Wiring 15A 240V compressor question

[Max]

In this situation we aren't concerned with the current that the wire can carry constantly.

During a short circuit #18 can carry enough current to reliably trip a 20A breaker. Smaller sizes of wire may not carry enough current to trip the breaker.

I think that the same argument could be made about a 50A receptacle and a #12 power cord, no?

Going back to the #18 case, I would not expect UL to assume that the short was instantaneous. I’ve designed power supplies and there are many ways for things to fail that are 2X or 3X the rated current. And in that case the 18 ga wire burns but the outlet and breaker are just fine.

But, I’m not a UL engineer so I don’t know what they would think. So we are both just talking about our opinions here.

@Firebrick43 asked for a NEC cite for his specific case and so far no one has come up with one. I’m out until someone does, and if I’m wrong then I’ll happily admit it.

 

[Bert_]

Yes, that is true, only the wire in the wall and the receptacle its attached to.

Your confusing "Fixture wire" connected to branch circuits with flexible cords. Your absolutely correct if we were talking about fixtures but we are not. They have different rules.

The NEC covers the cord from plug to appliance.

"NEC 240.5(A) Ampacities. Flexible cord and flexible cable shall be protected by an overcurrent device in accordance with their ampacity as specified in Table 400.5(A)(1) and Table 400.5(A)(2). Fixture wire shall be protected against overcurrent in accordance with its ampacity as specified in Table 402.5. Supplementary overcurrent protection, as covered in 240.10, shall be permitted to be an acceptable means for providing this protection. "

Table 400.5(A)(1) allows only 7 amps for 18 gauge wire. Then you have to place an overcurrent protection on the appliance just as I have been saying. 240.6 thru 240.9 covers the types of overcurrent protection. It does not have to be a fuse in the plug.

240.9 is thermal devices which is what the OPs air compressor has, that is what protects the flexible cord not the main circuit breaker.

The breaker needs to protect ALL the wiring from short circuit. A " thermal device" doesn't not protect against short circuit.

It's so easy to pick and choose a few individual code articles that seem to support your argument. You aren't looking at the big picture. I'm not sure what your goal is? but I've noticed in several threads, it's you arguing with the world.

 

[Max]

The breaker needs to protect ALL the wiring from short circuit. A " thermal device" doesn't not protect against short circuit.

It's so easy to pick and choose a few individual code articles that seem to support your argument. You aren't looking at the big picture. I'm not sure what your goal is? but I've noticed in several threads, it's you arguing with the world.

Maybe we could avoid the personal attacks?

I am not arguing. What I am doing is trying to understand a fundamental concept. I get that the NEC controls (for example) the wiring, breakers, and receptacles in my house. I’ve got no issues with that, and I greatly appreciate the knowledge that the electricians contribute here on the NEC and practical aspects of makings things work to code. Bluntly, it‘s knowledge that I don’t have and I do not pretend to be an expert in that area.

I do not believe that the NEC controls the requirements of things that plug into those receptacles. For example, I am saying that the NEC does not control the design of my PC‘s power supply or the charger for my phone. Do you agree that the NEC is not relevant in that area?

As I noted before, many of the things that plug into standard 120V outlets are wired with much less than 14 ga wire. So for at least 15A 120V outlets it is possible to plug in a device that may only draw 1A, and the wire used for this application (say 18 ga) is only rated for < 10A. I believe that this is acceptable because the device has internal current limits (fuses, breakers, whatever). The main point is that for 120V, devices can be plugged in that do not have wire rated for 15A. Additionally many of those devices in normal operation will draw much less than 15A. For example, a USB dongle plugged into an outlet may only draw 50 mA. Do you agree with this aspect of things that plug into 120V outlets?

Multiple people here have said that for 240V you need to have the wires/breaker/receptacle roughly matched to the load. So for a 240V hard wire connection, it is not OK to hook up something that will only draw .1A to a 30A circuit. So the question is where in the NEC is that prohibited? It does not seem to be prohibited for 120V circuits, so why is it for 240V?

