Wire Question.

[G_P]

I want to hardwire my compressor. It is 3hp 240v 11a constant with 15a max.

I have a 100' roll of 14/3 romex. It is grey and I believe meant for direct burial.
IIRC 14ga is good for 15a. Currently I run it using a 50' extension cord that is 12ga and have no issues.

Can I run the grey romex indoors? It would probably be a 60-70 foot run depending on exactly how I have to route the wire. If I can use this wire will it be sufficient?

I plan on using a meter to check the actual amperage draw of the motor but one of the terminals on the pressure switch cracked in half. Guess years of vibration did it in so I am going to have to buy one of those as well.

If this all works I plan on putting in a 15a double breaker and then a disconnect above the compressor so I can shut it down without having to constantly use the breaker as a switch.

 

[theoldwizard1]

The answer is likely yes, depending on the distance from the compressor to the breaker.

UF (underground cable) is typically gray and yes, you can use it indoor.

 

[G_P]

I think I will put a plug on one end of the roll of wire and a socket on the other and plug the compressor in. If the wire gets hot or the breaker trips then I wont do it.

Good to know the UF cable can be ran indoors. That will save me a bit of money since I have it already.

 

[pattenp]

Technically with the peak amps being 15 you should use #12. Also 14/3 is 4 conductors and you only need 3 (2 hots and ground), so 12/2 is what you need..

 

[Rob_b]

If you follow the 125% rule, 14/3 is not enough. I'd go with #12 to give you some peace of mind. 15amp X 125% = 18.75amp

 

[theoldwizard1]

Can I run the grey romex indoors? It would probably be a 60-70 foot run depending on exactly how I have to route the wire. If I can use this wire will it be sufficient?

I must have been asleep the first time I read this because I missed that detail entirely !

I agree with the others. 12/2

 

[G_P]

Just checked and its only about 50 bucks for 12ga romex.

Id rather spend the 50 than burn my house down!

 

[justsam]

It's really easy for me to spend someone else's money, but if I were going to the trouble to wire that up, I would probably spring for 10ga.

My reasoning is that if you are to upgrade that compressor, it will probably be to something a bit larger. Most larger single phase compressors are going to need something greater than 20 Amps, but less than 30. The cost of the 10 over 12 is incremental at this point, and breaker cost is the same, as is the receptacle.

The 10ga gives you an honest 30 Amp circuit.

 

[G_P]

Preferrably I would like to run a 50-60a circuit so that I could plug my welder in without using the 50' extension cord from the range or dryer outlet.

Right now the house is from 1952 with an addition added in 1988. The main panel is now in the addition with the original screw in fusebox being used as a subpanel. I know that has to be replaced with breakers soon. There are porcelain light fixtures with fuses screwed in them being used as additional circuits!

To run from the main panel (only place I can add a breaker) means a hell of a long wire run across the addition and to the far corner of the original building so that I can put the compressor out of the way and near the basement doors. I really want to put in an outdoor outlet for my welder but right now that amount of heavy wire is not in my budget. If I run the 12/2 now I can always use it in the future for something else. Perhaps some additional outdoor lighting.

Maybe I should sell the big roll of 14/3 burial cable to offset the cost of the new wire?

 

[pattenp]

It sounds like another sub-panel is what you need.

 

[G_P]

I looked at the subpanel and it is fed by 6/3.
It is a 60a panel. Is 60a the max I can run on 6/3?

The box total is well over 100a but the 60a cartridge fuses have never blown.

Replacing this box would be nice and safer and let me easily add a compressor circuit.

Sent from my C5120 using Tapatalk 2

 

[pattenp]

If the 6/3 is NM(Romex) then 60A is the max.

 

[G_P]

It's a thick black cable and I can see the individual conductors bulging in the insulation. I'm assuming its some form of romex. 6/3CU. Guess I'm not upgrading that panel without upgrading the wiring to it.

Think I will just run 12/2 to the compressor for now. I can always upgrade later and use the 12/2 for something else.

 

[G_P]

It's really easy for me to spend someone else's money, but if I were going to the trouble to wire that up, I would probably spring for 10ga.

My reasoning is that if you are to upgrade that compressor, it will probably be to something a bit larger. Most larger single phase compressors are going to need something greater than 20 Amps, but less than 30. The cost of the 10 over 12 is incremental at this point, and breaker cost is the same, as is the receptacle.

The 10ga gives you an honest 30 Amp circuit.

100ft of 10/2 is $115. 250ft of 10/2 is only $131. how is it possible to get the extra 150ft of cable for 15 bucks? And where can I buy the 150ft of wire for $15

Right now its looking like 10ga is twice the money as 12ga so I think I will go with 12ga.

http://www.lowes.com/LowesProductCo...com/Electrical/_/N-1z0yt4x/pl?Ntt=10-2+romex#!

 

[Aceman]

A 3HP 240v motor by the NEC tables draws 17 amps.

17 amps x 125%= 21 amp wire.

10-2 Romex or #12 THHN are the minimum wire sizes to feed this motor.

 

[G_P]

A 3HP 240v motor by the NEC tables draws 17 amps.

17 amps x 125%= 21 amp wire.

