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Old 06-21-2011, 03:34 PM   #1
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hello, I need to now how to wire my compressor? Its a 5hp 230v 15amps 60 1 phaze compressor, I have 12/3 wire for it and its located about 5ft from panel, I have a 220 outlet in my laundry rm we dont use, so i have located the breaker for it and was planning on using those breakers for my compressor,which is a 30amp pole breakers, i just need to know which wires goes to the breaker and to my switch on compressor, the 12/3 has a red,blk,white, bare copper wire for ground,I just need to know where these wires go on the switch of compressor,and inthe panel??? the 220 outlet is wired in panel to the breaker as follows, red,blk to 30amp pole breaker,and white wire to the ground,with no bare copper wire.? i would appericate the help with this ..
Thanks Johnx

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Old 06-21-2011, 04:03 PM   #2
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Originally Posted by johnx View Post
hello, I need to now how to wire my compressor? Its a 5hp 230v 15amps 60 1 phaze compressor, I have 12/3 wire for it and its located about 5ft from panel, I have a 220 outlet in my laundry rm we dont use, so i have located the breaker for it and was planning on using those breakers for my compressor,which is a 30amp pole breakers, i just need to know which wires goes to the breaker and to my switch on compressor, the 12/3 has a red,blk,white, bare copper wire for ground,I just need to know where these wires go on the switch of compressor,and inthe panel??? the 220 outlet is wired in panel to the breaker as follows, red,blk to 30amp pole breaker,and white wire to the ground,with no bare copper wire.? i would appericate the help with this ..
Thanks Johnx
#12 is not large enough. Neither is the 30A breaker. You will need #8 copper with a 70A breaker.

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Old 06-21-2011, 04:46 PM   #3
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#12 is not large enough. Neither is the 30A breaker. You will need #8 copper with a 70A breaker.

Do not understand this #8 with 70 amp breaker. 5 HP is 3730 watts. At 240 volts that is a little over 15 amps. 12-2 with a 20 amp 2 pole breaker should be fine.

To the OP, if the compressor is labeled 240 VAC and not 120/240 VAC, you do not need a neutral connection. Only the 2 hots need be connected to the 2 pole breaker.
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Old 06-21-2011, 05:24 PM   #4
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#12 is not large enough. Neither is the 30A breaker. You will need #8 copper with a 70A breaker.
P'raps I missed something, but why on earth would a 15 amp machine require a 70 amp breaker?
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Old 06-21-2011, 09:03 PM   #5
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P'raps I missed something, but why on earth would a 15 amp machine require a 70 amp breaker?
The nameplate FLA (full load current) is not used for sizing branch circuit conductors or the OCPD. The following is the procedure to be followed for a 5HP, 240V single phase motor.

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 28 amps for a 230V 5HP 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).

28A x 125% = 35A

Table 310.16 indicates #8AWG is rate for 40A.

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 protecting a single phase motor it is to be sized at 250% of the FLA as stated in Table 430.248.

28A x 250% = 70A

Based on the above calculation a 70A 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.

28A x 400% = 112A

Since we canít exceed 400% of the motor FLA we round down to a 110A ITCB on a piece of #8 AWG conductor.
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Old 06-21-2011, 09:06 PM   #6
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Do not understand this #8 with 70 amp breaker. 5 HP is 3730 watts. At 240 volts that is a little over 15 amps. 12-2 with a 20 amp 2 pole breaker should be fine.

To the OP, if the compressor is labeled 240 VAC and not 120/240 VAC, you do not need a neutral connection. Only the 2 hots need be connected to the 2 pole breaker.
Sorry but that is not how it is done. Please see above post.
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Old 06-21-2011, 09:36 PM   #7
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Originally Posted by electures View Post
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 protecting a single phase motor it is to be sized at 250% of the FLA as stated in Table 430.248.
I read it as Tbl 430.52 allows a maximum up to 250%, not that it has to be rated @ 250%, otherwise I agree with what you said.
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Old 06-21-2011, 09:54 PM   #8
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You would be best to use a 30 amp breaker with #10 wire for that compressor. How is the compressor controlled? Does it just have a pressure switch? Any information on the compressor would be helpful....a picture would be great. We have run a 5 HP single phase compressor for nearly 9 years now with a 30 amp breaker and 10 ga wire. It's most likely you will need only 2 wires to the compressor, one for each hot leg. You will just need to tape the end of the conductor (white) with black tape to indicate it is a hot wire. Would you just consider running a whip from the panel to the compressor instead of your romex? It makes for a neater installation and you could pull two black or red wires instead of marking the cable.
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Old 06-21-2011, 11:21 PM   #9
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I read it as Tbl 430.52 allows a maximum up to 250%, not that it has to be rated @ 250%, otherwise I agree with what you said.
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.)


Look at the end of the sentence. "shall be used".
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Old 06-21-2011, 11:25 PM   #10
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You would be best to use a 30 amp breaker with #10 wire for that compressor. How is the compressor controlled? Does it just have a pressure switch? Any information on the compressor would be helpful....a picture would be great. We have run a 5 HP single phase compressor for nearly 9 years now with a 30 amp breaker and 10 ga wire. It's most likely you will need only 2 wires to the compressor, one for each hot leg. You will just need to tape the end of the conductor (white) with black tape to indicate it is a hot wire. Would you just consider running a whip from the panel to the compressor instead of your romex? It makes for a neater installation and you could pull two black or red wires instead of marking the cable.
I quoted exactly what the code requires. Anything less is unsafe. Just because your compressor is wired wrong is not justification for wiring another one illegally. It requires #8 wire and a 70A breaker.
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Old 06-21-2011, 11:31 PM   #11
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Two things. Electures just pointed out that SD515 is correct....and I'm wondering if electures has any practical experience wiring motor circuits? The nec is difficult to understand for many, so I understand if that is the interpretation problem. But overprotection is the best way to destroy a motor. This isn't that complicated. A motor with a FLA of 15 amps can be protected at 125% of that, which is 18.75 (or 20 amp). A simple look at the owners manual of any compressor will validate this.
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Old 06-21-2011, 11:37 PM   #12
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What do you want to bet that it is not a true 5hp motor.
If this is a compressor from the box store, I am sure it is not a 5 hp motor.

If the instructions say to use a 20 amp breaker, there you go.
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Old 06-21-2011, 11:41 PM   #13
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Two things. Electures just pointed out that SD515 is correct....and I'm wondering if electures has any practical experience wiring motor circuits? The nec is difficult to understand for many, so I understand if that is the interpretation problem. But overprotection is the best way to destroy a motor. This isn't that complicated. A motor with a FLA of 15 amps can be protected at 125% of that, which is 18.75 (or 20 amp). A simple look at the owners manual of any compressor will validate this.
SD515 is incorrect. 35 years wiring motors and controls. 21 years teaching it to electricians, contractors and inspectors. The 70A breaker has nothing to do with protecting the motor. It protects the branch circuit conductors (which is why it is called motor branch circuit protective device). The motor itself is protected by the overload device.
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Last edited by electures; 06-21-2011 at 11:58 PM. Reason: correction
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Old 06-21-2011, 11:42 PM   #14
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jbfan...very good point. They often use the term "develops 5 hp" which is a clever way to advertise.
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Old 06-21-2011, 11:48 PM   #15
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What do you want to bet that it is not a true 5hp motor.
If this is a compressor from the box store, I am sure it is not a 5 hp motor.

If the instructions say to use a 20 amp breaker, there you go.
I bet you are correct. Wonder what the nameplate reads.

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