compressor wiring help

[charger0926]

so after searching this forum to no avail here is my dilemma.

i have a quincy 5 hp 220v single phase unit.

i was initially going to use 6ga wire with a plug to connect to a outlet that i have in my garage for my welder (60 amp breaker in the main house box for this circuit) but it sounds like i need to hard wire it to be safe.

my question is what can i do to put a connection (disconnect box) inline with the 220 plug as the compressor will be next to the outlet, and if i decide to use the welder at the same time as the compressor kicks on, will i have a overload issue?

can the plug outlet and "box" be piggybacked together or is that a overload issue?

i have seen some boxes with the 220 plug in them but they look huge and i do have some room constraints.

any help would be appreciated and some pics or blueprints/drawings might be helpful also.

thanks again

 

[wyliesdiesels]

Compressor should be hardwired. Standard nema plugs arent rated for more than about 3HP.

Keep in mind Motors have in rush currents on startup that can be 4-8x FLA.

What model welder will u have?

 

[charger0926]

miller 211

 

[wyliesdiesels]

That welder doesnt draw a lot of power(17a @ 240v) so u could try putting in a small subpanel utilizing the existing feed and then running 2 circuits off of that- One for the welder and one for the compressor.

 

[American Locomotive]

Compressor should be hardwired. Standard nema plugs arent rated for more than about 3HP.

Keep in mind Motors have in rush currents on startup that can be 4-8x FLA.

What model welder will u have?

I agree the compressor should be hardwired, but it's important to understand why. It's not because the starting current is high, it's more because motors are inductors and have the potential to sustain an arc as the pins on the plug pull out of the outlet.

If you never ever planned to unplug the compressor while it was running, a standard Nema 6-50 would be more than adequate electrically to handle the currents involved. But it would be against code.

Special motor rated plugs have special insulators around the pins to snub out potential arcs, and some even internally disconnect the power as you go to release the plug.

 

[wyliesdiesels]

I agree the compressor should be hardwired, but it's important to understand why. It's not because the starting current is high, it's more because motors are inductors and have the potential to sustain an arc as the pins on the plug pull out of the outlet.

If you never ever planned to unplug the compressor while it was running, a standard Nema 6-50 would be more than adequate electrically to handle the currents involved. But it would be against code.

Special motor rated plugs have special insulators around the pins to snub out potential arcs, and some even internally disconnect the power as you go to release the plug.

Actually its the high starting current that becomes the issue when unplugging it.

And yes the U/L listing on the plug would be violated if used on a compressor that has a higher HP rating than the HP rating on the plug.

But my point about starting current wasnt about the plug but rather the load on the feeder with a welder running with the compressor starting.

 

[BCreekDave]

Still can't figure out why anyone would want to unplug a running compressor, especially a stationary one that is 5hp+.


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[mikesgabellone]

Still can't figure out why anyone would want to unplug a running compressor, especially a stationary one that is 5hp+.


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Maybe someone would be tempted to if the compressor malfunctions in way that builds pressure beyond its normal operating range. I had to kill power to my dad's compressor for that reason.

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[BCreekDave]

Good point. I in error relate it back to my setup where the plug is on the wall buried behind the compressor and the panel with the breaker is easy to get to. Much easier for me to throw the breaker than pull the plug. Not always the case for sure.
I guess the electrician that wired my house wasn't up on the code concerning this. I told him I was installing a compressor at that location and he installed a 4 prong dryer receptacle and a dedicated 30 amp breaker. It seems fine with my 5HP, 22 amp compressor.


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[sberry]

Remember, the welders are limit to 50A breakers too.

 

[charger0926]

So I am working today but when I get home I will take some pics of my main box and do a blueprint of what i would like to do and hopefully get some advice on how to do it. Thanks for all of the replies.

 

[American Locomotive]

Actually its the high starting current that becomes the issue when unplugging it.

An inductor resists changes in current flow, and will try as hard as it can to keep that current flowing. When you remove power from an inductor, the voltage across it will rapidly increase. If you suddenly shut the power off to a motor under load, the voltage at the motor terminals can spike to several thousands of volts or more. That high voltage pulse is what has the capability of creating a dangerous situation.

Have you ever heard a "pop" in some speakers or a radio when unplugging or turning some kind of motorized device before? That's from the HV pulse.

But enough derailing

 

[sberry]

I like those kinds of explanations.

