Wiring for future air compressor

[scoob8000]

I'm going to run a wire for the site of my future air compressor. Am I safe in assuming most 220v compressors do not need a neutral wire?

Ie, should I be running 10/2 or 10/3?

I don't have a big compressor yet, just want to run the wire before I put the wall up.

 

[nadogail]

Run the 10 gauge three conductor.

This will give you some option for future changes.

 

[scoob8000]

Run the 10 gauge three conductor.

This will give you some option for future changes.

Does it change anything if I already have the 10/2 I would need?

 

[FTG-05]

I'm in the process of wiring my 5 hp IR/Frankenpressor as we speak.

Using whatever/2 wasn't even a consideration. If I'm going to spend that kind of money and that much trouble getting that cable from one end of the shop to the other, there's no way I'm cutting off my 120 VAC nose to spite my 240VAC face!

6/3 with ground in my case. YMMV.

 

[pattenp]

All you need is 10/2 to power the compressor. In another thread the topic is how to add a light to know that the compressor is still on. That is one case where a neutral would be needed to power a standard 120V light. I think the odds of needing a neutral on the same circuit that the compressor is wired is slim to none.

Edit: Think about what size compressor you want to make sure #10 is enough.

 

[wyliesdiesels]

I'm going to run a wire for the site of my future air compressor. Am I safe in assuming most 220v compressors do not need a neutral wire?

Ie, should I be running 10/2 or 10/3?

I don't have a big compressor yet, just want to run the wire before I put the wall up.

The first thing u need to consider is what size compressor in HP (true HP) u will be getting since HP dictates wire size.

Example- a 5HP compressor would need 8/2 NM-b.

 

[scoob8000]

All you need is 10/2 to power the compressor. In another thread the topic is how to add a light to know that the compressor is still on. That is one case where a neutral would be needed to power a standard 120V light. I think the odds of needing a neutral on the same circuit that the compressor is wired is slim to none.

Edit: Think about what size compressor you want to make sure #10 is enough.

The first thing u need to consider is what size compressor in HP (true HP) u will be getting since HP dictates wire size.

Example- a 5HP compressor would need 8/2 NM-b.

I'll probably end up with a 4-5hp 60 gallon unit. It's going to be at most 25ft from the panel. Looking at some PDF manuals, 10/2 looks to be good but I'll upsize it to 8/2 just to be safe.

Thanks!

 

[teamo]

8/2 is fine for a 5HP compressor. You won't need the neutral.

 

[pepi]

You pulling bare wire or Greenfield with wire inclosed?

Also you probably should look at the compressor install guide for proper install procedures.

All the above posts maybe correct with the information offered. However conformation from the manufacture is the finial word.

 

[sberry]

I'm going to run a wire

I usually assume that the poster means cable.

 

[thymer]

The first thing u need to consider is what size compressor in HP (true HP) u will be getting since HP dictates wire size.

Example- a 5HP compressor would need 8/2 NM-b.

Why would a 5hp compressor need 8? 8/2 rated for 30A, 5hp ~21 amps.

 

[pattenp]

Why would a 5hp compressor need 8? 8/2 rated for 30A, 5hp ~21 amps.

To wire according to the NEC you need to use the HP to Amp table provided by the NEC. 5HP = 28A x 125% = 35A, so #8 NM-b or #10 THHN. That's only if the motor data label list the motor as 5HP. Those compressors that have 5HP on the tank need to be taken with a grain of salt because most likely they are not real 5HP motors.

 

[wyliesdiesels]

Why would a 5hp compressor need 8? 8/2 rated for 30A, 5hp ~21 amps.

#8 NM-b is rated at 40a NOT 30a.
#10 NM-b is rated at 30a.

NM-B wire is limited to 60* c ampacity.

NEC requires motor circuit wiring to be sized at 125% of NEC table FLC NOT motor nameplate amps.

As pattenp said, 5HP motor is 28a FLC...

