Help wiring compressor

[LS6 Tommy]

Am I the only one who noticed he's now WAY above the 80% rating for the 50 amp service? Regardless of what wire he used, he shouldn't have that compressor wired into that panel at all...

Tommy

 

[jtyson]

Am I the only one who noticed he's now WAY above the 80% rating for the 50 amp service? Regardless of what wire he used, he shouldn't have that compressor wired into that panel at all...

Tommy

I'm not clear on code, but isn't it based on continuous use? So basically if I had the compressor running for 3+ hours while running the 20 amp service for lights and such simultaneous, then I would be above the 80% rating? Or is it anything tied in to the panel at all?

 

[LS6 Tommy]

I stand corrected. I didn't recall the ratings correctly. Your branch circuit shouldn't exceed 80% of the breaker rating. Theoretically, you can fill the panel with breakers as long as none of the breakers are larger than 50A. I wouldn't do it, but it's not illegal. Just FYI, the feeder circuit to the panel must be rated for 125% of the panel rating...

Sorry for any confusion I caused!

Tommy

 

[jtyson]

I stand corrected. I didn't recall the ratings correctly. Your branch circuit shouldn't exceed 80% of the breaker rating. Theoretically, you can fill the panel with breakers as long as none of the breakers are larger than 50A. I wouldn't do it, but it's not illegal. Just FYI, the feeder circuit to the panel must be rated for 125% of the panel rating...

Sorry for any confusion I caused!

Tommy

By chance could I trouble you to put that in layman terms for me?

 

[jtyson]

Trying to do some more research on the 125% figure and it is racking my brain. From what I have found, something has to be related to the calculated load. 125% of continuous load plus 100% of non continuous load.

So in my situation, the 110 outlets and the lights would be my continuous loads. The compressor would be my non continuous load. I have 3 20amp breakers (the continuous load) and the one 30 amp breaker I just installed. 125% of my continuous load is 75 amps. 100% of the non continuous would be 30 amps. So 105 amps added up. Does that mean that my 50 amp panel was overloaded with just the 3 20 amp breakers for the lights and outlets? Or are my 20 amp outlets even considered continuous? Or is that based on what is plugged in to them?

If someone could clear this up for me that would be great. I'm totally confused. I was going to install another 30 amp breaker for my welder today, but if I can't, then I'll return the stuff I bought to do it.

 

[LS6 Tommy]

What I meant is the wire that feeds your sub panel must be rated for 125% of the sub panel rating. You have a 50A sub panel, so the wire feeding the sub panel must be rated for 62.5A. Real world, it would probably be rounded to 60A.

As for the "calculated load" the NEC doesn't do that. You can legally fill every spot in the panel as long as none of the breakers are rated higher than the 50A main breaker.

Tommy

 

[jtyson]

What I meant is the breaker & wire that feeds your sub panel must be rated for 125% of the sub panel rating. You have a 50A sub panel, so the breaker in your main panel & the wire feeding the sub panel must be rated for 62.5A.

As for the "calculated load" the NEC doesn't do that. You can legally fill every spot in the panel as long as none of the breakers are rated more than 50A.

Tommy

Is this based on the panel rating itself? Or the load to the panel? The sub panel is actually a 100 amp panel. But it has #8 run to it, so as far as I know that is only good for 50 amps. It had a 60 amp breaker feeding it from the main panel, but I was under the impression that the wire was undersized for the breaker, so I swapped the 60 amp breaker for a 50 amp breaker.

 

[sberry]

Install it. If the comp starts let off the welder. As long as the wire feeding the panel is heavy enough to be protected by the breaker it wont be a problem, you are not pulling 30A but the run current of the comp and only using as much power as you are using, not the breaker rating. I got an outlet with 2 dozen devices on it. You are not going to add 3 120V 20A loads along with the comp. I have seen guys work from 30A service in spec house garage, an air comp runs so little that you can avoid doing several things at the same time.

