Steps to find the Fault in solar DC cables (String Type Power Inverters)

Badar_2013 Registered Users, Users Awaiting Email Confirmation Posts: 1
If you have the Grid Connected string inverter and you find this fault: 
"Low Insulation Resistance" and invereter disconnected itself with Grid due to safety measures. So, there will the following possibility. 
1. Your DC cable may be attached/connected  to mounted structure and all the current is getting ground. So we have to follow the following steps: 
i. use the megger to check the cable insulation resistance and it will help you to locate the string which have the problem. But what if, "we do not have the problem in insulation resistance and our cable is not damaged" then what will be the next step to find the fault. 
If any expert have got my point please guide. 


  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    What brand/model of GT inverter do you have?

    Have you used a Megger and confirmed that your insulation is OK?

    Have you contacted the person who sold the GT inverter or the Manufacturer?

    There have been recalls of inverters for various issues.

    I cannot think of anything off hand unless you have an intermittent short (like water in a J-Box when it rains).

    Assuming you have not added anything on the PV Array Cabling (capacitors to reduce radio interference, other meter/test equipment, or connected to a second GT inverter, or other solar controllers).

    I guess you are out of Pakistan, so there is a good chance that few of us have heard of the brands of GT inverters you are using...

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    If using a megger to test for insulation breakdown, or water intrusion, isolate the inverter, some meggers use 1000V which could damage equipment.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.