210-21(b)(3)

[BarryO]

I've having a running discussion (argument?) with someone who claims to have been a "practicing electrician and code inspector in 5 states" about the interpretation 210-21(b)(3).

He's telling me the receptacle ratings in Table 210-21(b)(3) are maximums, and it is OK to use smaller receptacle ratings. An example he gave is 3 20A receptacles on a 50A branch.

I maintain that "shall conform" means the recpectacle ratings shall conform to those listed in the table. Only the entry for 15A branches is a maximum. For 20A and 40A branches, two ratings are permissible, but for a 50A only a 50A is permissable.

I've never heard of his interpretation, it does not seem supported in the text. From an enginerring POV is seems unwise to permit portable lamps with 18 AWG cords to be protected by 50A overcurrent protection devices, which is a situation that his interpretation would permit.

 

[infinity]

Re: 210-21(b)(3)

This table is for a duplex(two) or more receptacles. Single receptacles can exceed the size of the OCPD. For 3-20 amp receptacles the maximum OCPD would be 20 amps.

[ January 29, 2006, 04:38 PM: Message edited by: infinity ]

 

[charlie b]

Re: 210-21(b)(3)

If I said that the tabulated entries were neither minimums nor maximums, would that win or lose the argument for you? There are two things being prohibited by that table.

The first thing that they don't want you to do is to put a 30 amp receptacle on a 20 amp branch circuit. The hazard is that someone will see the 30 amp receptacle, think that it is capable of handling (for example) a 25 amp load, plug in such a load, overload the 20 amp branch circuit, and perhaps start a fire. There is no guarantee that a 20 amp breaker would trip to prevent the fire.

The other thing they don't want you to do is to put a single 15 amp receptacle on a 20 amp circuit. If you did, someone could plug in an 18 amp load, the breaker would not trip, and the receptacle might overheat and start a fire. What they do allow is to have two (or more) 15 amp receptacles on a 20 amp breaker. The theory is that each receptacle is likely to have a portion of the total circuit load. That is, there might be 5 amps of load on one 15 amp receptacle, 7 amps on another, 12 amps on a third, and so forth. Eventually, if you continue to overload the circuit, the 15 amp breaker will trip, but in the mean time none of the receptacles will have been loaded beyond its own rating.

So I would say that your views are correct. The tabulated receptacle ratings are not maximum values, but rather are acceptable values. You may put two or more 15 amp receptacles on a 20 amp circuit, and you may put two or more 20 amp receptacles on a 20 amp circuit. But you may not put a 20 amp receptacle on a 15 amp circuit. You may only use the receptacles that are shown on the table.

 

[infinity]

Re: 210-21(b)(3)

The first thing that they don't want you to do is to put a 30 amp receptacle on a 20 amp branch circuit. The hazard is that someone will see the 30 amp receptacle, think that it is capable of handling (for example) a 25 amp load, plug in such a load, overload the 20 amp branch circuit, and perhaps start a fire. There is no guarantee that a 20 amp breaker would trip to prevent the fire.

Since I've never seen a 30 amp duplex receptacle I'm assuming that all 30 amp receptacles are single receptacles. Single receptacles are permitted to be sized larger than the circuit ampacity. Although Charlie's example is logical it is not supported by the NEC. Look at 210.21(B)(1). The single receptacle is only required to be not less than the circuit ampacity. It can be more.

But you may not put a 20 amp receptacle on a 15 amp circuit.

A single 20 amp receptacle is permitted on a 15 amp circuit as well.

 

[steve66]

Re: 210-21(b)(3)

Infinity:

I can't agree with that. If you look at the begining of 210.21, it says:

"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). The way I see it, if you put a 30A receptacle on a 20A circuit, your outlet device only has a 20A rating since it is connected to a 20A circuit.

Or maybe it is table 210.24 that prohibits this.

At any rate, I just don't agree that you can use a receptacle larger than the branch circuit rating (except for a 50A outlet on a 40A circuit per table 210.24). I sure someone knows exactly what prohibits this.

Steve

[ January 30, 2006, 03:57 PM: Message edited by: steve66 ]

 

[infinity]

Re: 210-21(b)(3)

"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). The way I see it, if you put a 30A receptacle on a 20A circuit, your outlet device only has a 20A rating since it is connected to a 20A circuit.

How does this make the receptacle less than the load served? It's a 30 amp device on a 20 amp circuit. That seems like the"outlet device" is more than but not less than.


210.21 references 210.21(B) which states that the single receptacle is only not less than the circuit ampacity. It can be more.

210.21(B) Receptacles.
(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 .

 

[BarryO]

Re: 210-21(b)(3)

Originally posted by infinity:
Look at 210.21(B)(1). The single receptacle is only required to be not less than the circuit ampacity. It can be more.

That's my understanding, for 210(b)(1) only. For motor loads, I understand that plug connections are always considered to be disconnecting means, and one sometimes has to upsize the plug and receptacle in order to get sufficient horsepower ratings in them.

 

[lauraj]

Re: 210-21(b)(3)

210.23 "In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated."

This, in my opinion, prevents us from using a 30 amp receptacle on a 20 amp circuit for an individual branch circuit. It seems like if we used a 30 amp receptacle, that's inviting someone to plug in a 30 amp load (although I can't think of any 30 amp loads that I've ever plugged in), which would exceed the branch circuit ampere rating.

 

[George Stolz]

Re: 210-21(b)(3)

I don't think so. If they wanted to prohibit a 30 amp receptacle on a 20 amp circuit, there are more effective methods.

Outlet devices shall have an ampere rating that is not less than the load to be served...

That places the burden on the user of the system. Otherwise it should read:

Outlet devices shall have an ampere rating that is not less than the load to be served, and not greater than the rating of the circuit.

But that's not what it says.

Laura, I don't think 210.23 does the trick either. Once again, it's too weak. The load and the OCPD are addressed, not how the two meet at the receptacle.

 

[George Stolz]

Re: 210-21(b)(3)

My last post was just my opinion, by the way. I can understand the other view.

Originally posted by BarryO:
An example he gave is 3 20A receptacles on a 50A branch.

I maintain that "shall conform" means the recpectacle ratings shall conform to those listed in the table. Only the entry for 15A branches is a maximum. For 20A and 40A branches, two ratings are permissible, but for a 50A only a 50A is permissable.

I agree. The text referring to the table is quite clear, more than one receptacle on a branch circuit must conform to the table.

As a side note, you'll probably run across some that believe you can determine a circuit rating by using the table backwards. I don't quite follow the mentality, but it persists.

 

[infinity]

Re: 210-21(b)(3)

Originally posted by lauraj:
210.23 "In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated."

This, in my opinion, prevents us from using a 30 amp receptacle on a 20 amp circuit for an individual branch circuit. It seems like if we used a 30 amp receptacle, that's inviting someone to plug in a 30 amp load (although I can't think of any 30 amp loads that I've ever plugged in), which would exceed the branch circuit ampere rating.

I agree with George. By trying to apply 210.23 to receptacle circuits you negate the permission to, for example, install say 10 duplex devices on a 15 amp circuit. Certainly someone could come along and plug in multiple appliances and overload the circuit, but that's what the OCPD is for. The requirement is for the end user to meet, not the installation.


210.21(B)(1) permits a larger single receptacle on the circuit. Any reference to Table 210.21(B)(3) would be incorrect when using a single receptacle, since that table only applies to 2 or more receptacles.

[ January 31, 2006, 05:16 AM: Message edited by: infinity ]