What are MC Cables?

MC means "multi-contact". So what does multi-contact mean?

MC connectors are specially designed for low contact resistance and good stable connections under a wide range of conditions. The term "multi-contact" comes from the fact that the connectors have a bunch of little spring loaded gold plated fingers that insure good contact. The first company to manufacture them is also named Multi-Contact, but Tyco connectors are used on some panels, such as the Day4.

Because of the wiping action on the contacts, they are also self-cleaning - the wiping cleans off any film or corrosion when they are plugged in which improves reliability of the connections. The picture on the right shows a close up of the internal fingers in the female connectors.

So what do they do for me?

Commonly referred to as MC cables or MC connectors, these have started to take over much of the wiring of solar arrays. Nearly all major manufacturers now supply panels only with MC connectors, or as an option to the standard junction box with screw type terminals. All current production solar panels made for grid tie applications now come only with MC connectors.

Simplifies wiring, especially of medium and larger arrays Makes series and parallel wiring of panels much easier. Long series connections often needed for high voltage grid tie systems are 'plug and play".

Multi-Contact Company Solarline2 connector

Construction

All MC cables now being sold are made with UL-listed, 600 Volt, multi-stranded, #10 or #12 AWG RHH/RHW/USE-2, outdoor-rated, sunlight-resistant cable. The #10 wire is rated at 54 amps max per NEC in open air but we recommend no more than 30 amps for #12 wire and 45 amps for the #10 wire. Although the cable is made in 3 colors, black, blue, and red, about the only color generally available is black. Some heavier duty 30-Amp assemblies using the "SolarLine 2" connectors are available for larger systems.

Eventually all MC type connectors will have to be the latching type, which is the Solarline2 (MC4), or the Tyco brand connectors used on a few panels. Most newly manufactured panels are shipping with the latching connectors, but we don't expect a complete changeover until 2009.

Connecting Panels (parallel)

Typical MC2 combining adaptor plug

For parallel connecting panels, simply plug in the cables from two panels into the adaptor, and a single cable on the other end. These come in two types: 2F/1M and 2M/1F (male and female). You will need two (one of each type) for each parallel connection. For 2 panels you will need a pair - one of each type - for 3 panels, 2 sets, etc.

Connecting Panels (series)

MC connectors shine in large series arrays, such as for grid tie systems. You simple plug one panel into the next, up the max array size and voltage. Grid tie inverters commonly use up to 600 volts DC on the input, and it is a simple matter to just plug in 5 or 6 panels in series.

Downsides

All is not sweetness and light with these. Currently some local codes require that panel wiring be run in conduit, and since nearly all high power panels now made no longer have the junction box option available - and thus no way to install conduit at the panel - this can create some issues.

It can also add $20 to $50 per panel for installation costs for extension cable and adaptors. Where with a junction box all you needed was some outdoor cable to run to the array combiner or controller, now you need specially made cables and adaptors in many cases. Buying multiple cables for long runs can be expensive, but there are few options.