Proper Wiring For An Electric Motor From The Breaker Box (for An Air Compressor) - Electrical - Page 2 - DIY Chatroom Home Improvement Forum
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Old 12-21-2009, 09:37 AM   #16
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excellent jbfan,

you know, I do have one final question now in respect to the electrical panel now this has me thinking...

the main breaker is 100a, does this imply 100amp (so really 200amp) from each pole or 50 amps from each pole?

similarly, i ran out of space during my kitchen renovations so i installed a subpanel using a 60amp breaker leading to it. does this imply a total of 120 amps going into the sub panel or 30 amps from each pole?


thanks again for all of your help.
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Old 12-21-2009, 10:46 AM   #17
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You have a total of 100 amps in the main, and 60 amps in the sub.
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Old 12-21-2009, 11:49 AM   #18
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IF you have a Craftsman air compressor, with belt drive, with a dual (115/220) voltage motor, and you have a male plug on the cord from the factory with a "wink" (I've never heard that one) then you are wired for 220 volts/20 amps from the factory. Changing the motor voltage would require changing the male plug on the cord. That's why I ask if the male plug on yours is the one molded onto the cord from the factory. Use an appropriate 20 amp dual pole breaker, (not two single 20 amp breakers), and the appropriate size wiring, along with calculating the length of wiring into this. Good Luck, and Be Careful, David
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Old 12-21-2009, 12:13 PM   #19
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Quote:
Originally Posted by capslock View Post
jbfan and sparkplug,

so taking your input I went doesn to the box to take a look at it again, with all of the breakers in there I couldnt see 100%, though i started to get your idea.

When i went to home depot i seen the same sub panel model being sold and open so i looked at it and now I understand fully what you both are referring to.

The slimline 2-pole will have to sit in "the middle" between the two locations where full 1inch breakers would go. This will allow one side of the slimline 2-pole to be touching the plate leading from the one hot lead and the other side of the breaker will touch the plate leading from the other hot lead.

In this fashion I would still have available two me two small slots for single slimline breakers for expansion or current use (i would have one slot not in use but the other would be used with a slimline 15amp for my dining room).




I am assuming here you are talking about the single-pole minis and not the double-poll which i have decided to use?
Now, (after you have read jb's answer about the 2-pole slimline) There is one small precaution that must be observed. When you use the extra space on both sides of the 2-pole breaker. Do not use it to connect what is called a multi-wire branch circuit. That is 2 wires that use a common Neutral. That is actually a very good circuit to use. But it requires a "Common Trip", which is different than a 2-pole breaker. And in the present setup you can't have it.
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Old 12-21-2009, 12:55 PM   #20
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thurman,
yes it is still using the factory plug.

spark plug,

from your description and some light on-line reading, while good to keep in mind for the future I do not think I would require such a setup. At least from how i see it, everything in my panels have their own neutral and all of my work in the panel is definatley so.

If any additional wiring is made to either side of the 2-pole breaker, they would have their own hot lead and a neutral.

however, does this apply in some way to the 2-pole breaker? With the 2-pole breaker there is two hot leads going to the receptical, no 'neutral' but there will be a ground (which ends up on the neutral bar anyways).

A: I do not understand why there is not a neutral (my cooktop is the same way)
B: as the ground would be available to two poles, do i need to take this into account for wire size? i.e. I had intended to use 12aug wire for both leads and then the ground (standard 12aug wire with ground, coloring the white wire red)
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Old 12-21-2009, 02:18 PM   #21
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You have a straight 240 volt circuit that does not require a neutral wire.
2 hots and a ground.
Remark the white wire red on both ends and you are good.
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Old 12-22-2009, 12:52 PM   #22
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Quote:
Originally Posted by jbfan View Post
You have a straight 240 volt circuit that does not require a neutral wire.
2 hots and a ground.
Remark the white wire red on both ends and you are good.
Just expanding on JB fan's answer to Capslock. There is a difference between a 240 volt circuit, where you're using the power of both poles at the same time. Whereas, in a Multi-wire Branch Circuit, each HOT wire is used for its own 120 volt circuit. Only, they share a NEUTRAL wire. Which helps to balance the overall load in the panel. But if a problem develops in one circuit, the other needs to be shut off too, to prevent "Backfeeding" current to the other circuit. so they need a "Common" trip. (which is different than a 2-pole breaker. (This was addressed to Caplsock).
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Old 12-22-2009, 02:12 PM   #23
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Quote:
Originally Posted by capslock View Post
I bought an old, much used craftsman air compressor off of craigslist. It's belt-driven and worked like a charm at point-of-sale.