My own service is 400A, doesn't matter. I can run 2 welders, a cooler and if the comp comes on no big deal while we are pressure washing. Your 211 welder draws 23A wide screaming open while welding and nothing like the comp when it isn't, simply run one major at a time. Couple lights, a load like a chop saw can wait a minute or so for the comp to turn off and you wont be using it if you are running continuous such as sandblast anyway.

I could possibly apply another 60A provided I fire up a tig I havnt used in years and chances are if I was doing that wouldn't do much else at the same time. .

It would be interesting to see my peak load, I got a 3hp well, a cooler that runs 26A, I got 3 hp air comp on demand, could weld or cut, most sawing would be done off that cycle, a few A of lights, couple 3 fridges and a pinch of AC on 120V, I bet my all time peak isn't much north of 100 with the cooler being the insulting factor due to the duty cycle being high in hot weather.

 

[sberry]

I bet he couldn't trip the 50 if he tried minus the addition of an oven and hot tub.

 

[LS6 Tommy]

Is this based on the panel rating itself? Or the load to the panel? The sub panel is actually a 100 amp panel. But it has #8 run to it, so as far as I know that is only good for 50 amps. It had a 60 amp breaker feeding it from the main panel, but I was under the impression that the wire was undersized for the breaker, so I swapped the 60 amp breaker for a 50 amp breaker.

I edited my earlier post about the 125% feeder rating. I should not have included the main breaker in that rating.

The rating is based on the panel rating itself. Since you said your wire feeding it is only #8 NM, you need to swap the 50A main breaker out for a 40A. The options to keep the 50A main breaker would be:

1) Upsize to #6 NM feeder.
2) Replace the #8 NM feeder with a #8 THHN/THWN feeder.

Hope I didn't make you more confused. I tried to be as simple as possible.

Tommy

 

[jtyson]

It's based on the panel rating itself. Since you said your wire feeding it is only #8 NM, you need to swap the 50A main breaker out for a 40A. The options to keep the 50A main breaker would be:

1) Upsize to #6 NM feeder.
2) Replace the #8 NM feeder with a #8 THHN/THWN feeder.

Hope I didn't make you more confused. I tried to be as simple as possible.

Tommy

It is #8 THWN feeding the sub panel. Sorry I didn't specify wire type. I have romex feeding the lights and the compressor.

 

[LS6 Tommy]

Gotcha. Boy, I don't think I've ever edited posts so many times. I'm really getting sloppy!

Tommy

 

[wyliesdiesels]

I tried posting this on my compressor thread, but no response so hopefully I can get some help here. I'm renting currently, but I can install a new service in the garage from the sub panel. I'm not an electrician by any means, but I can do a bit here and there. Just like guidance from more experienced folks so I don't fry anything.

I'm going to need to wire both the machine, and put a new breaker in the box. I'm looking for advice on both.

The service to the garage is only 50 amp. I have a fridge, deep freezer and lights in there. Otherwise, any other equipment I use is one at a time. I'm hoping to be able to install a circuit that I can use for both my welder, and this compressor, although not at the same time. Welder is a Miller 211 (multi voltage) that I currently just run on 110v and that is okay, but since I'll be installing a larger service, being able to use it on that too would be great. If I can't, oh well, save that for another day or another house. I've attached a picture of the spec sheet on the motor, as well as the pressure switch, and I'm hoping someone can either help direct me, or point me towards somewhere that can.

I appreciate any information anyone has. Although, if you are going to advise that I hire an electrician, I would love to trust me, I hate dealing with electrical, but it just isn't in the budget.

Thanks!

First off, since youre renting, you need to get written permission from your landlord to be able to do this legally. Even then, some jurisdictions/states do not allow this and you could get into legal hot water/liability issues if a problem such as a fire occurs down the road!

You need to know the HP rating of the compressor you plan on buying before you can decide what size circuit you will need.

