![MC4 Male Connector](https://upload.wikimedia.org/wikipedia/commons/6/62/MC4_Male_Connector.jpg)
MC4 connectors are single-contact
electrical connector
Components of an electrical circuit are electrically connected if an electric current can run between them through an electrical conductor. An electrical connector is an electromechanical device used to create an electrical connection between ...
s commonly used for connecting
solar panel
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
s. The MC in MC4 stands for the manufacturer Multi-Contact (now
Stäubli Electrical Connectors) and the 4 for the 4 mm diameter contact pin.
MC4s allow ''strings'' of panels to be easily constructed by pushing the connectors from adjacent panels together by hand, but require a tool to disconnect them to ensure they do not accidentally disconnect when the cables are pulled.
The MC4 and compatible products are universal in the solar market today, equipping almost all solar panels produced since about 2011. Originally rated for 600 V, newer versions are rated at 1500 V, which allows longer strings to be created.
Background
While small
solar panels
A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a phot ...
used for
battery charging
A battery charger, recharger, or simply charger is a device that stores energy in a battery by running an electric current through it. The charging protocol (how much voltage or current for how long, and what to do when charging is complete) depen ...
and similar tasks may not require special connectors, larger systems normally connect the panels together in series to form ''strings''. In the past this was accomplished by opening a small electrical box on the back of the panel and connecting user-supplied wires to screw terminals within. However, in the USA, bare terminals of this sort are limited to 50V or less by the
National Electrical Code
The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Prote ...
(NEC). Above 50V only a licensed electrician can make the connections . Additionally, these sorts of connections were subject to problems caused by water leakage, electrical corrosion and mechanical stress on the wires.
Starting in the 2000s, a number of companies introduced products to address these issues. In these systems, the junction box was sealed and two wires were permanently attached using
strain reliefs. The cables ended with push-fit connectors that met the definition of a ''convenience receptacle'', meaning they could be (legally) connected together by anyone. Two connectors became somewhat common during this period, the
Radox connector {{short description, Obsolete electrical connector used to connect solar panels
RADOX Solar connectors are a largely obsolete electrical connector used to connect solar panels together in series to form ''strings''.
The RADOX Solar brand covere ...
and
MC3 connector
MC3 connectors are a mostly obsolete type of single contact connector commonly used for connecting solar panels. MC3 are named for the original manufacturer Multi-Contact (now part of Stäubli Electrical Connectors) with a 3 mm² contact assemb ...
, both of which essentially looked like weather-sealed
phono jack
A phone connector, also known as phone jack, audio jack, headphone jack or jack plug, is a family of electrical connectors typically used for analog audio signals. A plug, the male connector, is inserted into the jack, the female connect ...
s.
In 2008 the US Electrical Code was updated to require solar panel connectors to offer "positive locking", so that they were able to be plugged together by hand but only separated again using a tool. Radox, a European manufacturer, did not respond to this specification and has since disappeared from the market. Two US-based companies,
Tyco Electronics
TE Connectivity is an American Swiss-domiciled technology company that designs and manufactures connectors and sensors for several industries, such as automotive, industrial equipment, data communication systems, aerospace, defense, medical, o ...
and Multi-Contact, responded by introducing new connectors to meet this requirement.
Tyco's Solarlok became a market leader for a period in the late 2000s, but a number of factors conspired to push it from the market. Among these was the fact that the system had two sets of cables and wires, which led to considerable annoyance in the field when equipment from different vendors could not be plugged together. By 2011, the MC4 was already in a strong leadership position, which led to the introduction of compatible products from a variety of major connector vendors. Among these are the Amphenol Helios H4 and SMK PV-03.
Description
The MC4 system consists of a plug and socket design. The plugs and sockets are inside plastic shells that appear to be the opposite gender - the plug is inside a cylindrical shell that looks like a female connector but is referred to as male, and the socket is inside a square probe that looks male but is electrically female. The female connector has two plastic fingers that have to be pressed toward the central probe slightly to insert into holes in the front of the male connector. When the two are pushed together, the fingers slide down the holes until they reach a notch in the side of the male connector, where they pop outward to lock the two together.
For a proper seal, MC4s must be used with cable of the correct diameter. The cable is normally double-insulated (insulation plus black sheath) and both
UV and higher temperature resistant (most cables deteriorate if used outdoors without protection from sunlight). Connectors are typically attached by
crimping, though soldering is also possible.
The MC4 connector is UL rated at 20A and 600V maximum, depending on the conductor size used. Standards efforts in Europe also allow special 1000V versions and 30A or higher when used in pairs.
Application and safety
MC Multilam Technology claims that constant spring pressure provides reliable low contact resistance. However, it is very important to never connect or disconnect them under load, even on low-voltage (12–48V) systems. An
electric arc
An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma (p ...
may form which can melt and seriously damage contact materials, resulting in
high resistance
A resistor is a passive two-terminal electrical component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active el ...
and subsequent overheating. This is partly because
direct current
Direct current (DC) is one-directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even ...
(DC) continues to
arc
ARC may refer to:
Business
* Aircraft Radio Corporation, a major avionics manufacturer from the 1920s to the '50s
* Airlines Reporting Corporation, an airline-owned company that provides ticket distribution, reporting, and settlement services
* ...
, whereas commonly used alternating current (AC) more readily self-extinguishes at the zero-crossing voltage point.
Large arrays of panels are commonly interconnected in series, made of strings of panels generating 17 to 50V each, with overall voltages up to 600V per string or 1500V in special large arrays with high voltage panels.
Connectors made by other manufacturers may be mated with original Stäubli parts and are sometimes described as "MC compatible", but may not conform to the requirements for a safe electrical connection with long term stability.
Interruption requires a special DC
circuit breaker
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by an overcurrent or short circuit. Its basic function is to interrupt current flow to protect equipment and to prevent the risk ...
which allows opening the circuit without
arc
ARC may refer to:
Business
* Aircraft Radio Corporation, a major avionics manufacturer from the 1920s to the '50s
* Airlines Reporting Corporation, an airline-owned company that provides ticket distribution, reporting, and settlement services
* ...
damage. Typical 120/230V AC switches and circuit breakers are not generally suited for DC applications or may work at much lower currents.
See also
*
Daisy chain (electrical engineering)
In electrical and electronic engineering, a daisy chain is a wiring scheme in which multiple devices are wired together in sequence or in a ring, similar to a garland of daisy flowers. Daisy chains may be used for power, analog signals, digit ...
*
DC connector
A DC connector (or DC plug, for one common type of connector) is an electrical connector for supplying direct current (DC) power.
Compared to domestic AC power plugs and sockets, DC connectors have many more standard types that are not interchan ...
References
External links
* {{commonscat-inline, MC4 connectors
Solar panel connectors