14/2 on a 20A circuit

[Greg Hampton]

An electrical company (very reputable) recently installed a sub panel in my shop and added a couple cirucuits. They insalled 3 20 amp breakers and I noticed that all the wire that was used is 14/2.

It's my understanding that wires must be large enough for the amperage rating of the circuit. The American Wire Gauge system wire size chart states 12/2 should be used on 20 amp circuits and 14/2 on 15 amp circuits.

Can anyone enlighten me on why this company wired things in my shop the way they did ?

Thanks

[Jason Beam]

Provided there is more than one "device" on the circuit, the exception in the NEC which allows 14ga on a 20a circuit is valid. By "device" you basically mean a single outlet. Remember that most recepticals we think of are actually duplex, one "outlet" automatically qualifies as two devices since two things could be plugged in at the same time. This is the only exception that I know of like this.

Correction: I was off on this advice. Keep reading to learn why.

[Greg Hampton]

Hey Jason,

Thanks for the reply and the scoop.

But, you lost me regarding the "exception". Do you mind spelling it out for me ?

Also, for future reference, is it just safe to use 12/2 on anything connected to a 20 amp breaker ? I know 14/2 is a lot cheaper but just wanta make sure.

Thanks

[Jason Beam]

There's an exception in the NEC that allows 20a circuits to be wired with 14ga wire provided the circuit contains "multiple devices" - a duplex outlet qualifies as multiple devices so it passes code. I do believe that you must use regular 15a outlets, which prevent the plugging of 20a devices in (there's a special 20a plug, but i never see 'em).

As for safe ... I know millions of homes are likely wired exactly as your circuits and they are deemed safe.

It's really only unsafe when you start reaching the max draw. In a shop, I would personally have (and had) used 12ga wire for all my 20a circuits but I'm pretty anal and in a shop, I might verywell come close to that 15-20a draw on a given circuit. Nothing curls my toes more than opening a wall and seeing blackened romex or scorch marks near an outlet, so I go overboard on that kind of stuff.

You're probably fine - and it DOES meet code to do what you describe - but it may not meet PREFERENCE. I would have preferred to see 12ga there, but the way you're reporting is perfectly accepted and considered safe.

CORRECTION: Later in this thread it is made clear to me that my understanding was off on the above advice.

[Von Bickley]

Greg,

I would say they did it because 14/2 is a lot cheaper than 12/2. That wouldn't pass inspection around here.

14/2 - 15 amp breaker
12/2 - 20 amp breaker

[Jason Beam]

Also, for future reference, is it just safe to use 12/2 on anything connected to a 20 amp breaker ? I know 14/2 is a lot cheaper but just wanta make sure.


I forgot to address this one...

It's more than just safe .. in a long run (upwards of 75-100 feet) the larger size wire actually becomes almost required because the wire itself in those kinds of lengths actually becomes some of the load. This resistance causes a voltage drop which means your devices may not see a full 120v at the outlet. As a consequence, due to the way induction motors work, the current draw rises to basically compensate.

A 14a motor on a big long length of 14ga wire may only see 105v (these are just arbitrary numbers, there's actually a formula for calculating voltage drop) and thus pull 16a to get the same kind of power. That puts you in the danger zone of 14ga wire, nevermind what it can do to the motors - they usually run much hotter and don't last as long.

The same 14a motor on the same length of 12ga wire could see 115v at the outlet and thus pull current well within the design limitations of the motor.

I hope that made sense - i'm hardly an expert on the subject - there are many of those on this forum that will likely be chiming in soon :)

[Richard Wagner]

I think you need to get advise from someone in your specific area. Where I live, putting 20a breakers on a 14/2 feed is a code violation without discussing the number of devices.

Also, putting outlets rated at 20 amps on a 14/2 feed is a code violation.

Most houses are built using 14/2 and 15a breakers (except on specific circuits) and 15a receptacles. But then most houses don't have shops full of woodworking power tools to operate. My table saw just barely comes to speed if I connect it to a 15a circuit. It runs fine when I plug it in to a 20a circuit (wired with 12/2). I do not have a long home run - about 80' to the main breaker panel.

Someone said 20a outlets were hard to find. I find that to be very unusual. Are you shopping at a big box store? Try an electrical supply house.