For motor circuits, per code, the wire is sized at 125% of FLC in the NEC FLC tables, which is 28a for a 5HP motor. Breakers can be sized at a maximum of 250% FLC. Per code, you wire the circuit based on the NEC FLC chart and NOT the motor nameplate. If the motor nameplate doesn't list a HP rating, then you take the FLA on the motor nameplate and compare it to the FLC tables to figure out what size HP it is. Then use the the listed FLC and wire your circuit based off of that. You dont wire based on motor nameplate FLA rating because if u end up switching to another motor with the same listed HP, but that has a HIGHER FLA, then your circuit is undersized.

This question gets asked here a couple of times a week. Do a search and read the answers.

A compressor this size is usually direct wired to avoid having a plug and socket. Plugs have a horsepower rating.

Aint that the truth. :rollseyes:

Plug and socket is fine, there's no "size effect" when it comes to electricity, it's all linear. Another word, if your TV with 5A (110v) is using a plug, then it's ok if a 35A motor (7.5hp) to use a plug and socket. Just pay attention to the current capacity and voltage rating of the socket/plug.

electric water heaters were typically hardwired but it's typical now to see plug and socket now and those are on 30A 220V breaker rating. Those plug and socket are affordable these day are maybe reason why.

Not true. Standard NEMA outlets are rated at a maximum of 3HP. If its gonna be wired to code, then a true 5hp motor should be hard wired. When it comes to motor circuits, you cant just go off of the current rating. This is because motors have in-rush currents, which can be 4x-8x FLC. There IS other types of outlets that have higher HP ratings, such as non standard NEMA outlets and pin and sleeve outlets, which are EXPENSIVE.

Your example about the TV plug makes no sense.

And standard tank water heaters cant be on a cord and plug by definition because they aren't portable. And it would be just plain silly and a waste of money to put them on a plug when they aren't moved except when replaced.

Some of the MIG 200A with pulse pulls up to 40A. If so, you'll need #8AWG copper.

5HP compressor motors are run on 30A breaker with #10AWG (smaller wire) and that's pretty standard. And that's what I run my 5HP on.

I don't like to oversize for something I might not get, therefore #10AWG is what I would get for your compressor and future welder.

I doubt your motor is a TRUE 5HP because a 30a breaker is almost guaranteed to nuisance trip since a 5HP motor is around 28a FLC, with in-rush currents 4-8 times that!
And there is different types of wire. #10 THHN has an ampacity of 35a and would work for a 5HP motor. On the other hand #10 NM-b would not since it has an ampacity of 30a.

^^I don't know what you pointed to but electricity is electricity. Theoretically, you can have a motor that pulls 100A (@ 2% efficiency) and produce 5hp and you can have a motor that pulls 20A (@80% efficiency) and produce the same 5HP.

I'm not disputing if there's HP value to plugs or not. As a matter of fact, each motor is designed slight differently with loading characteristic (amp, torque, etc...). Again, you can have one 5HP that pulls different amp base on its efficiency rating. Therefore "HP" rating is not the true value for termination and wiring requirement. It just so happen that motors have an HP value, and people use the term "HP" for ease of conversation/understanding.

Electricity is electricity, termination is termination, wiring size is wiring size. Those three does not discriminates whether if it's a motor can be used or not with plugs. When you terminate the wires (hardwire or plugs) those two clamping forces better be rated at that current it advertised and that whats matter. If you're afraid the clamping force of plugs losing its strength over the time after usage (plug and unplug), then you can question all of the other 110V compressor out there.

Except if u want to do things to code, your logic doesn't work. Also there is different types of wire with different ampacities, so your 'wiring size is wiring size' doesn't make sense either. See above about #10 wire.

^welcome to GJ. You'll find different minded people with different background; some will act like robot and give you answer what they heard and some will provide you a direct answer.

That ROMEX wire #10AWG is proper for your Century 5HP motor.

Incorrect again. As I said above, #10 NM-b, aka Romex is limited to a 60* c ampacity or 30a. A 5hp motor needs 35a rated wire. #10 THHN would work, since its rated at 75* c ampacity or 35a. It helps to read your code book once in awhile....

