Why does having more than one receptacle on a 20A circuit make a difference?

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nogard1126

Member
Location
WI
I had an instance where something had to be changed. I wanted to make sure I was right before letting the customer know they had a code violation. I looked it up and confirmed my interpretation with a co-worker.

My new code book is at work, so I'm looking at an older one as I type this. In 210 there is a cord and plug connected load to receptacle chart, and a receptacle ratings for various size circuits.

I my instance I had a dedicated 20A circuit (hot, neutral, ground) to a cord drop. The THHN in the conduit was #12, but the cord was only #14 with a 15A 125V twist lock cord cap. To my understanding this is a code violation, so I changed it to #12 cord with a 20A 125V cord cap. Changing this was a big deal because now only the tools with the "new" 20A cord caps could be plugged in and the same tools from other machine lines with 15A cord caps can no longer be used. One of the tools used is rated at 10A, and other tool used I measured with a meter to draw 13A. I would have just changed the breaker to a 15A, but I didn't because of the 13A draw of the larger tool.

The way I interpret the code is that if the circuit is 20A and dedicated the receptacle or cord cap in this case has to match. Code states "A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit."

In 210 it does state that where a branch circuit is supplying two or more receptacles it shall conform with the table in 210.

So the way I understand it, if I have a dedicated 20A circuit with a single receptacle then I need to use a 20A receptacle and it would have a max load rating of 16A. Also if I put two or more receptacles on that same 20A circuit then I can use 15A rated receptacles, I know that a single duplex receptacle is actually "two" receptacles, so this one 15A device can be put on a 20A circuit by code. But each 15A receptacle of a duplex is only rated for a max load of 12A according to the chart.

Here are my three questions:

1. So in my instance even if the 20A circuit I was working on had two or more receptacles I wouldn't be able to put the larger tool that draws 13A on a 15A receptacle (only max rated to 12A)? By code it needs to be on a 20A receptacle (max rated to 16A)?

2. I try to put some logic behind the reason of the code. I understand having one receptacle on a dedicated 20A circuit would need a 20A receptacle. Why when adding two or more receptacles to the circuit this changes the rules, and 15A receptacles can be used?

Someone that doesn't know any better could plug a splitter into the 15A receptacle and have a combined load, or one large tool that will plug into the 15A receptacle. It could draw more than the 12A max load for the 15A receptacle overloading it, but stay under the trip level of the 20A breaker and stay functional without tripping the circuit.

3. Why wouldn't the code simply state the receptacles need to be rated at the same or higher ampere rating as the circuit the are connected to?
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
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Retired Electrical Contractor
The NEC stops at the recep. not the equipment that gets plug into it. I don't think the 14/3 cord would have been an issue.
 

iwire

Moderator
Staff member
Location
Massachusetts
3. Why wouldn't the code simply state the receptacles need to be rated at the same or higher ampere rating as the circuit the are connected to?

Say you had mobile equipment that needs a 70 amp circuit, the next size up receptacle is 100 amps, why should I be required to supply a 70 amp load with a 100 amp circuit? Would that increase safety?
 

One-eyed Jack

Senior Member
Say you had mobile equipment that needs a 70 amp circuit, the next size up receptacle is 100 amps, why should I be required to supply a 70 amp load with a 100 amp circuit? Would that increase safety?

The ampacity of your circuit is being determined by the ocpd. The 100 amp rec. is more than the ampacity of your branch circuit. This meets the requirement. Only the rec. is required to be NOT LESS THAN.
 

iwire

Moderator
Staff member
Location
Massachusetts
The ampacity of your circuit is being determined by the ocpd. The 100 amp rec. is more than the ampacity of your branch circuit. This meets the requirement. Only the rec. is required to be NOT LESS THAN.

You and I are saying the same thing, I was just answering the persons question 3. If the NEC was written the way the OP suggested here ...

Why wouldn't the code simply state the receptacles need to be rated at the same or higher ampere rating as the circuit the are connected to?


... if I used a 100 amp receptacle I would have to supply it with a 100 amp branch circuit.
 

One-eyed Jack

Senior Member
My new code book is at work, so

Code states "A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit."



Here are my three questions:

1. So in my instance even if the 20A circuit I was working on had two or more receptacles I wouldn't be able to put the larger tool that draws 13A on a 15A receptacle (only max rated to 12A)? By code it needs to be on a 20A receptacle (max rated to 16A)?



3. Why wouldn't the code simply state the receptacles need to be rated at the same or higher ampere rating as the circuit the are connected to?

See bold part of original post. Not less than means same or higher.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Dr. No, weclome to the forum! :)

. . . I changed it to #12 cord with a 20A 125V cord cap. Changing this was a big deal because now only the tools with the "new" 20A cord caps could be plugged in and the same tools from other machine lines with 15A cord caps can no longer be used.
Maybe you can find a cord cap with a T-slot configuration that will accept both 15- and 20-amp plugs.
 
I had an instance where something had to be changed. I wanted to make sure I was right before letting the customer know they had a code violation. I looked it up and confirmed my interpretation with a co-worker.