I am confident with installing electric, not a pro but i have remodeled our entire kitchen, i've done some reading but I am just not 100% sure on this so I want to make sure I understand the setup.

First the specs:
volts 230/115
hertz 60
hp 2.0
rpm 3450
amps 11/22

I was told at pos that the motor can be wired for 120 but it's currently set to 220 - i suppose this makes sense from the specs then. The plug is a standard plug except is has a "wink" to it (like a wink of an eye) - if you are looking straight at it the wink is on the left. I've never seen this before but my impression is that this represents 20amps?

I should note that my intentions are to use it per its current setup as a 220, so my questions below should apply to that.

questions:
do i install a single 20amp circuit? it that sufficient, plus/minus or is 15amp sufficient?
is this suppose to be a double poll or single poll? and how can i tell?
I get the impression that I can pick up any 20A receptacle as long as it has the 'wink' part of the outlet and I am good to go?
12 gauge amp for a 20amp circuit i believe, let me know otherwise.


Thank you all for your time.
Ther following is based on the 20078 NEC.

Motors
430.6(A) 1 states;
(1) Table Values. Other than for motors built for low speeds (less than 1200 RPM) or high torques, and for multispeed motors, the values given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches, branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate. Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary. Motors built for low speeds (less than 1200 RPM) or high torques may have higher full-load currents, and multispeed motors will have full-load current varying with speed, in which case the nameplate current ratings shall be used.

Table 430.248 indicates 12 amps for a 230V 2HP single phase motor.

430.22(A) General states;

(A) General. Conductors that supply a single motor used in a continuous duty application shall have an ampacity of not less than 125 percent of the motorís full-load current rating as determined by 430.6(A)(1).

12A x 125% = 15A

Table 310.16 indicates #14AWG is rate for 20A.

Now before you get your panties in a bunch the asterisk refers us to the bottom of Table 310.16 where it states: See 240.4(D).

240.4(D) states;

(D) Small Conductors. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.

240.4(E) refers to tap conductors which is not applicable here. However, 240.4(G) is a table and tells us that Article 430 applies for motor branch circuit conductors. This means that #14 AWG is specifically permitted to be used for conductors supplying this 20A motor load.

Next we look at sizing the ground fault, short circuit, overcurrent protective device.

430.52 states;

430.52 Rating or Setting for Individual Motor Circuit.
(A) General. The motor branch-circuit short-circuit and ground-fault protective device shall comply with 430.52(B) and either 430.52(C) or (D), as applicable.

(C) Rating or Setting.
(1) In Accordance with Table 430.52. A protective device that has a rating or setting not exceeding the value calculated according to the values given in Table 430.52 shall be used. (Also read the exception.)

Table 430.52 states that for an inverse time circuit breaker (ITCB) protecting a single phase motor it is to be sized at 250% of the FLA as stated in Table 430.248.

12A x 250% = 30A

Based on the above calculation a 30A ITCB is correct.

If the motor fails to start and run then 430.52(C) (1) Exception No. 2(c) can be applied which states;

(c) The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes.

12A x 400% = 48A

Since we canít exceed 400% of the motor FLA we round down to a 40A ITCB on a piece of #14 AWG conductor.

The real kicker is that if this was a pool filter motor it is code compliant.
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