 

[MrMark]

wylie, what's your take on the exception 3 deal?

 

[CoopVA]

Spot on...

First off, since youre renting, you need to get written permission from your landlord to be able to do this legally. Even then, some jurisdictions/states do not allow this and you could get into legal hot water/liability issues if a problem such as a fire occurs down the road!

You need to know the HP rating of the compressor you plan on buying before you can decide what size circuit you will need.

For motor circuits, per code, the wire is sized at 125% of FLC in the NEC FLC tables, which is 28a for a 5HP motor. Breakers can be sized at a maximum of 250% FLC. Per code, you wire the circuit based on the NEC FLC chart and NOT the motor nameplate. If the motor nameplate doesn't list a HP rating, then you take the FLA on the motor nameplate and compare it to the FLC tables to figure out what size HP it is. Then use the the listed FLC and wire your circuit based off of that. You dont wire based on motor nameplate FLA rating because if u end up switching to another motor with the same listed HP, but that has a HIGHER FLA, then your circuit is undersized.


Aint that the truth. :rollseyes:


Not true. Standard NEMA outlets are rated at a maximum of 3HP. If its gonna be wired to code, then a true 5hp motor should be hard wired. When it comes to motor circuits, you cant just go off of the current rating. This is because motors have in-rush currents, which can be 4x-8x FLC. There IS other types of outlets that have higher HP ratings, such as non standard NEMA outlets and pin and sleeve outlets, which are EXPENSIVE.

Your example about the TV plug makes no sense.

And standard tank water heaters cant be on a cord and plug by definition because they aren't portable. And it would be just plain silly and a waste of money to put them on a plug when they aren't moved except when replaced.


I doubt your motor is a TRUE 5HP because a 30a breaker is almost guaranteed to nuisance trip since a 5HP motor is around 28a FLC, with in-rush currents 4-8 times that!
And there is different types of wire. #10 THHN has an ampacity of 35a and would work for a 5HP motor. On the other hand #10 NM-b would not since it has an ampacity of 30a.


Except if u want to do things to code, your logic doesn't work. Also there is different types of wire with different ampacities, so your 'wiring size is wiring size' doesn't make sense either. See above about #10 wire.

[/b]
Incorrect again. As I said above, #10 NM-b, aka Romex is limited to a 60* c ampacity or 30a. A 5hp motor needs 35a rated wire. #10 THHN would work, since its rated at 75* c ampacity or 35a. It helps to read your code book once in awhile....

 

[jtyson]

I'm renting from family so I can do as I please to the place with no issue as far as permission goes. I've got it hooked up with the wire I had, and a 30 amp breaker. For the time being, that is how it will stay. So far no problems. If somehow I end up living here for longer than I anticipate, I will upgrade the sub panel and the wiring to the compressor.

 

[Trey T]

This is crazy because I tried to explain the logic behind it and thought many of y'all guys are good at reading the NEC; I guess I'm wrong about that. I'm no electrician but I can very well read codes and I'm very good at it.

If you want to follow the code, let's follow the code. Base on the NEC 2011 (430.22 (E)), the full-load current value to size the wire is 30.8Amps for that Century B384 motor. SO NO, IT'S NOT 35A.

Again, the OP isn't providing a service. If you want to use the table based on general 5HP design specs, go ahead and size it up based on 35A FLC (28A*1.25). As long as his breaker is 30A, the wire is protected and his motor will run under 30A - that whats matter!

Many of you mention start up in-rush current, so why not size that wire/breaker to ...let's say... #2/100A? ...why even mention it? Why? So silly!!!

If anyone of you is an electrician and wanting to bid on large project, you will never win any contract because your copper/aluminum cost will be too high!

 

[CoopVA]

Trey,

A 5hp single phase 230v Motor requires a 35 amp breaker. See Table 430.148.

