Why do >15A devices not have 20A circuit plugs on them?

dirtynails

Member
Location
NJ
A newish tenant texts me to say she keeps blowing her circuit breaker. Now, this is an old unrenovated apartment with 15A only circuits. And she's got an 1875W blow dryer! That's over 15A no matter how you slice it, and as I understand code, you shouldn't have a device pulling a steady load over 80% of circuit rating, right? The 1875W rating seems expressly designed to keep just under 80% of 20A.

I've told her she needs to get a 1200w blow dryer. But my question is: how is this hazard even possible, isn't this the reason 20A receptacles and plugs exist, to keep this from happening? Why does the 1875W device not have a 20A plug that won't go in a 15A receptacle? Even if I had a 20A bath receptacle circuit, it would have made no difference, she was doing her hair in the bedroom!
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Why does the 1875W device not have a 20A plug that won't go in a 15A receptacle?
Because we're generally allowed to use 15a receptacles on 20a circuits, but I do see your point here, electrically.

Even if I had a 20A bath receptacle circuit, it would have made no difference, she was doing her hair in the bedroom!
Then your response would be "you have to use this in the bathroom." So run a new 20a circuit to the bedroom.
 

dirtynails

Member
Location
NJ
Because we're generally allowed to use 15a receptacles on 20a circuits, but I do see your point here, electrically.
Then your response would be "you have to use this in the bathroom." So run a new 20a circuit to the bedroom.
Using 15a receptacles on 20a circuits is not the issue, since if a >15A device actually HAD a 20A plug it wouldn't go in, would it? It just seems so contrary to all the safeguards of the code to allow the mfr to put a 15A plug on a 17A device. And rewiring is not really practical for this middle floor apartment short of a really major reno. It WILL happen, but not with a tenant in place.
 

GoldDigger

Moderator
Staff member
1825 watts at 120V nominal would be 15.625A, so, yes it is higher than 15A. Note however that it is not a continuous load, so it would be more than acceptable on a 20A breaker and very close to acceptable on a 15A breaker. In fact it would likely not trip a 15A breaker in less than a few minutes as long as there were no other loads on that circuit.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Using 15a receptacles on 20a circuits is not the issue, since if a >15A device actually HAD a 20A plug it wouldn't go in, would it? It just seems so contrary to all the safeguards of the code to allow the mfr to put a 15A plug on a 17A device.
You are correct but unless the people that list these items get on board it will stay the same.

Roger
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
The point is if a 15 amp device is rated 15 amps then the unit should have a 20 amp male end on it. I have seen this alot.
 

JFletcher

Senior Member
Location
Williamsburg, VA
With hair dryers, they perhaps have inflated wattage ratings from the manufacturer to appear more powerful... It's like getting a 5 horsepower compressor from Sears that runs fine and continuously on a 15 amp circuit. 5 horsepower is like 3800 W, yet it never trips the breaker or melts the wiring or plugs or anything.

Short of a place like a beauty salon where hair dryers may on more or less continuously, hair dryers are not continuous loads no matter how you cut it.
 

jaggedben

Senior Member
I just looked at one. There is no amperage rating. All that's on the unit is 125V 60Hz 1875 watts. They have been that way for many years, so there must be some kind of loophole allowing them.
To repeat Wayne's math from above...

125V * 15 A = 1875W

So your device is rated 15A exactly. That's the loophole.

I wonder if voltage is running high on the OP's service.
 

dirtynails

Member
Location
NJ
With hair dryers, they perhaps have inflated wattage ratings from the manufacturer to appear more powerful... It's like getting a 5 horsepower compressor from Sears that runs fine and continuously on a 15 amp circuit. 5 horsepower is like 3800 W, yet it never trips the breaker or melts the wiring or plugs or anything.

Short of a place like a beauty salon where hair dryers may on more or less continuously, hair dryers are not continuous loads no matter how you cut it.
So it appears Jfletcher is right on, a cheap Conair 1875w dryer I have actually puts out 1475W! 12.85A @119V acccording to my Killawatt. Of course her dryer may be closer to rating. Amazing they can simply lie like that.