[Tom Veatch]

There's an exception in the NEC that allows 20a circuits to be wired with 14ga wire provided the circuit contains "multiple devices"...

I was aware of an NEC exception to allow 15 amp devices, i.e. NEMC 5-15 receptacles, on a 20 amp circuit when there are multiple devices. I can even somewhat understand the (presumed) logic to support that exception.

But, this is the first I've heard of an exception that allows downsizing the wire used in a 20 amp circuit. Nor can I get my mind around any logic that would support that exception. I certainly don't claim to be an expert in the various nuances of the NEC and I'm not saying the exception doesn't exist, simply that this is the first time I've come across it. You don't by any chance know the code section/paragraph that details that exception, do you? (Just trying to increase my knowledge, not intentionally be cantankerous.)

[Don Abele]

When I upgraded my main panel from fuses to circuit breakers a couple of years ago it was done by a very well known and reputable firm and fully inspected. They replaced all the 15A fuses with 20A breakers for the bedrooms and kitchen which are all wired with 14/2. When I asked they said it was allowed per an exception to the code and that the outlets were only 15A outlets. They said they routinely change out 15A for 20A in bedrooms and kitchens now due to the increase in appliances we have in those rooms. I didn't ask for specifics as I trust both the company and the inspector.

Be well,

Doc

[Greg Hampton]

I'm having no problems finding 20A breakers. HD has everything I need.

Thanks to everyone for the your posts and information.

The current wiring in my shop is very minimal. I had a sub put down there for the shop and for when I finish the basement. When they put in the sub, I had them add a few outlets. The sub currently has three 20 amp breakers and all the wire coming off of it is 14/2, but they're really short runs and the walls are not yet finished.

But, no worries. Thanks to all of you, I'm going to take care of it. I prefer to play it super safe. The wiring is going through an unfinished wall (just plastic over it) and unfinished ceiling ( just floor joists). So should be easy.

I'll use the 20 amp breakers, but change the wire to 12/2. I think I'm going to run the lights on a 15A circuit so I'll use 14/2 for that. I'm sure I'll find spots to use up the 14/2 thats currently in the wrong place.

I do have a couple more easy questions.

1. I need a 20A / 220V circuit for my DC. It's plug is a NEMA 6-20P. Should I use 10/2 or 10/3 ?

2. Also, regarding wiring for lights. I have an Air Filtration system that pulls 4.5 amps. I'm going to round it up to 5 amps for my calculations.

I'm going to have 8 lights (fluorescent 4 foot, two bulb 32 Watt T8's) that are .49 amps (rounding up to .5).

I'd like to have a receptacle in the ceiling for the Air Filtration unit and keep it on the same circuit as the lights so all the wire up there is one circuit.

My calculation has safe capacity for a 15 amp circuit (using 12/2) at 1400 watts (20% of 1800 then rounding down).

Again, my calcuation (I'm trying to learn this stuff), for 8 lights and the Air Filtration has it pulling 1100 watts.

Given that info, does everyone agree I've got the 15A 120V lights and Air Filtraton circuit covered and safe or am I missing something ?

Thanks !

[Rollie Meyers]

Unless its a motor circuit & not a general branch circuit it's a no go...
15 A receptacles are permitted on 20 A circuits, but 14/2 needs a 15 ampere overcurrent device.

[Greg Hampton]

Thanks Rollie. I'm assuming your post was in reply to that crazy 14/2 20A circuit.

Any thoughts on my last post that had some additional questions ?

thnx

[Gene Michael]

There's a lot of good information in the above answers. From a practical perspective, I run a 15 amp contractor's saw with a 15 amp plug on a 20 amp circuit with 12/2 wire. When this saw starts, there's a momentary draw that I suspect exceeds 15 amps. Also, I don't hesitate to use a small item (low amp draw) such as a box fan (less than 1 amp) on the same circuit as the saw. To me, the 12/2 is insurance, even though the run from the panel is short. As pointed out above, longer runs cause voltage drop - the smaller the wire, the greater the drop. There are tables on-line that you can consult regarding voltage drop.

[Greg Hampton]

I agree Gene. A lot of great information as always here at the Creek. What a great forum.

Thank you also for your post and info.

Any thoughts on my last post with the more questions I had ?

[Rollie Meyers]

I personally like lighting seperate from other uses( not liking being plunged into darkness if something else causes a breaker to trip comes to mind:D). And if your wiring for 20A no reason to use a 15 A breaker, unless manuf. instructions say otherwise.

