Voltage drop testing

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yursparky

yursparky

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WA
Anybody have any recommendations how to test for voltage drop in the field? Specs require to test for percent voltage drop at convenience receptacles under 15A load. For test instrument: digital wiring analyzer with digital readout or illuminated LED indicators of measurement.

I'm asking is there any device manufactured for such tests, or is it as simple as plugging in 1800W heater and checking voltage with my Fluke/Wiggy. Just trying to come up with something that would look semi-pro, if I have to show it to the owner :cool: :smile:

BTW, a value of 6 percent or higher is not acceptable.
 
080916-1126 EST

yursparky:

Use a Fluke that can resolve 0.1 V at 120. Plug this into the most remote outlet (at end of circuit). Read the voltage. Apply a known load current. Consider a 1500 W heater. Mine is 10.6 ohms at 118 V, lower with no current. Use an ammeter to measure the current or if you determine what your load resistance is at about 120 V, then you can calculate current.

When you know the change in voltage for a change of current, then you can calculate the source impedance. Knowing the source impedance, then multiply by 20 or 15 A and you get the change in voltage for that current. Divide that by the no-load voltage for your % regulation.

.
 
The IDEAL Suretest is supposed to measure voltage drop under various loads. Since it can't drop 20A at 120V for a long period of time, this must be a short duration test. I do not have personal experience with this tester.

-Jon
 
What are they trying to prove with these tests? VD is dependent on load. No load = no voltage drop. Variable load = variable voltage drop. Sounds like some engineer knows just enough to get himself into trouble and cost somebody a pile of money. Why do we care what the voltage drop is at 1800 watts if the circuit is never loaded to 1800 watts? If the circuit is loaded "typically" measure the supply voltage and the voltage at the furthest outlet - the difference is the voltage drop. Many utilities supply voltage higher than nominal which will allow you to have higher than optimal voltage drop and still have very acceptable voltage. For example, in this area the POCO supplies most 120/240 volt services with the 120-volt legs reading 125 - 127 volts, thus a 5 - 7 volt VD still would provide 120-volt power.
There are so many variables that field testing of voltage drop is almost impossible unless you have a fixed motor load for example, then you could do a meaningful test. On a receptacle circuit with variable loads, it is little more than guessing game.
 
Ideal Suretest 61-165 will do full load test at 12, 15, and 20 amps. It will do a number of other things. I have an older model 61-157 and the only thing it will not do is AFCI testing. IT is one of the best meters I have used in a long time and will do exactly what you want plus a whole lot more.

They are a snap to use, plug it in the receptacle, push a button, and it will read out VD in percentage or voltage, plus give you N-G, impedence, etc...
 
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Just measure impedance of the circuit with no power connected. Then you can calculate the maximum VD by using maximum possible alowable current, based on breaker size. This way it is in percentage and the actual voltage supplied when connected does not matter.
 
haskindm said:
What are they trying to prove with these tests? VD is dependent on load. No load = no voltage drop. Variable load = variable voltage drop. On a receptacle circuit with variable loads, it is little more than guessing game.
Click to expand...

I have completed several of these jobs. Many specs call for a certain VD based on specified loads. I quit questioning why they specify certain items I test and bill accordingly.

I use a variac, resistive heater and a Fluke multimeter or a Fluke 435 for recording, depending on what the guy with the MONEY wants.

As noted find the furthest outlet from the distribution panel, if in doubt do a preliminary VD test, you find the furthest.
 
Thank you all for help.

I think the ideal SureTest is what I was looking for. Will have to get one of these around trim time.

I don't ask why they put this crap in the specs either. If it's something they want done and willing to pay for it, so be it. What bothers me is that I'm supposed to put together a written report of the testing and interpret the results to the engineer.... :grin:
 
080916-2132 EST

yursparky:

If you analyze my earlier post you will see that you do not need to apply a full load test current to determine % voltage drop at full load. For determining % drop all the special instrument does for you in comparison to a voltmeter and known load is to automatically calculate % drop.

.
 
dereckbc said:
Ideal Suretest 61-165 will do full load test at 12, 15, and 20 amps. It will do a number of other things. I have an older model 61-157 and the only thing it will not do is AFCI testing. IT is one of the best meters I have used in a long time and will do exactly what you want plus a whole lot more.

They are a snap to use, plug it in the receptacle, push a button, and it will read out VD in percentage or voltage, plus give you N-G, impedence, etc...
Click to expand...


That little thing does all that huh? Pretty cool! not too bad of a price either.

~Matt
 
gar said:
080916-2132 EST

yursparky:

If you analyze my earlier post you will see that you do not need to apply a full load test current to determine % voltage drop at full load.

.
Click to expand...

gar,

I thank you for your method and explanation, yet in this case the specs require me to apply 15A for this test. And the IDEAL can do that with a push of a button. And when there are 5 buildings to test receptacles in, anything that makes it fast and idiot proof (for the engineer, of course) is going to be worth the $300
 
yursparky said:
Thank you all for help.

I think the ideal SureTest is what I was looking for. Will have to get one of these around trim time.

I don't ask why they put this crap in the specs either. If it's something they want done and willing to pay for it, so be it. What bothers me is that I'm supposed to put together a written report of the testing and interpret the results to the engineer.... :grin:
Click to expand...

Put together a simple spead sheet,

Outlet location, Panel, circuit #, No load reading, full load reading, ampacity.

Enclosed for you review are the results of the voltage drop test performed at the above referenced location, the results should be self explanatory. Should you have any questions do not hesitate to contact me.
 
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