1875W Appliances

[John Allingham]

I'm starting to see more advertisements for 1875W hairdryers like this one
http://www.walmart.com/catalog/produ...uct_id=3999276
Isn't 1875W too much for a bedroom circuit? Do breakers have a built in time delay that allows them to run for five or ten minutes with an overcurrent? If not, wouldn't the breaker trip immediately?

[Greg Fretwell]

Look at them like 5hp air compressors with 120v cords. It is a lie.
I put the amp probe on a bunch of hair dryers that say 1600, 1700 and 1800 watts. They are more like 1300 to 1400w.

[Jay Moge]

yeah but what about when it's 3 years old, and that little screen on the back is packed with lint, and dust. that alone will over heat a hair dryer and cause it to "trip" it's own little thermal switch. it cools down for 10 min. and you up and running again, but only for 3 min. how many watts does an 1800w hair dryer pull when stressed like that. maybe that's how they rate them, by the max for the thermal switch inside??

[Greg Fretwell]

They won't pull any more power dirty than they would pull clean. When you "throttle" an air moving machine the current draw actually falls (think of how a vacuum cleaner speeds up when the hose is blocked).
I am not sure how they come up with these numbers and since the actual is less than the labelled they don't run into listing issues.

[Jay Moge]

Originally Posted by Greg Fretwell

They won't pull any more power dirty than they would pull clean. When you "throttle" an air moving machine the current draw actually falls (think of how a vacuum cleaner speeds up when the hose is blocked).
I am not sure how they come up with these numbers and since the actual is less than the labelled they don't run into listing issues.

another one of those little things in life that doesn't make sense but is true. like eating more food in smaller portions and more frequent meals will help you loose weight. or how turning a light switch on and off uses more power than leavin it on. sounds like 2 more "Myth Buster" challanges to me.

[ddelaney]

Originally Posted by Greg Fretwell

They won't pull any more power dirty than they would pull clean. When you "throttle" an air moving machine the current draw actually falls (think of how a vacuum cleaner speeds up when the hose is blocked).
I am not sure how they come up with these numbers and since the actual is less than the labelled they don't run into listing issues.

Greg,

I would be inclined to disagree with this. Although the analogy of the vacuum cleaner is true, the hairdryer has purely resistive elements, which will have a higher resistance when less air is passed over them, creating higher power consumption. And, because the voltage is the constant (P=i*e), amperage also inclines proportionally.

Therefore, the less air flow, the more wattage consumed. So make your ladies keep them puppies clean !

[Jay Moge]

Originally Posted by ddelaney

Greg,

I would be inclined to disagree with this. Although the analogy of the vacuum cleaner is true, the hairdryer has purely resistive elements, which will have a higher resistance when less air is passed over them, creating higher power consumption. And, because the voltage is the constant (P=i*e), amperage also inclines proportionally.

Therefore, the less air flow, the more wattage consumed. So make your ladies keep them puppies clean !

I LOVE when my wife cleans her puppy.

[Greg Fretwell]

Originally Posted by ddelaney

Greg,

I would be inclined to disagree with this. Although the analogy of the vacuum cleaner is true, the hairdryer has purely resistive elements, which will have a higher resistance when less air is passed over them, creating higher power consumption. And, because the voltage is the constant (P=i*e), amperage also inclines proportionally.
!

The flaw in your logic is summed up by Mr Ohm. If R increases. I decreases and that shows up as a proportional decrease in power.

The reality is, if this element gets much hotter than the design temperature, the thermal fuse blows and she tosses the dryer. It becomes dangerous when some guy who is handy with tools jumpers out the fuse.

[Russel Ray]

Originally Posted by Jay Moge

turning a light switch on and off uses more power than leavin it on.

I haven't heard that one.

I have heard and seen test results that light bulbs last longer if you don't turn them on and off. Rarely does a light bulb burn out while it is on; they always burn out when you flip the light switch on. So one then has to do the calculations of

longer-lasting light bulb using more electricity because it's constantly on but buying fewer light bulbs

versus

shorter-lasting light bulb using less electricity but buying more light bulbs.

I haven't done the calculations yet (and never will, Ms Margarta's demands notwithstanding), but I prefer to turn my lights on and off. As my wise ol' grandmother taught me, "If it is on, then it is using electricity."

[Greg Fretwell]

The on/off thing refers to old style flourecents (ferro ballast). They take more current to start than they use running but I think the crossover time is in minutes, not hours.

[Paul W. Abernathy]

As greg said most have a listing but usually pull much less, however we are to take into ACTUAL listing consideration when we wire for these items.

This is why the concept of hair dryers in the bathroom requires a 20A circuit...if you state it is just on the bedroom circuit then a problem lies their since it really depends on what ELSE is on and running on that branch circuit.

Within the bathroom....in new construction the bathroom should have a 20A circuit minimum....and would allow the operation of the hair dryers with no problems...unless of course you were prior to 99 NEC when many put bathroom GFCI's and outside GFCI's on the same circuit....

But I digress.....gotta run......guys are calling and moaning I am not at the job

[Jay Moge]

Originally Posted by Greg Fretwell

The on/off thing refers to old style flourecents (ferro ballast). They take more current to start than they use running but I think the crossover time is in minutes, not hours.

i was reffering to the fact that while in electrcity "101" in high school, we hooked up 2 incondesent light rigs to 2 seperate meters. both meters measured accumilated power usage and were identical. on one rig we left the light on for one minute. the other we flicked the switch on and off repeatedly for one minute (about 120 flicks). i can't remember the actual numbers but i do remember that the "flickering" light rig used about 50% more power in that minute. the teacher said it was because the bulb draws more power to light up than it does to stay lit. it made sense to me at the time, and i've always beleived it. is this wrong Greg? i don't want to keep using this as an example if it's wrong.

[Greg Fretwell]

I am not sure that is relevent to any real world experience. There may be a short spike on start up because the filiment draws more current until it is hot but that is a pretty small amount over the course of the average time you leave the light on.
If we were willing to say 500ms cycles was worst case and it was 50% greater for that 500ms the crossover time (when it becomes cheaper to turn off the light and take the "start up" hit again) is about a second and a half.

[Jay Moge]

Originally Posted by Greg Fretwell

I am not sure that is relevent to any real world experience. There may be a short spike on start up because the filiment draws more current until it is hot but that is a pretty small amount over the course of the average time you leave the light on.
If we were willing to say 500ms cycles was worst case and it was 50% greater for that 500ms the crossover time (when it becomes cheaper to turn off the light and take the "start up" hit again) is about a second and a half.

understood. thanx.

[John Allingham]

Originally Posted by jallingham

I'm starting to see more advertisements for 1875W hairdryers like this one
http://www.walmart.com/catalog/produ...uct_id=3999276
Isn't 1875W too much for a bedroom circuit? Do breakers have a built in time delay that allows them to run for five or ten minutes with an overcurrent? If not, wouldn't the breaker trip immediately?

Hey, how did my thread get hijacked by light bulb discussions. Get your own thread (just kidding).