[Tom Veatch]

...I'll use the 20 amp breakers, but change the wire to 12/2.

I think that's wise.



1. I need a 20A / 220V circuit for my DC. It's plug is a NEMA 6-20P. Should I use 10/2 or 10/3 ?


12/2 unless the 1-way cable run is greater than 60 feet (2% voltage drop) or 150 feet (5% voltage drop)

No need to go to 10 ga wire for a 20 amp circuit. The gauge is determined by the required ampacity of the circuit (and allowable voltage drop), not by the supply voltage. NMC 12/2 (or 10/2 for that matter) has 2 conductors + a bare ground wire and that's all you need for a straight 240v circuit. The only time you'd need the /3 configuration (3 conductor + ground) for a 240v circuit is if you also needed to supply 120 volts through that circuit. Examples would be for an electric range, clothes dryer, etc. In other words, some appliance that uses both 120v and 240v and equipped with a 4 blade NEMA 14-() plug.

If you use a /3 cable for this application, the white wire will not be connected to anything on either end, so why buy it if you're not going to use it.



...Again, my calcuation (I'm trying to learn this stuff), for 8 lights and the Air Filtration has it pulling 1100 watts.

Given that info, does everyone agree I've got the 15A 120V lights and Air Filtraton circuit covered and safe or am I missing something ?



As far as load on the circuit is concerned, you're fine. As far as codes are concerned, I'm not sure. Generally, it's not a good idea to include anything but lights on a lighting circuit. Reason being that if the "foreign" device trips the circuit, it will leave you in the dark by taking out the lighting with it.

[Gene Michael]

Tom Veatch's comments are right on re the 240 V wiring. Regarding the lighting circuits, I read your description 2 ways - once using 14/2 and once with 12/2. I'm not sure if code states you can't have a non lighting item on the same circuit as your lights (air filtration) - call your inspector ans ask. He's the one who will have to pass you. From a safety perspective, I'd recommend at least 2 lighting circuits in the shop so you don't get caught in the dark in the middle of using a power tool with sharp teeth. If your shop is in a basement or aera with concrete floors, code specifies ground fault protection for outlets. Because GFCI protected circuits tend to trip far more easily than the standard breakers in your panel, this would be another reason to keep the circuit for the filtration different (I'm assuming you will be hard wiring your shop lights). One last thing. I wired our entire house and did one 20 amp lighting circuit with 12/2. Because its thicker (and stiffer), it can be a pain to work with in boxes containing multiple switches. After that, I stuck with 14/2 for the lights.

Be sure to post some pics when you get the shop set up.

[Jason Beam]

I was aware of an NEC exception to allow 15 amp devices, i.e. NEMC 5-15 receptacles, on a 20 amp circuit when there are multiple devices. I can even somewhat understand the (presumed) logic to support that exception.

But, this is the first I've heard of an exception that allows downsizing the wire used in a 20 amp circuit. Nor can I get my mind around any logic that would support that exception. I certainly don't claim to be an expert in the various nuances of the NEC and I'm not saying the exception doesn't exist, simply that this is the first time I've come across it. You don't by any chance know the code section/paragraph that details that exception, do you? (Just trying to increase my knowledge, not intentionally be cantankerous.)

Tom, That may well be the exception i was thinking about. It's very possible that I was speaking out of turn. I should know better than to get into such a nuance as a code exception. My apologies.

[Greg Hampton]

Tom: I didn't see your post prior to mine when I was inquiring about replies. Thanks a bunch. That helped big time.

Gene: Thanks a ton to you as well.

I can't seem to say enough how valuable and enjoyable SWC and it's members are.

I really appreciate all of your help.

I'll definitely post some pics when it's done.

Thanks

[Rick Christopherson]

Tom, That may well be the exception i was thinking about. It's very possible that I was speaking out of turn. I should know better than to get into such a nuance as a code exception. My apologies.Jason, due to the nature of the information you provided in your first two postings, it might be a good idea to edit them to indicate that there is an error in them. Someone could read that information and not see that it was redacted later on.

