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Does a 'normal 3ph-AC motor' include capacitors? #220268 09/15/19 12:30 AM
Joined: Sep 2019
Posts: 21
pcsailor Offline OP
Member
I ask because I got this question wrong:
"You need three over load units for a normal 3 phase AC motor."
True or False
Answer: "Yes 430.27"

Does a 'normal 3 phase AC motor' include capacitors?
My background is shipping and that is not normal from my experience, perhaps with small HP motors only.

My answer was False based on this code trace:
430.37(Ex) --> Table 430.37(Ex)
430.111
430.32
240.15
240.84

What's your thoughts?

Thanks,
Phil

Last edited by pcsailor; 09/15/19 12:31 AM.

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2017 / 2014 NEC & Related Books and Study Guides
Re: Does a 'normal 3ph-AC motor' include capacitors? [Re: pcsailor] #220271 09/15/19 02:17 PM
Joined: Jul 2004
Posts: 9,623
G
gfretwell Online Content
Member
Since here is a phase displacement in 3 phase motors they do not need a capacitor to start. The function of the capacitor is to create phase displacement and create a magnetic field to "chase" on a single phase motor. Once it gets spinning the rotating field is created within the windings. Thank you Mr Tesla.


Greg Fretwell
Re: Does a 'normal 3ph-AC motor' include capacitors? [Re: pcsailor] #220276 09/16/19 05:45 AM
Joined: Sep 2019
Posts: 21
pcsailor Offline OP
Member
Hi,

Yes, I get why the capacitor is needed for starting and phase rotation.

I'm still not getting this question and answer though. What am I missing here?
Why is the given answer True, due to the need for capacitors on a 3Ø motor?
Perhaps this is a typo in the answer and the code should be 430.37, not .27.

Question:
"You need three over load units for a normal 3 phase AC motor."
True or False
Answer: "Yes 430.27"
Code
430.27 Capacitors with Motors. Where capacitors are installed in motor circuits, conductors shall comply with 460.8 and 460.9.

Code
460.8 Conductors.
(B) Overcurrent Protection. An overcurrent device shall be provided in each ungrounded conductor for each capacitor bank. The rating or setting of the overcurrent device shall be as low as practicable.
Exception: A separate overcurrent device shall not be required for a capacitor connected on the load side of a motor overload protective device.

Thanks,
Phil


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Re: Does a 'normal 3ph-AC motor' include capacitors? [Re: pcsailor] #220277 09/17/19 01:43 PM
Joined: Apr 2002
Posts: 7,261
HotLine1 Offline
Member
"You need three over load units for a normal 3 phase AC motor."
True or False
Answer: "Yes 430.27"

Is it me having a brain freeze, or are not 'overloads' what us older guys called 'heaters'? What does the verbage within the question have to do with capacitors.??

Seems like the conversation is leaning towards capacitors that are installed for power factor correction reasons!


Last edited by HotLine1; 09/17/19 01:50 PM. Reason: added comment

John
Re: Does a 'normal 3ph-AC motor' include capacitors? [Re: pcsailor] #220283 09/18/19 01:20 AM
Joined: Jul 2004
Posts: 9,623
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gfretwell Online Content
Member
I see what happened, There is a typo in the code reference. They really mean table 430.37


Greg Fretwell

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