residential outlet tailing wire size

[Jim W in Tampa]

What happens if that duplex has 2 items plugged in that together draw maybe 25 amps for a minute and then back off to 20 amps ? Its not A receptacle it is 2 receptacles and the load could reach 20 amps.What are you planning on doing ? back stabbing ?

 

[celtic]

....such as an incandescent luminaire that only allows a 60 watt bulb maximum.
.

What..incandescent lamps greater than 60W have a different sized base or something?

 

[iwire]

....such as an incandescent luminaire that only allows a 60 watt bulb maximum.
.

What..incandescent lamps greater than 60W have a different sized base or something?

:lol:

No but at the same time I don't think you will find a med base lamp that is rated higher than 600 watts.

The 16 AWG cord can handle a 600 watt lamp at 120 volt.

 

[peter d]

If I am correct in this you could place a 30 amp load on the one outlet.

That would trip the breaker.

However, a #14 pigtail could be overloaded bya 20 amp load with a 20 amp OCPD. The breaker won't trip in this case.

 

[don_resqcapt19]

Peter,

However, a #14 pigtail could be overloaded bya 20 amp load with a 20 amp OCPD.

How? A #14 is rated at 20 amps in the 60?C column in Table 310.16.
Don

 

[peter d]

Yes, but why are we limited by 240.4(D)then? Surely we can't have it both ways. :?

 

[izak]

hey....

why 'tail out' with #14 when you can just land 2 sets of #12 under the screws and crawl to the next recep??

save time on twisting joints and cost of wirenuts, and lets face it, 15 amp receps are like 70 CENTS

commercial- tie joints on everything

residential- oh, theres more screws? COOL!

 

[iwire]

Yes, but why are we limited by 240.4(D)then? Surely we can't have it both ways. :?

IMO Don is not suggesting we have it both ways.

But a 14 AWG will not be 'overloaded' by a 20 amp load, we can use 14 AWG to supply a motor that requires a 20 amp conductor.

Keep in mind 240.4(D) is not an ampacity rating it is just a rule we must follow for typical branch circuits.

 

[Jim W in Tampa]

Yes, but why are we limited by 240.4(D)then? Surely we can't have it both ways. :?

IMO Don is not suggesting we have it both ways.

But a 14 AWG will not be 'overloaded' by a 20 amp load, we can use 14 AWG to supply a motor that requires a 20 amp conductor.

Keep in mind 240.4(D) is not an ampacity rating it is just a rule we must follow for typical branch circuits.

Yes and a rule he would be breaking if he does this.

 

[don_resqcapt19]

Peter,

Yes, but why are we limited by 240.4(D)then? Surely we can't have it both ways.

I have no idea why 240.4(D) exists, but you didn't ask about code required overcurrent protection. You stated that a 20 amp load with a 20 amp OCPD would overload #14. That installation would not meet code, but the #14 would not be overloaded.
Don

 

[peter d]

But a 14 AWG will not be 'overloaded' by a 20 amp load, we can use 14 AWG to supply a motor that requires a 20 amp conductor.

Yes, I realize that, it was my mistake. That's what happens when you fire off an answer without checking the book. :roll:

 

[Pierre C Belarge]

I believe that 240.4(D) exists to provide extra "cushion" as a safety margin for the protection of the most commonly installed conductors.

With that being said, I am curious just how much current a short tail (8 in) of 14 AWG Type THHN conductor can actually have applied before failure.

If I have a 20 amp overcurrent device, and put a 20 amp load on it indefinitely, I do not believe we would see any degradation to the insulation.

If I have a 20 amp overcurrent device, and put a 30 amp load on it, it will open the overcurrent device in a relatively short amount of time, of which I still think that there would be no damage to the conductor, as not enough time would pass or not enough current would pass to damage the conductor. What is the current carrying capability of this short piece of conductor?

 

[JohnE]

I believe that 240.4(D) exists to provide extra "cushion" as a safety margin for the protection of the most commonly installed conductors.

I was under the impression that 240.4(D) is there since earlier #14, 12 and 10 could not handle as much ampacity as newer insulations, so just keep the overcurrent protection lower for all of them and avoid any confusion. I really don't know why I've though this, for what it's worth. :?

 

[charlie b]

I was under the impression that 240.4(D) is there since earlier #14, 12 and 10 could not handle as much ampacity as newer insulations, so just keep the overcurrent protection lower for all of them and avoid any confusion.

That might be one reason. I can suggest another, but it is only a guess.

Yes, but why are we limited by 240.4(D)then?

First I will repeat that I think it's just an added safety margin.