It is not very critical, but your 3rd posting also has a trivial (but somewhat common) mistake in it too. The voltage drop on a wire is dependent on the wire size and length, as you stated, but it is also dependent on the actual current flowing at the time. A 14 gauge wire could be a mile long, but if it only has 1-amp flowing through it, it will have almost no voltage drop. But that's not really the main mistake.

You said that due to Ohm's Law, that as the voltage goes down, the current goes up. This is the opposite of Ohm's Law, but the reason why this gets confused so frequently is because of the way inductive motors react when given an under-voltage condition.

When an induction motor (only induction motors, not universal motors) is driven by an under-voltage condition, it cannot maintain its proper speed, and slows down. When the motor slows down, its impedance decreases, and this is what causes the current to go up. In layman's terms, the resistance of the motor goes to zero as the motor's speed goes to zero, and the motor becomes a short circuit. That is why the current goes up when the voltage goes down on a motor circuit. For any other type of load (universal motors, resistors, etc.) when the voltage goes down, the current goes down proportionally, because the resistance of the circuit is not dependent on the rotational speed of the load.

[Greg Hampton]

I forgot to add so you don't worry about me doing this incorrectly, I'm going to have pro's do it but I'm just trying to better understand. In addition, I'd like to know if things are being done correctly.

Especially since I found the 14/2 wire on 20 amp circuits.

Anyway.. thnx again.

[Bob Ross]

I'm having no problems finding 20A breakers. HD has everything I need.

Thanks to everyone for the your posts and information.

The current wiring in my shop is very minimal. I had a sub put down there for the shop and for when I finish the basement. When they put in the sub, I had them add a few outlets. The sub currently has three 20 amp breakers and all the wire coming off of it is 14/2, but they're really short runs and the walls are not yet finished.

But, no worries. Thanks to all of you, I'm going to take care of it. I prefer to play it super safe. The wiring is going through an unfinished wall (just plastic over it) and unfinished ceiling ( just floor joists). So should be easy.

I'll use the 20 amp breakers, but change the wire to 12/2. I think I'm going to run the lights on a 15A circuit so I'll use 14/2 for that. I'm sure I'll find spots to use up the 14/2 thats currently in the wrong place.

I do have a couple more easy questions.

1. I need a 20A / 220V circuit for my DC. It's plug is a NEMA 6-20P. Should I use 10/2 or 10/3 ?

2. Also, regarding wiring for lights. I have an Air Filtration system that pulls 4.5 amps. I'm going to round it up to 5 amps for my calculations.

I'm going to have 8 lights (fluorescent 4 foot, two bulb 32 Watt T8's) that are .49 amps (rounding up to .5).

I'd like to have a receptacle in the ceiling for the Air Filtration unit and keep it on the same circuit as the lights so all the wire up there is one circuit.

My calculation has safe capacity for a 15 amp circuit (using 12/2) at 1400 watts (20% of 1800 then rounding down).

Again, my calcuation (I'm trying to learn this stuff), for 8 lights and the Air Filtration has it pulling 1100 watts.

Given that info, does everyone agree I've got the 15A 120V lights and Air Filtraton circuit covered and safe or am I missing something ?

Thanks !

1. 10/2 will work. You don't need a neutral conductor unless the machine
has 120v. components. Actually, 12/2 is OK for a 20 amp/240 v. circuit.
2. I don't think it's a problem, but are you sure the lights will be adequate?

On the 14/2 issue, I have upgraded a bunch of the old 60 amp, 4 fuse panels. I have seen a lot of scorched insulation on 14 ga. wire when the fuse has been changed to 30 amps. I have not seen the scorching with 20 amp fuses unless the clamp was loose. That said, 20 amp circuits should be wired with 12 ga. I would call the electrician on his choice and make him change it or give me an adjustment. Any permits or inspections?

[Rollie Meyers]

I forgot to add so you don't worry about me doing this incorrectly, I'm going to have pro's do it but I'm just trying to better understand. In addition, I'd like to know if things are being done correctly.

Especially since I found the 14/2 wire on 20 amp circuits.

Anyway.. thnx again.

You need another electrical contractor, 14/2 on 20 A a circuit breaker is hack work. There are situations where the circuit breaker may seem to be oversized but is OK, this is not one of those times.

[Rob Russell]

Greg,

I would contact the electrical contractor that did the work and make them replace the cabling with #12. If they refuse, I'd have a chat with your local building inspectors about the work the contractors did because it's clearly not up to code.

