Changing an MC4

Polar101 · Feb 18, 2023

Just finished a pv system and found that we didn't have power on one of two strings when we started the inverter. Traced our cables back and found one of the mc4 connectors on the feed in to the fireman switch from the panels wasn't making for some reason. Need to swap out the MC4 connectors and wondering how to do it safely. Can't disconnect it from the panels without getting back up on a 2 story roof. Is there a safe way of swapping out this connector. There was 260V on the line yesterday and it was dull.

Murdoch · Feb 18, 2023

If you decide to touch it, do it at night.

Polar101 · Feb 18, 2023

Murdoch said:
If you decide to touch it, do it at night.

Is there typically voltage on a line at night, even residual? Is starlight enough to create voltage. There was only 90W being generated yesterday so the current was low but the voltage was still high.

binky · Feb 18, 2023

Polar101 said:
Is there typically voltage on a line at night, even residual? Is starlight enough to create voltage. There was only 90W being generated yesterday so the current was low but the voltage was still high.

You can get a voltage on the panels under a full moon, but it's got no 'welly' behind it. If you are still worried, get a good pair of rubber gloves, and try not to touch any metal parts of your tools.

Phoenix · Feb 18, 2023

Should be electrically separate, so make sure DC isolator is open (to reduce as low as possible risk of any fault connecting the other pole to earth), check for any voltage between the pole you want to work on and earth / anything earthy in the vicinity. Ensure covers are refitted over connections on the other pole while you are working. And as binky says, work in a way that doesn't put you in contact with the conductor (either directly or through metal tools)

johnb2713 · Feb 18, 2023

Phoenix said:
Should be electrically separate, so make sure DC isolator is open (to reduce as low as possible risk of any fault connecting the other pole to earth), check for any voltage between the pole you want to work on and earth / anything earthy in the vicinity. Ensure covers are refitted over connections on the other pole while you are working. And as binky says, work in a way that doesn't put you in contact with the conductor (either directly or through metal tools)

Surely that's not a good thing to do, it guarantees the pole that's being worked on will have the greatest potential to earth? Leaving the other pole open in the event of contact with the pole being worked on would drag that end down to ground due to it floating?