Mike in Ohio
Well-known member
My air compressor tag reads 15.0 amp 208-230 volt 5 hp. It will be about 25 feet from the breaker box. I have a bunch of #10 wire left from another project, is this big enough or do I need something bigger? Thanks Mike
Another wire size question
- Thread starter Mike in Ohio
- Start date
LoneGunman
Well-known member
That's fine, in fact it's oversized which is not a bad thing.
that must be a 3 phase motor?
if so, #10 w/a 30A CB is fine...
because 230/1 draws close to 30A
OP
Mike in Ohio
Well-known member
Thanks a lot guys, Mike
Gary S
Well-known member
30A seems like a lot for a 5hp motor. My 5hp 230 single phase has 21A-22.5A stamped on the motor plate.
Stuart in MN
Well-known member
Per the tables in the NEC, a 5hp 230vac single phase motor has nominal full load current of 28 amps. They can vary from that number, as shown by your motor.
15 A is almost 1/2 the table value of 28 A, I don't recall them varying THAT much...but who knows...
I could see 21A at 230 (the 22.5 is the 208 value)
15 x 230 x 0.6 pf (typical for many 1 ph motors) ~ 2070 W ~ 2.77 HP
NEC table lists a 3 HP at 17A, very close to the calculated if adjusted....
15/17 x 3 ~ 2.65 HP
a nameplate rating is a NEC/NEMA standard, not much room for messing around...
honestly, not sure of what is going on...but 5 HP/230-1/15A sounds wrong
who knows
nate379
Banned
Where do you get that from. A motor drawing 15 amps at 240v is about 3hp according to the info I have.
Stuart in MN
Well-known member
From the 2008 NEC:
Per table 430.250, a 5hp 230vac three phase motor's full load current is nominally 15.2 amps.
Per table 430.248, a 5hp 230vac single phase motor's full load current is nominally 28 amps.
As was mentioned earlier, this one sounds like a three phase motor since it's labeled 208-230, but that hasn't been confirmed.
Per table 430.250, a 5hp 230vac three phase motor's full load current is nominally 15.2 amps.
Per table 430.248, a 5hp 230vac single phase motor's full load current is nominally 28 amps.
As was mentioned earlier, this one sounds like a three phase motor since it's labeled 208-230, but that hasn't been confirmed.
1 HP = 746W.
15A * 230V = 3450W.
3450W / 746W = 4.62HP.
That assumes 100% efficiency, which no motor has.
So at a best case scenario of 85% efficiency (possible, but inlikely since even 80% is considered "high efficiency", and that comes at a cost) you'd have 3.93HP.
At a 60% efficiency like ArthurPE suggested, you'd get 2.77HP.
So like I said, best case scenario you'd have about 4HP, but more likely much less.
5HP at 230VAC/15A is impossible, so somone is clearly fudging the numbers somewhere.
the actual effeciency of modern motors > 90% in larger HP...
it's the power factor that affects the power...
P = V I pf
pf = cos of the phase angle between V and I due to the inductive nature of the load...most 1 ph motors are ~ 0.60 range
efficincy = Pout/Pin...so for a 5 HP motor with 80% eff Pin = 4660 W, 6.25 HP
with a unity pf that's still 20A, with a pf of 0.8, 25A...
very interesting, and probably explains our dilemma:
http://www.kevinsbrady.net/motors.pdf
the links in the article are also very useful reference...
compressor HP http://truetex.com/aircompressors.htm
the 5 HP is a peak torque number, not running...running is <3....
http://www.kevinsbrady.net/motors.pdf
the links in the article are also very useful reference...
compressor HP http://truetex.com/aircompressors.htm
the 5 HP is a peak torque number, not running...running is <3....
nadogail
Well-known member
Stop all your worries about using the 10 Guage wire. If you have it, it is paid for.
Yes it is bigger than you need, but there is no shame in having used something you have that exceeds requirements, rather than spending your time and money to buy a few feet of 12 AWG wire.
Yes it is bigger than you need, but there is no shame in having used something you have that exceeds requirements, rather than spending your time and money to buy a few feet of 12 AWG wire.
rinny_tin_tin
Well-known member
Actually, most single-phase induction motors in the 5 hp range are about 90% pf
or better
We're talking 3HP motors here. Hardly "larger HP".
It's also single phase. The more efficient "larger HP" motors are typically 3-phase. Sounds like something I said earlier in the thread...
really?
3 phase motors are in that range
and 1 phase is MUCH less efficient than 3 phase for obvious reasons...
hence a 5 HP motor drawing 28 A per code
pf = (5 x 746)/(28 x 230) ~ 0.58...
it's hard to seperate pf from eff...but the eff is ~ 80%
therefore pf ~ 0.58/0.8 ~ 0.72, not close to 0.90
We're talking 3HP motors here. Hardly "larger HP".
hence the clarification...larger motors
and to illustrate why your assumptions and calculations were incorrect...
hidollartoys
Well-known member
Again a simple question gets blown completely out of proportation.
"mike in ohio" has left the building.
"mike in ohio" has left the building.
a truer statement was never uttered lol
we (me included) like to engage in mental ************...
the motor is rated at 15A, use the #10 with a 25 or 30A CB
OP
Mike in Ohio
Well-known member
I haven't actually left the building I just went to the basement to get my materials and tools and started to work while you all argued the finer points. Thanks alot for the replys, I'll be back with wire size questions for my welder when get time to read the tag on it. Thanks again, Mike
rinny_tin_tin
Well-known member
My bad - you are correct. I got 3P on mind!
that 'sq root of 3' **** messes everyone up
tcianci
Well-known member
I opened up this post thinking I may have had some useful information to add to it. All it did was make me realize how much I had forgotten over the years! It was reassuring to know that no matter what I have forgotten, a #10 wire will still carry 30 amps!