Knowing the current is both legs doesn't tell you anything about power. The current is the same in both legs. If you put both phases in an amp probe, you will get double, but it is a useless value.
Get used to it! Also get used to the dick-waving, altho there is less of that here than it many places. I guess when one's house is falling apart, there's less active testosterone....
Ackshooly, I hadn't realized that this is what you were driving at in your original post, but mebbe it registered subliminally, and unknowingly was the root of my li'l sleuthing.
But it was a very good insight! And neat experiment. Altho, by reversing one of the wires you are approx. doubling the current reading. Your point proly didn't register because current directionality hadn't registered, cuz you normallly don't think of such in AC circuits. But indeed there is physical directionality in two wires, even if that directionality is at 60 Hz!
But, iirc, wasn't it multiple Kill-a-watt ditties we were talking about, not multiple clampons??
I'd say the more fundamental problem in how blueman is looking at things is that he's trying to add the current in the two hots as if they were totally different currents, or out of phase currents, etc. In fact, with a pure 240V load or a 120V balanced load, all he's doing is measuring the same exact current as it flows through the circuit. It's like counting the current twice in a flashlight, once as it enters the bulb, once at it leaves.
If the load has a 120V unbalanced component, then the current will be higher in one hot than the other, with the difference being in the neutral.
I agree, you could do the power calcualtion by using the sum of the current measurements in the two hot legs and then multiplying by
120Volts. Which gets back to what I said before, that to correctly calculate the power, you need to correctly factor in both the voltage and the current.To recap, let's say there is a 20 amp 240V load and a 3 amp 120V load on the circuit. You'd mesure 23 amps in one hot, 20 amps in the second hot, 3 amps in the neutral. So, per the formulas I gave above, by measuring the two hots you'd get P =3D 240VX20 + 120VX3. Or you could do it by adding the current measurements in both hots and then USING 120V, P=3D 120VX43
I don't know why you find this so interesting, nothing new here, it's just basic physics.
After trying to impress us by presenting basic physics as if it were something surprising, are you sure you want to start hurling insults?
Strange that nobody considered the COST of the machine. Suppose you buy a dryer for $500 which includes installation costs and it lasts 15 years. During its lifetime, it dried 2000 loads of clothes, making the average cost of the load (based on the washer's initial cost)
500/2000 = 25 cents a load. You have to add the depreciated cost to the energy consumed, unless you got a free dryer.
OK, I get it now. I think I'm set for life with a 200 amp service/panel in the garage.
I'd say the more fundamental problem in how blueman is looking at things is that he's trying to add the current in the two hots as if they were totally different currents, or out of phase currents, etc. In fact, with a pure 240V load or a 120V balanced load, all he's doing is measuring the same exact current as it flows through the circuit. It's like counting the current twice in a flashlight, once as it enters the bulb, once at it leaves.
If the load has a 120V unbalanced component, then the current will be higher in one hot than the other, with the difference being in the neutral.
I agree, you could do the power calcualtion by using the sum of the current measurements in the two hot legs and then multiplying by
120Volts. Which gets back to what I said before, that to correctly calculate the power, you need to correctly factor in both the voltage and the current.To recap, let's say there is a 20 amp 240V load and a 3 amp 120V load on the circuit. You'd mesure 23 amps in one hot, 20 amps in the second hot, 3 amps in the neutral. So, per the formulas I gave above, by measuring the two hots you'd get P = 240VX20 + 120VX3. Or you could do it by adding the current measurements in both hots and then USING 120V, P= 120VX43
I don't know why you find this so interesting, nothing new here, it's just basic physics. ==================================================
Mebbe, but I didn't see *you* mention the Biot-Savart law....... In fact, you're *still* multiplying volts x amps in various forms, when that wasn't even the Q. The Q was: why can't you put a clamp-on around *both* wires at the same time?
After trying to impress us by presenting basic physics as if it were something surprising, are you sure you want to start hurling insults? ======================================================
The surprise here, which has apparently gone clear over your head (much the same way climb/conventional cutting went over the heads of the above Assaholic Triumvirate), is how "basic" physics can be so neatly demonstrated by, well, an *appliance*.