All cable does not have the same ampacity, which is exactly what wyliesdiesel explained.

Different insulation on wires is what makes the difference. #10 NB cannot be used on a 5hp motor.

Everything he said is correct.

Are you an Electrician? You sound like you may be an Engineer...

 

[sberry]

It should be made clear in this ******* match that the OP who has a 20A motor is in no danger of overheating the wire in this installation. While this may not meet the letter for the future install of a bigger comp it meets the intent of being adequate for the particular application.

 

[CoopVA]

It should be made clear in this ******* match that the OP who has a 20A motor is in no danger of overheating the wire in this installation. While this may not meet the letter for the future install of a bigger comp it meets the intent of being adequate for the particular application.

I always abide by the rule that if you're going to do it, do it right the first time.

The OP asked how he should wire up a 5hp 230v compressor motor and a welder for future use.

Yes, a 30 amp cb and #10 wire will "work"...

Is it the correct way to do it? NO.

The right way to do it is with a 70a breaker in the panel, #8 NM-B (Romex) to a junction box near the compressor and then flex to the motor. You can use #10 THHN in the flex...

Go to table 430.148
For a 5HP motor @ 230V Amps = 28
Min. wire size is: 28 x 125% = 35A ie. 10 AWG. (#10 NM-B is not rated for 35a)

Table 430.152 permits the circuit breaker size to be 250% of amps (28) 28 x 250% = 70A

Section 430.52 allows a larger breaker allows for the starting current (short time) of the motor.

#10 AWG (THHN) or #8 (NM-B) circuit protected by a 70 amp circuit breaker is code compliant in this application.

Run a separate circuit for the welder. Both units "should" have dedicated circuits.

 

[sberry]

So, would this 35A breaker,,, not usually on the shelf at a common store be the minimum or max?

 

[sberry]

Is there an electrical service guide in the owners manuals to these things or do they assume every installer is going to be fluent in code and NEMA? An oven has a guide, a welder has one, where is the owners manual for this or is it exempt because of the motor?

 

[sberry]

While it is admireable to do it right or attempt to and we do know the run of the motor, its no mystery there is no real reason to leave the impression there is a dangerous faulty install he has to run out and do over. Next time he does it he can wire for this class of comp like he did.

My pressure washer comes with 30A plug, recept, got a 5 hp motor that pulls 22A, (might even be more) machine designed to be plugged in to a 30A circuit.

I just looked at the om for giggles, because it plugs in to this listed circuit they don't appear to have a true service guide. Only service guides I would have are so much older.

The washer doesn't have any overcurrent protection of its own but the thermal on the motor I assume.

I bought it in 82 maybe,, run every day since on a 30, not one trip. I inherit a 3 hp comp, 18 run a, was hooked to a 12 20 for fukkin years and then some till I got it and up the wire a size,,,, 1000's and them some starts on a 20 from old service, never ever trip, wire didn't get hot, probably didn't help it but have never serviced one single thing on the motor, several starts a day for decades.
I guess I never paid attn. but does a new small air comp come with a plug?

 

[sberry]

Millions of 10 cable 50A plug welders in the world. For people that don't want to be a code expert and for those who do we need to help with some understanding of the nature of the circuit.

You dont see me advocating the absolute minimum standard for that circuit which would be a 12 in pipe but heavy it up a size to a 10 and I buy it for a safe install to my buds garage, my neighbor a lic master and then some has a garage circuit for his been there for 40 yrs.

The big fault with it all from some point of view is simply no one thinks including the people that list the connection that its a great idea and not at the breaker either.

Now you could argue that it is or isn't legal to put that 10 cable on the welder circuit but with the buzzer will melt it in to a cinder before it makes the wire hot. Never been a fire started cause some joker overheated a 10 cable with a buzzer with a factory cord on it.

 

[sberry]

I see a foot note that the controls and fan, transformer are supplied with 14 wire on the steamer.

 

[CoopVA]

So, would this 35A breaker,,, not usually on the shelf at a common store be the minimum or max?

