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I have a 240 V dryer which when measured with an ammeter has 24 A on one leg and 22.7 A on the other. If the ammeter is kept in place, one leg drops to 13 A, and the other leg drops to 4.5 A.

Because my home has the neutral landed on the ground, I believe that the delta between the two legs when they are in the 13/4.5 A mode is lost to ground. Regardless whether that's the case, should this dryer have vastly different current measurements on the two legs at the same time? Seems a bit hinky to me.

As you can see from the pictures, I'm measuring the same wires with different currents (24 A on the black conductor, and then 13 moments later. 22 A on the red conductor, and then 4.7 A at the same time the black wire drops to 13). I checked the connections on the back of the dryer. Everything is copacetic there. I had an appliance technician come out, and he says that the dryer is 100% operationally correct from his perspective. I am very interested in hearing people's thoughts.

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  • What problem are you trying to solve?
    – isherwood
    Commented Feb 25, 2021 at 21:18
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    I'm trying to find an energy hog. I have a 2500 square foot house that consumes 37,000 kWh per year, and my friend has a 2500 square foot house down the street that consumes 12,500 kWh per year. I believe that the delta in amperage between the two legs is going to ground via the neutral which is potentially wasting 750,000 Wh to 1,000,000 Wh per year (or more).
    – Allen Stanion
    Commented Feb 25, 2021 at 21:28
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    @AllenStanion, is there a difference in insulation between the two houses? How often does your HVAC system run compared to theirs? Is their furnace/water heater/range gas, and yours electric? I think one of those is a much more likely culprit than a dryer, unless you do a whole lot more laundry than a typical household.
    – Nate S.
    Commented Feb 25, 2021 at 21:44
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    If you suspect the dryer is using power while it's off, (which I sincerely doubt) just keep its breaker off except when you are actually using it. I'll bet it makes no difference in your use, and that you have actual loads that you are failing to think of, or have not found (a hot water leak in a place where you don't notice the leaking water will use a HUGE amount of power from an electric water heater, for instance. Electric resistance heating of the house will use a huge amount of power. The latter would follow temperature annually, the former not so much.)
    – Ecnerwal
    Commented Feb 25, 2021 at 21:48
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    Please ask a different question about your mystery power hog load question, and make it a good one by documenting how the 37 megawatt hours are distributed around the year, and your climate at the times of year, along with details of how your house is heated, where your hot water comes from, and if you have any loads like a walkway or steps you never need to shovel snow from due to the electric heating cables embedded in them.
    – Ecnerwal
    Commented Feb 25, 2021 at 22:07

4 Answers 4

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Dryer connections have 2 hots, and neutral, and often a safety ground.

Anything since 1990? 1996? requires neutral and ground as separate wires.

Dryers do NOT connect "2 hots and ground", if you thought that, that's incorrect unless you're dealing with a Philippine-model or 5-continent model dryer made for 230/400V.

(the Philippine model dryers are typically North American dryers reconfigured to run on 240V-only, by adding a transformer to support 120V loads and using a 240V tumble motor. The Philippine government requires people in the former American-built districts stop using neutral; to harmonize the whole country to Euro-style 230/400V power.)

Those numbers

24A - 1.3A - 22.7A

That's perfectly normal draw for a dryer. The 22.7A is the heating coil, and the 1.3A is the tumble motor and miscellaneous 120V electronics.

13A - 8.5A - 4.5A

Exceedingly improbable on a dryer circuit. 99.9% of dryer circuits are dedicated circuits that serve only the one 30A receptacle. (mind you 30A circuits are allowed to supply as many 30A receptacles as they please; just 99.9% of the time, they do not).

Now, 13A@120V + 4.5A@120V is 2100W, which is a lot of heat - about 1-1/2 hair dryers going full tilt. So the point of loss will be rather warm.

We can cross off the dryer. First, there's nothing in a dryer that could possibly draw 8.5A of imbalance current (tumble motor stalled and pulling LRA???? It would burn up quickly) and nothing that would draw only 4.5A of 240V that wouldn't also burn up from lack of air movement. (I assume you'd hear the blower running?)

So job 1 is chase that circuit and find out what else is on it. Other 30A receptacles are allowed. Sockets of any other amperage are not allowed. Nothing hardwired should be there either (because it with the dryer would overload the circuit - and why isn't that happening, by the way?)

I don't see anything wrong with your ammeter reading methods. Klein is a perfectly respectable vendor, and the "dryer on" readings are right in line.

Also, get rid of that Square D breaker.

It doesn't belong in a GE panel and will burn up the bus. GE breakers only (or Eaton CL type not BR). The correct GE "THQL2130" is $10.

Ditto that Murray breaker at bottom right, again a THQL1120", $5-ish.

