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Old 12-18-2008, 04:13 PM   #1
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Receptacle Rating question


Hi;
I am reading the 2005 NEC, and found this interesting:

210.21 Outlet Devices. Outlet devices shall have an ampere
rating that is not less than the load to be served and
shall comply with 210.21(A) and (B).


Then, subpart (3), and table 210.21(B)(3)

(3) Receptacle Ratings. Where connected to a branch circuit
supplying two or more receptacles or outlets, receptacle
ratings shall conform to the values listed in Table
210.21(B)(3), or where larger than 50 amperes, the receptacle
rating shall not be less than the branch-circuit rating.

Table 210.21(B)(3) Receptacle Ratings for Various Size Circuits
Circuit Rating
(Amperes)
Receptacle Rating
(Amperes)
15
Not over 15
20
15 or 20
30
30
40
40 or 50
50
50

So, if I read this correctly, a 20A receptacle cannot be used on a 15A branch.
This makes no sense to me, since there is really no difference between a 15A and a 20A receptacle; at least not in the ability of each to carry at least the 15A load.

Anyone care to comment on this?

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Last edited by KE2KB; 12-18-2008 at 06:27 PM. Reason: Want to remove redundant post
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Old 12-18-2008, 09:29 PM   #2
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Receptacle Rating question


there is a physical difference between them...

20A

15A

Notice that the 15A doesn't have the horizontal on the neutral like the 20A does this is meant to keep people from plugging in a 20A device (with the appropriate plug) from being plugged into a 15A outlet, and constantly tripping the breaker

20A plug

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Old 12-18-2008, 09:37 PM   #3
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Receptacle Rating question


It's just a preventative measure to keep someone from tripping breakers as you mentioned. I assume the other way around, using 15amp outlets on a 20amp circuit would be fine.
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Old 12-18-2008, 09:50 PM   #4
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Receptacle Rating question


Lets not also forget the the word OUTLET by the NEC definition means receptacle.
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Old 12-18-2008, 09:54 PM   #5
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Originally Posted by dgbehrends View Post
It's just a preventative measure to keep someone from tripping breakers as you mentioned. I assume the other way around, using 15amp outlets on a 20amp circuit would be fine.
as long as its a more than one 15A, so a 15A duplex receptacle is good.
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Old 12-18-2008, 10:03 PM   #6
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Originally Posted by Sliver View Post
as long as its a more than one 15A, so a 15A duplex receptacle is good.

But you can install a SINGLE 20a receptacle on a 15 amp circuit. Sorry to confuse everyone.
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Old 12-18-2008, 10:09 PM   #7
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Originally Posted by chris75 View Post
But you can install a SINGLE 20a receptacle on a 15 amp circuit. Sorry to confuse everyone.
You can but it wouldn't be up to code... i don't have my code book here... but as a remember 15A circuits can only take 15A or less (if you can find one) receptacles
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Old 12-18-2008, 10:11 PM   #8
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Quote:
Originally Posted by Sliver View Post
You can but it wouldn't be up to code... i don't have my code book here... but as a remember 15A circuits can only take 15A or less (if you can find one) receptacles
Umm. Not going to argue, but it meets code. And why would you say it does not meet code without looking it up first?

Ever install a 50 amp range receptacle supplied by a 40A branch circuit?

Last edited by chris75; 12-18-2008 at 10:26 PM.
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Old 12-18-2008, 10:40 PM   #9
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Quote:
Originally Posted by chris75 View Post
Umm. Not going to argue, but it meets code. And why would you say it does not meet code without looking it up first?
Right now I'm in school and we just talked about this in class...

so if you look at Table 210.21(b)(3)
Circuit Rating | Receptacle Rating
(amperes).....| (amperes)
15...............| Not over 15
20...............| 15 or 20
30...............| 30
40...............| 40 or 50
50...............| 50

Quote:
Originally Posted by chris75 View Post
Ever install a 50 amp range receptacle supplied by a 40A branch circuit?
Well if you look at that table it specifically says on a 40 A circuit you may install 40A or 50A receptacles...

So unless there is an exception I'm missing....

Last edited by Sliver; 12-18-2008 at 10:44 PM.
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Old 12-18-2008, 10:54 PM   #10
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Quote:
Originally Posted by Sliver View Post
Right now I'm in school and we just talked about this in class...

so if you look at Table 210.21(b)(3)
Circuit Rating | Receptacle Rating
(amperes).....| (amperes)
15...............| Not over 15
20...............| 15 or 20
30...............| 30
40...............| 40 or 50
50...............| 50


Well if you look at that table it specifically says on a 40 A circuit you may install 40A or 50A receptacles...

So unless there is an exception I'm missing....
Read the code section just above that table...

(3) Receptacle Ratings. Where connected to a branch cir-
cuit supplying two or more receptacles or outlets
, recep-
tacle ratings shall conform to the values listed in Table
210.21(B)(3)

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Old 12-18-2008, 11:22 PM   #11
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Wow... reading comprehension finally hits...

...rating not less than the branch circuit....

doesn't say anything about being more...

Sorry i got a test on Art. 210 tomorrow.. and I red that wrong

Last edited by Sliver; 12-18-2008 at 11:27 PM. Reason: I was wrong
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Old 12-18-2008, 11:42 PM   #12
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Sliver.. you gotta watch out on this forum we have some pretty sharp fellas here and they like this stuff.....

I wouldn't be surprised if your instructor might get caught on what Chris75 proposed to you. His hint came with the word 'Single' in capitals. Take a look at 210.21(B)(1) and see if you catch on.

Also don't let conductor size fool you as to the branch circuit rating especially when looking at the small conductors of 240.4(D). The circuit breaker determines the branch circuit rating not the conductor size. Just something I observe from time to time that is confusing to some new at the trade.
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Old 12-19-2008, 07:52 AM   #13
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Quote:
Originally Posted by chris75 View Post
Lets not also forget the the word OUTLET by the NEC definition means receptacle.
Outlet. A point on the wiring system at which current is taken to supply utilization equipment.


Receptacle. A receptacle is a contact device installed at the outlet for the connection of an attachment plug. A single receptacle is a single contact device with no other contact device on the same yoke. A multiple receptacle is two or more contact devices on the same yoke.
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Old 12-19-2008, 08:07 AM   #14
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So, the way I read 210.21(B); It is acceptable to use a 20A receptacle on a 15A branch if there are no other outlets on that branch (a dedicated line).
However, if there are 2 or more outlets on the branch, that 20A receptacle cannot be used on a 15A branch.

That doesn't seem to make sense. Why would the 20A receptacle be acceptable as the only outlet on a 15A branch, but not if there are 2 or more?
Either way, equipment using that 20A receptacle, and drawing more than 15A would trip the breaker.
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Old 12-19-2008, 08:30 AM   #15
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Quote:
Originally Posted by KE2KB View Post
So, the way I read 210.21(B); It is acceptable to use a 20A receptacle on a 15A branch if there are no other outlets on that branch (a dedicated line).
However, if there are 2 or more outlets on the branch, that 20A receptacle cannot be used on a 15A branch.

That doesn't seem to make sense. Why would the 20A receptacle be acceptable as the only outlet on a 15A branch, but not if there are 2 or more?
Either way, equipment using that 20A receptacle, and drawing more than 15A would trip the breaker.
Yea I agree. I'm not an electrician and haven't studied the code extensively, but what makes sense to me is that you shouldn't use 20amp receptacles on 15amp circuits, and it shouldn't matter whether there is 1 or more outlets. I don't see any problem using 15amp recepticales on a 20amp circuit.

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