 

[mm08822]

Garage Journal Followers,.....You are now all experienced in gas-lighting (no, not the Blu-Gin or Jeanie) Think Alfred Hitchcock.
Follow this:
Post 9:

only when the motor load is hardwired.

Firebrick: (In response to Wiley's post - has to be hard wired.)
Have the section of the NEC for that?

How does nearly every low power appliance plugged into a 20 amp circuit plugged into a 5-15p work with that?

Post 12:

Any appliance with a 5-15P plug is designed to be protected by a 15A or 20A breaker.

Firebrick:
No its not. A blender that draws 5 amps and has a 20 or 18 gauge cord in no way is protected by a 20 amp breaker.

ANY protection for the appliance has to be on the appliance. That can be in the form of a fuse, an on appliance circuit breaker, or thermal overload.

Post 23:

Have the section of the NEC for that?

How does nearly every low power appliance plugged into a 20 amp circuit plugged into a 5-15p work with that?

MM08822:
1 HP motors are considered protected on a 120V branch circuit @20A or less. NEC 430.32 (D) (2) exception.

Post 32

1 HP motors (edit: or less) are considered protected on a 120V branch circuit @20A or less. NEC 430.32 (D) (2) exception.

No, they don't have to have protection if they are within sight of the controller, ie the Circuit breaker panel or a disconnect. They person operating is the circuit protection.

"A. Within Sight from Controller. Overload protection shall be permitted to be furnished by the branch-circuit short-circuit and ground-fault protective device; such device, however, shall not be larger than that specified in Part IV of Article 430."

If its not within sight of the controller it has to have overload protection.

"B. Not Within Sight from Controller. Overload protection shall be in accordance with 430.32(B)."

And again out of context. How is a 1hp motor on a 20 amp circuit a “low power? load on the circuit?
****************************
He's given the answer from the NEC (NFPA70 if you weren't sure).
The appliances he asked about in Post 9 are not permanently installed, portable, not automatically started and generally insight of the operator (again, it's about appliances so some details are spared for brevity).
Seems in context to me.....he brought it up, it got answered.
Tells me my (and exranger's) answer back to me, now aligned with the code article.
Then claims not in context.
This is Gaslighting. By the time the conversation is over you will have forgotten the point of the conversation, wonder if you have ADHD, and won't want to stop hitting your head against wall.

 

[mm08822]

I think that the same argument could be made about a 50A receptacle and a #12 power cord, no?

Going back to the #18 case, I would not expect UL to assume that the short was instantaneous. I’ve designed power supplies and there are many ways for things to fail that are 2X or 3X the rated current. And in that case the 18 ga wire burns but the outlet and breaker are just fine.

But, I’m not a UL engineer so I don’t know what they would think. So we are both just talking about our opinions here.

@[COLOR=rgb(0, 0, 0)][B]Firebrick43 asked for a NEC cite for his specific case and so far no one has come up with one[/B][/COLOR]. I’m out until someone does, and if I’m wrong then I’ll happily admit it.

Read post 22. Delivered.

How many table or floor lamps have circuit protection for incandescent bulbs?

Lets forget the bulbs, what happens if the cord feeding the "thing" gets damaged, creates a short or ground where all this happens before any protective devices, what do you think happens? When you touch the leads of a multi-meter together, they read~0-0.1 ohms. Let's say the ground or short has a resistance of 1 ohm. 120/1= 120A 6-8x the branch ocp value, the cb trips. And there are also arc-fault cb's to provide even further sensitivity for those times when intermittent connections occur.

 

[wyliesdiesels]

You missed his point. A quick look around my house shows me lights, stereos, and battery chargers that all have line cord wiring that is much smaller than 14 ga. Yet they plug into 15A receptacles. If nothing was done at the appliance level, any short in the appliance would burn those wires causing a fire.

The answer is that the appliance has internal protection (fuse, breaker, whatever) that in the case of an internal short it operates and stops the current flow. This is done all of the time for products that plug into 120V 15A circuits. Clearly it is within the NEC to do this.