If you aren't positively tickled by this clamp-on thing, then, well, you really don't appreciate "basic" physics, and anyone who doesn't appreciate "basic" physics proly doesn't understand "basic" physics.
In fact, imo, the very term "basic physics" is a kind of high-handed and pretentious dismissal of what the greatest minds in history labored for decades to develop. Newton himself did not properly grok "energy". Yet, you and your ilk will call energy/momentum "basic" or "simple".
Newton's Cradle
Btw, Wiki has a nice article on Newton's Cradle, which was in fact not invented by Newton, but was a wonderful homage to Newton by the inventor.
Imo, it is the philistine who confuses "simple" and "basic" with "profound" and "fundamental". And Einstein himself observed, If you think something is simple, you probably don't understand it.
Ultimately, "basic" physics is VERY surprising.
Excuse me, but the question under discussion was how to measure the POWER going to a dryer. At which point you posted this gem:
"I think the Kill-a-Watt EZ will do all that. I believe it measures instantaneous wattage AND accumulates kWhrs.... about $25 at Costco. I have one, but haven't used it yet. "
Which obviously won't work for a whole host of very simple reasons:
1 - The Kill-a-Watt is not a 240V device2 - Dryers far exceed the current limitations of your Kill-a-Watt
3 - The plug from a dryer won't fit into the Kill-a-Watt4 - The Kill-a-Watt will not plug into a dryer outlet
Need, I go on?
Then blueman posted this:
"I think the easiest thing would be to put a clamp-on ammeter on it
-- which shouldn't be too hard since one typically has easy access to the dryer end of the cord where the wires terminate. Don't forget to measure current in both legs of course.
Actually, with a clamp-on meter, would you get an accurate rating of
220v current if you clamped around both hot legs but with the direction of the wire in one of the legs reversed 180 degrees -- my thinking is that reversing the wire direction would make both currents appear in phase and hence be additive... "To which you replied:
"No, you still can't clamp around both wires. This is 220/240
*single phase* -- true, you are using two legs of opposite phase, but the net voltage is still single phase. Iow, there is single phase and three phase, but no two phase -- heh, funny how that works.But the clamp-on is a good idea, because it is esp. accurate on a purely resistive load -- no power factor to worry about. You would, however, have to subtract out the the motor current of one leg, tho. If one hot were reading 20 A, and the other leg were reading 16 A, the total wattage would be:
16 x 240 + 4 x 120 x .8 , where .8 would be a typical (inductive) power factor for motors. "In fact, both of you have parts of it wrong. Blueman is wrong because if it's 220v current he's measuring, there is no need to clamp around BOTH conductors. What is coming in on one is going out on the other. But if he did what he described, by reversing the direction of one hot wire, he'd be measuring 2X the actual current. And yes, he could calculate the power that way if he treated it as all 120V load instead of 240V load.
And you have it wrong, because despite what you said, he could do what he described. In fact, the measurement technique he described is exactly what you are now harping about as surprising physics.
It's also rather strange that you accuse me of talking about power, when you yourself answered about power and gave the correct power calculation.
Actually, it was why can't you put it around both wires at the same time after reversing one to measure the 220V current. The answer is still the same, if it's 220V current he's interested in, there is no need to clamp both. Just take the lower reading of the two. If it's all a 240v load, then they are the same. If not, the lower is the 220V current. And last time I checked, the standard is actually
240V, at least everywhere that I'm familiar with in the USA.
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Glad you've found something to amuse and fascinate yourself with. That's still no excuse for hurling insults at a bunch of us who did nothing to you. Did any of us launch off at you after that whopper about using the Kill-a-Watt meter on a dryer?
There's your problem. You've been tickling yourself too much.
Look, we're not solving Maxwell's equations here. The concepts involved with correctly measuring dryer current are basic physics.
It would also help if you could learn how to trim posts.
To tell you the truth, I thought it would be obvious that you multiply by 120v rather than 240v since each leg is obviously only 120v. My apologies for not mentioning that distinction if that confused people.
