breaker size for compressor and welder
 

I ordered a new compressor (ingersoll rand SS3L3) that runs on 230v (230-1-60) and
plan to install a box about two feet from my breaker box. I plan on installing the outlet
box and running the wire between the two (as well as have the right breaker there).

I'm going to have a licensed electrician connect the dots, ok? No flames please!
However, they prefer to JUST connect the dots, not cut the holes, mount the
boxes, and pull wires, which is cool. I can do that part.

I figure when I put in the 230 outlet for the compressor, I might as well pull
another set of wires for a second breaker/outlet in case I get a 230v welder
one day.

I'll never need a welder any bigger than, say, a 225A Lincoln buzz box and/or a HH175
for the 230V welder.

Questions:

Can I run these on 20A 230V breakers?
If so, is 10/4 is thick enough?

Bob

You need a 50 amp breaker for most welders. Check but I think the wire size would be #6.

6 is right for 50 amps. didn't know I'd have to go that high for a welder (checked with hobart and they say max 19.2 amps for their HH175 so I was hoping that a 30A would do the trick, but, no matter.

any idea how much the compressor will take? 30A as well?

thanks!

Bob

Checked around - although IR doesn't list the amperage requirements for their compressors, it's a 3hp continuous duty motor, which I guess has a peak requirement of something around 30-35A.

Looks like I'd be best off just putting two 50A receptacles and breakers in....

Thanks guys.

I have a 3 hp compressor. I used a 30 amp breaker. I measured the current when I set it up but forgot what I read.

I use a 30 amp breaker on my five hp two stage I.R. compressor. It said that the draw was 25 amps (220volts) on start up.

So, you guys say I can easily get by with two 30A breakers and receptacles (3hp IR compressor, HH175)? That means I can run #10 wire, too.

Bob

Ok. I stopped by Lowe's on the way home and got 2 50A double pole breakers for my box along with a 30A single pole breaker. Figured I'd add another 110V outlet while I was in there. Found out the hard way that all my garage outlets as well as the outlet in the laundry room are on the same 20A 110V circuit. Which means when my cheesey compressor and shop vac are running while using my blast cabinet, and when someone turns on the light in the laundry room, the ethernet hub I have hooked up in the laundry room fails when the circuit trips. Within minutes, my sons (who were having IM chats with their favorite womenfolk) are wondering "Dad, Dad, Dad, what happened to the internet?". Argh.

Also got two 5' lengths of 6/3 copper cable (for the two 50A 230V sockets), a 10' length of 10/2 (for the additional 30A 110V socket), and three "old wall" boxes to mount the receptacles in.

I did NOT find any NEMA 6/50P or 6/50R plugs or receptables (Hobart recommends 6/50P plugs and 6/50R receptacles). They did have some 10/50 and 14/50. What's the difference? Does the leading 6 or leading 10 mean the wire number it accepts? That is, is a NEMA 10/50R meant to accept #10 wire and be rated for 50amps? And a NEMA 6/50 mean 50 amps and #6 wire? That doesn't make much sense for the 10/50 if #6 wire is recommended for a 50amp receptacle.

Can someone clue me in here?

Bob

Ahhhh. Found the following:

http://www.moldedcord.com/nema.cfm

which helps somewhat. The NEMA number isn't quite related to the wire size.

Bob

A five hp motor will run at approximately 25 amps [(5hpX1000)/230VAC] but start up draw (locked rotor amps) is by rule of thumb six times running amps. In this case it would be 150 amps but that is momentary. That's why the lights dim when the motor starts.

The breaker (30 amps) in your case is properly sized for this load but according to the NEC your wiring from the breaker to the motor must be sized at 125% of the motor running load or the breaker, whichever is larger. That would mean a wire size that can carry 31.25 amps. For the sake of safety I would upsize the conductor to the next larger size. That way the breaker will protect the conductor from any possible overheating. You're really protecting the wiring, not the motor. The motor has its own overload protection.

You can also work it in reverse. Size the breaker for 80% of the conductor capacity.

This example in no way assumes that I know any of your local codes, it just shows an example of what goes into the sizing of breakers and wiring. When in doubt or required by law, pay the man.

A three hp motor will run at approximately 13 amps [(3hpX1000)/230VAC] but start up draw (locked rotor amps) is by rule of thumb six times running amps. In this case it would be 40 amps but that is momentary. That's why the lights dim when the motor starts. The motor should have a nameplate listing the running amps as well as the NEMA code which would allow you to accurately calculate the start up current draw.

A twenty amp breaker (if in fact the running current is 13 amps) in your case is properly sized for this load but according to the NEC your wiring from the breaker to the motor must be sized at 125% of the motor running load or the breaker, whichever is larger. That would mean a wire size that can carry 25 amps. For the sake of safety I would upsize the conductor to the next larger size. That way the breaker will protect the conductor from any possible overheating. You're really protecting the wiring, not the motor. The motor has its own overload protection.

You can also work it in reverse. Size the breaker for 80% of the conductor capacity. As long as the breaker rating is slightly above the running current of the motor and the breaker is sized at 80% of the conductor ampacity then it will work.

This example in no way assumes that I know any of your local codes, it just shows an example of what goes into the sizing of breakers and wiring. When in doubt or required by law, pay the man

A 30A double pole breaker and 10 wire is plenty for the compressor. A 50 a is too big for the comp. The weldor is slightly different. With that class of welder, the stick unit you talked about can run on a 10 wire also, with a 50A breaker. This is a welder circuit and not a general use 50A circuit, like for a pottery kiln, that would take number 6 wire and a 50A breaker. Welding machines of this type have different requirements than equipment that may run continious. If there is any chance someone might put a kiln or oven on his circuit then use 6 wire. As for your 30A single pole breaker,, take it back and get a 20. 30 A breakers are not for general use circuits, they are for special circumstances on dedicated circuits not where you can plug just anything in to them. They are mostly used n compressor or motor circuits.

MikeH, if it's run is 13 it would only require a 20A wire (16.25 ampacity) The way thats worded in the post 80% of conductor size for the breaker??? Actually for 13A motor they allow a number 12 wire with up to a 40A breaker,,, if it trips on startup. (A 20 would likely nuisance trip, a 30 would be appropriate) You would never need to run a breaker smaller than the wire ampacity. Or am I misunderstanding your explanation? It certainly isnt going to hurt to upsize the wire to 10, but as short as this is it wouldnt be neccessary. The motor only has to be wired to the 125% factor regardless of the breaker. I believe this is in 430.52

You can call Ingersol with your breaker questions. That's what I did, and found them to be very helpful. BTW...I love my Ingersol compressor. It pays to spend a few extra bucks and buy good quality stuff.

MR

About the only thing anymore that the avg guy is going to buy new that wont run on a 10/30 setup is the 7 1/2 hp units. The rest could just put them on that circuit and they would be fine. These types of motors have their own thermal protection and run intermitantly (do they all even say continious duty?) The internal thermal protects the wire from overload and the breakers only real job in this scenerio is to provide short circuit interuption and ground fault protection.