28a * 125% = 35a...

 

[md21722]

Because motors have high startup current the code has different rules for motor circuits. When the wiring sizing and thermal protection rules are followed they also allow maximum 250% FLC for the breaker. For example, a 2HP 230V motor has a FLC of 12A. 12 x 125% = 15A (14 gauge wire). 12 x 250% = 30A breaker maximum.

 

[thymer]

Cool thanks for the explanation.

 

[zmaxmotorsports]

Having the spare neutral in the box would give you more options in the future in case you decide to move the compressor or add something in the future.
Heavier wire is never a bad thing either for the same reason.

 

[brewchief]

To me the best solution is to run a 3/4" or 1" emt conduit from panel to a box at the compressor location and pull whatever size wire I need when I have the compressor in place.

 

[Pwrgeek]

I'd suggest carrying the neutral if it is a cable install. 8/3 NM-b isn't that much more than 8/2. There are any number of things that can go along with a compressor that need 120V (auto dewatering, auto oiling, monitoring stuff, etc). If it a pipe install then adding it later isn't that big a deal so it doesn't really matter.


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[Norcal]

I'd suggest carrying the neutral if it is a cable install. 8/3 NM-b isn't that much more than 8/2. There are any number of things that can go along with a compressor that need 120V (auto dewatering, auto oiling, monitoring stuff, etc). If it a pipe install then adding it later isn't that big a deal so it doesn't really matter.


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But the 120 volt items are not suitible for 40 or 50 ampere circuits.

 

[Pwrgeek]

So long as you carry large enough wire #8 is plenty there is nothing preventing you from adding an aux 120v outlet to a 120/240 (with neutral) wired circuit. This is how I have my compressor wired. 30A 2 pole breaker feeds #8THHN with neutral and EGC in conduit to the compressor location. There is a 30A 2 pole safety switch there to provide local disconnect. On the load side of that switch I have the two hot legs and ground wired to the compressor. I also have 1 of the hot legs and neutral and ground wired to an outlet box mounted to the side that runs my auto dewatering system. That way when I turn off the compressor at the end of the day I turn off the dewatering too.


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[zmaxmotorsports]

#8 NM-b is rated at 40a NOT 30a.
#10 NM-b is rated at 30a.

NM-B wire is limited to 60* c ampacity.

NEC requires motor circuit wiring to be sized at 125% of NEC table FLC NOT motor nameplate amps.

As pattenp said, 5HP motor is 28a FLC...

28a * 125% = 35a...

 

[brewchief]

So long as you carry large enough wire #8 is plenty there is nothing preventing you from adding an aux 120v outlet to a 120/240 (with neutral) wired circuit. This is how I have my compressor wired. 30A 2 pole breaker feeds #8THHN with neutral and EGC in conduit to the compressor location. There is a 30A 2 pole safety switch there to provide local disconnect. On the load side of that switch I have the two hot legs and ground wired to the compressor. I also have 1 of the hot legs and neutral and ground wired to an outlet box mounted to the side that runs my auto dewatering system. That way when I turn off the compressor at the end of the day I turn off the dewatering too.


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This way puts a 15 or 20 amp receptacle on a 30 amp circuit, not legal in the eyes of the NEC unless there is a loophole I'm missing.

 

[Norcal]

So long as you carry large enough wire #8 is plenty there is nothing preventing you from adding an aux 120v outlet to a 120/240 (with neutral) wired circuit. This is how I have my compressor wired. 30A 2 pole breaker feeds #8THHN with neutral and EGC in conduit to the compressor location. There is a 30A 2 pole safety switch there to provide local disconnect. On the load side of that switch I have the two hot legs and ground wired to the compressor. I also have 1 of the hot legs and neutral and ground wired to an outlet box mounted to the side that runs my auto dewatering system. That way when I turn off the compressor at the end of the day I turn off the dewatering too.


