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I'm looking at making a DIY ring light using multiple fluorescent light bulbs. I'm in New Zealand and we get 230-240V and an current of 10A. I know from this I could rig up to 24 100W bulbs in series onto the ring. Although it is likely I won't have more than 10-15.

Here is an example ring light.

Example ring light

My question is this, how should I go about grounding this circuit? I've done some physics and am happy with power and voltage equations but was always a bit fuzzy on the concept of grounding and how it should properly be carried out.

Thanks in advance!

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  • \$\begingroup\$ What material is it mounted on? wood, metal. What material is the bulb holders made out of? plastic, metal. If metal is the reply to any then GND those parts \$\endgroup\$ – JonRB Jun 14 '15 at 9:46
  • \$\begingroup\$ Hmm I hadn't got that far with the design but I was planning on using wood for the ring. The light bulb holders look like they're usually plastic but I could try get some metal ones. Would plastic bulb holders usually have a metal grounding strip on the bottom? \$\endgroup\$ – Finn LeSueur Jun 14 '15 at 10:13
  • \$\begingroup\$ Plastic is fine. If the ring is wood and the holders are plastic you won't need an EARTH point as there is no exposed metal for a stray LIVE to connect to \$\endgroup\$ – JonRB Jun 14 '15 at 10:31
  • \$\begingroup\$ Ohhhh the penny drops. That makes a lot of sense! Thanks man! \$\endgroup\$ – Finn LeSueur Jun 14 '15 at 10:32
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    \$\begingroup\$ If those are mains-powered fluorescent bulbs you cannot connect them in series. \$\endgroup\$ – WhatRoughBeast Jun 14 '15 at 11:32
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Assuming that it is an inhouse installation.

In practice, for lamps under 40~60W does not required grounding. For lamps 100W, grounding it is mandatory, as well as the use of porcelain socket. This fixtures provides a third screw for ground.

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The main reason is to increase the safety in case of socket melting because of high temperature caused by lamp itself.

In any case sould be ensured that the live wire does not connected to the collar of the socket.

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The main reason is to provide additional safety in case of removal of a brocken lamp.

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The grounding question is simple - any exposed metal parts that may become connected to the live feed need to be grounded. This is the play-safe rule I would follow.

As regards the body of your question and the connection of 24 100W bulbs, I suspect a misconception. You have said your supply is 240V but the load doesn't have to equal 10 amps. The 10 amps is the maximum current that an individual power circuit can safely supply i.e. 2.4 kW (240V x 10A). This does not mean you need to wire up 24x 100W bulbs. You can use 24x 10W bulbs and draw 1A from a 240V circuit.

In fact if you had 2.4kW of fluorescent bulbs all closely packed into a circle you'd have a fire hazard and may damage your eyesight.

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  • \$\begingroup\$ My questions is more about where I would ground the bulb holders? Do they usually have a metal grounding strip on the bottom or do I need to wire something else? As for the number of bulbs, that information is useful. I mentioned I likely would have more than 10-15. It would most likely be closer to 10 in reality. \$\endgroup\$ – Finn LeSueur Jun 14 '15 at 10:15
  • \$\begingroup\$ If they are metal holders there is usually a stud underneath to screw in an earth wire. If you do use metal holders, link the holders all together and then to the incoming EARTH. plastic+wood setup and you should be ok without. \$\endgroup\$ – JonRB Jun 14 '15 at 10:32

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