My new code book is at work, so I'm looking at an older one as I type this. In 210 there is a cord and plug connected load to receptacle chart, and a receptacle ratings for various size circuits.

I my instance I had a dedicated 20A circuit (hot, neutral, ground) to a cord drop. The THHN in the conduit was #12, but the cord was only #14 with a 15A 125V twist lock cord cap. To my understanding this is a code violation, so I changed it to #12 cord with a 20A 125V cord cap. Changing this was a big deal because now only the tools with the "new" 20A cord caps could be plugged in and the same tools from other machine lines with 15A cord caps can no longer be used. One of the tools used is rated at 10A, and other tool used I measured with a meter to draw 13A. I would have just changed the breaker to a 15A, but I didn't because of the 13A draw of the larger tool.

The way I interpret the code is that if the circuit is 20A and dedicated the receptacle or cord cap in this case has to match. Code states "A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit."

In 210 it does state that where a branch circuit is supplying two or more receptacles it shall conform with the table in 210.

So the way I understand it, if I have a dedicated 20A circuit with a single receptacle then I need to use a 20A receptacle and it would have a max load rating of 16A. Also if I put two or more receptacles on that same 20A circuit then I can use 15A rated receptacles, I know that a single duplex receptacle is actually "two" receptacles, so this one 15A device can be put on a 20A circuit by code. But each 15A receptacle of a duplex is only rated for a max load of 12A according to the chart.

Here are my three questions:

1. So in my instance even if the 20A circuit I was working on had two or more receptacles I wouldn't be able to put the larger tool that draws 13A on a 15A receptacle (only max rated to 12A)? By code it needs to be on a 20A receptacle (max rated to 16A)?

2. I try to put some logic behind the reason of the code. I understand having one receptacle on a dedicated 20A circuit would need a 20A receptacle. Why when adding two or more receptacles to the circuit this changes the rules, and 15A receptacles can be used?

Someone that doesn't know any better could plug a splitter into the 15A receptacle and have a combined load, or one large tool that will plug into the 15A receptacle. It could draw more than the 12A max load for the 15A receptacle overloading it, but stay under the trip level of the 20A breaker and stay functional without tripping the circuit.

3. Why wouldn't the code simply state the receptacles need to be rated at the same or higher ampere rating as the circuit the are connected to?

If I understand your post correctly, You could have just put in a '15 amp' breaker and been code compliant since this was a 'single' dedicated receptacle. The total cord and plug connected load of 12 amps on a 15 amp 'single' receptacle is only required if there are TWO (2) OR MORE outlets. You ONLY have ONE (1) outlet, and that's for the dedicated circuit of the single receptacle.

In fact, you can have up to 14 amp load running on a 15 amp single receptacle when it's the ONLY outlet (and assuming its not a contiunious load of 3 hrs or more). I think you did more work than required for nothing. ;)
 

nogard1126

Member
Location
WI
12-27-2009 07:21 PM
btharmy Just install a duplex receptacle, plug the cord drop into that, and be done with it.


This was a consideration. It is a strange way to work around the code to make what I wanted to do work, but this would make it work.

I don't think I got my point across. I feel the cord drop needed to be #12, it is good for 25 amps. A #14 with 2 current carrying conductors is only good for 18 amps, if it was protected by a 20 amp breaker how can this be legal?

As far as a single cord cap or receptacle on a 20 amp circuit, it does make sense to me to have a minimum of equal ampacity (20 amp) cord cap or receptacle on the circuit, anything lesser would be the weak link and could melt.

I didn't understand the simple point of why you can put a 15 amp receptacle on a 20 amp circuit if there are two or more, but can't if there is just one.

If I understand your post correctly, You could have just put in a '15 amp' breaker and been code compliant since this was a 'single' dedicated receptacle. The total cord and plug connected load of 12 amps on a 15 amp 'single' receptacle is only required if there are TWO (2) OR MORE outlets. You ONLY have ONE (1) outlet, and that's for the dedicated circuit of the single receptacle.

In fact, you can have up to 14 amp load running on a 15 amp single receptacle when it's the ONLY outlet (and assuming its not a contiunious load of 3 hrs or more). I think you did more work than required for nothing.

What about the table 210.21 (B)(2)?
It's it saying receptacle rating 15 amp has a max load of 12 amps, and receptacle rating of 20 amp has a max load of 16 amps?

Thanks for the help, I'm just trying to understand better by trying to grasp the point behind the code.
 
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This was a consideration. It is a strange way to work around the code to make what I wanted to do work, but this would make it work.

I don't think I got my point across. I feel the cord drop needed to be #12, it is good for 25 amps. A #14 with 2 current carrying conductors is only good for 18 amps, if it was protected by a 20 amp breaker how can this be legal?

As far as a single cord cap or receptacle on a 20 amp circuit, it does make sense to me to have a minimum of equal ampacity (20 amp) cord cap or receptacle on the circuit, anything lesser would be the weak link and could melt.

I didn't understand the simple point of why you can put a 15 amp receptacle on a 20 amp circuit if there are two or more, but can't if there is just one.