35a breaker would be minimum. They can be had in any electrical supply house.

Is there an electrical service guide in the owners manuals to these things or do they assume every installer is going to be fluent in code and NEMA? An oven has a guide, a welder has one, where is the owners manual for this or is it exempt because of the motor?

There is usually a "recommended circuit size" from the manufacturer, but, the Code and the Local Jurisdiction Having Authority overrides that...

While it is admireable to do it right or attempt to and we do know the run of the motor, its no mystery there is no real reason to leave the impression there is a dangerous faulty install he has to run out and do over. Next time he does it he can wire for this class of comp like he did.

My pressure washer comes with 30A plug, recept, got a 5 hp motor that pulls 22A, (might even be more) machine designed to be plugged in to a 30A circuit.

I just looked at the om for giggles, because it plugs in to this listed circuit they don't appear to have a true service guide. Only service guides I would have are so much older.

The washer doesn't have any overcurrent protection of its own but the thermal on the motor I assume.

I bought it in 82 maybe,, run every day since on a 30, not one trip. I inherit a 3 hp comp, 18 run a, was hooked to a 12 20 for fukkin years and then some till I got it and up the wire a size,,,, 1000's and them some starts on a 20 from old service, never ever trip, wire didn't get hot, probably didn't help it but have never serviced one single thing on the motor, several starts a day for decades.
I guess I never paid attn. but does a new small air comp come with a plug?

Millions of 10 cable 50A plug welders in the world. For people that don't want to be a code expert and for those who do we need to help with some understanding of the nature of the circuit.

You dont see me advocating the absolute minimum standard for that circuit which would be a 12 in pipe but heavy it up a size to a 10 and I buy it for a safe install to my buds garage, my neighbor a lic master and then some has a garage circuit for his been there for 40 yrs.

The big fault with it all from some point of view is simply no one thinks including the people that list the connection that its a great idea and not at the breaker either.

Now you could argue that it is or isn't legal to put that 10 cable on the welder circuit but with the buzzer will melt it in to a cinder before it makes the wire hot. Never been a fire started cause some joker overheated a 10 cable with a buzzer with a factory cord on it.

I'd plug a piece of equipment that is provided with a plug from the factory into an appropriate wall socket all day long and not worry about it. Hard wiring a 230v motor is a whole different animal. Like I said, a 30 amp breaker on #10 NM-B will work. The risk is minimal. Is it "legal" to do it that way? No, it's not. On the off chance that something does happen, and his building burns down, if they find that a circuit was installed incorrectly he would be screwed...

I can not, and will not, recommend to anyone advice on electrical issues that is inconsistent with the NEC or the Local Authority Having Jurisdiction.

My best advice is if you have any doubts about your installation, contact your Local Authority and ask them what they require.

 

[CoopVA]

I see a foot note that the controls and fan, transformer are supplied with 14 wire on the steamer.

Wow... Is that your subpanel there behind that piece of equipment? Major code violations there...

 

[Trey T]

All along, I was just trying to make some practical sense from experience and most of y'all guys say I didn't read the NEC. Well fine, I haven't looked at the NEC in ages. Well, the truth is you and others obviously did not read NEC section 430.22.

The code usually are general and flexible but y'all guys are stuck with sizing wire only with "HP" value. AGAIN, FUNDAMENTALLY, HP VALUE IS NOT DIRECT RELATION TO CURRENT (AMP). W/o gripping the idea behind electricity well, and NEC is the only thing you got, I can understand why one would use "HP" to size their wire. Maybe the old quote "can't teach old dog with new tricks" comes into play here. Anyways, I can't believe I'm quoting NEC again when most of y'all guys claimed to understand what y'all read, but here it is:

Code 430.22 allows two methods of determination: 1)table style for general ; 2)narrative style based on specific use.
1. Code 430.6(A)(1) - Table 430.148 : this yield 35A (28A*1.25)
2. Code 430.22(E) - Table 430.22(E) : this yield 30.8A (22A*1.4)

430.22 Single Motor. Conductors that supply a single motor
used in a continuous duty application shall have an ampacity of not less than 125 percent of the motor full-load current
rating, as determined by 430.6(A)(1), or not less than specified
in 430.22(A) through (G).

