Troubleshooting questions

Status
Not open for further replies.
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
100212-0520 EST

zappy:

Yes, 10 amperes thru #12 copper wire will produce about 16 MV drop across any 1 foot section you want to measure.

Make two test probes with a 3 prong plug on each. Connect the test lead wire, I use Belden 8521 stranded #16 because I have lots of this in stock, to the neutral pin in the plug. These might be 6 ft long. Get some banana plugs or just use your normal clip leads to connect to these probe wires.To extend one use a standard extension cord.

Find two outlets on the same circuit where you can guesstimate the wire size and length. Connect your meter to the two outlets thru these leads.

With no load on that circuit your meter reading should be close to 0.0 MV. Now plug a 1500 W heater into the other half of one of the outlets. Does the meter reading change by very much? If not the heater is on the source side of the two outlets. Now move the heater load to the other outlet. If the previous assumption was the case, then this voltage will be much larger and if you do not measure the current to the heater assume it is 12 A. Then calculate your wire length.

If the length seems excessively long, then you might have some bad connections. Use 0.0016 ohms per foot for #12 copper and for #14 use 0.0025 ohms/ft. If you want the values for aluminum look up the ratio of aluminum to copper.

I also have plugs with the hot brought out, and others with the EGC. Finally one plug with hot and neutral brought to a dual banana plug, another with hot and EGC, and last neutral and EGC.

All these plug cable assemblies need to be properly labeled or color coded.

You may want to use shrouded banana plugs.

.
 
Last edited:
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
zappy said:
So if I had a one ft. piece of 12awg wire, with ten amps on it, put one lead on one end, and one on the other end, I would have a reading of 16mv drop?
Click to expand...
Yep, and if you did the same thing with each segment of the circuit, including across the load itself, and even the drop across the breaker, and added them all up, the total of the individual voltage drops would equal the supply voltage. That's what fall-of-potential is.

The voltage across the length of one conductor will approximately equal that across the other one, so for each volt the hot conductor's voltage-to-earth sags away from the full supply voltage, the voltage on the groundede conductor rises away from zero volts.

That's why a grounded conductor can not be relied upon to be at zero volts to earth, which is also why we cannot use the neutral as a reliable EGC. It's expected to have some voltage on it, and that's when it's functioning properly. Open it, and the EGC becomes energized.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Strahan said:
If you can and it has probably been mentioned string a run of romex from the panel to the recep in question and take readings.
Click to expand...
Or just plug a 3-wire extension cord into a known-properly-wired receptacle on another circuit, preferably a single-outlet one, such as the laundry, or one you temporarily install at the panel.
 
Strahan

Strahan

Senior Member
Location
Watsontown, PA
This may be a little off course, but.... Personally I am a fan of wiggy's (solenoid tester). All through school it was driven into me that the wiggy was the industrial electricians meter of choice and in a lot of cases it is (as well as any electrician). But now that I've entered into a different field of electricity (controls PLC's etc...) I find that the solenoid testers can be harmful to the triac outputs of certain PLC cards (CEMF). Is there something out there besides the old handy dandy light bulb that can be used? I tell my guys all the time if you connect your fluke 87 across a triac output you will read 120 or something voltage. Load it down and suprisingly there is nothing.
 
Status
Not open for further replies.
Top