Receptacle Rating question

[S'mise]

I was looking at Table 210.21(B)(3) that lists Receptacle Ratings.

Why is it OK to put a 50amp receptacle on a 40amp circuit?

 

[John120/240]

Have you ever seen a 40 A rated receptacle ? Look at it like this: There are situations where it is necessary to use a 15 A breaker with

12 or 10 wire. This would be done to accommodate for voltage drop. You are not violating any rules. The receptacle is rated above

and beyond the amps you are supplying.

 

[Little Bill]

Have you ever seen a 40 A rated receptacle ? Look at it like this: There are situations where it is necessary to use a 15 A breaker with

12 or 10 wire. This would be done to accommodate for voltage drop. You are not violating any rules. The receptacle is rated above

and beyond the amps you are supplying.

John, did you ever figure out what makes your line breaks appear wrong when you post?

For example: from the above in red, there was plenty of room to complete the sentence on the same line.
"violating any rules. The receptacle is rated above and beyond the amps you are supplying."

It's kind of hard to read the posts when the sentence is broke up like that and doubled spaced down.

Are you typing in a word text program, then pasting in here?
Or are you hitting "enter" before you reach the end of the space.

I'm not picking on you, just trying to figure out why your posts appear this way.

 

[infinity]

I was looking at Table 210.21(B)(3) that lists Receptacle Ratings.

Why is it OK to put a 50amp receptacle on a 40amp circuit?

This is common on 40 amp range circuits. One other note this concept only applied to single receptacles.

 

[S'mise]

Have you ever seen a 40 A rated receptacle ? Look at it like this: There are situations where it is necessary to use a 15 A breaker with

12 or 10 wire. This would be done to accommodate for voltage drop. You are not violating any rules. The receptacle is rated above

and beyond the amps you are supplying.

Yes, Its fine to use wire larger than necessary, but not a receptacle. (I thought so anyway)

So, what happens when I try to draw 50 amps thru wire and breaker thats only good for 40a? (Then there will be voltage drop)

It may be common for stoves, put it still don't make much sense to me.

It appears the 50a recept is the only place this is ok with the NEC.

 

[augie47]

I have seen a couple of industrial situations where equipment was plugged and unplugged on a consistent basis leading to short life of the receptacles. To reduce the frequency of the problem, they actually installed 50 amp receptacles on a 20 amp circuit.

 

[John120/240]

So, what happens when I try to draw 50 amps thru wire and breaker thats only good for 40a.

Just because the receptacle is rated 50 A the breaker at the panel will limit you to 40 A. In certain situations we can say put a 40A
breaker on 12 AWG, air conditioners come to mind.

 

[suemarkp]

Also note that if the circuit has a SINGLE receptacle, that receptacle rating needs to be equal to or greater than the over current protection (210.21(B)). So on a dedicated circuit, you can put that 50A outlet on a 15A circuit.

Why you can put one 50A receptacle on a 30A circuit, but not two, I don't know.

The 40A exception is there since there are no 40A receptacles. You also can't use 25A, 35A, 45A breakers on multi-outlet circuits, only individual.

 

[S'mise]

Just because the receptacle is rated 50 A the breaker at the panel will limit you to 40 A. In certain situations we can say put a 40A
breaker on 12 AWG, air conditioners come to mind.

Yes, You can put a 40a breaker on #12 because of the next size up rule, that makes sense.

So why not alow a 20a recept to be fed by a 15a breaker? Same thing.

Thanks for your thoughts on this, still trying to wrap my mind around it. :?

 

[infinity]

Yes, You can put a 40a breaker on #12 because of the next size up rule, that makes sense.

So why not alow a 20a recept to be fed by a 15a breaker? Same thing.

Thanks for your thoughts on this, still trying to wrap my mind around it. :?

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

 

[jap]

Yes, You can put a 40a breaker on #12 because of the next size up rule, that makes sense.

So why not alow a 20a recept to be fed by a 15a breaker? Same thing.

Thanks for your thoughts on this, still trying to wrap my mind around it. :?

You could'nt have a 40a breaker protect #12 wire because of the next size up rule, you could only do this if there was an overload device downstream of the 40a breaker, such as a thermal overload or or other overcurrent device used on the line side of a motor load. The 40a breaker would be the short circuit protection not the overload protection.
If the overloads were not in place you would be required to protect the #12 wire with a 20a max overcurrent device.

You can think of the receptacles like a balloon. if we have a balloon that will hold 50 psi and we only fill it with 40 lbs of air it will hold that pressure no problem. Now, if we have a balloon that is only rated at 40psi and we fill it with air to the point it exceeds 40psi then the ballon will pop. (simulating an overload). The only diffence is that in electricity we have breakers in place so that if load exceeds 40 amps it trips and shuts the circuit down before damaging the conductors.

 

[S'mise]

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

Not true. If you have a 20amp receptacle it must be supplied by at least a 20amp circuit. Table 210.21(B)(2)

You are probably thinking of putting a 15a receptacle on a 20a breaker, because its rated for 20a feed thrugh current.

 

[jap]

Table 210.21 B2 gives the Maximum Cord and Plug connected load to the receptacle, which boils down to 80% of the receptacle rating.

 

[infinity]

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

Not true. If you have a 20amp receptacle it must be supplied by at least a 20amp circuit. Table 210.21(B)(2)

You are probably thinking of putting a 15a receptacle on a 20a breaker, because its rated for 20a feed through current.

You're incorrect. The table that you've mentioned is not for single receptacles.

(2) Total Cord-and-Plug-Connected Load. Where con-
nected to a branch circuit supplying two or more receptacles
or outlets, a receptacle shall not supply a total cord-and-plug-
connected load in excess of the maximum specified in Table
210.21(B)(2)

 

[S'mise]

You could'nt have a 40a breaker protect #12 wire because of the next size up rule, you could only do this if there was an overload device downstream of the 40a breaker, such as a thermal overload or or other overcurrent device used on the line side of a motor load. The 40a breaker would be the short circuit protection not the overload protection.
If the overloads were not in place you would be required to protect the #12 wire with a 20a max overcurrent device.

You can think of the receptacles like a balloon. if we have a balloon that will hold 50 psi and we only fill it with 40 lbs of air it will hold that pressure no problem. Now, if we have a balloon that is only rated at 40psi and we fill it with air to the point it exceeds 40psi then the ballon will pop. (simulating an overload). The only diffence is that in electricity we have breakers in place so that if load exceeds 40 amps it trips and shuts the circuit down before damaging the conductors.

Yes your right, but I could protect it with a 35a breaker per (240.4 (b)(2). Or, possably a 30a ocpd (protecting a motor) if used for overcurrent prot.

But we are digressing.......

I understand how ratings work ,and usually its best to have devices rated higher than needed.

In the case of a receptacle, It always seemed to me that it should be capable of supplying 50amps if its rated 50amps.

I guess its clear, I need to go back and review this chapter.:huh:

Thanks.

 

[S'mise]

You're incorrect. The table that you've mentioned is not for single receptacles.

Thanks infinity, I caught that shortly after I posted it.

Good feeling to learn something.