than total Motors amperes and loads inside mill (which some motors he still doesn’t have - unknown Exact load values).

What then became confusing to me as an example was that If sizing a cable for 380 amp capacity at 75 degree termination for circuits over 100 amps And using 90 degree THHN conductor sized for 75 degree Ampacity you’ll have to use 400 kcmil conductor rated at 380 amperes with a Breaker at 380. But this is not a standard size Breaker so going up gives you 400 ampere Breaker which then violates Conductor termination Above 75 degree ampacity

How can you follow one code just to break and contradict another?

 

[dkarst]

The largest motor has two ampere ratings on nameplate for 3 phase 380 volt source one at 225 amperes and another for rotor current at 150 amperes. Since this is a low RPM motor under 1200 rpm code 430.6A says to use nameplate current rather than FLC based on Horsepower and NEC tables. I assume I go off of 225i ampere rating?

I’m not sure when you would go off of field current vs rotor current. Rotor current is merely induced voltage current from field.

This seems odd to me... I don't think the rotor current would be listed on nameplate if it is induced as you state. Maybe this is some wound rotor motor which is doubly fed for speed control? I think you need more investigation before ignoring the 150A.

 

[Jpflex]

This ball mill is from the 1920 - 1950s I tried to upload photo nameplate but didn’t work. It does indeed give two ampere ratings. I assume field is one listing and rotor another

 

[Jpflex]

Last photo was blurry possibly due to reducing size for upload

 

[ptonsparky]

Wow, I haven't seen a wound rotor setup for 40 plus years. Mine was a 40 ton overhead crane and some smaller ones at a Rockwell international Valve making plant.

Does it have a bank of resistors to control speeds?

 

[dkarst]

Wow, that's a great old motor. I'm a bit out of my expertise here but how are you planning to start it? After sleeping on my earlier response and reading some information on ball mills, there are a few starting methods from liquid rheostats to now even VFDs. My original thoughts were if you were thinking you were going to start this across the line with such a high inertia load you would upset power provider but now I see you are in a mine so maybe not an issue depending on source stiffness and voltage drop. I'll wait until someone with more experience in this area stops by.

 

[Jpflex]

Wow, I haven't seen a wound rotor setup for 40 plus years. Mine was a 40 ton overhead crane and some smaller ones at a Rockwell international Valve making plant.

Does it have a bank of resistors to control speeds?

How do you tell if it’s a wound motor? Can you tell by liking into windings and I know it’s not series connecting such as field and rotor. As far as resistors I doubt and I believe it isn’t speed controlled. Oddly the speed is under 1200 rpm and NEC says to go off of nameplate amperes instead of FLC table when determining conductor and overload protection

 

[Jpflex]

Wow, that's a great old motor. I'm a bit out of my expertise here but how are you planning to start it? After sleeping on my earlier response and reading some information on ball mills, there are a few starting methods from liquid rheostats to now even VFDs. My original thoughts were if you were thinking you were going to start this across the line with such a high inertia load you would upset power provider but now I see you are in a mine so maybe not an issue depending on source stiffness and voltage drop. I'll wait until someone with more experience in this area stops by.

Indeed even the engineer here who I spoke with mentioned the Possibility of the utility not having enough ampere potential from pole lines

 

[Jpflex]

Up in the attic of some old houses here I found old mail from 1950 and pages of coloring and school math test from a child who may be dead by now? It felt weird holding on to someone’s old memory from the past when once young

 

[ptonsparky]

Wound rotor motors have a lower start up current. High torque. Mine had banks of resistors.

Were you given the motor without the control?