So @Firebrick43 has asked what in the NEC prevents a similar approach on 240V?

flawed comparison...

 

[Max]

Read post 22. Delivered.

How many table or floor lamps have circuit protection for incandescent bulbs?

Lets forget the bulbs, what happens if the cord feeding the "thing" gets damaged, creates a short or ground where all this happens before any protective devices, what do you think happens? When you touch the leads of a multi-meter together, they read~0-0.1 ohms. Let's say the ground or short has a resistance of 1 ohm. 120/1= 120A 6-8x the branch ocp value, the cb trips. And there are also arc-fault cb's to provide even further sensitivity for those times when intermittent connections occur.

Thank you. I read your post and the relevant sections of the NEC. To me, that section controls the wiring to an outlet and the outlet itself. It does not control what is plugged into that outlet.

I understand your points about the wires to a lamp. Wires are generally straightforward in that they work, they are open, or they are shorted. To @Bert_ point earlier, in a a case with 18 ga. power cord wires, they still conduct enough current for long enough that a CB trips before the 18 ga wires burn up. I understand the point.

The problem is whatever appliance is plugged in may not fail catastrophically with a short. An awful lot of devices these days are powered by switching power supplies that are always on - TV’s, stereos, LED lamps, USB wall warts, PCs, etc. Switching power supplies can fail in a way where they draw much more than their rated current but there is no instantaneous short that will trip a breaker.

My takeaway is this:
1. The NEC controls all internal wiring, breakers, receptacles, etc. for a house. (I don’t think that was ever in dispute so this is here for completeness only.)
2. The NEC does not cover products like a PC or a TV that plugs into a standard 15A outlet. Granted the wall plug may be covered by the NEC or an associated standard, but the line cord and internal circuitry of the TV or PC is not covered by the NEC.
3. For things like PCs, there must be another standard separate from the NEC that labs like UL test to.

If #2 and #3 are wrong let me know.

 

[mm08822]

You missed his point. A quick look around my house shows me lights, stereos, and battery chargers that all have line cord wiring that is much smaller than 14 ga. Yet they plug into 15A receptacles. If nothing was done at the appliance level, any short in the appliance would burn those wires causing a fire.

See my last reply........supply cord damage circumvents all of the protection downstream in the device.

The answer is that the appliance has internal protection (fuse, breaker, whatever) that in the case of an internal short it operates and stops the current flow. This is done all of the time for products that plug into 120V 15A circuits. Clearly it is within the NEC to do this.

So @[B]Firebrick43 has asked what in the NEC prevents a similar approach on 240V[/B]?

The NEC controls building wiring & temp wiring........nothing to do with appliance specifications.

The motor in the OP's case could compliantly be plugged into a 240v, 20a receptacle protected by a 20A CB. Control the compressor with an intergral pressure switch. However, he may find that it trips the cb due to inrush current and/or a combination of other loads on the same circuit.

But you do not jack up the ocp rating on a circuit supplying multiple recepts. This is where the issue is. Multiple receptacles provide the opportunity to load the circuit above its rating and no longer trip on overload at the required safe value. Even a single receptacle can have the compressor unplugged and someone use them thar fancy adapters to plug in a 10KW heater.

What similar approach to what?

 

[Max]

See my last reply........supply cord damage circumvents all of the protection downstream in the device.

Sure. No disputing that. Although I do think that a device should have internal protection for other types of failures. That’s just my personal opinion…

The NEC controls building wiring & temp wiring........nothing to do with appliance specifications.

Thank you.

The motor in the OP's case could compliantly be plugged into a 240v, 20a receptacle protected by a 20A CB. Control the compressor with an intergral pressure switch. However, he may find that it trips the cb due to inrush current and/or a combination of other loads on the same circuit.

