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Old 07-29-2017, 05:28 PM   #1
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Default FLA discrepancy

Wiring a cabinet makers shop and he tells me he has a 5 hp saw and 2 other 3 hp tools.

Looked up 5hp 240v single phase in NEC and shows 28 amps.

His is in storage so I looked at a friends that's is identical and wired with a 20a 240v cord cap on a 20 amp circuit and the nameplate reads 18amps.....

Any ideas why the large discrepancy?



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Old 07-29-2017, 05:37 PM   #2
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The NEC tables are worst-case circuit sizing numbers.
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Old 07-29-2017, 06:47 PM   #3
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Originally Posted by Glock23gp View Post
Wiring a cabinet makers shop and he tells me he has a 5 hp saw and 2 other 3 hp tools.

Looked up 5hp 240v single phase in NEC and shows 28 amps.

His is in storage so I looked at a friends that's is identical and wired with a 20a 240v cord cap on a 20 amp circuit and the nameplate reads 18amps.....

Any ideas why the large discrepancy?



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The MARKETING department.

They'll call anything this or that horsepower.

And there's no law against such claims.
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Old 07-29-2017, 07:16 PM   #4
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Sometimes they will label the "stall" horsepower...that's not the normal running amps. It sounds much better.....hey I have a 2hp vacuum cleaner ! Yours is only a little 1/3hp !
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Old 07-29-2017, 08:16 PM   #5
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It the same way with some of the portable air compressor motors they really undergross the HP rating sorta like market hype so if it say "" 5 HP motor "" actually it may be more like 2 or 3 HP the most.

it the same way with other power tools too they can really askew the rating pretty much.

so I just sized whatever the factory cord came out so most common 120 volts tools can be sized up to 15 amp while 240 volt tools or motors if not in NEMA size or IEC size then it is a oddball one.
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Old 07-29-2017, 09:02 PM   #6
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In my experience, 18 amps @ 230 volts would be on the slightly high side for 3HP but it'd be unrealistically low for 5HP.

I'd venture to say that if this motor is loaded to 5 actual HP, it'll produce it but it'll draw more than 18 amps and will overheat in a minute or so.
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Old 07-30-2017, 02:25 AM   #7
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Buy my calculation -
5 hp = 3750w
3750w / 240v = 15.62A.
So the quoted figure of 18A.
is close enough to the "RUNNING" current.

But this does not take into account start up current.
The most common rule of thumb is to use a minimum
of double the running current as the breaker.

This is why the other figure is approx twice the running current.
Cause they have factored in a margin for start up.



my 2c !
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Old 07-30-2017, 06:24 AM   #8
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Is this a DIY table saw or professional grade, that is the difference in a honest name plate and one that uses LRA as the Max HP. In sak=le literature they call it Peak HP in lieu of honest running HP.
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Old 07-30-2017, 07:32 AM   #9
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Is this a DIY table saw or professional grade, that is the difference in a honest name plate and one that uses LRA as the Max HP. In sak=le literature they call it Peak HP in lieu of honest running HP.
Even better, I assume it is a foreign saw his buddy got a great deal on.
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Old 07-31-2017, 02:40 AM   #10
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Quote:
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Is this a DIY table saw or professional grade, that is the difference in a honest name plate and one that uses LRA as the Max HP. In sak=le literature they call it Peak HP in lieu of honest running HP.
It's a professional cabinet grade saw.

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Old 07-31-2017, 03:39 AM   #11
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It's a professional cabinet grade saw.

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Such units are sold with motors optional.

The last unit I personally owned was rated from 2hp to 7.5hp ... you pick the motor.

I had to dump it for a painful loss: it took up too much space... and I'm not a cabinet maker.
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Old 07-31-2017, 10:32 AM   #12
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Sometimes they will label the "stall" horsepower...that's not the normal running amps. It sounds much better.....hey I have a 2hp vacuum cleaner ! Yours is only a little 1/3hp !
Exactly, maximum 'developed' HP!
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Old 07-31-2017, 11:20 AM   #13
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"Developed HP" has been deemed perfectly legal by the FTC in some lawsuits going back to the 70s, in spite of the deceptive nature of it. A standard AC induction motor with a Design B torque-speed curve will develop 200% of its rated torque when the motor is slowed down to its "Break-Down Torque" speed. When it does so, it will also pull 200% current, and a standard NEMA class 20 overload curve means the motor can handle that for about 30 seconds, but that assumes it was cold to start with. What they "ASSume" in a power tool like this is that you are not going to try to push the envelope like this very often, and even if you do, you will have some cooling off time in between current surges.

So 200% rated torque is used, in conjunction with the speed at which BDT occurs, to calculate that "developed" HP. The "real" motor HP is not listed, but it's likely 3HP as mentioned. You however must size the circuit based on the nameplate amps if the nameplate does not show the HP. So in this case, 18A x 1.25 = 22.5A, so #10 portable cord or NM, #12 individual conductors in conduit.
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