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    +1 for the good catch of alien breakers. But I'm not so sure a US dryer would never be so unbalanced. If it has multiple heat level settings, on some of the cooler settings it may indeed apply only 120V to some of its heating elements. That's a perfectly valid, inexpensive way to modulate heat output with only relay switching.
    – Nate S.
    Commented Feb 26, 2021 at 0:39
  • @NateS. but a 240V element on 120V gives 1/4 the heat. That's such a steep drop-off that it's usually a waste of time; you're better off having a 2800W and a 2400W element (and switch one off) than having a 2000W and 3200W element (and power the 3200W element on 120V.) It's not like you can cut down to a single element that'd be 5200W, on 120V that would be only 1300W.
    – Harper - Reinstate Monica
    Commented Feb 27, 2021 at 18:44
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Those numbers seem fairly reasonable -- dryers often have a mix of 120V and 240V loads, and the exact current draw on each leg at a given time probably has a lot to do with the dryer's settings and place in the cycle. Typically the heating elements are 240V and the tumble motor is 120V, and each of those might use more or less depending on the heat and speed settings. 240V loads will appear evenly on both hots, whereas 120V loads will appear on only one of the two.

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  • One of my questions is, does the difference between 13 amps (1,560 Watts) and 4.7 amps (564 Watts) which equals 996 watts go directly to ground as my neutral and ground are connected in the box? It's my understanding that the neutral carries the unbalanced load between the 240 legs to ground...
    – Allen Stanion
    Commented Feb 25, 2021 at 21:34
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    @AllenStanion, I think you're a little confused about how the neutral works. It is bonded to ground, but it also goes to the neutral connection on the utility transformer. That's where your neutral current is going -- nothing's going "to ground", and no energy is wasted -- your dryer is using that power.
    – Nate S.
    Commented Feb 25, 2021 at 21:41
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    @AllenStanion In theory, your dryer is pulling 1,560 watts (corresponding to 13 amps) from one leg and 564 watts (corresponding to 4.7 amps) from the other leg, so it's pulling a total of 2,124 watts from the box. The difference between those two power values is irrelevant and insignificant. It's also producing 8.3 amps on the neutral wire, but those 8.3 amps correspond to 0 watts, because the voltage of the neutral wire is 0. No power is going into the ground.
    – Sophie Swett
    Commented Feb 25, 2021 at 21:50
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    In reality, the situation is slightly different from what I just described, because the voltage on the hot wires is not exactly 120 V, and the voltage on the neutral wire is not exactly 0 V. The dryer is probably pulling a little bit more or a little bit less than 2,124 watts, and it is probably losing a little bit of power (5-10 watts? dunno) into the neutral wire. If I'm not mistaken, most of the lost power is absorbed by the wires themselves and converted into heat.
    – Sophie Swett
    Commented Feb 25, 2021 at 21:55
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Dryers (in the USA/Canada) typically have 120V and 240V components in them - otherwise they would not need a neutral wire.

For ANY 120V-0V-120V (240V with neutral) connection on this type of system, be it a dryer or a sub-panel, the hot wires (120V from neutral, which is grounded) carry the power. The neutral wire carries only the imbalance between hots. So:

If you only had 240V components, current in L1=L2 and neutral current = 0 Power is that current (once) times 240V (or that current twice, times 120V which is the same.)

Since you don't only have 240V components, you have an imbalance equal to the 120V draw on one line that is not matched by an equal 120V draw on the other line. That current is carried on the neutral. Given that a dryer switches various things during it's cycle, the current imbalance may vary. The power is L1 current * 120V + L2 current * 120V. If the dryer is not sucking down vast amounts of current when it's switched off (it would get quite warm, even hot if it was) it's not your "mystery power hog load" and it's very likely that your mystery power-hog load will be something blindingly obvious once you notice it.

tldr: An imbalance between hot leg currents is perfectly normal and in no way a smoking gun for 37MWh/year.

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This seems out-of-balance to me. As previously stated, there is the heater circuit which (for a traditional dryer) is either on or off, and controlled by a thermostat. This circuit is across both hots, and should not even have a neutral connection. The tumble motor is on one hot leg. Its current flows through the one hot and neutral. When the heater is switched off, you should have zero current in one hot leg, and only the tumble motor current flowing in the other.
So I would expect with the heater on: Heater current in one leg (22.7A), Heater current plus motor in other leg (24A)
With heater off: No current in one leg (0), motor current in other leg (1.3A)
Perhaps try disconnecting the thermostat and see what readings you get. You should only see the motor current in one leg. There may be a small amount of current in one leg or the other, whether it's a computer controller board (from a transformer) or a timer motor on the dryer.

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