PV modules have traditionally been built with junction boxes on the back. When wiring modules together, the installer would attach wires directly into the j-box. Currently, many PV module manufacturers – especially grid tie modules – use MC (multi-contact) connectors brand which are attached to wires that come directly out of the junction box. These connectors provide safe, weatherproof, and reliable connections and make wiring modules in series even easier. Because there is more than one type of MC connector used on the cables, there is often confusion.
All current MC type connectors are the latching type, but the confusing part is solar panel manufacturers use different brands – such as MC4, H4/Amphenol, Tyco, etc. Several few years ago, when there were shortages on MC4’s – module manufacturers had to make provisions on their connectors, so that they could continue production. Customers were left with the only option of mating with “compatible” connectors. Manufacturers were hearing from their customers that these “compatible” connections were starting to fail. The issue, they found, was that the metallurgical chemistry of the contacts were going to be different unless they were from the same manufacturer. Over time, the difference in chemical composition could cause oxidation that could lead to temperature rise and other problems. Another issue is that, the manufacturers don’t release tolerances for their products, which could result in possible gaps in the contacts when cross mating. This could lead to arcing, or possibly eventual connector failure.
So, what should you do to ensure a UL approved connection in your solar panel array?
- Ideally, you want to choose modules with the same connector types in a single array.
- If, for whatever reason, you need to add or replace a module, and you find you must mix the connector types, the best solution is to use a small Connector Adapter Cable – for example: MC4 to H4, SMK to MC4
- In addition, National Electric Code (NEC) now stipulates that when PV modules are installed in readily accessible locations, connectors that click and lock must be utilized. You’ll need a special tool (key) to unlock the connectors.
Bottom line, is that even if two brands of connectors were found “compatible” or “connectable”, either one of the manufacturers could change their specifications without notifying all necessary parties, since there is no standard currently. So for now, it’s up the installer to be mindful of the connectors.