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

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augie47

augie47

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Smart $ said:
Well that works for me :cool: ... 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.
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and 430 part III uses "overload protection"..... does make things a bit difficult, I agree.
 
kwired

kwired

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ActionDave said:
My first thought when I read the op.
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I was imagining pulling conductors up to the 75 Hp leg almost immediately, done that before when it was 480 volt, never one with that large of a motor @ less than 480 volts though.:eek: You know this thing is probably at least 125 -150 feet tall minimum, even if you own a tugger of some type you still may need a crane to get that up there, and still need to find a way to power it since you haven't pulled any power up there yet.
 
david luchini

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Smart $ said:
Really...???

I've looked many times and I just don't see it. Please elaborate...
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Let me try it this way....

Wouldn't both "overload" protection and "Short Circuit/Ground Fault" protection be "overcurrent" protection by definition?

Art 100 - Defintitions: Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.
 
Smart $

Smart $

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david luchini said:
Let me try it this way....

Wouldn't both "overload" protection and "Short Circuit/Ground Fault" protection be "overcurrent" protection by definition?

Art 100 - Defintitions: Overcurrent. Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault.
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Let's proceed on that premise. Say you have a motor with SC/GFP rated 100A and overload based on FLC of 40A. What is your overcurrent protection rating?
 
david luchini

david luchini

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Smart $ said:
While I know that... let's say you have a feeder with multiple motors and other loads. At what and/or which rating does 240.4(C) kick in?
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I don't see "overload" protection anywhere in the Feeder requirements, only the branch circuit requirements.

Nor do I see where 240.4(C) would kick in for feeder conductors and OCPD's sized per the requirements of Article 430.
 
Smart $

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david luchini said:
I don't see "overload" protection anywhere in the Feeder requirements, only the branch circuit requirements.

Nor do I see where 240.4(C) would kick in for feeder conductors and OCPD's sized per the requirements of Article 430.
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I'm aware of that... so what is your point?

So any feeder with a motor load is not subject to 240.4(C)? What if we have 800A of non-continuous other loads and one motor? 240.4(C) would not apply because of the motor???

All your references thus far just keep sending me on section chases that I've already done countless times previously. Do you have anything which nails down whether or not 240.4(C) kicks in on any motor(s) or motor(s) w/other load(s) feeder when the OCPD is greater than 800A?
 
david luchini

david luchini

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Smart $ said:
I'm aware of that... so what is your point?

So any feeder with a motor load is not subject to 240.4(C)? What if we have 800A of non-continuous other loads and one motor? 240.4(C) would not apply because of the motor???

All your references thus far just keep sending me on section chases that I've already done countless times previously. Do you have anything which nails down whether or not 240.4(C) kicks in on any motor(s) or motor(s) w/other load(s) feeder when the OCPD is greater than 800A?
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You seem to be trying to find something that isn't there. 240.4(G) says Overcurrent Protection for specific conductors shall be permitted to be provided as referenced in Table 240.4(G), which includes motors. There is nothing in Article 430 that sends you back to 240.4(C). If you provide your feeder overcurrent protection in accordance with Art 430, you are done, even if the feeder OCPD is larger than 800A.
 
Smart $

Smart $

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david luchini said:
You seem to be trying to find something that isn't there.
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That's absolutely correct... but I'm fairly certain your perspective is quite different than mine ;)

240.4(G) says Overcurrent Protection for specific conductors shall be permitted to be provided as referenced in Table 240.4(G), which includes motors.
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Exactly... and you're saying a feeder with motor(s) and other load(s) is a specific conductor. Table 240.4(G) doesn't say that. It says, and I quote, "Motor and motor-control circuit conductors". Do you see "other load" or "non-motor load" in there anywhere?

There is nothing in Article 430 that sends you back to 240.4(C).
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Exactly... again!!!

240.4 general says, "Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G)."

  • 240.4(C) says "the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device".

  • 240.4(G) says "Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G)."
Its rather obvious which is permitted and which is required. Which has priority?

Note 240.4(C) places a requirement on the ampacity of the conductors contingent on OCPD rating. 240.4(G) only stipulates overcurrent protection.

If you provide your feeder overcurrent protection in accordance with Art 430, you are done, even if the feeder OCPD is larger than 800A.
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Certainly, if you totally put on blinders to the nuances I've been attempting to point out.... :blink:
 
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