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Is there a secret to the MC4 connector screw cap?

P

patssle

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Joined
Sep 6, 2023
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19
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Houston
I just cannot get the end cap screwed on even with pliers. It will start by hand but then tighten up and go no further. These are name brand Stäubli from Signature Solar and TEMCo 10 gauge solar panel wire. I bought name brand quality to avoid issues like this! I did exactly what all the youtube videos showed and crimped with the right tool.

PXL_20240507_003519202.jpg
 
Is the rubber gromnet that holds the wire completely compressed? Maybe that’s as far as it goes with that size wire?
You haven’t tried to put the wrong pin in the wrong housing, have you? Does it go together if it’s not mated?
 
wpns said:
Is the rubber gromnet that holds the wire completely compressed? Maybe that’s as far as it goes with that size wire?
You haven’t tried to put the wrong pin in the wrong housing, have you? Does it go together if it’s not mated?
Click to expand...
It does look snug around the cable with the cap removed. It looked like the panel wire was pretty similar in size. It's all in the correct housings, I had it hooked up and powered up.

I'll check with SS to see the intended wire size spec, there are no model #s on these connectors.
 
Do you have the grommet/holder on backwards? Post a picture with the cap off.
 
You do realize that the open C-shaped end of a MC4 tool is for tightening the cap, right?

1715046037126.png

When you grab anything plastic with pliers, you are mashing the whole assembly, deforming its shape and jamming up the threads, which makes it very difficult to turn. Hence the C-tool, which applies more or less uniform turning force around the circumference of the cap without any mashing.
 
Texas-Mark said:
Do you have the grommet/holder on backwards? Post a picture with the cap off.
Click to expand...
It's going on like this. (this pic is just an example, it's not crimped and installed)

When I hand tighten to max, the cable won't move anywhere there is enough force on the grommet. But that's with the cap halfway on.PXL_20240507_015730087.jpg
 
Last edited:
You have to insert the wire with crimped on terminal fully until it clicks into the body of the MC4. If it is not fully inserted it would be very difficult to attach the cable gland and screw.
 
Mattb4 said:
You have to insert the wire with crimped on terminal fully until it clicks into the body of the MC4. If it is not fully inserted it would be very difficult to attach the cable gland and screw.
Click to expand...
Yep it definitely clicked!
 
Hand tightening without a cable inserted really closes the grommet. I really wonder if these are for smaller gauge wires. Will see what SS says tomorrow regarding model # / specs.
 
I have had quite a few do this, but not that much. Thicker insulation definitely prevents the cap from screwing ALL the way down sometimes, I figure if it is sealed, then it should be fine.
 
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