Rick,

I agree with you that Jason should edit his early posts to include a statement that there is some incorrect info and people should read into the thread further.

Jason,

If you are unable to edit your posts (can't think of a reason why you couldn't, but one never knows) - let me know and I'll add a statement to your early posts in the thread that directs folks to keep reading through the thread.

Rob

[Bob Ross]

I tried to edit and got a headache.

12/2 will be adequate for your 20 amp 240 v. circuit

[Tom Godley]

I believe it is very important to have two light circuits -- and they be connected to lights that are normally on when you are working. That way you minimize the chance that the shop will go dark when you are using any power tool.

The lights should be able to be wired with 14g wire on a 15-amp breaker. I have seen a trend where everything in new homes is being wired with 12g -- seems like over kill for dedicated light circuits.

With the addition of a sub-panel -- I hope you were advised to install one with enough spaces!

[Jason Beam]

Jason, due to the nature of the information you provided in your first two postings, it might be a good idea to edit them to indicate that there is an error in them. Someone could read that information and not see that it was redacted later on.

It is not very critical, but your 3rd posting also has a trivial (but somewhat common) mistake in it too. The voltage drop on a wire is dependent on the wire size and length, as you stated, but it is also dependent on the actual current flowing at the time. A 14 gauge wire could be a mile long, but if it only has 1-amp flowing through it, it will have almost no voltage drop. But that's not really the main mistake.

You said that due to Ohm's Law, that as the voltage goes down, the current goes up. This is the opposite of Ohm's Law, but the reason why this gets confused so frequently is because of the way inductive motors react when given an under-voltage condition.

When an induction motor (only induction motors, not universal motors) is driven by an under-voltage condition, it cannot maintain its proper speed, and slows down. When the motor slows down, its impedance decreases, and this is what causes the current to go up. In layman's terms, the resistance of the motor goes to zero as the motor's speed goes to zero, and the motor becomes a short circuit. That is why the current goes up when the voltage goes down on a motor circuit. For any other type of load (universal motors, resistors, etc.) when the voltage goes down, the current goes down proportionally, because the resistance of the circuit is not dependent on the rotational speed of the load.

Rick, thank you for clarifying things. I've edited my posts to reflect their misgivings. :)

[Brad Sperr]

There are some specific tap rules in the NEC that would allow conductors with smaller ampacity on the same branch circuit, but it doesn't sound like any of those would apply to your installation.

I second the recommendation to go back to the contractor and have him install 12/2. You'll be putting some serious load on these wires when you start using them in the shop (far more than your typical household appliance circuit), so you need the proper wire size

[Rob Russell]

If you are unable to edit your posts (can't think of a reason why you couldn't, but one never knows) - let me know and I'll add a statement to your early posts in the thread that directs folks to keep reading through the thread.


FYI (as I've learned), posts can be editted by the poster for the first 24 hours. After that, only a Moderator or Administator can edit posts.

Now back to our regularly scheduled electrical thread ...

[Bill Brady]

There seems to be a number of peop;e replying to this who think they know the code but obviously do not. Wire sizes are as follows #12 wier is to be protected at 20 amps but should only be loaded to 80% or 16 amps, #14 wire should be protected at 15 amps but loaded to 12 amps. Motor circuits are to be rated at 125% of motor full load current this is to limit nuisance trips on startup of the motor. As far as receptacles go the receptacle is not sized to the wire or breaker it is sized for the device that will be plugged into it, or a 15amp receptacle can be on a 20 amp circuit but only devices rated at 15amps can be plugged into the receptacle. Most devices draw far less than 15amps. It there is ever a question about an electrical installation contact your local inspector they are more than happy to answer any questions you may have, and when having work done talk to an electrical distributor about a good contractor.

[Tom Veatch]

... Motor circuits are to be rated at 125% of motor full load current this is to limit nuisance trips on startup of the motor....

Define "Motor Circuit".

[David Parker]

My (limited) understanding is that the job of the circuit breaker is to protect the wiring and any devices (including switches and receptacles) in the circuit from carrying current in excess of their rating. Therefore, you want to match any outlets in the circuit to the capacity of the breaker. That way, the breaker will kick open before the wiring or outlet rating is exceeded. The one NEC-allowed exception is the use of multiple 15 amp outlets on a circuit protected by a 20 amp breaker. Since most consumer products that plug-in to a 15 amp outlet don't come close to 15 amps, the only condition that could potentially overload such an outlet would be an appliance fault. I've read that 15 amp outlets can tolerate exposure to 20 amps, so remain safe until the breaker kicks off.

