190929-2330 EDT
Eamp:
You need to do some basic experiments so that you get a feel for how things work. These I will call bench tests.
Study up on ohms law first.
An experiment I suggest is with a 250 ft roll of #14 copper Romex, your hairdryer, or a 1500 W heater, a couple voltmeters that resolve 0.1 V at 120 V, and an ammeter.
Leave the Romex coiled.
Connect a duplex receptacle at one end where you plug in the resistive load. Provide enough exposed copper at the duplex to connect voltmeter test leads to the wires. Better to be directly on the wires from a well designed experiment perspective.
At the input end provide some exposed copper for voltmeter test lead connection. Insert an ammeter in series at the input end. Provide a switched 120 V 60 Hz AC source to the input end.
Now you can perform various experiments.
Current thru copper wire creates heat and an increase in resistance with heating. The heater likely uses nichrome wire and this has about a 10% increase in resistance as it heats from room temperature to its orange glow. Take quick readings or wait until a reasonably steady state condition exists.
Running such an experiment on a 250 ft roll I got the following results:
1. Fluke 27 loop resistance measurement with the far end shorted was about 1.2 to 1.3 ohms. Correlates with published information for 20 deg C.
2. Input voltage 118.2 V, load voltage 103.8 V, at an I of 12.1 A.
3. Calculated resistance (118.2-103.8)/12.1 = 14.4/12.1 = 1.19 ohms. A good correlation.
You can make other measurements in this test circuit, change wire length, and change the load.
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