50 hp motor 3 phase 460 volts sf 1.15

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Jpflex

Jpflex

Electrician big leagues
Location
Victorville
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Electrician commercial and residential
I still get confused at times on how to treat OCPD when planning the complete circuit from source 3 phase panel to the motor load

What I have figured out so far is:

1) CONDUCTORS Branch circuit wires to motor feed = 4 AWG THHN at 75 degree termination

2) OCPD = 175 I inverse breaker (for branch circuit feed)

65 FLC x 250% max = 162.5 i amperes go to next standard size up = 175 ampere breaker

3) GEC = # 6 AWG based on upstream 175 ampere breaker

4) EMT 1/1/2 inch size based on 3 x #4 AWG THHN plus 1 # 6 AWG equipment ground conductor

However, I am aware that under certain conditions such as in dwellings (which this is not being installed in) must be broken or supply power must be divided when the load is over 60 ampere or more

I am not sure if this NEC rule affects my set up in an industrial setting or how to go about doing this? Do I get a three phase panel with 3 individual breakers for each phase rated for 175 amperes, 1 three phase breaker with 3 ties, or do I assume each phase is 1/3 of the total 175 amperes and thereby get three 60 ampere breakers for each phase?
 

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ptonsparky said:
A 50 hp motor cannot be broken down to smaller loads.

Tell me why you would want anything but a single three phase breaker?

Can that motor be started at less than 250% ?
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I normally do not break up larger loads when they exceed 60 amperes. However, reading the NEC code book and the requirement to break down /divide loads higher than 60 amperes has brought me confusion. However, this rule may only apply to dwellings and stoves and I probably am over thinking.

Should I get a 225 ampere main 3 phase panel 480 volts with a single tie three phase 175 ampere breaker for the motors branch circuit OCPD then?
 
The breaking loads that exceed 60 amps only appears in a few specific Code areas such as some heating equipment.
When dealing with motors you need to concentrate on Art 430 and not confuse the issue from other Code sections.
 
The Sw D motor data calculator is a very handy slide calculator or for desk drawer. I they used to give away at trade shows , likely there is an on line version now.
 
augie47 said:
The breaking loads that exceed 60 amps only appears in a few specific Code areas such as some heating equipment.
When dealing with motors you need to concentrate on Art 430 and not confuse the issue from other Code sections.
Click to expand...
Would there be a requirement for an adjacent disconnect switch rated in horsepower or 115% of motor FLC within 50 feet of this motor outside be required if the main panel branch circuit breaker is indoors over 50 feet away and out of sight BUT the motor has a turn dial knob disconnect switch pre installed before but not known by who? See pic
 

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ptonsparky said:
That knob is a control. NOT a disconnect.
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The knob also disconnects power to the motor via starter controller circuit acting as a relay to disconnect higher voltage to the motor.

I’m assuming an additional outdoor rated panel with an appropriately rated snap switch with fuses, hp rated switch or inverse breaker as a disconnect will be needed?

I only asked about this knob because the NEC book says that a molded switch can be used as a disconnect.
 
Jpflex said:
The knob also disconnects power to the motor via starter controller circuit acting as a relay to disconnect higher voltage to the motor.

I’m assuming an additional outdoor rated panel with an appropriately rated snap switch with fuses, hp rated switch or inverse breaker as a disconnect will be needed?

I only asked about this knob because the NEC book says that a molded switch can be used as a disconnect.
Click to expand...
That is just a control switch. The disconnect itself must physically open the ungrounded conductors. A disconnect is always a manually operated device and not operated by a control switch.

A molded case switch looks just like a breaker but does not have any means to automatically open the circuit. It is simply a physical switch and is a means of disconnect.
 
don_resqcapt19 said:
That is just a control switch. The disconnect itself must physically open the ungrounded conductors. A disconnect is always a manually operated device and not operated by a control switch.

A molded case switch looks just like a breaker but does not have any means to automatically open the circuit. It is simply a physical switch and is a means of disconnect.
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Got you se it seems I must have an adjacent disconnect for the 3 phase wires before the motor?
 
zbang said:
Assuming you're in Victorville CA, the local community has courses and financial aid. At least get the NEC handbook and read up through the 400s.
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I read the book almost every day but there is too much content and thousands of codes
 
ptonsparky said:
Get yourself into a classroom of some sort. Online or at a local tech school.
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I also must live on sight all week because of the remote location of this mine sight (not regulated by NEC but by MSHAW). So I cannot take typical traditional classes for the same reason. My goal has been to obtain 8,000 hours working under the companies C 10 license while self studying prior to taking the journeyman test.

I do have former education and licenses through the FCC / central electronics technicians association, advance level ASE L1 certification and ASE electrical certification so I am not without schooling as you may assume. The issue is not having an instructor to interpret code wording / meaning
 
S so
Jpflex said:
I still get confused at times on how to treat OCPD when planning the complete circuit from source 3 phase panel to the motor load

What I have figured out so far is:

1) CONDUCTORS Branch circuit wires to motor feed = 4 AWG THHN at 75 degree termination

2) OCPD = 175 I inverse breaker (for branch circuit feed)

65 FLC x 250% max = 162.5 i amperes go to next standard size up = 175 ampere breaker

3) GEC = # 6 AWG based on upstream 175 ampere breaker

4) EMT 1/1/2 inch size based on 3 x #4 AWG THHN plus 1 # 6 AWG equipment ground conductor

However, I am aware that under certain conditions such as in dwellings (which this is not being installed in) must be broken or supply power must be divided when the load is over 60 ampere or more

I am not sure if this NEC rule affects my set up in an industrial setting or how to go about doing this? Do I get a three phase panel with 3 individual breakers for each phase rated for 175 amperes, 1 three phase breaker with 3 ties, or do I assume each phase is 1/3 of the total 175 amperes and thereby get three 60 ampere breakers for each phase?
Click to expand...
From Sq D motor data 460 motor
4 AWG min wire
100 amp TM breaker
 
augie47 said:
Same guide shows an H363 100 amp 600v Heavy Duty Disconnect switch.
Click to expand...
I tried telling the lineman here and he argues with me that we don’t need a “third switch” because he says that on/off knob will turn motor off outside.

I told him that the main panel breaker inside the blacksmith shop cannot count as the motor disconnect because it is out of site and more than 50 ft from the motor

The third switch that he is referring would have been the added outdoor 3 phase snap switch rated for proper HP based on motor code LRC assuming it’s listed on name plate. The first would be inside main branch circuit breaker and finally the rotary knob relay on/ off knob.

But how did you come up with a 100 amp switch? Wouldn’t the switch ampere setting be based on motor LRC code LRC per x horsepoer?
 
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