Similarly, you don't want the outlet rating to be greater than the breaker size, since the outlet is the end-user's visual cue as to what size load he/she can plug into the circuit. If you put a 20 amp outlet on a circuit protected with a 15 amp breaker, the end-user would only see the 20 amp outlet and assume it was fine to plug in loads close to 20 amps, resulting in tripping of the breaker.

Since the end-user cannot see the wiring, it's fine to use whatever gauge wire you want whose ampacity meets or exceeds the size of the breaker.

Is my understanding correct? Thanks.

Dave

[Rollie Meyers]

Motor circuits are to be rated at 125% of motor full load current this is to limit nuisance trips on startup of the motor.

Read art. 430 which covers motors, depending on the type of motor and other things, table 430.52 states for single phase motors protection can be chosen as a percentage of full load current anywhere from 175 - 800% for the protective device, Dual element (time delay) fuse 300%, non time delay 175% , instantantanous trip breaker 800%, Inverse time* breaker 250%, motors are a whole different breed then general purpose circuits the "rules" as a lot of people think ain't there, the same applies to air conditioning where you can find 12 AWG on a 40 A breaker and be fully code compliant.:D(it depends on how a unit is labeled)

* Most residentail circuit breakers are inverse time, if they have a "HACR" tag on them they are a inverse time C/B.

[Tom Veatch]

... I've read that 15 amp outlets can tolerate exposure to 20 amps, so remain safe until the breaker kicks off...

I've never broken a -15 or -20 receptacle apart and tried to reverse engineer either one. But, simply from manufacturing economic considerations, I strongly suspect that the only difference between the two is the keying of the face plates. IOW, I suspect the 15 amp receptacles are actually "derated" 20 amp receptacles. Don't know that for a fact and would appreciate anyone with credible knowledge of their design and manufacture offering either support or rebuttal of that suspicion.

[Greg Hampton]

This turned into to quite the thread.

I just wanted to say thanks to everyone. You helped a bunch like always.

Take care.

[Bill Brady]

Motors are to be protected at 125% of the rated current this will alow for the high inrush on startup. In your house you may notice the dimming of the lights when the water pump or frig starts this is the high inrush dragging the voltage down for a split second.

If as you are thinking 15amp receptacle, 15 amp circuit etc. this would mean either 1 receptacle per circuit or you would need to alway skeep a total of the power being used. The code uses the calculation of 1.5 amps per outlet, this means each light is 1.5 amps or each duplex (double) receptacle is 3 amps. The rough calc used is 5 receptacles on a 15 amp circuit and 7 on a 20 amp curcuit. The thing to remember is not all the load will ever be pulled from the circuit under normal use. This is also why you can load a 40 circuit 200 amp panel to 800 amps if you fill it with 20 amp breakers, never going to load all the circuits at oncce.

[Rick Christopherson]

There seems to be a number of peop;e replying to this who think they know the code but obviously do not. Wire sizes are as follows #12 wier is to be protected at 20 amps but should only be loaded to 80% or 16 amps, #14 wire should be protected at 15 amps but loaded to 12 amps. Motor circuits are to be rated at 125% of motor full load current this is to limit nuisance trips on startup of the motor. As far as receptacles go the receptacle is not sized to the wire or breaker it is sized for the device that will be plugged into it, or a 15amp receptacle can be on a 20 amp circuit but only devices rated at 15amps can be plugged into the receptacle. Most devices draw far less than 15amps. It there is ever a question about an electrical installation contact your local inspector they are more than happy to answer any questions you may have, and when having work done talk to an electrical distributor about a good contractor.With an intro phrase like that, you probably want to be doubly careful about the remaining content. :D

Outlets are installed according to the circuit, not the device.


A 15 amp circuit must use only 15 amp receptacles.
A 20 amp circuit may use either 15 or 20 amp receptacles, so long as there is more than one 15 amp receptacle (i.e. a duplex).
A 30 amp circuit must use only 30 amp receptacles.
A 40 amp circuit must use only 40 amp receptacles.
A 50 amp circuit can use either 40 or 50 amp receptacles (I don't think the same exception about more than 1 applies here though).