But you do not jack up the ocp rating on a circuit supplying multiple recepts. This is where the issue is. Multiple receptacles provide the opportunity to load the circuit above its rating and no longer trip on overload at the required safe value. Even a single receptacle can have the compressor unplugged and someone use them thar fancy adapters to plug in a 10KW heater.

Still agreeing with you.

What similar approach to what?

We agree that the NEC doesn’t apply to 120V appliances. So there are 120V appliances that use line cords or internal wiring that are much smaller than 12 ga. and that is ok.

The similar comment is that way the things are for 120V appliances is also true for 240V appliances. As an example, my 240V appliance may have much less than 10 ga plugged into a 240V 30A receptacle. Like the 120V case, it is on the appliance maker to meet whatever the required standards are - which is not the NEC. Note I am talking plugs here and not hard wired.

 

[mm08822]

Thank you. I read your post and the relevant sections of the NEC. To me, that section controls the wiring to an outlet and the outlet itself. It does not control what is plugged into that outlet.

If an electrical load comes complete with a supply cord, the item has been tested, approved and listed for use with that supply cord. The set up/installation instructions are part of the approval. The user is expected to meet those installation requirements.

When the item does not come with a supply cord, then the NEC comes into play for the cord used. The specs of the motor is the first place to look for nameplate data and confirm if overload protection is integral to the motor. NEC article 430 takes care of the details.

I understand your points about the wires to a lamp. Wires are generally straightforward in that they work, they are open, or they are shorted. To @Bert_ point earlier, in a a case with 18 ga. power cord wires, they still conduct enough current for long enough that a CB trips before the 18 ga wires burn up. I understand the point.

The problem is whatever appliance is plugged in may not fail catastrophically with a short. An awful lot of devices these days are powered by switching power supplies that are always on - TV’s, stereos, LED lamps, USB wall warts, PCs, etc. Switching power supplies can fail in a way where they draw much more than their rated current but there is no instantaneous short that will trip a breaker.

And this is where arc fault cb's are supposed to operate.

My takeaway is this:
1. The NEC controls all internal wiring, breakers, receptacles, etc. for a house. (I don’t think that was ever in dispute so this is here for completeness only.)
2. The NEC does not cover products like a PC or a TV that plugs into a standard 15A outlet. Granted the wall plug may be covered by the NEC or an associated standard, but the line cord and internal circuitry of the TV or PC is not covered by the NEC.
3. For things like PCs, there must be another standard separate from the NEC that labs like UL test to.

If #2 and #3 are wrong let me know.

I believe 2 & 3 are correct, just don't know where segregation starts/ends and how many parties involved.


Added website....lists several standards

IEC 60335-1 Explained: Safety Standards for Household Appliances | CUI Inc

IEC 60335-1 is part 1 of an international standard that addresses the general requirements for electrical/electronic household appliances and similar applications. The standard covers devices with rated voltages up to 250 V for single phase and up to 480 V for multi-phase. The evolution of IoT,...

www.cui.com

 

[mm08822]

Any appliance with a 5-15P plug is designed to be protected by a 15A or 20A breaker. That doesn't mean you can chop the plug off, install a 5-30P on the appliance, plug it into a 5-30 receptacle, and expect it to be fine and safe. Similarly, the OP cannot chop the plug off the compressor and install any other plug to match an existing receptacle.

The breaker protects the wiring in the wall AND receptacles (if any are installed). 210.21(B)(1) Single receptacle on an individual branch circuit: A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
So if he replaces the receptacle with a 30A receptacle (for example), the breaker cannot be greater than 30A. I didn't find anything specifically that prohibits installing a receptacle larger than the breaker though (ex. a 50A receptacle with a 30A breaker). Maybe there's language somewhere in the code that says it.

430.109(F) Cord and plug connected motors: For a cord and plug connected motor, a horsepower-rated attachment plug and receptacle...having ratings not less than the motor ratings shall be permitted to serve as the disconnecting means.

430.110(A): The disconnecting means for motor circuits rated 1000V nominal, or less shall have a current rating not less than 115% of the full-load current rating of the motor.

