Kaliko Systems Limited

Make a Low-Power Media Server

Need for a Case

A relay board case needs to provide:
  1. Safety from high voltages by enclosing all the high voltage electronics and wiring (i.e. a physical barrier).
  2. Reduced fire risk from overload currents by housing suitably rated fuses.
  3. Limited protection of the circuit board from minor knocks and small liquid spills.
  4. For control of mains electrical equipment, direct support for 2 wire (i.e. live and neutral) and 3 wire equipment (i.e. live, neutral and earth).
  5. Flexibility and ease of use, by providing all inputs and outputs on standard plugs and sockets, with numbered output sockets and corresponding status lights.
  6. Hopefully some elegance, by hiding the circuit board/internal wiring and presenting a good-looking internal and external appearance.
A few commercial cased relay boards are available, but these seem to be targeted at industrial applications as they use screw terminal connections and do not directly support 2 or 3 wire mains connections. On one of my earlier cases I only provided support for 2 wire electrical connections, as this was all I required at the time. Unfortunately, I later wanted to control 3 wire electrical equipment and had to replace the case. As 3 wire electrical connections can be used for 2 wire electrical equipment, this convinced me that it is always best to provide 3 wire electrical connections.


For my mains controlling boards I considered using regular mains sockets, but the UK mains sockets are too large. Most of the equipment to be controlled uses either standard 3 wire IEC connectors (the C13/C14 connectors), or 2 wire figure-8 connectors (shotgun). I think that the standard 3 wire IEC connectors are particularly suitable for relay board case use, as they are small but easy to use, rated at 10 amps, widely available and have a good range of options, particularly: wirable plugs, snap-in plugs and sockets, fused plugs and pre-made power cords.


Lets consider the case materials available.

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