MC4 connectors: everything you need to know to avoid burning your install

MC4 (Multi-Contact type 4) has been the PV standard since 2010. If you've seen photos of burned solar installs, 70% of origin points are bad-crimped or counterfeit MC4s.

Male, female and polarity

Each panel ships with one + (male) and one - (female) cable. To series, you mate the male of one to the female of the next. Outer shell is identical; the inner contact is what differs. Mixing them up doesn't break anything but won't connect either.

Correct crimping

You need a dedicated MC4 crimper ($15). Strip the 10/12 AWG solar cable exactly 7 mm, insert into the contact, crimp with the right die. Doing it with regular pliers: burns in 6 months. Pull test: 30 lb with no movement.

Genuine vs counterfeit

Stäubli (formerly Multi-Contact) cost $4-5 per pair. Chinese clones cost $0.60 per pair. Visually identical but the clone's inner contact is cheap brass that oxidizes and grows resistance. Mating a genuine to a clone (mixed) is worst: defective IP67 seal.

Series two panels

Plug panel A's male MC4 into panel B's female MC4. Voltages add, current stays the same. Repeat for 3 panels. Important: use cables from the same manufacturer or the IP67 seal fails.

When to replace old ones

If your install is 10+ years old and untouched, OEM MC4s start oxidizing in coastal areas. Symptom: unexplained power drop on one string. Fix: cut and crimp a new pair. 5 minutes per panel.

For everything wiring, read correct wire gauges and series vs parallel.