MC4 Connector

[bcroe]

Anyone have an idea what the resistance of an MC-4 coupling is, new and over time? I
expect it is equal to some feet of the 10 gauge wire used. Also, are there panel mount
(into protected enclosures) versions? The alternative could be a gland nut. Bruce Roe

[bcroe]

MC-4 Resistance

Anyone have an idea what the resistance of an MC-4 coupling is, new and
over time? I expect it is equal to some feet of the 10 gauge wire used. Also, are there
panel mount (into protected enclosures) versions? The alternative could be a gland nut.
Bruce Roe

More research turned up numbers like 1/4 to 1 milohm. Or like up to a foot of #10. I
have some concern of MC-4s stored un connected for a while may start increasing over
time. Guess the best way to check, is periodically pick a high output day, and use my
thermal gauge to spot any warm connectors. Bruce Roe

[mbrick]

More research turned up numbers like 1/4 to 1 milohm. Or like up to a foot of #10. I
have some concern of MC-4s stored un connected for a while may start increasing over
time. Guess the best way to check, is periodically pick a high output day, and use my
thermal gauge to spot any warm connectors. Bruce Roe

That would be W=(5A^2) * 0.001 ohm = 0.025 W. I wonder if that will be enough to visibly warm up the connector?

[bcroe]

Failure

That would be W=(5A^2) * 0.001 ohm = 0.025 W. I wonder if that will be enough
to visibly warm up the connector?

Not trying to detect good ones here. But developing failures might rise to 1 ohm and burn out. I
just hope to spot them before they get that bad. Bruce

[inetdog]

Not trying to detect good ones here. But developing failures might rise to 1 ohm and burn out. I
just hope to spot them before they get that bad. Bruce

And so, I will broaden your inquiry and ask is anyone has experience with failures of MC4 connectors over time?
If so, was the problem a connector failure (i.e. contact to contact) or was it the result of a bad wire crimp?
The open barrel, fold back design of the crimp connector is very dependent on use of the correct tool as well as proper preparation of the wire (e.g. not nicking strands, etc.)

[bcroe]

Failures

And so, I will broaden your inquiry and ask is anyone has experience with failures of MC4 connectors over time?
If so, was the problem a connector failure (i.e. contact to contact) or was it the result of a bad wire crimp? The open barrel, fold back design of the crimp connector is very dependent on use of the correct tool as well as proper preparation of the wire (e.g. not nicking strands, etc.)

Panels received and immediately installed shouldn't have a problem. Here, some
panels were in storage outdoors many seasons. When a skid was unloaded, there
was some water collected and the open connectors were lying in it. Smarter now,
but will have to check on these. The thing to do is immediately plug them together
(short the panel) before any weather gets in.

Some pairs simply refused to plug together & subsequently were broken trying.
Others took more than normal insertion force, I suspect damage. A few were replaced,
there are maybe 80 more in service that will need monitoring. Another 160 immediately
installed, shouldn't have these issues.

Some MC-4s had a thin overlay which prevented inserting the separation tool, at least
till removed. And some wouldn't come apart again. I didn't use the "PROPER" crimp
tool at first. But since I also solder all the crimps, repairs have been trouble free.

One more issue, I've managed to break a few of the (plastic) separation tools. A
home brew tool is now being tested, made out of steel. Bruce

[inetdog]

Panels received and immediately installed shouldn't have a problem. Here, some
panels were in storage outdoors many seasons. When a skid was unloaded, there
was some water collected and the open connectors were lying in it. Smarter now,
but will have to check on these. The thing to do is immediately plug them together
(short the panel) before any weather gets in.
...
Some pairs simply refused to plug together & subsequently were broken trying.
Others took more than normal insertion force, I suspect damage. A few were replaced,
there are maybe 80 more in service that will need monitoring. Another 160 immediately
installed, shouldn't have these issues.
....

Thanks for the additional info, Bruce.

I would not worry too much if the failure to connect or disconnect properly resulted from distortion of the plastic shell for some reason.
But if the condition of the metal contact parts was what made the difference, I would indeed be worried.
Any fit issues would either come from crud deposited on the metal or corrosion of the metal surfaces themselves. The connectors are designed to be "weatherproof", but only when connected so that the plastic to plastic and metal to metal contact protects the metal contact surfaces. Sitting in water which might even have a high acidity (acid rain) could have compromised the terminals to the point where they would no longer be reliable for the 20 or so years the panels are expected to be in service.

Did you do the shorting and disconnecting with the panels covered? The MC4 connectors are not designed to be plugged in or unplugged "hot".

[bcroe]

disconnecting the panels

Did you do the shorting and disconnecting with the panels covered?
The MC4 connectors are not designed to be plugged in or unplugged "hot".

The panels were no where near in optimum sun, I was not careful about shorting
them. What really matters is: A. UNplugging them at high current; and B. having
them in a series string of substantial voltage. I do have a careful process for
working on a full string in service. Bruce