430.22(E) Other Than Continuous Duty. Conductors for a motor
used in a short-time, intermittent, periodic, or varying
duty application shall have an ampacity of not less than the
percentage of the motor nameplate current rating shown in
Table 430.22(E), unless the authority having jurisdiction
grants special permission for conductors of lower ampacity.

Also, why are you and the other guy regurgitating the Table 430.148 (formerly 430.248) that I already posted way-earlier? Silly!!

If y'all speak on behalf of the entire electricians on the internet, then we got a bigger problem than this. NEC reading comprehension!

...

Yes, a 30 amp cb and #10 wire will "work"...

Is it the correct way to do it? NO.

The right way to do it is with a 70a breaker in the panel, #8 NM-B (Romex) to a junction box near the compressor and then flex to the motor. You can use #10 THHN in the flex...

Go to table 430.148
For a 5HP motor @ 230V Amps = 28
Min. wire size is: 28 x 125% = 35A ie. 10 AWG. (#10 NM-B is not rated for 35a)

....

 

[Trey T]

While I'm trying to be helpful, y'all guys are attacking me and making it into a ******* contest - LET'S GO!

I guess if you're to size a motor for "Varying Duty" (NEC 430.22(E)), y'all guys will size the continous rated motor by the Table 430.148 because it's "HP" rated, right?

Quick calculation check:
Table 430.148 : 5HP 220V 28A yield 35A FLC
Table 430.22 : name plate 5HP 220V 22A yield 44A FLC(or FLA, like one guy disputed the technical writing way)

There you go! does that 430.148 work? Or like one of you stated "is it correct?"

 

[CoopVA]

Attacking you? Come on man, this isn't even a heated discussion, yet... Trey, the NEC is a very fickle bird. Just about everything in it is debatable.

The nameplate on the motor says it is a Continuous Use motor. Therefore 430.22(E) - Table 430.22(E) does not apply here. I stand by my previous comments on what should be the correct way to do it.

That is my interpretation. Certainly not trying to make it a ******* contest. Personally, I don't give a rat's a$$ how anybody wants to do their own thing. I'm just giving my professional opinion on the matter. Considering I've been in the Trade for over 20 years take it for what it's worth.

If you don't like it, don't follow it.

If it were me, I would use a 40 amp breaker at the panel, wire it with #10 THHN in conduit to a non fused disconnect at the compressor and then flex with #10 THHN to the motor.

Done.

 

[Trey T]

Wow. Read my last post again. Didn't I say it's a continuous rated motor?

Everybody: read 430.22 before you make a fool out of yourself.

\thread

 

[CoopVA]

I think I see where the disconnect is between us Trey...

Correct me if I'm wrong here, but it appears to me that you are going on what the minimum rated conductors and disconnecting means are based purely on what the actual ratings of the motor are based upon the nameplate.

In that theoretical frame of observation, you are absolutely correct. A #10 AWG wire on a 30 Amp breaker is sufficient. As I stated in a previous post...

From an installation standpoint, consideration must be taken for NEC and Local Code restrictions, type of motor, method of wiring, safety and craftsmanship of the installation.

Minimum Code for the installation of a 230v single phase continuous duty motor, according to my interpretation, would be a MINIMUM of a 35 amp circuit breaker at the panel, (but I would not use less than a 40 amp, and with inrush current the Code allows up to 70 amps in this situation...) with #10 THHN in conduit to a motor rated switch/disconnect within 6' of the motor then flex from the switch to the motor.

A 30 Amp circuit breaker is not sufficient for this installation.
#10 NM-B is not rated for the Code minimum 35 amps for this motor.