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This way puts a 15 or 20 amp receptacle on a 30 amp circuit, not legal in the eyes of the NEC unless there is a loophole I'm missing.

Yup, not proper in any way.

 

[zmaxmotorsports]

So long as you carry large enough wire #8 is plenty there is nothing preventing you from adding an aux 120v outlet to a 120/240 (with neutral) wired circuit. This is how I have my compressor wired. 30A 2 pole breaker feeds #8THHN with neutral and EGC in conduit to the compressor location. There is a 30A 2 pole safety switch there to provide local disconnect. On the load side of that switch I have the two hot legs and ground wired to the compressor. I also have 1 of the hot legs and neutral and ground wired to an outlet box mounted to the side that runs my auto dewatering system. That way when I turn off the compressor at the end of the day I turn off the dewatering too.


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Why not just use the #8s to feed a small sub panel by the compressor location,Then you could feed the compressor and a seperate 120v circuit from it?

 

[wyliesdiesels]

So long as you carry large enough wire #8 is plenty there is nothing preventing you from adding an aux 120v outlet to a 120/240 (with neutral) wired circuit. This is how I have my compressor wired. 30A 2 pole breaker feeds #8THHN with neutral and EGC in conduit to the compressor location. There is a 30A 2 pole safety switch there to provide local disconnect. On the load side of that switch I have the two hot legs and ground wired to the compressor. I also have 1 of the hot legs and neutral and ground wired to an outlet box mounted to the side that runs my auto dewatering system. That way when I turn off the compressor at the end of the day I turn off the dewatering too.


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Do u have inline breaker or fuse feeding the 15a outlet?

 

[Pwrgeek]

Why not just use the #8s to feed a small sub panel by the compressor location,Then you could feed the compressor and a seperate 120v circuit from it?

Cost and complication. No need for it. A single switch takes care of it for about half the cost.


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[Pwrgeek]

Do u have inline breaker or fuse feeding the 15a outlet?

Don't need one. The breaker at the panel protects everything.


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[Norcal]

Don't need one. The breaker at the panel protects everything.


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Your wrong, a 15 or 20 ampere receptacles are NOT PERMITTED TO HAVE HIGHER OVERCURRENT PROTECTION.

See table 210.21(B)(3)

 

[zmaxmotorsports]

Cost and complication. No need for it. A single switch takes care of it for about half the cost.


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$30.00 worth of parts and the ability to have a correct disconnect/breakers for everything is too expensive and complicated?
How long have you been wiring things that way?

 

[Pwrgeek]

Your wrong, a 15 or 20 ampere receptacles are NOT PERMITTED TO HAVE HIGHER OVERCURRENT PROTECTION.



See table 210.21(B)(3)

Actually 210.21 is requiring that the circuit conductor and breaker be at least able to supply the rating of the largest rated receptacle not the other way around. It is for instance permissible to have multiple 15 or 20 amp outlets fed by a single 30A branch circuit but it is not permissible to have a 20A outlet fed by a 15A branch circuit. The idea is that the breaker will protect the wire from overload and the outlet will protect itself.


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[Aceman]

The idea is that the breaker will protect the wire from overload and the outlet will protect itself.

How does an outlet protect itself?

 

[Norcal]

How does an outlet protect itself?

Magic & voodoo.

 

[pattenp]

Actually 210.21 is requiring that the circuit conductor and breaker be at least able to supply the rating of the largest rated receptacle not the other way around. It is for instance permissible to have multiple 15 or 20 amp outlets fed by a single 30A branch circuit but it is not permissible to have a 20A outlet fed by a 15A branch circuit. The idea is that the breaker will protect the wire from overload and the outlet will protect itself.


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You are not understanding the code section correctly. You are not to put a 20A rated device (outlet) on a 30A circuit. The receptacle rating to circuit size has to comply with table 210.21(b)(3).

 

[Slowgsr]

Nah... Can't put a 15 or 20a rated device on anything larger... Regardless of wire sizes

 

[wyliesdiesels]

Wow!