So, assuming this is a 3 HP motor, which has an FLA of 17A, means the receptacle has to be at least a 20A receptacle (rated for at least 3 HP) (17 * 1.15 = 19.55 A). But if he uses a 20A receptacle, he'd have to use a 20A breaker to comply with 210.21(B)(1).

The conductors need to have an ampacity of at least 21.25A (430.22): 17A * 1.25 = 21.25A. So that means at least #10 NM-b, or #12 THWN in conduit. That doesn't have much bearing on breaker size or receptacle size, though.

Table 430.52(C)(1) says he can use UP TO a 50A breaker, BUT 210.21(B)(1) again says he'd need a 50A receptacle in that case.

Theoretically, he could install #10 NM-b wire, a 50A breaker, and a 50A receptacle, even though #10 can't handle 50A. 240.4 says that "conductors...shall be protected against overcurrent in accordance with their ampacities specified in 310.14, unless otherwise permitted or required in 240.4(A) through (H)." And 240.4(G) refers you to Article 430 for motor circuits, which allows you to oversize overcurrent protection, and doesn't mention anything about overcurrent protection being different if you're using a cord and receptacle.

I think it becomes a gray area when it's a receptacle that someone can plug any appliance (with the corresponding plug) into. #10 on a 50A breaker is fine on a motor circuit, but if someone plugs something else into it, it's no longer a motor circuit and 240.4(G) no longer applies.

If this were my compressor, I'd install a 30A breaker, and either hardwire an A/C disconnect next to the compressor, or install a 6-30 receptacle and plug, run either #10 NM-b wire or #12 THWN (if hardwiring) or #10 THWN (if using a receptacle, just to be on the safe side), and call it a day.

Total agreement until here....6-30 only rated for 2 hp.

 

[Max]

If an electrical load comes complete with a supply cord, the item has been tested, approved and listed for use with that supply cord. The set up/installation instructions are part of the approval. The user is expected to meet those installation requirements.

When the item does not come with a supply cord, then the NEC comes into play for the cord used. The specs of the motor is the first place to look for nameplate data and confirm if overload protection is integral to the motor. NEC article 430 takes care of the details.

And this is where arc fault cb's are supposed to operate.

I believe 2 & 3 are correct, just don't know where segregation starts/ends and how many parties involved.

I agree except for arc faults. I do agree that an AFCI should add another degree of protection. But the possible faults I am talking about are not necessarily arcs. As an example, a leaky cap on a LED power supply that pulls enough current to burn the PCB but it’s a constant current. But a failure there is not on the NEC - it’s on the design of the LED power supply.

 

[Firebrick43]

****************************
He's given the answer from the NEC (NFPA70 if you weren't sure).
The appliances he asked about in Post 9 are not permanently installed, portable, not automatically started and generally insight of the operator (again, it's about appliances so some details are spared for brevity).
Seems in context to me.....he brought it up, it got answered.
Tells me my (and exranger's) answer back to me, now aligned with the code article.
Then claims not in context.
This is Gaslighting. By the time the conversation is over you will have forgotten the point of the conversation, wonder if you have ADHD, and won't want to stop hitting your head against wall.

You are a lying.

You didn't come into the conversation to post 22. You took my statement in post 2 and made a statement about it without reading(or purposely ommiting) what I posted 12.

That is taking things out of context.

Further more, you and your amigos seem to like to gang up. When I pointed out that L5-20 to 5-15 adapters were UL listed (i did incorrectly say approved) Norcal said they were not.

To be clear I have nothing against Norcal.

When I posted a screen shot of Hubbles web page showing it was, Wyliediesels tried to infer that I forged a website to show it was UL listed. Then YOU come on and accuse me of cherry picking and list 3 "marine adapters" in an attempt to purposely confuse things further

And you accuse me of gaslighting.

 

[exranger06]

Total agreement until here....6-30 only rated for 2 hp.