 

[charger0926]

so i got home late so i couldnt get good pics due to darkness, but i did pull of the main panel cover and found that the existing wire to the 220 outlet in the garage is 10/4 wire on a double pole 30 amp breaker.

i think that im going to leave that alone and run a new 6/4ga wire to a disconnect box and mount it next to the 220 plug in the garage for the compressor and use a double pole 60amp breaker as it is only approx 30 ft away from the main box and it appears that i have 3 or 4 empty spots in the main box.

without pics, does this sound like the correct/safest way to install this set-up?

thanks for all of the replys

 

[American Locomotive]

So you're going to run 6 gauge and a 60 amp circuit to the compressor?

 

[charger0926]

So you're going to run 6 gauge and a 60 amp circuit to the compressor?

that was my thought as the website i bought the compressor recommends a 60 amp breaker.

is this not correct/safe? is it overkill?, which i am fine with

 

[charger0926]

here is some info on the compressor

http://www.aircompressorsdirect.com/Quincy-351CS80VCB-Air-Compressor/p11489.html

Motor
Voltage 230 Volt AC
Phase 1-Phase
Magnetic Starter Yes
Recommended Breaker 60 Amp Breaker

 

[American Locomotive]

Generally a 5HP motor would be wired with #8 wire on a 35-40 amp breaker. #6 or 4 wire on a 60 amp breaker seems ridiculous overkill for a 5HP motor.

 

[charger0926]

Generally a 5HP motor would be wired with #8 wire on a 35-40 amp breaker. #6 or 4 wire on a 60 amp breaker seems ridiculous overkill for a 5HP motor.

i gotcha. i was just going with the info on the link that i just posted that says they recommend a 60 amp circuit and since i was running the new wire approx 40 feet i should use 6ga wire.

aside from major overkill, am i going to hurt anything by doing this as i have the 6ga wire already available from another project so i didnt want to buy 8ga if i didnt have to.

here is the disconnect switch i am thinking of using...any thoughts?

https://www.zoro.com/square-d-safety-switch-240vac-2pst-60-amps-ac-d222n/i/G3217794/

wondering what fuses to use in this also

thanks again for all of the input

 

[wyliesdiesels]

Yeah the #6 is overkill but if u already have it i can understand that.

As for the disconnect, fuseable is overkill.

Get an AC pull out disconnect.

 

[American Locomotive]

There's nothing you can really hurt. If the compressor ever becomes severely overloaded, the motor might burn if it doesn't have internal protection, but circuit breakers are really only meant to protect the wires - not the motor, anyways.

 

[wyliesdiesels]

There's nothing you can really hurt. If the compressor ever becomes severely overloaded, the motor might burn if it doesn't have internal protection, but circuit breakers are really only meant to protect the wires - not the motor, anyways.

The OP already stated that it has a starter so that has the overload protection.

Breakers for motor circuits are not sized to protect the wire. Thats the job of the overload in the motor or motor starter.

 

[Drill Sergeant Arc]

Still can't figure out why anyone would want to unplug a running compressor, especially a stationary one that is 5hp+.

I believe their primary reason for this is when the compressors have been without power long enough they will lose pressure through leaks and any intentional draw down from air tools. At some point the auto pressure switch will eventually engage and be ready to energize the motor when the cord is finally plugged in again.

You likely will never get use to this occasional game of Russian roulette and forget that the air may be low enough to produce a substantial arc at the plug and the sudden start of the compressor. A switch at the compressor itself could prevent this surprise but lets face it, we would all forget to switch that off when we unplugged the cord. So that is why they don't want to have cords on compressors, it would not take very long at all for the prongs to be so badly burned they would become a fire hazard or weld themselves into the receptacle. A sudden arc and welding of the assembly may be so exciting that someone may panic and start yanking on the cord, it could only get worse from there.

 

[sberry]

[/b]

The OP already stated that it has a starter so that has the overload protection.

Breakers for motor circuits are not sized to protect the wire. Thats the job of the overload in the motor or motor starter.

Just to add some babble, As wylie pointed out the breaker in this system isn't really protecting the wire directly, that is due to the applied load. Put a 100 watt light on a 12 wire with a 16 fixture wire and the breaker only has 1 function, short circuit protection. The load is limited by the light. Putting a 20A load on a 30A wire is the protection, it wont overload on thermal to overheat the wire. The thermal on the unit sort of "back protects" the wire so to speak but really is there for the motor and any internal wiring or parts that need thermal and are not large enough to shorts with the breaker protection.
My pressure washer doesn't have any internal thermal but for the blower motor on the furnace, even the leads in to it are sized for 30A shorts.

 

[BCreekDave]

I always thought and please correct me if I am wrong that the breaker was sized to protect the wiring "in the wall", meaning any wiring downstream of it until the point of termination (most generally receptacles). Anything really beyond this point is either unprotected of has to provide its own protection (motor overloads or fusing). Is my understanding incorrect?


