Chris is like the videos. I have a question that I hope that you can help with. After a system has been in commission for some time when I have to go and perform a periodic test on the system, performing any test that requires access to the roof is difficult when the scaffolding has been removed. I am thinking of IR tests. Due to the inability gain access during a test on an EICR on a typical electrical installation I would LIM the area with no access. I am hoping and expecting you to say the LIM can be applied to the IR test on a PV system especially if the Panel String produces Open Circuit Voltage in line with expectations regarding the manufacturers figures and the irradiance test on the day. I hope you will comment on this. Thanks for the vids. P.s. I have bought your testing book in the past after viewing other videos.
Test positive to earth, clamp earth to exposed part of the inverter which could be bear metal screw or grill repeat the process with negative. Same applies above 1MOhm or 0.5Mohm @250v if the total voltage of array is
Hey Chris, great vid. If you don't mind sir, please clear up the following: 1) I assume this is an ungrounded array, meaning neither + or - from the array is solidly or functionally grounded, correct? 2) I understand when you short the array, there is 0 volts at Isc but the array Isc current (I think you said 14A) is still flowing in both cables and now you are back-feeding 500V from the megger to produce a 2nd possibly high leakage current to ground to measure insulation resistance (megger doing ohms law). I understand the megger current is normally very low with good wires but is there an issue with the megger accuracy when both current sources are flowing on the shorted cables at once?
Hi Jon, Because this is a pv panel once the ends are joined the current will not flow anywhere other than within the panel. (Its a bit like shorting the ends of a current transformer for safety). It will have no effect on the accuracy of the insulation resistance reading. I hope this answers your question. Best regards Chris
Great idea with the isolator; I'm going to make one. I assume that, since this is a 2-pole isolator, it connects diagonally. So, terminal 1 connects to 4, and 3 connects to 2. Then make a link between 2 and 4 with a second cable in terminal 4 with a female MC4 connector on it, correct?
I’m afraid you have picked up some wrong information somewhere John. As long as you isolate inverter from AC side first you just unplug the MC4 connectors and you will be fine
The reason we have DC isolators adjacent to the Inverter is so if the Inverter needs to be serviced off site, we can isolate the 'Tails' that go to the Inverter, instead of leaving the Live MC4 end waving in the breeze. But some Inverters have an integrated Isolator that you can unclip from the Main Inverter, so will negate the need for a seperate DC isolator
I think you will find that unplugged MC4 connectors meet all IP requirements and would not present a problem if identified and tucked away safely while any servicing carried out. My view is that providing the inverter has its own integral DC isolator the addition of an additional isolator is of no value and adds an additional possible point of fault. It’s a matter of choice I guess.
Sir, when you connect the positive and the Negative ends of your solar PV string into the isolator, you basically shorted them? Will that be ok? No damage to the panels. Pardon my being a newbie. 😅
Very instructive, thanks!!
Glad it was helpful!
Thank you Sir!
Hi Chris got a diagram of the connections for your DC test box?
I will draw one and put it on my channel for you. Give me a few days
Thank you Chris
Chris is like the videos. I have a question that I hope that you can help with. After a system has been in commission for some time when I have to go and perform a periodic test on the system, performing any test that requires access to the roof is difficult when the scaffolding has been removed. I am thinking of IR tests. Due to the inability gain access during a test on an EICR on a typical electrical installation I would LIM the area with no access. I am hoping and expecting you to say the LIM can be applied to the IR test on a PV system especially if the Panel String produces Open Circuit Voltage in line with expectations regarding the manufacturers figures and the irradiance test on the day. I hope you will comment on this. Thanks for the vids. P.s. I have bought your testing book in the past after viewing other videos.
Test positive to earth, clamp earth to exposed part of the inverter which could be bear metal screw or grill repeat the process with negative. Same applies above 1MOhm or 0.5Mohm @250v if the total voltage of array is
thanks
Hey Chris, great vid. If you don't mind sir, please clear up the following:
1) I assume this is an ungrounded array, meaning neither + or - from the array is solidly or functionally grounded, correct?
2) I understand when you short the array, there is 0 volts at Isc but the array Isc current (I think you said 14A) is still flowing in both cables and now you are back-feeding 500V from the megger to produce a 2nd possibly high leakage current to ground to measure insulation resistance (megger doing ohms law). I understand the megger current is normally very low with good wires but is there an issue with the megger accuracy when both current sources are flowing on the shorted cables at once?
Hi Jon, Because this is a pv panel once the ends are joined the current will not flow anywhere other than within the panel. (Its a bit like shorting the ends of a current transformer for safety). It will have no effect on the accuracy of the insulation resistance reading. I hope this answers your question. Best regards Chris
Hi Chris, thanks for your videos, Any idea when the DC Test Device build video will be available?
I will try and get it done over next few days
Great idea with the isolator; I'm going to make one. I assume that, since this is a 2-pole isolator, it connects diagonally. So, terminal 1 connects to 4, and 3 connects to 2. Then make a link between 2 and 4 with a second cable in terminal 4 with a female MC4 connector on it, correct?
It doesn’t matter which way you connect just link bottom terminals
Hi Chris, what was the lead you used from the bottom of the isolator to the Megger tester?
If you do not have a stand alone isolator you cannot change the inverter should you need to.
I’m afraid you have picked up some wrong information somewhere John. As long as you isolate inverter from AC side first you just unplug the MC4 connectors and you will be fine
The reason we have DC isolators adjacent to the Inverter is so if the Inverter needs to be serviced off site, we can isolate the 'Tails' that go to the Inverter, instead of leaving the Live MC4 end waving in the breeze. But some Inverters have an integrated Isolator that you can unclip from the Main Inverter, so will negate the need for a seperate DC isolator
I think you will find that unplugged MC4 connectors meet all IP requirements and would not present a problem if identified and tucked away safely while any servicing carried out. My view is that providing the inverter has its own integral DC isolator the addition of an additional isolator is of no value and adds an additional possible point of fault. It’s a matter of choice I guess.
Sir, when you connect the positive and the Negative ends of your solar PV string into the isolator, you basically shorted them? Will that be ok? No damage to the panels. Pardon my being a newbie. 😅
No damage will occur, joining them together is the correct way to carry out a short circuit test. Always ask if you are unsure.