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I have a 3.5kW central inverter-based system installed around July 1 of 2016. It has fourteen 250W Trinasmart panels. I have an ABB/Power One Aurora main inverter. The ABB inverter makes a safety check for insulation/isolation resistance (called "RISO", measured in mega-Ohms) every morning at startup. It also measures ground fault leakage current constantly. During the hot/dry month of July, the RISO readings were ALWAYS 20 mega-Ohms every morning.
About a month ago, the startup RISO readings began to drop and vary based on morning ambient relative humidity. On foggy humid mornings with a lot of dew and 92% relative humidity, the RISO would drop all the way down to around 9 mega-Ohms, with a 4 mA leakage current. On most mornings in my area, the relative humidity in the last couple of months has hovered around 85%, and the RISO would be around 12 to 15 mega-Ohms, with zero leakage current.
The RISO has rarely gone back up to 20 mega-Ohms like it was when the system was a month old. Are these 9 to 15 mega-ohms typical RISO readings for a properly functioning system? Is the 20 mega ohm reading only for new systems? Or has the insulation on my system been compromised?
I have sent one email to my installer but he's been silent so far because the system still starts up normally. If based on your experience, my 9 to 15 mega-ohms of RISO readings definitely indicate a safety problem, then I will pester the installer to look into it before the inverter trips out.
About a month ago, the startup RISO readings began to drop and vary based on morning ambient relative humidity. On foggy humid mornings with a lot of dew and 92% relative humidity, the RISO would drop all the way down to around 9 mega-Ohms, with a 4 mA leakage current. On most mornings in my area, the relative humidity in the last couple of months has hovered around 85%, and the RISO would be around 12 to 15 mega-Ohms, with zero leakage current.
The RISO has rarely gone back up to 20 mega-Ohms like it was when the system was a month old. Are these 9 to 15 mega-ohms typical RISO readings for a properly functioning system? Is the 20 mega ohm reading only for new systems? Or has the insulation on my system been compromised?
I have sent one email to my installer but he's been silent so far because the system still starts up normally. If based on your experience, my 9 to 15 mega-ohms of RISO readings definitely indicate a safety problem, then I will pester the installer to look into it before the inverter trips out.
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