But why add a margin for #14, 12, and 10, but not others? I think it has to with the fact that when a number is small, a small change can represent high percentage of change. Consider two brothers at ages 2 and 6. The younger looks on the older as being far, far advanced in the wisdom of the world. But 50 years later, that that same 4 year difference in age will not be as significant.

Now consider two identical circuits using #14 wire. Put 15 amps through one, and 20 amps through the other. The circuit running at 20 amps will experience a heat generation that is 77% higher than that of the circuit running at 15 amps. Do this with a pair of #12 circuits running 20 amps and 25 amps, and the difference is 56%. Do this with a pair of #10 circuits running 30 amps and 35 amps, and the difference is 36%. Do this with larger wires, and the percentage differences get smaller.

So if you use #12 wires but add a #14 pigtail at the end, and if you use a 20 amp breaker, then the heat that could be generated in the #14 wire could be up to 77% higher than it would have been, if you had used a 15 amp breaker. When you also consider that #14 wire is small, fragile, and easily damaged, it just makes sense to be a bit more protective.

 

[DGrant041]

OK gents, you can tell by my low number of replies that I'm new here. FYI: My background is in industrial maintenance and manufacturing. But my goals include becoming a master electrician in the next couple of years.

That said, I was under the impression that 15 amp branch circuits were as permissible as 15 amp receptacles. [Ref: 210.19 (A) (2), 210.21 (B) with tables and Table 210.24] Charlie B mentioned that you couldn't stop someone from connecting 20+ amps to it. Wouldn't the style of plug prevent that from happening? (Please don't argue that the homeowner is handy with a pair of pliers--they're on they're own.)

Only one thing I'd like to add: even though I haven't posted very many times, I've done A LOT of reading. I like seeing how different members of the electrical community can add a new perspective to a discussion. That said, Dirty Harry, please don't yell at me. :wink: (Just kiddin??you can yell if you want to.)

-Dale

"still-learnin" thanks for posting. I hope we're all still learning however "learned" we are.

 

[charlie b]

Charlie B mentioned that you couldn't stop someone from connecting 20+ amps to it. Wouldn't the style of plug prevent that from happening?

I had in mind, for example, a duplex receptacle with two 1500 watt (12.5 amp) hair dryers plugged into it.

 

[charlie b]

....such as an incandescent luminaire that only allows a 60 watt bulb maximum.

What..incandescent lamps greater than 60W have a different sized base or something?

Celtic, I suspect that this post was intended to be in the "tongue in cheek" line. I am sure you know (though others in the industry and homeowners might not know) that the 60 watt limit (i.e., 1/2 amp limit) is not based on ampacity. Rather, it is there to prevent too much heat from being generated by the bulb itself.

 

[bthielen]

I wonder if it is possible that this may be one of the rare situations where the code writers are trying to protect against the unknowing H.O. replacing a 15A receptacle with a 20A. Fixtures have statements specifying the wattage limit of the light bulbs but circuits do not specify the maximum rating of the receptacles for the DIYer. The inexperienced DIYer is very likely not to know the difference between a 15A and a 20A receptacle by visual inspection or may even know enough to see a 20A circuit breaker and think he's perfectly OK to use the 20A receptacle not noticing the 14ga. wire.

I realize that the code cannot provide protection against what some H.O. might do in the future, but receptacle replacement is something very few H.O.s will not do on their own.

Bob

 

[charlie b]

I strongly suspect that most homeowners (including half of the owners of my home) would not know that the numbers 12 and 14 describe the size of a wire, nor that there is any difference between one receptacle and another.

For my part, speaking as a long time home renter and/or homeowner, I have never once been unable to plug a flexible cord into a receptacle outlet, only then to discover that the plug was a different shape than the outlet. Put another way, I have never attempted to plug anything into a 15 amp receptacle, and have it not fit. I do not even know if I have ever held a 20 amp plug in my hand. What sorts of 120 volt single phase devices use a plug that would not fit into a 15 amp receptacle, but that would fit into a 20 amp receptacle?

 

[peter d]

What sorts of 120 volt single phase devices use a plug that would not fit into a 15 amp receptacle, but that would fit into a 20 amp receptacle?

I can't think of anything myself that you would find in a home.

Perhaps a large room AC, however, usually they are 240 volts. Maybe a large shop compressor, though those are usually hardwired.


I have only enountered a few things that had a 20 amp, 120 volt cord cap: A large table saw, and a PVC bender (aka: hot box). {The hot box had its cord cap "modified" by my former employer to fit a 15 amp receptacle. :roll: }