How is a hair dryer not a continuous load if it's running for at least 10 minutes. I thought "non-continuous load" was motor startup and the like momentary draws. So shouldn't drawing even 100% of rated load for ANY length of time be disallowed? Like I said, it sure looks like the 1875W units are designed to stay under 80% of 20A.

Here's a question, please try not be horrified. The breaker in question is a screw in replacement for glass fuses. (yes, a new riser and panel is due when the place is renovated, I haven't just replaced the panel because the new one will be in a different location). Could this breaker "break in" from being tripped too many times and start to trip at lower current levels? I have already replaced it with a new one, and am waiting for her report.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
So it appears Jfletcher is right on, a cheap Conair 1875w dryer I have actually puts out 1475W! 12.85A @119V acccording to my Killawatt. Of course her dryer may be closer to rating. Amazing they can simply lie like that.

How is a hair dryer not a continuous load if it's running for at least 10 minutes. I thought "non-continuous load" was motor startup and the like momentary draws. So shouldn't drawing even 100% of rated load for ANY length of time be disallowed? Like I said, it sure looks like the 1875W units are designed to stay under 80% of 20A.
I
Here's a question, please try not be horrified. The breaker in question is a screw in replacement for glass fuses. (yes, a new riser and panel is due when the place is renovated, I haven't just replaced the panel because the new one will be in a different location). Could this breaker "break in" from being tripped too many times and start to trip at lower current levels? I have already replaced it with a new one, and am waiting for her report.
Oh those Minor details....
 

Strathead

Senior Member
So it appears Jfletcher is right on, a cheap Conair 1875w dryer I have actually puts out 1475W! 12.85A @119V acccording to my Killawatt. Of course her dryer may be closer to rating. Amazing they can simply lie like that.

How is a hair dryer not a continuous load if it's running for at least 10 minutes. I thought "non-continuous load" was motor startup and the like momentary draws. So shouldn't drawing even 100% of rated load for ANY length of time be disallowed? Like I said, it sure looks like the 1875W units are designed to stay under 80% of 20A.

Here's a question, please try not be horrified. The breaker in question is a screw in replacement for glass fuses. (yes, a new riser and panel is due when the place is renovated, I haven't just replaced the panel because the new one will be in a different location). Could this breaker "break in" from being tripped too many times and start to trip at lower current levels? I have already replaced it with a new one, and am waiting for her report.

Your mission for today, should you choose to accept it, is to read the definition of "Continuous load in article 100 of the NEC. There you will find your answer Padawan.
 

JFletcher

Senior Member
Location
Williamsburg, VA
So it appears Jfletcher is right on, a cheap Conair 1875w dryer I have actually puts out 1475W! 12.85A @119V acccording to my Killawatt. Of course her dryer may be closer to rating. Amazing they can simply lie like that.

How is a hair dryer not a continuous load if it's running for at least 10 minutes. I thought "non-continuous load" was motor startup and the like momentary draws. So shouldn't drawing even 100% of rated load for ANY length of time be disallowed? Like I said, it sure looks like the 1875W units are designed to stay under 80% of 20A.

Here's a question, please try not be horrified. The breaker in question is a screw in replacement for glass fuses. (yes, a new riser and panel is due when the place is renovated, I haven't just replaced the panel because the new one will be in a different location). Could this breaker "break in" from being tripped too many times and start to trip at lower current levels? I have already replaced it with a new one, and am waiting for her report.
The higher wattage rating maybe with a dead cold heating element in it... For those few seconds, it may actually achieve its wattage rating at the voltage listed. As that element heats up though, its resistance increases, and the wattage decreases. Therefore the manufacturer claim is not really fraud. The rating could also be achieved at 125 or 130 volts, which are common but above nominal voltages. 1875 Watts exactly 15 amps at 125 volts.

Continuous load by definition, as you've probably already found out by now, is 3hrs or more.

A 15 amp breaker should hold a 15 amp load indefinitely... However if you had a constant load, like an exterior light that never shut off, you're only allowed to use 80% of the breakers ampacity.

Screw in breaker replacements for fuse sockets? I have never run across one, we'll have to do some research on that.

And yes, breakers can trip at lower values then their designation, though it is very rare.
 
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