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5 hp. electric motors

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Forum topic by Steve posted 09-19-2014 01:58 AM 1313 views 0 times favorited 18 replies Add to Favorites Watch
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Steve

167 posts in 1460 days


09-19-2014 01:58 AM

Trying to find out how many amps a 5 hp. Electric motor draws. I asked the powermatic dealer but he is a little unsure of the specs on the motor plates. I wired my shop with #10 and 30 amp breakers on independent circuits. I am a little hesitant to order these tools without knowing if my power supply is adequate.


18 replies so far

View Pezking7p's profile

Pezking7p

3097 posts in 1112 days


#1 posted 09-19-2014 02:15 AM

This should be run on a 40 Amp circuit.

-- -Dan

View crank49's profile

crank49

3980 posts in 2431 days


#2 posted 09-19-2014 02:17 AM

A 5 hp 240 volt single phase moter will usually draw about 18 – 22 amp; depending on efficiency.
You should be fine.
Certainly will be safe with 30 amp breaker on #10 wire.
Might have to use a special slow trip breaker to handle motor inrush current at starting.

The next bigger wire would be #8 and it is rated for 40 amps in NM-B or UF-B wire, only rated for 60 degree C.
I would rather run conduit and use THHN #8 wire which is rated for 55 amps and is good for 90 degree C.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View B4B's profile

B4B

129 posts in 818 days


#3 posted 09-19-2014 02:28 AM

There’s a wealth of information on manufacturer websites.

This table saw http://www.powermatic.com/Products.aspx?Part=1792010K&cat=P200 is single phase/230, and draws 21 amps.

This Grizzly motor: http://cdn0.grizzly.com/manuals/h5389_m.pdf is 5 HP, single phase/220 and draws 25 amps.

Here is a couple of charts with some generalized information (notice that none of the charts are exactly the same?):
http://www.engineeringtoolbox.com/elctrical-motor-full-load-current-d_1499.html
http://frentzandsons.com/Hardware%20References/ampdrawofelectricmotors.htm
http://www.bristolinc.com/resource/motor-load-chart

Here’s some info based on the NEC for electric motors: http://ecmweb.com/code-basics/motors-and-nec

-- There's two routers in my vocab, one that moves data and one that removes wood, the latter being more relevant on this forum.

View Pezking7p's profile

Pezking7p

3097 posts in 1112 days


#4 posted 09-19-2014 02:34 AM

I want to reiterate, this should be run on a 40 amp circuit. Full load current for a 5 hp motor is around 28 amps, The nec requires that the wire for this motor be sized to handle 125% of the full load current, or 35 amps.

-- -Dan

View TheFridge's profile

TheFridge

5764 posts in 946 days


#5 posted 09-19-2014 02:37 AM

That is correct

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View Loren's profile

Loren

8295 posts in 3108 days


#6 posted 09-19-2014 02:44 AM

Assuming it isn’t hard-starting like an air compressor,
35 amps should do. I have run 5hp single phase
motors on a 40 amp circuit and on a 60 amp
circuit with no problems. Understand a 220v
line has two breakers so the breakers were a
pair of 20 amp and a pair of 30 amp breakers
respectively.

View crank49's profile

crank49

3980 posts in 2431 days


#7 posted 09-19-2014 02:56 AM

My compressor is a 5 hp compressor and it is rated for 18.9 FL Amps at 240V. It starts and runs under pretty much a full load all the time. That’s the nature of compressors. It works just fine on a 30 amp circuit, but my breaker was rated for motor service.

Now, if you have an old 50% or 70% efficient motor and your line voltage is 220 volts or less, then by all means, jack that sucker up to a 40 amp or, as I suggested earlier, a 55 amp circuit. You will need it.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

View Woodmaster1's profile

Woodmaster1

736 posts in 2047 days


#8 posted 09-19-2014 03:51 AM

I have my 5hp unisaw on a 30amp circuit and have had no problems. The power cord is only 12ga from the factory.

View ScottKaye's profile

ScottKaye

471 posts in 1413 days


#9 posted 09-19-2014 09:56 AM

On a side note. How are you enjoying your new shop welcon? Shes a thing of beauty and its sounds like you are filling her with quality machines!

