Ohm’s Law, Clamp Ammeter, Line Splitters, and Heaters (and Honorable Mention for the Receptacle Strip)

We have a few 120V plug-in heaters. One, a Dairy Heater, still available, and the other a Honeywell, the Honeywell is much quieter. Pictures of the Heaters were found online from Ebay Auctions, but the name plate shown with each Heater is from ours.

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Notice the Dairy Heater has the Wattage Marked on the control on the front, the Honeywell has Fan, Low, Medium, and High Heat. If I couldn’t find the instructions, or if I wanted to find out if the Heater was properly working, I can use the following technique to verify the Current on Each Setting, Calculate the Wattage, and Compare.

E=IxR is the Basic Ohms Law formula.
E=Voltage I=Current R=Resistance (Voltage equals Current Multiplied by Resistance)

This formula is for Resistive Circuits, the heaters here are Resistive.

There is also Impedance, essentially Resistance for Inductive Circuits, but that’s dependent on Frequency as well. But for all practical purposes, most Heaters are Resistive.

But other formulas derived from E=IxR

P=IxE is the one we’ll be using.
P=Power I=Current E=Voltage (Power= Current Multiplied by Voltage).

There’s also (and more)

I = E/R




But to get these values, you need to Measure them. The Voltage is 120V, we can assume that. Resistance changes when hot, increasing in value, so measuring cold may not produce the desired values. Let’s measure the current with the Heating Elements on.

The safest, easiest way is with a Clamp on Ammeter.

But, for most; though there were a few models that would measure using both conductors; Clamp Ammeters, going across both conductors reads zero, or nearly zero amps.


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To Facilitate Measurement, a Splitter is used, it separates the conductors, and has two sections, one is x1, the other x10. Using the x1, the current read on the meter is the actual current. Using the x10 the Meter Reads 10 times the value, so the displayed amount needs to be divided by 10 for the actual reading.

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Using it is easy peasy. You turn off the desired appliance, unplug the 120V Plug, Plug the Line Splitter into the 120 Volt Receptacle (there are no active circuits on the Line Splitter, the Current is just being passed through to the Receptacle end) and Plug the Appliance into the Line Splitter.


The above is where I took the measurements on the Dairy Heater. It used to be on the floor, but I mounted it to the side of a Microwave Cart we use as a portable shelf. The Meter is in the x10 Position. The Heater Plug is on the bottom of the picture.

The Receptacle, we use a few of these around the house, we plug things in that can be turned off nightly, and we shut them off prior to bed, or to going out. It eliminates the likelihood that transformers, chargers, etc., will ignite when no one is near to see it.

Yellow Power Strip

This one, slightly different internally than the former one, is in the bedroom. The Honeywell Heater has the Replacement Plug shown, the plug didn’t burn up from use, it was showing signs of insulation breakdown from excessive flexing over the years.

My Upstairs Heater Draws about .2 Amps on Fan, and 5/7.5/12 Amps on the three heat settings.

What wattage is it delivering?

We’ll ignore the .2 Amps. Technically, it needs to be subtracted from the Heat Setting Values, as it’s on when they are on, but it’s low enough to ignore, and much of it is converted to heat in the motor, so to a degree, it’s heating too.

Remember, Honeywell has Fan Only, Low, Medium, and High Heat.

P=IxE works out as:

5 x 120 = 600 Watts

7.5 x 120 = 900 Watts

12 x 120 = 1440 Watts

Here are the readings for the Dairy Heater. The images are upside down to facilitate reading. The Heater has Fan Only, 1300, and 1500 Watt Settings. Each left to right image is the reading on the x1 position and the x10 position.


So, P=IxE works out x1 as:
.2 x 120 = 24 Watts (Fan Only)
10.3 x 120 = 1236 (1300 Watt Setting)
11.8 x 120 = 1416 (1500 Watt Setting)

And P=IxE works out x10 (rounded) as (after the display result is divided by 10):
.23 x 120 = 27.6 (Fan Only)
10.2 x 120 = 1224 (1300 Watt Setting)
11.7 x 120 = 1404 (1500 Watt Setting)

Since I did not measure the voltage, I can’t really say if the above numbers are as accurate as possible, but it’s close.

The x10 comes in handy for very low current draws on some things, since the meter resolution may be poor, digits wise, as in the meter shown. It only has one place after the decimal. The motor draws .2 Amps on the x1, and 2.3 Amps on the x10, but 2.3 divided by 10 is .23 we’ve gained a little more knowledge of the actual current.






Author: Dr-Artaud

A Doctor that is not a Doctor, but named after a character in the movie "No Such Thing", as is the Avatar.

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