Also, indeed there *is* a need to clamp around both conductors since the
120v leg feeding the motor only goes through one of the conductors. So if you measure only one conductor and multiply by 240v then you either are missing the 120v component completely or you are mistakenly doubling its power contribution.You could do it in two steps. But the OP (or someone in the thread) mentioned that the power draw varied over time. So if you wanted to measure the power over time it might be easiest to clamp both wires in the way I suggested.
Anyway -- I think we all understand the point and I certainly have no desire to jump into the middle of a flame war here... But thanks to all who contributed positively to this thread.
The whole point is you *don't* get exactly double because the 120v leg feeding the motor only goes through one of the legs.
And calculating the power is a trivial calculation that follows from knowing the voltage in each leg (120v) and assuming a power factor (which I proved in the previous post can be assumed to be just 1 and not lose more than 1% accuracy). To tell the truth I'm puzzled why people seem to be hung up by the voltage which is the one known factor while the clear unknown is the current.
I got a free dryer...
Yes, I agree 100%
Yeah, but then you get a reading approx'ly double the true value!
Remember, in most cases, one hot is carrying only the heating element current, while the other is carrying the heating element plus the 120 V loads. Altho it is possible to have the 120 V loads distributed over both hots!
To check this, run the unit with air only (no heat), see what the power draw is on each hot. Usually one will be zero, but it could be that there is a little bit of current in each hot, even without the heating element, if they distribued the 120 V load..
But, with the heat off, and some draw in both hots, this *could* also indicate that the controls/motor are also 220V!! To rule that out, with the heat off, disconnect one hot at a time, see if everything goes off if *either* hot is removed. Usually, with one hot removed, everything except the heat will work, but if both hots are required for the motor/controls, then other stuff is operating at 220 in addition to the heating element.
Ultimately it's best -- and ultimately easiest -- to clamp each wire separately. You get more complete info this way. Clamp-ons are real cheap now, anyway -- used to be very expensive. $11 from HF -- I must have 6 of'em! Three are used to monitor the 3 phases on a rotary phase converter, the other three are in case I lose two.
The way to be able to use a clamp-on "at will", at least for 120 V circuits, is to fashion an adapter from a 2-prong plug with zipcord, going to a receptacle, and "split" the zip cord. Basically a mini-extension cord, with the cord split. Now, you can put the clamp-on easily around a single conductor.
You can do the same with a "regular" 220V plug/receptacle, but this starts getting a little expensive for 30 and 50 A plugs/receptacles.
Indeed. Hopefully Trader4 learned about Biot-Savart. :) :)
Oh, and to his comment about "we're not solving Maxwell's equations here....." Well, in a sense we did, cuz Maxwell's equations subsumes all those disparate experimental observations on E&M.
This whole thing really was a very neat, very elegant demonstration of physical principles. "Simple" for Trader, but neat for me.
I was gonna say that. A lot of people get a new matching set of washer and dryer even though the dryer still works fine. There are always free or cheap dryers available.
They are also fairly common I think as housewarming gifts from parents.
Which is why I would consider them as 120v legs (which I guess would implicitly be dividing by 2 for the 240v circuit portion).
May be possible but I am not aware of any units that do this -- do you know of any that are wired this way?
Personally, I haven't seen this on US units -- but I am no expert. Are you aware of any US brands that have 220v controls?
And you are less likely to make a mistake. I was just trying to suggest a "clever" trick. In practice, I too would have done each leg separately. In part, because it would give me the added information of being able to separate the
120v component from the 240v component (by taking the difference of the current in the 2 legs, assuming that the 120v current is not "distributed").Yup - I have a HF version -- but issue for me isn't price but room to store all the "wonderful stuff"/"junk" I buy at HF.
Actually, HF used to sell a cheap ($4.99) line splitter (#92072) that did effectively the same thing - they seem to have discontinued it. It also has two loops - one for 1x and one for 10x so that you can get better resolution of low currents. I found a pic of it on
No. I'm just a little bored, is all. :) Just an inneresting scenario for possible sleuthing.
No. I'm just a little bored, is all. :) :) More possible sleuthing.... :)
If you shop right, a cheap plug will be 50c, HD outlets are 50c, and the zip cord should be 12c. :)
It also
Now THIS is ingenious!!!! In Trader4-like hindsight, "super obvious", and I'm kicking myself for not having thought of it myself! Deeee-licious!! But more Biot-Savart!!! A potentially very useful little trick, and super-easy to do yourself -- just count loops for your multiplier!! Zip cord will loop just fine, too. Excellent!