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[American Locomotive]

That's how I have always been taught. Breakers prevent fires happening with your own wiring. Motor starters and device fuses protect the equipment.

 

[manwithtools]

It's a little bit of both actually. From Mike Holt:

"Motor overload protection devices like heaters (in a motor starter arrangement) protect the motor, the motor control equipment, and the branch-circuit conductors from motor overload and the resultant excessive heating (430.31). They don't provide protection against short-circuits or ground-fault currents. That's the job of the branch and feeder breakers, which don't provide motor overload protection."

 

[charger0926]

so i decided to go with a square d 60 amp 2 pole fuseable disconnect switch (i know overkill but got it on the cheap) and overkill being the name of the game on this project, i put in a 60 amp double pole breaker in the main box and am planning on running the 6/3 wire this weekend.

my questions are,

what kind of fuses to use, i assume 60 amp, but are they time delay or slow blow style fuses, or are these the same thing, any brand recommendations would be helpful (remember overkill)

also, i will be mounting it flush on the wall so i am wanting the wire to come in from the back, so what is recommended to secure the wire to the box?

what do i use to run the wire from the box to the compressor as far as conduit? looking for something flexible.

any other thoughts on this would be appreciated also

thanks for all of the info., and sorry for the newb questions

 

[wyliesdiesels]

Just to add some babble, As wylie pointed out the breaker in this system isn't really protecting the wire directly, that is due to the applied load. Put a 100 watt light on a 12 wire with a 16 fixture wire and the breaker only has 1 function, short circuit protection. The load is limited by the light. Putting a 20A load on a 30A wire is the protection, it wont overload on thermal to overheat the wire. The thermal on the unit sort of "back protects" the wire so to speak but really is there for the motor and any internal wiring or parts that need thermal and are not large enough to shorts with the breaker protection.
My pressure washer doesn't have any internal thermal but for the blower motor on the furnace, even the leads in to it are sized for 30A shorts.

yes the overloads on a starter protect the motor as well as the branch circuit wiring. that is how it was engineered to function

I always thought and please correct me if I am wrong that the breaker was sized to protect the wiring "in the wall", meaning any wiring downstream of it until the point of termination (most generally receptacles). Anything really beyond this point is either unprotected of has to provide its own protection (motor overloads or fusing). Is my understanding incorrect?


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That is true for general purpose circuits.

branch circuits for motors and welders are a different animal.

For motor circuits, the wire is sized @ 125% of the NEC listed running current. and the main breaker is sized to allow for in-rush current which sizes it in most cases larger than the circuit wire. This is ok because the motor or the motor starter has overload protection which protects circuit wiring and motor. The breakers job is to protect against ground faults/short circuits which have very high fault currents.

Welder circuits are allowed to have wire that is a lot smaller than the breaker rating and this is based on welder duty cycle. The welder can only run for so long because of duty cycle ratings so the idea is while, for example #12 wire, is carrying 50a, its only for a very short duration and this allows the wire to cool in between duty cycles...

That's how I have always been taught. Breakers prevent fires happening with your own wiring. Motor starters and device fuses protect the equipment.

the starters protect the branch circuit wiring as well.

so i decided to go with a square d 60 amp 2 pole fuseable disconnect switch (i know overkill but got it on the cheap) and overkill being the name of the game on this project, i put in a 60 amp double pole breaker in the main box and am planning on running the 6/3 wire this weekend.

my questions are,

what kind of fuses to use, i assume 60 amp, but are they time delay or slow blow style fuses, or are these the same thing, any brand recommendations would be helpful (remember overkill)

also, i will be mounting it flush on the wall so i am wanting the wire to come in from the back, so what is recommended to secure the wire to the box?

what do i use to run the wire from the box to the compressor as far as conduit? looking for something flexible.

any other thoughts on this would be appreciated also

thanks for all of the info., and sorry for the newb questions

Use an nm-b cable clamp for securing the wire to the box

for the compressor wiring u could either use liquid tight whip or an MC whip with stranded THHN conductors of appropriate size. your compressor is 5HP so #10....

 

[BCreekDave]

Thank you for the clear explanations. It makes much better sense now.


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[charger0926]

so i ran my cable this weekend and got my whip and misc parts to install the box in a few days.

just to recap, i have 6/3 cable on a double pole 60 amp breaker to a square d d222n 60 amp fused disconnect switch. yes overkill...i know...i know.

i am wanting to know what fuses to use. i initially thought that i should go with a 60 amp fuse(s) but now i am thinking that i should use a 40 amp slow blow.

also not sure what type i need either, the box said that you can use a few different types including type R J or T i believe. just wondering what is recommended?

thanks again for all of the help