Testing for Array Losses

Hi All

I'm new on this site I'm an installer and O & M Contractor from Ontario. I have recently ran into a request from one of my customers that has me scatching my head. So I thought I would try and put it out there and see what other guys are doing.
I've been ask to go to one of our 500kw roof top installations and test each string to the combiner and give the voltage drop or percent losses on that string as well as the losses on the home runs back to the Inverter. Now how do you test for vdrop as they want total losses from the module to the combiner so that includes the wiring on the array. Is there some way of getting a resistance test on a live circuit?


  • BB.BB. Super Moderators, Administrators Posts: 29,509 admin
    If you can measure voltage drop (or voltage at each end of the cable run) relatively accurately--Remember:
    • V=IR
    • R=V/I = change in voltage / change in current
    Say you have 10 amps flowing through a cable run and measure 245 volts at one end and 242 volts at the other (use two calibrated meters--i.e., should read the same voltage when connected to the same circuit at the same time--Use a phone to measure the voltage and current at the same time).:
    • R= (245-242Vrms) / 10 amps rms = 0.3 Ohms
    Or, if you can only measure one end--And you can change the current (say disconnect one string), you can estimate the system resistances... Say 10 amps at 245 volts and 5 amps gives you 242 volts:
    • R = delta V / delta I = (245-242) volts / (10-5) amps = 0.6 Ohms (estimated effective resistance)
    Does this help?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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