Concern regarding unplugging MC4 Connector

[skyman]

Hello!

I am a new member here, but i often come across to read interesting discussions on this forum.

I have set up a solar system 5 years ago ( 20 Panels that are connected in series ) everything is up and running but a few weeks ago i started getting
an earth Fault error on my string inverter, i performed recently an insulation resistance test and could identify the position of the fault in the string (the ground fault is between 11 and 12th panel !) so it's quite in the middle of the string ( the VOC voltage at the 12th panel is expected to be 396 V )

The panels are installed on the roof and are a little bit difficult to reach, i think one MC4 connector is damaged and needs to be replaced.

I am concerned on how i can replace that MC4 connector, as i've never unplugged/plugged MC4 under daylight, i am aware that MC4 should never be unplugged under load!

is it safe to unplug the MC4 Connector just after opening the circuit at the inverter level (unplugging String's DC wires from the inverter ) ?

 

[Sennen]

If you have RSD, you can turn that on and suddenly there's no current (theoretically, still test).
If you don't have RSD, you'll have to cycle the inverter to not be drawing current (load). (Turn off DC inputs)

edit: If you're working live on this, I hope you have live work gloves.

 

[hwy17]

Turn off the inverter, or open the inverter's AC output breaker. Then disconnect wherever you want.

The goal is for the inverter to not be producing, before you disconnect any DC connection. If the inverter was running and you unplugged the strings DC wires from the inverter that would still be a DC disconnect under load.

 

[skyman]

@Sennen

Thx for the reply, unfortunately i don't have RSD!
all i have is a string inverter and two DC wires coming from roof into the inverter, the panels are on the roof.

so you mean it's enough to turn off DC inputs in the inverter ?
Dunno but i am a bit afraid of the quite high voltage (396 V) at the position where that MC4 Connector needs to be unplugged /replaced!

 

[skyman]

Turn off the inverter, or open the inverter's AC output breaker. Then disconnect wherever you want.

The goal is for the inverter to not be producing, before you disconnect any DC connection. If the inverter was running and you unplugged the strings DC wires from the inverter that would still be a DC disconnect under load.

Okay, thanks

This confirmation is exactly what i looked for !

However there is still one major issue, the panel and /or its wiring has an earth fault so i expect there is current leakage into ground at that point.
i've read that one should be very careful before touching /working on such panel as there is current leakage into ground, i am afraid that i would close the circuit if if touch a live wire with my grounded feet!!

 

[hwy17]

Okay, thanks

This confirmation is exactly what i looked for !

However there is still one major issue, the panel and /or its wiring has an earth fault so i expect there is current leakage into ground at that point.
i've read that one should be very careful before touching /working on such panel as there is current leakage into ground, i am afraid that i would close the circuit if if touch a live wire with my grounded feet!!

The MC4 will protect you from touching the live wires, and the voltage of one panel is safe, so disconnect both MC4's on a panel before removing its panel ground and handling it. That's my take, not an expert in that particular hazard though.

 

[Sennen]

If the panel has an earth fault, it's seeping into the frame or there's a compromised section of the cable.

Hook a meter between either lead from the panel to the frame to check for the first condition. If there's no voltage, then check the wires. If it's an intermittent issue, I'd bet on the wire.

 

[skyman]

@hwy17
well, i believe unless i isolate that panel completely from the rest panels, there is a risk that i would close a high voltage circuit with my grounded feet! perhaps the safest approach here is to isolate the panel completely from the array by unplugging the MC4 at the previous and successive panel as well

 

[Sennen]

If you plan on doing this on your own, PPE is in order. EH rated shoes, Live Work Gloves at a minimum.

 

[Checkthisout]

Cover the panels with Harbor Freight moving blankets to block the sun.

Black plastic works too.

 

[skyman]

@Sennen

well i am at this point just weighing the potential risks and benefits from doing it by myself!
working in the dark is also an option but require additional preparation

​

 

[hwy17]

@hwy17
well, i believe unless i isolate that panel completely from the rest panels, there is a risk that i would close a high voltage circuit with my grounded feet! perhaps the safest approach here is to isolate the panel completely from the array by unplugging the MC4 at the previous and successive panel as well

Presumably while it is on the racking, it is grounded through whatever panel ground system is in place, so you cannot form a better path to ground than it already has. And, after you disconnect both it's MC4's, and lift it off the racking, it becomes isolated, so there's nothing to flow to ground.