# please read this tag and tell me

Thread Starter

#### ohpoppy

Joined Nov 10, 2017
5

please tell me if I can wire it 115 house current. its an old kellogg 2 stage compressor dated '57 which was rated at 11.2 cfm @ 100psi. not a powerhouse but enough for a single operator doing most everything. garage wiring is 12 with a 20 amp breaker.

kind of suggests there are wiring options but I havn't read a tag in many years and always relied on my builders to know.some things.

#### bertus

Joined Apr 5, 2008
22,133
Hello,

Reading the tag, the motor uses 33 Amps at 115 Volts.
You can not use it on the 20 Amps breaker.

Bertus

Thread Starter

#### ohpoppy

Joined Nov 10, 2017
5
Hello,

Reading the tag, the motor uses 33 Amps at 115 Volts.
You can not use it on the 20 Amps breaker.

Bertus
is 12 wire enough and replacing the 20 amp with a 40 amp..will that work? why does this use many amps, its a 3 hp. what does that imply.

#### gerty

Joined Aug 30, 2007
1,303
#12 wire is rated at 20 amps, to putt a 40 amp breaker in its place invites a fire. And don't forget the starting current is much higher than the running current. If the source of the power is not in the immediate area the voltage drop on the wire would cause the motor to burn out due to low voltage. In other words the motor would just hum while trying to start, then the magic smoke would leave..

#### spinnaker

Joined Oct 29, 2009
7,830
I think this is one of those, if you have to ask then you shouldn't be messing with it sort of thing.

#### AnalogKid

Joined Aug 1, 2013
10,222
1 hp is approx. 755 watts, so 3 hp = 2265 W. If this were a resistive load, that would equal 20 A at 115 Vac. Since it is a motor, and a motor is almost a pure inductance to AC, the current is higher than that due to a power factor that is less than 1.0.

ak

Thread Starter

#### ohpoppy

Joined Nov 10, 2017
5
#12 wire is rated at 20 amps, to putt a 40 amp breaker in its place invites a fire. And don't forget the starting current is much higher than the running current. If the source of the power is not in the immediate area the voltage drop on the wire would cause the motor to burn out due to low voltage. In other words the motor would just hum while trying to start, then the magic smoke would leave..
1 hp is approx. 755 watts, so 3 hp = 2265 W. If this were a resistive load, that would equal 20 A at 115 Vac. Since it is a motor, and a motor is almost a pure inductance to AC, the current is higher than that due to a power factor that is less than 1.0.

ak
I think this is one of those, if you have to ask then you shouldn't be messing with it sort of thing.

#### wayneh

Joined Sep 9, 2010
17,201
View attachment 139060

please tell me if I can wire it 115 house current. its an old kellogg 2 stage compressor dated '57 which was rated at 11.2 cfm @ 100psi. not a powerhouse but enough for a single operator doing most everything. garage wiring is 12 with a 20 amp breaker.

kind of suggests there are wiring options but I havn't read a tag in many years and always relied on my builders to know.some things.
You’d be better off wiring it for 240V to reduce the current draw. It’s not that hard to run a new line.

#### MaxHeadRoom

Joined Jul 18, 2013
26,674
Is there any way to supply your garage with 240v?
Max.

Thread Starter

#### ohpoppy

Joined Nov 10, 2017
5
as far as asking.. I asked before I built my house.. restored min 20 vintage cars, started a business employing 100's of people.I asked my wife to assist me and we had 2 children. The ones that don't ask are the ones to worry about.. I did wire my own house and rewired my mothers after hurricane sandy. I look both ways before I cross a busy intersection.

#### spinnaker

Joined Oct 29, 2009
7,830
I asked my wife to assist me and we had 2 children.
Good thinking asking for her assistance in that.

Thread Starter

#### ohpoppy

Joined Nov 10, 2017
5
there is but the breaker box is in a hallway with nice sheetrock around it with artwork over it. I would likely have to go to the main box thats far awayand add a sub-box to it since I have no extra slots. I may check my 5hp single stage compressor motor. It never tripped the breaker.. maybe it will operate the 2 stage pump. I just can't understand why a 3hp requires that many amps.. more then my 5 hp motor. I check RPM's amps etc. My friend has a new 5 hp single stage that does 10 cfm at 100psi. Its running on 115

#### tcmtech

Joined Nov 4, 2013
2,867
I just can't understand why a 3hp requires that many amps.. more then my 5 hp motor. I check RPM's amps etc. My friend has a new 5 hp single stage that does 10 cfm at 100psi. Its running on 115
Most likely he has a cheap non commercial single stage air compressor which has the typical grossly over rated motor on it which in reality maybe does an honest 1.5 -2 HP.

You have an older commercial grade one which given the rough number you mention fits the more honest rating and air pressure and flow numbers of ~ 3.5 - 4 CFM@100 PSI per motor HP a good 2 stage compressor would have.

That's where the numbers discrepancy between yours and his likely comes from.

#### wayneh

Joined Sep 9, 2010
17,201
No way! That HP rating is likely some bogus “peak” HP like they use for shop vacs. You’d need over 30A for 5HP at 120V. Homes aren’t wired for that.

#### spinnaker

Joined Oct 29, 2009
7,830
as far as asking.. I asked before I built my house.. restored min 20 vintage cars, started a business employing 100's of people.I asked my wife to assist me and we had 2 children. The ones that don't ask are the ones to worry about.. I did wire my own house and rewired my mothers after hurricane sandy. I look both ways before I cross a busy intersection.

You wired your own house but you ask if you can use #12 wire with a 40 amp breaker?

https://forum.allaboutcircuits.com/threads/please-read-this-tag-and-tell-me.142040/#post-1199321

I am glad I don't live in that house.

#### GopherT

Joined Nov 23, 2012
8,009
The motor in Post 1, with a real Nameplate and all important specifications will really draw 33 amps at full load and during startup.

The motors on consumer products like shop vacs and air compressors typically measure max current draw (even it it is for a microsecond) during startup from stopped position. This amperage May be 30 to 50 amps for a 120V system. The duration of this peak current draw is short enough not to trip a breaker. The consumer products companies look at that peak startup current draw and then advertise peak horsepower (about 5 amps per horsepower).

I don't think any 120V ac consumer product sold in the US has a motor more than 2.5 HP for continuous output.

Your motor from post 1 will either trip the circuit breaker or heat the 12 gauge wires supplying the motor to 451°F or more and burn down your house. Especially if any of those wires are nicely insulated with Fiberglas insulation so heat cannot be dissipated.

#### gerty

Joined Aug 30, 2007
1,303