Whoops, you're right. I thought they were rated for 3 HP. That being the case, I recommend using a 30A breaker, #10 NM-b or #12 THWN, and hardwiring with a disconnect, OR:
A 50A breaker, 6-50R receptacle, and #6 NM-b or #8 THWN. Even though he probably could still use #10/#12 wire and still be code compliant, I'd feel better with #6/#8 knowing it can handle anything that gets plugged into that receptacle and eliminates gray areas and arguments with inspectors.
My first choice is hardwiring though. Receptacles are great for portable devices, but I don't see the point of using one on a 60 gallon compressor that's never going to move anywhere. It's like using a receptacle for a central air conditioning unit.

 

[NDJ]

Looks like theres some guys who know stuff here but its hard to follow.
You guys should have a look at this post before you all get thrown out. https://www.garagejournal.com/forum/threads/hey-fellas-im-tired.521325/

 

[American Locomotive]

First, the NEC does not apply to manufactured appliances with their own cords.

Secondly, some appliances do not have internal fuses, but in general, pretty much everything has a line cord heavy enough to trip a 15 or 20A breaker. A 5ft long of 22AWG cord will have a combined resistance of 0.160 Ohms. V=IR. So if a dead short developed in the appliance, that cord will pass 750A. That's an instant or near instant trip for any 15 or 20A breaker. Appliances designed for 15 or 20A outlets will have that fact in mind when sizing their line cords. Where you may run into an issue is if you plugged an appliance with a 22AWG cord into a 50A outlet. That might not actually be in 50A breaker's instant trip zone.

...but that's not what's going on here. We have a 240v air compressor with a presumably 12AWG line cord. Really the only thing OP needs to do is change the outlet to a NEMA 6-20, put a new 6-20 Plug on the compressor (since that one is smoked), and shove in a 20A breaker. Then everything is all safe and everyone is happy.

 

[u2slow]

The motor is marked "SPL" and therefore does not have a HP rating for Code purposes.

Circuit breakers are fairly tolerant of inrush currents. Like i said in my earlier post, a 6-20R/#12/20A circuit seems appropriate for this compressor.

 

[alfredeneuman]

The motor is marked "SPL" and therefore does not have a HP rating for Code purposes.

I don't know how it works in Canada, but in the US.

NEC 430.6 (A)
1. Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches,branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate. Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary.

The figures listed are the regular horsepower ratings for all motors.
The motor in question is rated at 5HP, but because it's listed as a unit these rules don't apply.
They would if the cord is cut off and the motor hardwired or the cord cap changed.

 

[u2slow]

The motor in question is rated at 5HP, but because it's listed as a unit these rules don't apply.

No, the motor is rated SPL per the nameplate. My compressor has a similar motor with the same specs. 3hp at best.

Sanborn has a misleading HP label... just like my Rigid shop vac.

 

[sparky 1971]

Nevermind

 

[sparky 1971]

I don't know how it works in Canada, but in the US.

NEC 430.6 (A)
1. Table 430.249, and Table 430.250 shall be used to determine the ampacity of conductors or ampere ratings of switches,branch-circuit short-circuit and ground-fault protection, instead of the actual current rating marked on the motor nameplate. Where a motor is marked in amperes, but not horsepower, the horsepower rating shall be assumed to be that corresponding to the value given in Table 430.247, Table 430.248, Table 430.249, and Table 430.250, interpolated if necessary.

The figures listed are the regular horsepower ratings for all motors.
The motor in question is rated at 5HP, but because it's listed as a unit these rules don't apply.
They would if the cord is cut off and the motor hardwired or the cord cap changed.

I have the same compressor with the same labels. The motor is labeled SPL and the compressor tank is carrying the 5HP sticker It's a chickenshit deal if someone thinks they are actually getting a 5HP compressor. I knew better and was more concerned with tank capacity and price.

 

[alfredeneuman]

No, the motor is rated SPL per the nameplate. My compressor has a similar motor with the same specs. 3hp at best.

Reading post #4 again...it isn't on the motor, but on the compressor itself.