What about the table 210.21 (B)(2)?
It's it saying receptacle rating 15 amp has a max load of 12 amps, and receptacle rating of 20 amp has a max load of 16 amps?

Thanks for the help, I'm just trying to understand better by trying to grasp the point behind the code.


Table 210.21(B)(2) only applies when the branch circuit is supplying two or more receptacles or outlets. You only have one receptacle (outlet). You have to read the code in context and under the proper headings that apply. Go back and read NEC 210.21(B) again. Like I said in my previous post, so long as its a 'single' outlet or receptacle, you can load it up to a rating of the receptacle so long as its not a continous load.

Basically, a single 20 amp receptacle, (so long thats the only outlet), can have a load of 19 amps on it. I see this alot in commercial applications that have freezers, refrigerators in stores, hospitals etc.. Those refrigertors have a name plate of 19 amps on them.

Hope that it helps clear things up. ;)
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
It's it saying receptacle rating 15 amp has a max load of 12 amps, and receptacle rating of 20 amp has a max load of 16 amps?

Thanks for the help, I'm just trying to understand better by trying to grasp the point behind the code.
You should understand that, with rare exception, 15a and 20a receptacles of a given grade have identical ampacities. The only difference is the slot shape, which is a rejection feature.

I repeat my suggestion of the T-slot receptacle cord end if you can find one.
 

nogard1126

Member
Location
WI
It is a twist lock, I can't get a t-slot that will work for both 15 and 20 amp, that is a good idea and would solve the problem. But twist locks have different configurations for the voltages and amperes.

Brother, I agree with what you are saying. Just a few things I want to clear up. I understand that a continuous load is defined as 3 hours or more. At that point am I supposed to only use 80% of the over current protection or size the load at 125%? I know both of these are the same thing. If I'm under 3 hours non continuous load do I size at 100%? If that is the case, then yes simply replacing the breaker does seem to be the way I should have fixed it.

Also I don't feel I as wrong to want to put a 20 amp rated cord cap on a 20 amp breaker protected circuit. A cord cap less than the over current would be a code violation, correct? Needs to be equal or greater (not less than) I get that it is common sense.

I do understand what you are saying about Table 210.21(B)(2) it is for two or more, not the ONE that I have. I agree with what you are saying a 20 amp single receptacle could have 19 amps non continuous protected by a 20 amp breaker.

The part I don't get is why on the same 20 circuit when I add a second receptacle does the amount of current the receptacle was rated for drop from 19 amps as you say to 16 amps according to 210.21(B)? And now I have the option to put two or more 15 amp rated receptacles on the circuit if I have two or more?

I'm not trying to be annoying, I understand where you are coming from, and you are right about what you've said and I agree. But the question in the paragraph above is the one thing no one has touched on yet. I feel we have all the other questions cleared up and we are on the same page, thank you.
 
It is a twist lock, I can't get a t-slot that will work for both 15 and 20 amp, that is a good idea and would solve the problem. But twist locks have different configurations for the voltages and amperes..
Yes this is true, thats how I come to the conclusion of you not using the t slot receptacles.

Brother, I agree with what you are saying. Just a few things I want to clear up. I understand that a continuous load is defined as 3 hours or more. At that point am I supposed to only use 80% of the over current protection or size the load at 125%? .
Basically yes, when you have continous load both the OCPD and branch circuit conductors are sized at 125% per 2008 NEC 210.20(A) and 210.19(A)(1)

I know both of these are the same thing. If I'm under 3 hours non continuous load do I size at 100%? If that is the case, then yes simply replacing the breaker does seem to be the way I should have fixed it..
Yes you can size the OCPD and branch circuit conductors to 99.99% so long as its not a continous load. Thats why I say a 15 amp breaker can carry a single 14 amp load, or a 20 amp breaker can carry a 19 amp load on a single receptacle.

Also I don't feel I as wrong to want to put a 20 amp rated cord cap on a 20 amp breaker protected circuit. A cord cap less than the over current would be a code violation, correct?
It would be a violation if its a 'single' outlet/cord cap, if there were 2 outlets then it would not.

I do understand what you are saying about Table 210.21(B)(2) it is for two or more, not the ONE that I have. I agree with what you are saying a 20 amp single receptacle could have 19 amps non continuous protected by a 20 amp breaker.

The part I don't get is why on the same 20 circuit when I add a second receptacle does the amount of current the receptacle was rated for drop from 19 amps as you say to 16 amps according to 210.21(B)? And now I have the option to put two or more 15 amp rated receptacles on the circuit if I have two or more?..
Thats for someone from the CMP to explain. I can only speculate, but maybe it was an extra safety measure to try to keep people from overloading circuits even though they still do.

I'm not trying to be annoying, I understand where you are coming from, and you are right about what you've said and I agree. But the question in the paragraph above is the one thing no one has touched on yet. I feel we have all the other questions cleared up and we are on the same page, thank you.
Hope I answered your questions, but like I said, thats something the CMP (Code Making Panel) would have to answer why its written that way. ;)
 
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