As for circuit loading, the 80% applies only to continuous loads. The sum of continuous and non-continuous loads can be 100%. Most residential circuits are made up of non-continuous loads.

I am not confident enough about the 1.5 amp per outlet to emphatically say this is not correct, but I do have a strong suspicion that it is not correct. Without rifling through the code to verify this, I am pretty confident that this is not listed as a code requirement.

[Rick Christopherson]

I've never broken a -15 or -20 receptacle apart and tried to reverse engineer either one. But, simply from manufacturing economic considerations, I strongly suspect that the only difference between the two is the keying of the face plates. IOW, I suspect the 15 amp receptacles are actually "derated" 20 amp receptacles. Don't know that for a fact and would appreciate anyone with credible knowledge of their design and manufacture offering either support or rebuttal of that suspicion.Yes Tom. The internal metallic conductors in a receptacle are not the weak link in a circuit, and will handle far more than the rating of the device. The cross sectional area of the conductors is far larger than the cross sectional area of the wires connected to them. (By the way, the "weak link" in a receptacle is the compression connection between the plug prongs and the receptacle sockets. This is where heating and voltage drop will be the highest from anywhere else in the whole circuit.)

Receptacles are designed so that only an applicable plug can fit into the receptacle. Consider even the design of polarized outlets. If you have an old non-polarized outlet, you cannot connect a newer polarized device. The wider blade on the Neutral was specifically chosen to prevent this.

The 20 amp receptacles are designed to accept either a 15 amp device or a 20 amp device, but a 20 amp device cannot fit into a 15 amp receptacle. (this applies to both 120 volt and 240 volt receptacles). This is why the 20 amp versions of these receptacles (NEMA 5-20 or 6-20) have the T-shaped inlet.

[Rollie Meyers]

With an intro phrase like that, you probably want to be doubly careful about the remaining content. :D

Outlets are installed according to the circuit, not the device.


A 15 amp circuit must use only 15 amp receptacles.
A 20 amp circuit may use either 15 or 20 amp receptacles, so long as there is more than one 15 amp receptacle (i.e. a duplex).
A 30 amp circuit must use only 30 amp receptacles.
A 40 amp circuit must use only 40 amp receptacles.
A 50 amp circuit can use either 40 or 50 amp receptacles (I don't think the same exception about more than 1 applies here though).
As for circuit loading, the 80% applies only to continuous loads. The sum of continuous and non-continuous loads can be 100%. Most residential circuits are made up of non-continuous loads.

I am not confident enough about the 1.5 amp per outlet to emphatically say this is not correct, but I do have a strong suspicion that it is not correct. Without rifling through the code to verify this, I am pretty confident that this is not listed as a code requirement.

See NEC 2005 table 210.24 for requirements on branch circuits.A 40 A circuit can have a 50 A receptacle on it.

The 1.5 ampere per outlet is bogus, for NON dwelling loads they are calculated at 180 volt-amperes for a single or for each multiple receptacle on one yoke IE: a duplex receptacle NEC 2005 220.14(I).220.14(J) states no additional calculations are required for dwelling occupancies for receptacles used in a them* which means in the absence of any local rules you may put as many as you want on 1 circuit (My opinion, not always a good idea).
*They are already included in the general lighting calc's.

[John Sanford]

Greg,

I'm not an electrician, nor do I play one on TV, so I'll skip the discussion of amperages, circuit loading, etc. What I will do is second the point of having two lighting circuits. If possible, have one lighting circuit drawn from the HOUSE wiring, not the subpanel. This way, if by some freakish event the subpanel's breaker itself trips, you wont' be left in the dark.

Second, for the air filtration unit. I would put a 15a or 20a circuit up there in the ceiling with an outlet for it, another outlet directly over your bench so you can put in a reel extension cord, and scatter a couple more where it seems appropriate. Having the drop reel extension can be really handy. Having the outlets up there will allow you to put in directional track lighting if you find it necessary, a strobes and a disco ball, whatever. Just don't be running the strobes and disco ball at the same time as you're working at the tablesaw. :eek:

[Eugene Wigley]

Greg,
This is what I do for a living. If I can help email me at ewigley@w3electric.com . Woodworking is a great hobby. Electricity is not.

good luck

Eugene