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Old 04-01-2017, 10:14 AM   #21
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Originally Posted by sbrn33 View Post
Not on a 3 phase motor.
Kobalt is Lowes house brand...

This is a civilian duty 1-phase compressor destined for someone's garage or shed.

They come with embedded overload protection. IIRC it even resets automatically.

Last edited by telsa; 04-01-2017 at 10:17 AM.
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Old 04-01-2017, 08:57 PM   #22
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Originally Posted by eddy current View Post
Interesting. Same rules apply up here except we must round down, not up. So if we got a value of 23.5 amps, we would have to round down to a 20 amp breaker. (Canada Table 29)

In Canada, we must use %250 for breakers, %125 for wire.
15.7 x 2.5 = 39.25
15.7 x 1.25 = 19.6

14 awg wire and 30 amp breaker.
For any 'larger' motor I've set up, that is what I followed.

28-200 , and whatever is the NEC equivalent, is seriously missing something with these 'small' motors.
First, this overcurrent rule does not say 'use 250%' OC protection .. it just says not to exceed. Not sure if NEC does as well. With larger motors, you definetly need that headroom on startup. These smaller motors ... not so much.
@micromind posted a year or so ago, about mfr's 'overestimating' their HP. Hope you chime in here bud ... what's up with these small motors ... are the mfrs just looking to advertise their HP, are these motors actually the rated HP but just seriously under loaded ? Is it an IEC / Nema thing, or (c) all the above ?
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Old 04-01-2017, 09:47 PM   #23
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Most of these cheap compressors are criminally overrated on HP. The one you have is very likely advertised as 5HP on the compressor nameplate but 'SPL' or nothing at all on the motor nameplate. Lets look at some figures.......

1HP = 746 watts so 5HP would be 3730 watts. 15.7 amps at 230 volts = 3611 watts. If it actually is 5HP, then its efficiency would be more than 100%.

If I knew how to get a motor to be more than 100% efficient, I seriously doubt that I'd be manufacturing air compressors.......lol.

In reality, a 15.7 amp motor operating on 230 volts is likely producing about 3HP.

The reason they advertise it at 5HP is because this is the maximum HP the motor can produce. This usually occurs somewhere around its breakdown RPM and the current is a lot higher than 15.7 amps.......

If this motor is made to produce 5HP, it will;

(A) Trip its overload in about a minute or so.

(B) Burn up in a couple of minutes if it doesn't have an overload.

The NEC doesn't have a minimum breaker or fuse size, only a maximum. It also doesn't have a maximum wire size, only a minimum.

Interesting note; the NEC states in 430.52(C) that the breaker needs to be a standard size. The lowest standard size as listed in 240.6(A) is 15 amps. Therefore, every single phase motor operating at 115 volts and 1/2HP and smaller that is connected to a 20 amp breaker is in violation. It needs to be a 15.

Interesting note #B......a 1HP single phase motor operating at 115 volts can have #14s on a 40 amp breaker.
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Old 04-01-2017, 09:56 PM   #24
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Originally Posted by micromind View Post
Most of these cheap compressors are criminally overrated on HP. The one you have is very likely advertised as 5HP on the compressor nameplate but 'SPL' or nothing at all on the motor nameplate. Lets look at some figures.......

1HP = 746 watts so 5HP would be 3730 watts. 15.7 amps at 230 volts = 3611 watts. If it actually is 5HP, then its efficiency would be more than 100%.

If I knew how to get a motor to be more than 100% efficient, I seriously doubt that I'd be manufacturing air compressors.......lol.

In reality, a 15.7 amp motor operating on 230 volts is likely producing about 3HP.

The reason they advertise it at 5HP is because this is the maximum HP the motor can produce. This usually occurs somewhere around its breakdown RPM and the current is a lot higher than 15.7 amps.......

If this motor is made to produce 5HP, it will;

(A) Trip its overload in about a minute or so.

(B) Burn up in a couple of minutes if it doesn't have an overload.

The NEC doesn't have a minimum breaker or fuse size, only a maximum. It also doesn't have a maximum wire size, only a minimum.

Interesting note; the NEC states in 430.52(C) that the breaker needs to be a standard size. The lowest standard size as listed in 240.6(A) is 15 amps. Therefore, every single phase motor operating at 115 volts and 1/2HP and smaller that is connected to a 20 amp breaker is in violation. It needs to be a 15.

Interesting note #B......a 1HP single phase motor operating at 115 volts can have #14s on a 40 amp breaker.
Nice post!
P&L
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Old 04-01-2017, 10:09 PM   #25
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Originally Posted by micromind View Post
Most of these cheap compressors are criminally overrated on HP. The one you have is very likely advertised as 5HP on the compressor nameplate but 'SPL' or nothing at all on the motor nameplate. Lets look at some figures.......

1HP = 746 watts so 5HP would be 3730 watts. 15.7 amps at 230 volts = 3611 watts. If it actually is 5HP, then its efficiency would be more than 100%.

If I knew how to get a motor to be more than 100% efficient, I seriously doubt that I'd be manufacturing air compressors.......lol.

In reality, a 15.7 amp motor operating on 230 volts is likely producing about 3HP.

The reason they advertise it at 5HP is because this is the maximum HP the motor can produce. This usually occurs somewhere around its breakdown RPM and the current is a lot higher than 15.7 amps.......

If this motor is made to produce 5HP, it will;

(A) Trip its overload in about a minute or so.

(B) Burn up in a couple of minutes if it doesn't have an overload.

The NEC doesn't have a minimum breaker or fuse size, only a maximum. It also doesn't have a maximum wire size, only a minimum.

Interesting note; the NEC states in 430.52(C) that the breaker needs to be a standard size. The lowest standard size as listed in 240.6(A) is 15 amps. Therefore, every single phase motor operating at 115 volts and 1/2HP and smaller that is connected to a 20 amp breaker is in violation. It needs to be a 15.

