OK, I’m not a EE, and I’ve searched around a bit and I’m getting confusing and conflicting answers from folks online. Here is my question:
If I was to buy something like this clamp-on ammeter (Fluke Clamp Meter 323 | True-RMS Digital Clamp Meter | Fluke) and put it around the cable to by clothes dryer while it was running, what would it read? From my searching online, it appear it will either:
Read the true amps (which is what I want)
Read “0” amps because the two hot wires will “cancel each other out” to the view of the meter.
Read 2x the amps, for reasons which are not entirely clear to me.
Read 1.71* the amps, for reasons which are not entirely clear to me.
Read the works of Shakespeare in the original Russian.
Can someone help me out here? My goal is to find out how many amps my clothes dryer, air conditioner, and other 220V items use without having to open the units up and clamp around individual hot wires.
Warning: Answer based on a hazy memory of a project years ago:
These things work by measuring the magnetic field generated by the current flowing through the wire. If you put it around both wires, the current will be equal but in opposite directions, and thus will be generating equal and opposite magnetic fields. The device will then read zero.
As far as the 2x or 1.71x thing, you are probably getting confused with voltage here. 2x probably refers to the range from highest positive to highest negative, where normally we just refer to the 0 voltage to highest/lowest. 1.71x is likely referring to the RMS value of the voltage. As you are aware, the voltage in AC systems varies overtime. This makes it difficult to calculate power. The root mean square is a way to average the value, allowing you to get a constant V or I in order to use in power calculations.
Well, if you put it around the entire power cable, it will read 0 A.
You want to put it around one of the two hot wires. I don’t know much about driers, but it probably doesn’t matter which hot wire you use. (The heater and motor are the biggest users of power, and I *think *both are powered from 240 VAC, i.e. both are powered from the two hot wires.) The current the meter reads will be the current in the wire.
There *might *be things in your drier that are powered from one of the hot wires and neutral (120 VAC). Which means one of the hot wires may have more current than the other. But if this is the case, I wouldn’t worry too much about it, as I’m guessing anything powered from 120 VAC in your drier doesn’t use much power.
As for calculating real power, that can get a bit complicated. I would just calculate VA.
you need one current path to go through the clamp.
there are plug-in accessories to do this for 120V.
if your 220V cord is flat. with the cord unplugged make a small slit (using razor, carefulness to not damage insulation around conductors), in the thin area separating the conductors, to fit an arm of the clamp through. clamp up, plug in, turn on, read value. you would need to do that for each appliance.
And how to make the measurement. I guess I would just try pulling the receptacle out a few inches, and clamping around one of the hot wires going to the back of the receptacle.
Or open the breaker panel and clamp it around one of the wires coming from the dryer’s circuit breaker. That’s probably what I would do, to be honest. Just exercise caution when doing it, obviously.
the person at the breaker/fuse panel needing to know electrical safety and the insides of the breaker/fuse panel.
it can be a serious hazard to have things hanging or without stationary support in a breaker/fuse enclosure. a person should be holding the meter at all times.
using a clamp ammeter in a breaker box or at receptacles needs to be done with caution and having a person in control of the meter the whole time.
it is probably best for a person not experienced with working close to open conductors to find a way to take only with insulated wires because that is all that is needed.
OK, that sounds pretty much like I’m out of luck, as I did not want to be cutting into the wires or disassembling anything. I understand I might have to, but I do not think I will.
A follow-up question: does anyone know of something akin to a “Kill a Watt” meter to track power use, except for 220V? I have searched, and in vain.
I would think that just opening up the dryer is likely to be much safer than opening the breaker box or cutting into the wires. IANAElectrician, but on the couple of dryers I’ve changed the pigtails on, there’s a little metal access panel on the back held on with one or two screws. When you take it off you’ll see a wiring connector block where the individual wires in the pigtail connect. It should be pretty easy to put a clamp meter on the individual wires back there, assuming you can get behind your dryer while it’s running.
If the dryer was hooked up cleanly, the wires should be completely insulated going into and out of the wire block, so as long as you don’t touch the recessed screws on the connector block it should be pretty safe. I would definitely unplug the dryer before opening the panel, though since you don’t know what untrained schmoe (such as yours truly) wired the thing up.
What do you do for a living? I seem to associate your user name/ posting with some technical field. Maybe I’m remembering that wrong.
While I agree with johnpost and Crafter_Manwholeheartedly, depending the type of breaker box you have, it’s location (read: access), what type of direction you get from a pro, and how cluttered it may or not be in the panel itself, taking an amp draw inside the panel might be quite doable.
All electrical panels need to be treated with caution. But taking an amp draw is not nearly as involved as wiring something up, or pulling new wire etc.
Don’t the things have name plates giving the amps or watts? Of course, those usually give maximums. Some A/C units have a 2 speed set up and don’t always run at the maximum. I think electric driers and water heaters always are either full on, or off. Maybe water heaters have a separate thermostat for each element.
You also need to know how long things run to know how much power they use.
I have seen questions on a 240 volt Kill a Watt before, but don’t remember a source.
Driers and stoves are always wired up with a neutral for the lights, timer, and perhaps the blower in the drier.
True, but the clearances and access on the pig tail will be somewhat harder [potentially] than the panel if the panel has good access, is well lit and uncluttered.
I do this all the time, so I am biased, however. So…it may be better for him/her to unplug the unit and read from the pig tail.
Electrical code doesn’t allow extensions on dryers, but for limited-time experimentation it wouldn’t be a problem. The extension might make it easier to read the meter, also.
I am an expert on fossil power plants, boilers, combustion, coal, the environment, and have a Masters in Engineering and am a licensed Professional Engineer. I am not an electrician, nor have experience with electricity, and I took a single course in circuits for which I received a 79.9% which was rounded up to a “B”. I know my limitations and am not filled with hubris to just rush into popping a panel off without some research and preparation.
My breaker box is archaic and scary, more than 50 years old and has many odd, dead, possibly dead, and other wires with crumbling insulation. I have been trying for a year to replace it but as I’ve ranted many times before, I cannot get a contractor who is not either retarded, unethical, oppositional-defiant, or unable to read and write English for any amount of money.
I intend to do a series of experiments on my dryer and air conditioner for Cecil, and I didn’t want to be continuously opening things up and clamping them.
Yes, no problem you can get them herebut there is a catch. They won’t fit your US plugs. You could buy a US to Australian converter for one side and an Australian to US converter for the other, but it might start to get unwieldy.
Let me know if you want to do this and are having problems with shipping.
Can one even get an Australian 220V to US 220V converter, and the reverse? I mean, I’m sure someone makes them…since I could only use it on the dryer (the AC and oven have no plug I can get access to easily) I may choose the extension cord route.