Scott

-- "Nothing happens until you build it"

View WhyMe's profile

WhyMe

611 posts in 1021 days


#10 posted 09-19-2014 02:31 PM


A 5 hp 240 volt single phase moter will usually draw about 18 – 22 amp; depending on efficiency.
You should be fine.
Certainly will be safe with 30 amp breaker on #10 wire.
Might have to use a special slow trip breaker to handle motor inrush current at starting.

The next bigger wire would be #8 and it is rated for 40 amps in NM-B or UF-B wire, only rated for 60 degree C.
I would rather run conduit and use THHN #8 wire which is rated for 55 amps and is good for 90 degree C.

- crank49

This is misleading info. #8 THHN is to be used at a max of 50A @ 75 degree C. 90 degees C is used only when derating wire amps. Beside wiring devices such as breakers have a max rating of 75 degrees C. This is per the NEC.

View verdesardog's profile

verdesardog

137 posts in 2072 days


#11 posted 09-19-2014 03:06 PM



Assuming it isn t hard-starting like an air compressor,
35 amps should do. I have run 5hp single phase
motors on a 40 amp circuit and on a 60 amp
circuit with no problems. Understand a 220v
line has two breakers so the breakers were a
pair of 20 amp and a pair of 30 amp breakers
respectively.

- Loren

A pair of breakers on a 220 volt circuit does not double the amps of the circuit, both legs would carry the complete current of the load. So you have a 20 amp 220 circuit when using 20 amp breakers and a 30 amp 220 volt circuit when using 30 amp breakers.

-- .. heyoka ..

View Fred Hargis's profile

Fred Hargis

3927 posts in 1954 days


#12 posted 09-19-2014 04:36 PM

Is that the table saw? The manual lists the motor at 21 amps, meaning the 30 amp is plenty adequate.

-- Our village hasn't lost it's idiot, he was elected to congress.

View nicksmurf111's profile

nicksmurf111

361 posts in 911 days


#13 posted 09-19-2014 05:35 PM

I second what Dan (Pezking7p) said. He is correct. A 5hp motor will draw a LOT of current on startup. While a 30amp will technically work, it’s not proper.

Efficiency will be a lot better if it has a run capacitor. Most new motors I’ve seen produced in the last 15 years have run capacitors. Some older motors do not and are not as efficient. I have a few of these on my equipment. Also, I believe that FLA don’t include any overage on the service factor. So if your motor has a service factor of 1.25, it can draw 25% more amps than listed as FLA.

-- Nicholas

View Mainiac Matt 's profile

Mainiac Matt

5989 posts in 1789 days


#14 posted 09-19-2014 06:34 PM

as noted already… not all 5 HP motors and loads are the same….

A TS does not start under full load conditions, so the starting surge of current is low.

On the other hand, an air compressor will always start under pretty much full load, so it has a much higher starting current.

5HP x .75 KW/HP = 3.75 KW
3,750 W / 220 V = 17 A
17 A / 80% efficiency = 21.3 A

So at full load your looking at ~ 21.3A

The starting surge for the typical capacitor start single phase induction motor can be as high as 3 to 5x that current, but it only persists for a fraction of a second.

Most breakers must see their rated trip point amperage for a certain duration of time in order to trip.

If a motors starting current doesn’t trip the breaker and the wiring can handle the full load constant current, you should be good to go.

If the breaker does trip upon start up, you may need to get a breaker designed for use with larger motors that allows a longer window of time before tripping.

My best understanding (I’m not a licensed electrician) is that wire gauge and breaker rating for industrial machinery is NOT based on the current surge at start up.

Just as a side point… this is exactly why 3 phase is used… 3 ph motors do not require a starting capacitors and do not have a high starting current surge. They also run smother at a more constant speed.

-- Pine is fine, but Oak's no joke!

View nicksmurf111's profile

nicksmurf111

361 posts in 911 days


#15 posted 09-19-2014 06:44 PM


On the other hand, an air compressor will always start under pretty much full load, so it has a much higher starting current.

- Mainiac Matt

I think a lot of people miss the fact that just about all air compressors have unloaders. The motor needs to turn the flywheel and the piston(s), but doesn’t experience much load until the unloader valve switches (I think there are differences based on the design, so I’m not sure what the proper word is). It’s still a difficult load to start, but not as difficult as folks make it out to be. Take the belt off any belt-driven compressor and give it a spin and you will see what I’m talking about.

Also, I think most of the ratings are based on heat. But that’s really not my field of expertise. If the book says use 40A, we know 30A works…whatever.

-- Nicholas

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