Someone is smoking crack tonight!

An outlet protects itself? Thats the funniest **** Ive read on here in a long while! Thanks for the laugh! I nearly spit my soda out.

Funny u said that.

I once had a service call where half the outlets in a condo didnt work but none of the breaker had tripped.

After pulling several outlets out of j boxes, i pulled out an outlet that was all melted on the hot side.

I thought sweet easy fix. Go to the breaker panel and discover that this particular circuit was fed by a 30a breaker. I said what the f*ck and did a double take.

Obviously, the outlet didnt protect itself...

 

[zmaxmotorsports]

Wow!

Someone is smoking crack tonight!

An outlet protects itself? Thats the funniest **** Ive read on here in a long while! Thanks for the laugh! I nearly spit my soda out.

Funny u said that.

I once had a service call where half the outlets in a condo didnt work but none of the breaker had tripped.

After pulling several outlets out of j boxes, i pulled out an outlet that was all melted on the hot side.

I thought sweet easy fix. Go to the breaker panel and discover that this particular circuit was fed by a 30a breaker. I said what the f*ck and did a double take.

Obviously, the outlet didnt protect itself...

It apparently didnt get the memo.
And for the record the only drug Ive done today is too much stinking mountain dew/caffeine,Which is why Im still up being a pain in the ***!

 

[Pwrgeek]

See this is what happens when I try to read in a hurry. I read it wrong (and wired it wrong in my install). Re reading it now I see that you all are correct and I would need an appropriately rated protective device between the higher rated circuit and lower rated outlet. I will be adding a 15A fuse in a 30A rated fuse holder to the line that feeds the outlet. Thanks for pointing out my mistake. To anyone reading this later nothing I have said earlier in this thread is correct.


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[MFortie]

#8 NM-b is rated at 40a NOT 30a.
#10 NM-b is rated at 30a.

NM-B wire is limited to 60* c ampacity.

NEC requires motor circuit wiring to be sized at 125% of NEC table FLC NOT motor nameplate amps.

As pattenp said, 5HP motor is 28a FLC...

28a * 125% = 35a...

And so the breaker would be 40a as well?

 

[machsnell]

You are not understanding the code section correctly. You are not to put a 20A rated device (outlet) on a 30A circuit. The receptacle rating to circuit size has to comply with table 210.21(b)(3).

If I am wiring a compressor (I have a 60 gal 16.6 amp compressor) and plan to possibly upgrade in a few years, can I run 8/2 and have the correct outlet and just not put a 40 amp breaker in it but rather use a 25? Amp brker? Basically outlet and breaker need to match? And I think the plug on compressor is a 20 amp 240 plug.

I thought it was fine to have 40 amp breaker on 8 awg wire and whatever outlet you needed on the end to power whatever device you had.

This thread has taught me that is not the case?

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[pattenp]

If I am wiring a compressor (I have a 60 gal 16.6 amp compressor) and plan to possibly upgrade in a few years, can I run 8/2 and have the correct outlet and just not put a 40 amp breaker in it but rather use a 25? Amp brker? Basically outlet and breaker need to match? And I think the plug on compressor is a 20 amp 240 plug.

I thought it was fine to have 40 amp breaker on 8 awg wire and whatever outlet you needed on the end to power whatever device you had.

This thread has taught me that is not the case?

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Outlets are part of the circuit. For general purpose outlet circuits just think of it as you don't use higher overcurrent protection (breaker) than the lowest amp rated outlet device or wire that's part of the circuit. Now the twist to this is where a 15A duplex can be used on a 20A circuit. Single purpose/dedicated circuits for things such as compressor motor loads have different rules and so do welders. Those circuits can have overcurrent protection that exceeds the amp capacity of the wire. There are several parts in the NEC that cover requirements for branch circuits and the components so you need to consider the use of the circuit and all the different parts of the circuits to determine code requirements.