Adding compressor to 220v in my garage

[Scotty Dive]

ROFL!!!!

Anyways, What I would do is pull the wire out of "rv" plug. Move that wire into a subpanel with 15 and 30 amp breaker in the sub panel. run new wire from subpanel 30 amp breaker back into the "rv" plug box so you can keep same setup for welder. run second wire from 15 amp subpanel into the air compressor directly unless you have plans to move AC around. in the later case install the correct plug.

I think that is exactly what I am going to do. Question though on sizing the breakers. If the welder draws 30 amps, do you install a 30 amp breaker or is there a formula. I thought I remembered that it was something like 80% of rated amperage. So in the case of a 30 amp welder, I would need 36 amp breaker or the next size up to 40. For the compressor it would be a 20 amp breaker. Is this correct?

 

[buickanddeere]

I think that is exactly what I am going to do. Question though on sizing the breakers. If the welder draws 30 amps, do you install a 30 amp breaker or is there a formula. I thought I remembered that it was something like 80% of rated amperage. So in the case of a 30 amp welder, I would need 36 amp breaker or the next size up to 40. For the compressor it would be a 20 amp breaker. Is this correct?

I told you what the code calls for in a previous post. Did you not see it?
Put the welder on 240V. It evens out the line current .
Is the 50amp to the garage two wire or three wire?

 

[Scotty Dive]

I told you what the code calls for in a previous post. Did you not see it?
Put the welder on 240V. It evens out the line current .
Is the 50amp to the garage two wire or three wire?

I did see it but I was not aware that was code. sorry - I am not an electrcian so I am trying to leverage the brain trust here for the proper and best way to do the job. If you are one or have a ton of expereince, please let me know as I am trying to go the best route. I can turn a wrench but am still learning on the electrical side.

The welder is already on 240V. It has always been like that - its just using a 30 amp 125 volt oultet and plug
The 50 amp in the garage has two wires and the ground is bare twisted aluminum.

Given that the 3HP runs at 15amp, it must have a large PF correction capacitor. 12awg wire will do. 45amp non time delay fuse, 25amp time delay fuse or a 35amp max breaker for short circuit protection. Odds are it will start and run fine on a 30amp breaker.

Not sure what that all means. Can I assume that the PF correction capacitor is built into the motor I have? All of the other stuff confuses me. Its seems having a 35 amp breaker is on the large size for a 15 amp motor? Would love to know how that gets calculated. I guess at the end of the day I am looking for someone to say....install a sub panel that has this and that and feed this with that and be done with it.

 

[Turbys_1700]

Several year ago I had my shop wired for a 220V compressor...
I then added my welder later and yes it is a PITA to unplug one or the other...
Eventually I will get a dedicated line run from my 50A box but the darn line is 40' long and that wiring is not cheap...

 

[grsthegreat]

The NEMA classifications assigned to receptacles and plugs is there to help prevent the exact thing your experiencing. Ive had dozens of people ask me to install a receptacle that matches their plug...wont do it. The reason that outlet is embossed with 125 v 30 amp is so no one would plug a 120 volt 30 amp machine in and find out that the idiot electrician attached 220 to it.

I make my clients change out the plugs to match the required outlets every time. if they dont want to, i walk.

So far ive never had anyone say thay dont want me to. they always want it done safely. Also, the NEC doesnt say anywhere that you cant have 2 or 3 or 4 individual 50 amp 240 outlets under the command of a single 50 amp 2 pole breaker. Its done in commercial shops all the time. What is expected is the operators to have the skill level not to overtax the system.

I set up commercial cabinet shops with a table surrounded by 8-10 different 220 pieces of equipment.... shapers,router tables,saws,etc.

All on one breaker. The operator runs the door thru the 1st piece of equipment, shuts it down and starts the next and runs the door thru...etc.

All 100% NEC approved and inspector passed. The main difference is....skill level.

Alot of home mechanics tend to forget what to do after 6 months of not using a piece of equipment and may run both at the same time. but thats what the breaker is for. it trips ( in your case a 30 amp breaker would add a safer level of protection).


As far as circuit size. I usually rate equipment circuits at 125% of listed amperage to allow for start up surges. The cheaper the motor, the greater the starting load tends to be.

Thats why alot of welders have a 50 amp circuit, but if you actually test the line while welding,. it may only read 20 amps. But thees a large starting spike.

In my own shop, i run the compressor at 30 amp breaker... not 50. If my compressor ever trips the 30 amp circuit, then that tells me to check its condition. Its my fail safe device since the motor doesnt have a motor control and heaters.


anyways.thats my 2 cents worth.

 

[buickanddeere]

The breaker or fuse at the panel only supplies short circuit protection for the conductors with motor and transformer loads. The high 30 or 35amp current rating on the 20amp wire is to prevent nusance trips caused by high inrush starting current.
Thermal protection for the wiring and motor is provided by the thermals in the motor or motor starter.

 

[buickanddeere]

The NEMA classifications assigned to receptacles and plugs is there to help prevent the exact thing your experiencing. Ive had dozens of people ask me to install a receptacle that matches their plug...wont do it. The reason that outlet is embossed with 125 v 30 amp is so no one would plug a 120 volt 30 amp machine in and find out that the idiot electrician attached 220 to it.

I make my clients change out the plugs to match the required outlets every time. if they dont want to, i walk.

So far ive never had anyone say thay dont want me to. they always want it done safely. Also, the NEC doesnt say anywhere that you cant have 2 or 3 or 4 individual 50 amp 240 outlets under the command of a single 50 amp 2 pole breaker. Its done in commercial shops all the time. What is expected is the operators to have the skill level not to overtax the system.

I set up commercial cabinet shops with a table surrounded by 8-10 different 220 pieces of equipment.... shapers,router tables,saws,etc.

All on one breaker. The operator runs the door thru the 1st piece of equipment, shuts it down and starts the next and runs the door thru...etc.

All 100% NEC approved and inspector passed. The main difference is....skill level.

Alot of home mechanics tend to forget what to do after 6 months of not using a piece of equipment and may run both at the same time. but thats what the breaker is for. it trips ( in your case a 30 amp breaker would add a safer level of protection).


As far as circuit size. I usually rate equipment circuits at 125% of listed amperage to allow for start up surges. The cheaper the motor, the greater the starting load tends to be.

Thats why alot of welders have a 50 amp circuit, but if you actually test the line while welding,. it may only read 20 amps. But thees a large starting spike.

In my own shop, i run the compressor at 30 amp breaker... not 50. If my compressor ever trips the 30 amp circuit, then that tells me to check its condition. Its my fail safe device since the motor doesnt have a motor control and heaters.


anyways.thats my 2 cents worth.

I'm confused about the safe wiring job then your having a compressor without thermal protection?

 

[grsthegreat]

I'm confused about the safe wiring job then your having a compressor without thermal protection?

well, theres not a small air compressor on the market that has motor circuit protection in the form of heaters. they all rely on breakers.

So in reality there is no reliable protection on these motors. I could add a motor starter on the compressor, but it would cost 2x what my compressor cost me.

I just figure the 30 amp breaker would trip way before a 50 amp would if the motor was getting long on brushes or a bad bearing was causing the amperage draw to increase.

who knows...some day i may come by a used motor starter that i can utilize.

 

[buickanddeere]

3HP unit Porter Cable unit in my garage has built in factory thermal protection.

 

[TCJatko]

For the electricians here: Wouldn't having a 50A sub-panel require a four-conductor feed, that is two hot wires, a neutral, and an equipment(case) ground? OP states he only has three wire, if I read this correctly.