Interesting note #B......a 1HP single phase motor operating at 115 volts can have #14s on a 40 amp breaker.


Well said. I would just remind everyone the only reason you can have #14s on a 40 amp breaker is the breaker is only being used for short circuit and ground fault protection. The motors internal overloads are what actually protects the wire from an overload situation.

I know I am not telling you anything you don't know micromind, I was just using your post to remind everyone why you are allowed to use smaller wire on a larger breaker.


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Old 04-01-2017, 10:28 PM   #26
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Well said. I would just remind everyone the only reason you can have #14s on a 40 amp breaker is the breaker is only being used for short circuit and ground fault protection. The motors internal overloads are what actually protects the wire from an overload situation.

I know I am not telling you anything you don't know micromind, I was just using your post to remind everyone why you are allowed to use smaller wire on a larger breaker.


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Ya I know ya refering to that.,,


But for small single phase motors without interal overloads that will change the game a bit so pay attetion to that.
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Old 04-01-2017, 10:49 PM   #27
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Another thought: I do things differently depending on whether it's
direct wire or plug-in. If it's plug-in, then I'm wiring a receptacle
just like any other receptacle on that sized breaker, regardless of
expected load by current property owner. Next owner might plug
their construction heater in there.
P&L
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Old 04-01-2017, 10:50 PM   #28
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Ya I know ya refering to that.,,





But for small single phase motors without interal overloads that will change the game a bit so pay attetion to that.


It will, which means you can put a disconnect with fuses ahead of the motor. In the situation he is talking about I would put in a 30amp breaker with #10's running to it with a 6-30 receptacle or 5-30 receptacle. It would accommodate all requirements of the code as this is a cord and plug connected item.

Which is what it breaks down to. He is installing a receptacle to accommodate the piece of equipment. So in reality what he is looking for is 210.19(A)(1) in the NEC.

210.19(A)(1)(a) - where a branch circuit supplies continuous loads or any combination of continuous and no continuous loads, the minimum branch-circuit conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.




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Old 04-01-2017, 11:03 PM   #29
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Originally Posted by PlugsAndLights View Post
Another thought: I do things differently depending on whether it's
direct wire or plug-in. If it's plug-in, then I'm wiring a receptacle
just like any other receptacle on that sized breaker, regardless of
expected load by current property owner. Next owner might plug
their construction heater in there.
P&L
Near as I can tell, the NEC does not allow a larger breaker on a receptacle even with a motor.

For the very reason you stated.
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Old 04-01-2017, 11:20 PM   #30
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Originally Posted by micromind View Post
Near as I can tell, the NEC does not allow a larger breaker on a receptacle even with a motor.

For the very reason you stated.
Hmmm. Do you think it would be OK to run 3 wires to a 50 amp 4 wire receptacle if it was for a battery charger?
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Old 04-01-2017, 11:40 PM   #31
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Hmmm. Do you think it would be OK to run 3 wires to a 50 amp 4 wire receptacle if it was for a battery charger?
Interesting question.......

I don't think there's anything in the code that states 'Thou shalt run as many wires to a receptacle as there are terminals' but the manufacturers instructions indicate that each terminal has a wire landed on it.
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Old 04-01-2017, 11:48 PM   #32
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Hmmm. Do you think it would be OK to run 3 wires to a 50 amp 4 wire receptacle if it was for a battery charger?
And here I thought that argument had died.............
P&L
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Old 04-02-2017, 07:55 AM   #33
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Originally Posted by PlugsAndLights View Post
Another thought: I do things differently depending on whether it's
direct wire or plug-in. If it's plug-in, then I'm wiring a receptacle
just like any other receptacle on that sized breaker, regardless of
expected load by current property owner. Next owner might plug
their construction heater in there.
P&L
This is exactly my thought as well. Like when Hax was talking about putting in the outlet for the Tesla charger and wanted to make it specific to the charger when it was basically and outlet that anyone could come along and put in any cord that had a matching plug end.

Wire a receptacle to match the NEMA configuration design of your installed device.
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Old 04-02-2017, 09:01 AM   #34
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In Real Life nothing is more annoying than having the AHJ shoot down your install -- out of his own ignorance.

What's worse is that once you shame any given AHJ -- you'll rarely be forgiven.

It's for this reason that I have abandoned "Value Engineering" for nickel and dime jobs.

And I have to tell you, there are many inspectors who don't know as much as they think they do... especially about motor loads.

As a practical matter, you'll make more money 'wasting' money on materials to save time.

That saved time often means not slowing down to straighten out an AHJ, or to come back to calm down a customer.

Saved time may mean that you're not triggering collateral damage -- letting the smoke out -- because while you're doing your best -- a neutral return became un-connected and you 'seriesed' a MWBC.

And so forth.
while I agree with you somewhat, there are times that you simply must bitch slap inspectors that don't know these code sections. This can be done in a nice way, and does not necessarily have to develop a confrontational posture with the inspector. if you are going to be working on a regular basis with inspectors, it is also a proactive approach to confront them when they are wrong, so that their error doesn't become a recurring thing, costing you money along the way. In those terms, setting it right from the getgo, even if it required a second trip, might save you a lot of money later on.

As a side not to this, you must also keep in mind that inspectors are people. they have feelings, and quirks like everyone else, so they have to be treated differently depending on their own quirks. Some you can have friendly discussions with, some need to be bitch slapped, some need to be treated with kid gloves and spanked when it is appropriate, etc.

your results may vary.
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Last edited by wildleg; 04-02-2017 at 09:05 AM.
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Old 04-02-2017, 10:01 AM   #35
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And here I thought that argument had died.............
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