10-2 Romex or #12 THHN are the minimum wire sizes to feed this motor.

Motor tag says 11.0 amps @ 240v. Max current 15.0 amps @ 240v.

It runs fine on the 50' 12/2 extension cord I'm using now and the cord does not even get warm. I now understand that 14ga is too small. I measured the run of wire today and it will be 67' from panel to compressor with a few feet to spare. That's routing the wire neatly. If I was to drill through a ton of joists I could probably get it down to 50' But I am going by following the current wiring routes.

I do have 2 500' spools of 12ga THHN in white and red. Problem is that would need to be in conduit and I only have 14ga green for ground. It might work out cheaper to buy a bunch of conduit though as I have cases of solvent weld PVC conduit fittings sitting around downstairs......

 

[Norcal]

Motor tag says 11.0 amps @ 240v. Max current 15.0 amps @ 240v.

It runs fine on the 50' 12/2 extension cord I'm using now and the cord does not even get warm. I now understand that 14ga is too small. I measured the run of wire today and it will be 67' from panel to compressor with a few feet to spare. That's routing the wire neatly. If I was to drill through a ton of joists I could probably get it down to 50' But I am going by following the current wiring routes.

I do have 2 500' spools of 12ga THHN in white and red. Problem is that would need to be in conduit and I only have 14ga green for ground. It might work out cheaper to buy a bunch of conduit though as I have cases of solvent weld PVC conduit fittings sitting around downstairs......

The NEC table values are what is required.....

 

[G_P]

To be honest I'm not too concerned with it meeting code. The part of the house the compressor will be installed in still has it's original wiring from 1952. As long as it's not going to catch on fire Its good in my book. My parents currently own this house and I am now staying with them to provide care as my father just had open heart surgery. (5 bypasses and a valve replacement) They have no plans on moving and I am an only child and will Inherit the house eventually. (hopefully a very long time away)! Not sure If there will be an inspection required then but if there is CT wont allow a house to be "sold" while it still uses fuses so I will be facing a full rewire of half the house anyways and will bring this compressor up to code then with an upgraded subpanel in the old part of the house.

I guess if it's a huge deal I will put the compressor closer to the panel and just have to run much longer air pipes. I really want the compressor in the old part of the house as it will be under the bedroom and obviously I won't be running it if I'm asleep.

 

[Norcal]

A cheap pull out A/C disco can be had for less then $10 at the big boxes, and if you don't care about "code" then you should not even be doing the work. JMO

 

[eddie1278]

I'm an electrician.

You are fine with 12/2 because the NEC allowable ampacity of #12 is 25 amps under the 60 degree column. Ampacity table 310.16

Also you should worry about doing things to code because these codes are the MINIMUM safest way to do things. They codes aren't made to bust balls they are made to protect lives and property.

 

[pattenp]

Just what table are you looking at? 12/2 NM is 20 amps at 60 degrees. #12 THHN is 25 at 75 degrees.

I'm an electrician.

You are fine with 12/2 because the NEC allowable ampacity of #12 is 25 amps under the 60 degree column. Ampacity table 310.16

Also you should worry about doing things to code because these codes are the MINIMUM safest way to do things. They codes aren't made to bust balls they are made to protect lives and property.

 

[eddie1278]

Just what table are you looking at? 12/2 NM is 20 amps at 60 degrees. #12 THHN is 25 at 75 degrees.

Under the 60 degree column you have TW and UF. Also the conductors inside NMB-90 are not labeled as THHN they are just conductors rated for 90 degree C so you are reading the tables wrong.

For motor and AC circuits 25 amps on NMB-90 #12 is allowed by the NEC

 

[wyliesdiesels]

NM-B is limited to 60c deg ampacity regardless of the conductors being 90c deg rated because of the insulation and paper in the jacket! Also, 240.4(D) comes into play!

 

[eddie1278]

OP use 12/2 romex and be done with it. Perfectly safe and accepted by the NEC. Forget the armchair electrician responses.

 

[pattenp]

Who said anything about the conductors in NM being marked as THHN? I was saying #12 THHN is rated at 25 amps at 75 degrees. #12 NM is not to be over current protected to more than 20A per NEC 334.80. Please be so kind to cite the NEC section that approves #12 NM-B to be overcurrent protected at 25 amps when used for motor circuits.

Under the 60 degree column you have TW and UF. Also the conductors inside NMB-90 are not labeled as THHN they are just conductors rated for 90 degree C so you are reading the tables wrong.

For motor and AC circuits 25 amps on NMB-90 #12 is allowed by the NEC

 

[eddie1278]

Who said anything about the conductors in NM being marked as THHN? I was saying #12 THHN is rated at 25 amps at 75 degrees. #12 NM is not to be over current protected to more than 20A per NEC 334.80. Please be so kind to cite the NEC section that approves #12 NM-B to be overcurrent protected at 25 amps when used for motor circuits.

You stated thhn under the 75 degree column. The only person who brought up "thhn" was you. Romex NM does not have thhn conductors in it.

As far as your other questions I do not have time to educate you. If you want to learn the trade sign up for a 4 year apprenticeship and work for an electrical contractor. Electricity is not something you should be playing with.