I do this for a living, and I troubleshoot design and installation issues on a daily basis... There always seems to be a disconnect between Engineers and Installers, very much like the disagreement we are having here. I have come to the conclusion that Engineers think Conceptually and Installers have to take that Concept and make it a Reality. Sometimes the Concept may be valid, but in Reality, it is not Constructible...

In know way shape or form is my intent here to "attack" anyone. Just because I disagree with you and am arguing my point doesn't mean I'm on the "attack".

We are all adults here and we can have a discussion and disagree.

 

[sberry]

and his building burns down, if they find that a circuit was installed incorrectly he would be screwed...

This is why he has insurance. This concept is widely threatwened but I don't know personally or by any reliable account that this is true.

 

[CoopVA]

This is why he has insurance. This concept is widely threatwened but I don't know personally or by any reliable account that this is true.

And if the insurance company can in any way shape or form show that a non code compliant electrical installation MAY have caused said fire, they will NOT pay...

 

[CoopVA]

Why would anyone want to cut corners and do the bare minimum (or less...) when it comes to anything? I can't believe we are even arguing about this...

 

[sberry]

Have you ever actually seen or heard of a case of this to be true, if it was they would deny almost any electrical fault. Faulty equipment is insured every day, faulty installations too.

Yes, some of the equipment connected to that panel couild be removed, we don't use it. Anywhere for a "user" to plug on is out of the way or gfci and the panel is bolted to a steel plate welded to the building. Some of it remained after moving in, I still clean up a violation I run across from old stuff and things I wired as a kid.

I got a bud in the city an investigator, never recall him saying he went thru a fire with a mic measuring wiring in a building,,, especially to a comp that wasn't even likely on at the time of the cause.

I had one and the old building it originated in had a huge amount of wire in, the guy asked me,,, I said, no, abandoned with the service disconnected and a single service circuit that was new romex for a couple lights and a battery charger in, never looked for or found a couple switch loops of 14 I stuck on to a couple fixtures on a 20, they were not running at the time anyway.

 

[CoopVA]

Have you ever actually seen or heard of a case of this to be true, if it was they would deny almost any electrical fault.

Then why do we even HAVE the NEC and Local Electrical Codes??? The NFPA is the entity that publishes the NEC. The NFPA is the National Fire Protection Association. I am a member...

Think about it...

 

[MrMark]

He's not an engineer, at least not electrical. His first post let that out of the bag.

CoopVA, there is this exception 3, that was brought up by an electrician. It has some merit. See my earlier post. I'd like your take on it.

 

[CoopVA]

He's not an engineer, at least not electrical. His first post let that out of the bag.

CoopVA, there is this exception 3, that was brought up by an electrician. It has some merit. See my earlier post. I'd like your take on it.

Mr.Mark, the air compressor can be considered as an "appliance", but, look at 422.3: "The requirements of Article 430 shall apply the installation of motor-operated appliances..." and 422.12(G): "Motors of motor-operated appliances shall be provided with overload protection in accordance with Part III of Article 430."

Which brings us back to Table 430.148... Welcome to the wonderful topsy turvy world of the NEC...

It's all a matter of interpretation. Bottom line is, what is the interpretation of your Local Authority Having Jurisdiction? If you present your case well, and they like you, you may get approved... I do not consider an air compressor to be an appliance, but that is my own humble opinion.

It's always better to install better than Code. That way, you avoid any misinterpretation. Alot of times, the cost is negligible, especially if the Local Authority rejects you and then you have to rip it out and do it over... That's why its always better to consult with the LA before you begin...

 

[MrMark]

Yes, it is an open issue for any equipment like this that is really primarily a motor. Does it have a UL listing as a "motor-driven appliance." If I did it for a living I would absolutely wire it as a motor at 35A FLC to avoid a dispute as to whether exception 3 applies and whether the compressor is a listed appliance.

Do I think it is going to burn down with that #10 nmb? Probably not but why not do it the most conservative way when the cost is small.