There are over thirty other connector manufacturers in the PV industry today: Amphenol, Weiland, Radox, Tyco, Bizlink, and SMK, just to name a few. MC4, or Multi Contact connector for four square millimeter cable, is the standard locking system in the PV industry today.
There are some manufacturers that will make the claim that their connectors are compatible with MC4. It is important to note that even though it is often possible to physically connect these, it does not mean it is an approved connection.
Though H4 connectors are often marketed as “fully intermateable with industry standard,” this interconnection is not approved by UL, or Underwriters Laboratories. Amphenol, the manufacturer of H4 connectors, has released reports TUV tests to confirm the compatibility between H4 with MC4. In fact, these connectors have frequently been intermated with MC4 connectors, but it still does not have UL approval. Even if both connectors have UL approval individually, connecting the two is not approved by UL.
Cross-mating can cause additional problems, therefore GoGreenSolar.com does not recommend cross-mating connectors as a general rule of thumb.
Unless the connectors come from the same manufacturer, they often times have different chemical compositions, which can lead to oxidation and other complications.
When different connectors are interconnected, potential gaps in the connection can also cause arcing and ultimately, failure.
Just because they will “fit” doesn’t mean it is kosher.