 

[pattenp]

Man what is your problem? I am not asking you to educate me because I know the NEC and what you are saying where the NEC approves the use of #12 NM-B at more than 20 amps is just wrong. Come back when you don't have a holier than thou attitude. And just how up-to-date are you on the NEC, because the table number 310.16 is not correct, it's 310.15.

You stated thhn under the 75 degree column. The only person who brought up "thhn" was you. Romex NM does not have thhn conductors in it.

As far as your other questions I do not have time to educate you. If you want to learn the trade sign up for a 4 year apprenticeship and work for an electrical contractor. Electricity is not something you should be playing with.

 

[eddie1278]

Man what is your problem? I am not asking you to educate me because I know the NEC and what you are saying where the NEC approves the use of #12 NM-B at more than 20 amps is just wrong. Come back when you don't have a holier than thou attitude. And just how up-to-date are you on the NEC, because the table number 310.16 is not correct, it's 310.15.

Like I said before I don't have time to educate you. Sign up for an apprenticeship with a local contractor and they will teach you. You think you know the code but it's clear you don't by saying #12 can't have a higher ampacity rating then 20 amps. And the ampacity table is 310.16 I should know I'm an electrician that runs his own shop.

 

[MrMark]

I don't think Eddie is too long for this forum. He is pretty typical though.

 

[wyliesdiesels]

Wow! Just wow! Anyone want some popcorn?

I know theres several electricians on here, myself included, and Eddie clearly doesnt know what he's talking about starting with the right code section!

 

[Aceman]

Like I said before I don't have time to educate you. Sign up for an apprenticeship with a local contractor and they will teach you. You think you know the code but it's clear you don't by saying #12 can't have a higher ampacity rating then 20 amps. And the ampacity table is 310.16 I should know I'm an electrician that runs his own shop.

What I posted above is 2011 code. In case you missed it:

A 3HP 240v motor by the NEC tables draws 17 amps.

17 amps x 125%= 21 amp wire.

10-2 Romex or #12 THHN are the minimum wire sizes to feed this motor.

I don't know where you're from or what cycle your on but this is NEC code minimum for the 2011 cycle.

For the record, I have my Oregon Supervisors license, so you don't have to worry about my education.

 

[G_P]

Ok. All bickering aside can I just run some 12/2 and call it good?

Sent from my C5120 using Tapatalk 2

 

[Alchymist]

After all the posts I've read by the 3 previous posters, Eddie is gonna teach them something?

 

[Aceman]

Ok. All bickering aside can I just run some 12/2 and call it good?

I can see now that it was a waste of time even posting in this thread. Hopefully, someone else will learn something when they come upon this thread.

This is why diy'ers need permits.

 

[eddie1278]

Wow! Just wow! Anyone want some popcorn?

I know theres several electricians on here, myself included, and Eddie clearly doesnt know what he's talking about starting with the right code section!

Ok for the armchair ec's

start at
334.80 then go to 310.16


I never stated a code section just the ampacity table 310.16. Type NM #12 in the 60 degree column has an ampacity of 25 amps. End of discussion.

By the way I'm on the 2008 code in PA

 

[MrMark]

Shame. I think this thread was very informative except for Eddy.

 

[eddie1278]

Ok. All bickering aside can I just run some 12/2 and call it good?

Sent from my C5120 using Tapatalk 2

Yes like I said before.

 

[pattenp]

This where we went in different directions. We're on 2011
NEC which is now 20A for #12 NM. And the table is now 310.15.

Ok for the armchair ec's

start at
334.80 then go to 310.16


I never stated a code section just the ampacity table 310.16. Type NM #12 in the 60 degree column has an ampacity of 25 amps. End of discussion.

By the way I'm on the 2008 code in PA

 

[Kevin C]

I can see now that it was a waste of time even posting in this thread. Hopefully, someone else will learn something when they come upon this thread.

Not a waste of time.... That was a section of code that I did not understand. It was news to me that the NEC table took precedence over the motor's name plate rating.

In short, if the motor has a 240 v 3hp rating, use the NEC table for the current (17 amps). Standard practice is to size for 125% so you end up with a 21 amp conductor requirement.

If we can stay on track.... My 25 year old, 3hp 240 volt Sears Craftsman compressor says to run it on a minimum of a 15 amp circuit. I went out and looked at the name plate on the motor, 15 amps, 3 HP. No UL / NTRL markings.

For a home compressor, do I use the NEC ratings and ignore the factory specifications, or does the manufacturers specifications take precedence?

I can almost understand the NEC 17 amp requirement, it covers the possibility of usage at a higher service factor or if the motor is ever replace with a less efficient design ( or voltage drops). It does seem excessive when combined with the 125% rule.

I'm curious if that was the rational behind using a set table vs nameplate.

 

[pattenp]

I'm a little lost on what you're saying about the motor plate saying 15A vs the specs saying to run it on a minimum 15A circuit. The two don't jive. If the motor plates says 15A then it needs to be on a 20A circuit. 15A X 1.25 = 18.75A so 20A circuit.

Edit: I'd use the motor plate amps. The HP rating is most likely baloney.