So, here we have it again folks. EA goes around hurling insults at a bunch of us here and he once again shows us that he is totally clueless and doesn't understand basic electricity on a 240V circuit.
One more time: Blueman is 100% correct. You could reverse the direction of one of the dryer hot leads, put both wires in a clamp on amp meter and measure the current. But then you treat the total current as a 120V load when calculating the power. Both blueman and I have stated that at least 6 times. It's clearly explained by blueman right above. Do we have to draw cartoons for you?
Say you have 23 amps flowing in one hot, 20 in the other, 3 in the neutral. Using the above method you would measure 43 amps using the clamp-on. The power is 120V X 43 amps. Capiche?
You figure that out all by yourself? Geez, the clueless guy who told us to use a Kill-a-Watt meter on a dryer is now trying to explain to us how a 240V circuit works.
No need to run experiments, the rest of us here know this. Again, last time I checked, in the USA the standard we use is 240V. How the hell do you get 120V off one leg and 220V between the two? Where do you live?
You really think so? Instead of reversing wires to clamp them both at the same time or playing with your panel wiring, which you seem to find so fascinating? LOL
More likely they'll get smoked like that Kill-a-Watt when you stick them and your fingers someplace they don't belong.
So, here we have it again folks. EA goes around hurling insults at a bunch of us here and he once again shows us that he is totally clueless and doesn't understand basic electricity on a 240V circuit.
One more time: Blueman is 100% correct. You could reverse the direction of one of the dryer hot leads, put both wires in a clamp on amp meter and measure the current. But then you treat the total current as a 120V load when calculating the power. Both blueman and I have stated that at least 6 times. It's clearly explained by blueman right above. Do we have to draw cartoons for you?
Say you have 23 amps flowing in one hot, 20 in the other, 3 in the neutral. Using the above method you would measure 43 amps using the clamp-on. The power is 120V X 43 amps. Capiche?
========================================================
Except for one thing: iirc, Blueman explicitly stated that calculating power was not his agenda -- all he was simply speculating on was the viability of measuring current of two wires simultaneously with a clamp-on. And I never disputed the above arithmetic.
Btw, what was YOUR response to his speculation???? iirc, he stated your response was irrelevant, ie, you missed the point altogether. Altho he said this a little more diplomatically, wihch, in your case, was wasted diplomacy.
Your example above is arithmetically correct, but still near pointless, becuz, well.....in your example, you don't *have* 43 amps!!!! So yeah, the power would be the same, but who was asking?? Dats why people run shit at 240 V, to avoid large currents, which results in better efficiency, ito wire size economy, IR drop, I^2R power losses, etc.
You figure that out all by yourself? Geez, the clueless guy who told us to use a Kill-a-Watt meter on a dryer is now trying to explain to us how a 240V circuit works. =================================================
Just because you didn't figger out the Biot-Savart stuff is no reason to become a hater....
No need to run experiments, the rest of us here know this. =============================================================
How could anyone possibly know this without doint the experiment? If you have 20 A in one dryer leg, and 23 in the other, we are ASSUMING that difference of 3 amps is the 120 V load in one leg, and that 20 A is running at 240 V.
It COULD be 16 A of heater, 4 amps of 120 V load in one leg, and 7 amps in the other. OR, it could be a *mixture* of 120 V loads on one or both legs, 240V heater load, and add'l 240 V control loads.
Not saying this is likely, or that it makes design sense, but be very clear that you *could not* know for sure unless you did the sleuthing.... Well, not you....
Again, our assumptions are reasonable assumptions, and likely to be accurate, but not absolutely know-able without the experiment.
Again, last time I checked, in the USA the standard we use is 240V. How the hell do you get 120V off one leg and 220V between the two? Where do you live?
=================================================
Many electricians use 220/230/240 V interchangeably, and 110/115/120 V interchangeably, as the basic point is that single hot to ground is 1/2 the voltage between two hots. Don't be a nitpicker, don't be a hater....
