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I'm wanting to design my own lighting fixtures, both for cost effectiveness as well as the design appeal (inspired by a particular designer's lighting fixtures) that uses a wooden base with metal pipes as the structure.

The lighting socket and wiring itself will be 3-conductor, and in the fixture I plan to have a touch-based (capacitance/metal sensor, not reverberation) dimmer controller.

I have verified all of the ratings are within compatible ranges.

The fixture itself will structurally be made up of metal pipes with the light sockets at the end of them (outside the ends of the pipes, not inside - the sockets have casing and everything). The metal pipes will serve as the sensing line's conduit, and consequently the light 'switch'.

My concern is with the grounding. Obviously I'm going to want to ground this thing since the majority of it is going to be metal - especially since the 'switch' consists of touching the metal piping.

However, does this mean by grounding the metal parts, I'll be shorting out the dimming mechanism thus rendering it useless? Or should I have a dedicated 'switch' piece of metal that is not in contact with the rest of the fixture?

Otherwise, should I be focusing more on insulation versus grounding in this scenario?

As per requested, here is a basic schematic:

schematic

simulate this circuit – Schematic created using CircuitLab

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  • \$\begingroup\$ Can you post a schematic so we can see what you are envisioning. There is a built in schematic tool Ctrl-M. \$\endgroup\$
    – Tyler
    Commented Mar 10, 2016 at 23:48
  • \$\begingroup\$ @Tyler - neat tool. Added. I'm not an engineer per se, but hopefully that gives a better idea. \$\endgroup\$ Commented Mar 10, 2016 at 23:58

2 Answers 2

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You can not ground the sensor wire - that will render the capacitive sensing useless.

In order to ensure safety (i.e. don't kill anyone) you can use double insulation. I.e. use a double insulated wire inside the pipe. This works well at least according to European rules.

Let me point out that according to my previous capsense experiences, having a long tube as a sensor will not work, since it will pick up too much noise from the environment.

You also have to be careful since you need to mount at least one end of the tube to some solid surface. That surface must be insulated from the ground, and shall not be metallic at all (i.e. a metal shelf is not a good choice). Otherwise the mounting base will be also part of the touch sensor.

Another idea you can try is to cover the tube with a thin layer of plastic wrap. These self-adhesive wallpapers could work, but also simple electrical insulation tape works well. The capacitive sensing does work trough a non-conductive material as well (e.g. you can have your sensor plate made of wood, plastic, glass, leather). (Note that if your sensor is not capacitive but works by picking up AC noise, you do need a metalic contact).

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I'm no electrician, but you want your fixtures to be able to 1) Not kill anyone or 2) burn someones house down. Usually people get their fixtures passed through a regulatory process. You would have to review the laws\regulations concerning the installation and sale of lighting fixtures in your area, and get your product to conform to the regulatory testing\requirements.

That being said a way around your grounding problem would be this:

schematic

simulate this circuit – Schematic created using CircuitLab

Add an insulator around the grounding box, drill a hole for the sense line to go through and run the sense line to the outside. Either that or you may only need the insulator and no grounding box, depending on what regulatory wants.

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  • \$\begingroup\$ It should be noted that the fixture's sensing line will be part of the structure itself - namely using metal pipes. \$\endgroup\$ Commented Mar 11, 2016 at 0:21

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