And if the Assaholic Triumvirate want citations, just look at many motor nameplates, which will say "220-240", with no change in wiring. Some, I believe, can even tolerate 208-240. Others will have specific taps.
But you get the point..... well, mebbe you don't.... hating does that....
You really think so? Instead of reversing wires to clamp them both at the same time or playing with your panel wiring, which you seem to find so fascinating? LOL =========================================================
Heh, it was news to you, wadnit? Mr. Everything is obvious/oh-so simple in hindsight.....
More likely they'll get smoked like that Kill-a-Watt when you stick them and your fingers someplace they don't belong. ==================================================
Well, what I would love to do is pluck out a wire from my 3 ph control panel (which switches in multiple staged 3-ph motors, and a switchable bank of capacitors for voltage/load balancing), bring you over to fix it, and watch you spend the next two months tryna figger out WTF's going on.
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Now you're simply lying. Here again is the exact question that Blueman asked:
"But clamping measures current, not voltage. So clamping both wires (with the direction reversed in one wire so that the opposite phases cancel as I mentioned before) should give you a measurement of the total current. Then you can multiply by the voltage (or maybe rms voltage) to get the total watts consumed. "
So, it's very clear Blueman was interested in calculating power. And he also never stated that he wasn't. Liar.
Yes you did. Blueman had outlined how to measure the power using his method. And he was correct. You could reverse the direction of one hot, put them together in a clamp on amp meter and determine the power. In fact we had been through the math, how you need to then calculate the power using 120V and I thought the matter was settled.
But then you chimed in with this:
"Yeah, but then you get a reading approx'ly double the true value! "
I seem to recall your being a bit confused about the premise of the question, etc.
"Blueman asked a very good Q: WHY can't you measure both together? And, afaict, it wasn't the notion of voltage that he was missing, as you stated. And since you just repeated my answer, his Q wasn't really answered. But he also mis-stated his own premise, in a couple of ways. "
I'd also point out that voltage is an important part of the whole thing and if you take the sum of the currents in both hots, YOU THEN MUST USE 120V TO CALCULATE POWER, NOT 240V. But 20 posts later, you come back and start telling him all over again that if he uses his method he's going to be counting the current twice. Which by the way is also factually inaccurate, because he's only counting the 240V current twice, not the 120V component. Capiche?
Blueman was asking
More tellling us what we already know. From the genius that first told us to use a Kill-a-Watt meter on a dryer. And then suggested using 2 of them. But maybe there is hope for you yet. I see you are now finally starting to use the term 240V instead of using 220V. You do much looking at any of those meters you have?
Anyone who cares to look can see it was you who started hurling insults:
"Now, Ricodjour, SaltyAss, and ShittyTwo are proly getting blisters from their bunched-up panties, screaming, Liar, Where's the Citation????? Proly Trader would too, if he didn't already agree -- altho he don't know the physics, apparently. "
Just for the record the first 3 guys you insulted were not even part of this discussion. But I can assure you that all 3 of them know:
A - You can't use a Kill-a-Watt to measure power in a dryer
B - You can't hook up two of them, one on each leg either
C - Voltage pairing at a dryer is 240V/120V, not 220V/120V
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Because we understand basic electricity. Do you need to drive a car off a cliff to know it will fall? BTW, one more time, you can't have
220V and 120V on a dryer circuit. There's an experiment you can try.Sure, in the case of a theoretical load, that is true. However, it matter not a wit in terms of measuring the power of the dryer. As Blueman pointed out, if you measure the current on the two hot legs, you can then calculate the power. In your own example above, all we need to know is (20+23amps)*120V.
Maybe the dryer has a little built-in nuke to run it. Better go check that too.
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You're the only guy I've seen using the pairing 220V/120V.
And you call me a hater? LOL
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It was never news to me that the easiest thing to do was use a clamp on meter on one dryer wire at a time.
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If you're really screwing around with that kind of stuff, at least we won't have to put up with you much longer.
I don't understand the need to have matching washer and dryer. These appliances are typically hidden behind doors, garage, or utility/laundry room. A "matching set" does nothing else than increase appliance dealer profit. I can't recall ever having a "matching set," let alone the same brand.
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