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I, with the help of a neighbor, installed an overhead light fixture. It was a little awkward and I'm not sure the unit came with the right bracket - it didn't match the one in the instructions. The awkwardness meant that it was impossible to attach the two ground wires to the green screw. The neighbor simply twisted the two ground wires together and added one of those plastic screw on wire connectors. He said it was perfectly safe.

My in-law's house just had a kitchen fire after an electrician had done some work so I'm spooked. Should I have a professional come in and reinstall the light? Is it necessary to use the green screw if the two ground wires are firmly connected?

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    Where is the green ground screw you speak of located? Is it on the bracket? Also, the two ground wires you are talking about, does one of those come from the fixture or were they just in the box? – ArchonOSX Jul 20 '17 at 18:48
  • Green screw is on the bracket. Ground wires - one from the ceiling (a thick one that was attached to the green screw on the prior bracket) and one from the new fixture (a much thinner one). – Sid Jul 20 '17 at 18:53
  • So you "pigtailed" the ground? That's normal – Joe Phillips Jul 20 '17 at 19:43
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The wire from the fixture grounds the fixture to the system. It is not required to ground the mounting plate.

That green screw is only there for convenience of grounding a metal fixture with no separate ground wire.

With the two wires you described connected together you are good.

Rest easy!

  • If you wanted to ground the box, a "pig-tail" a short piece of wire could be added to other two grounds in the wire nut and run to the screw. – DaveM Jul 20 '17 at 19:32
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The reason for grounding to the electrical box is so that the whole system is grounded. If the box is not grounded then there if the hot touches the box, then the box will become energized. This creates two possible problems:

  1. If the hot box is in contact with wood (like house framing), then it can leak electricity into the wood at high resistance. This will cause the wood to get hot. If it gets hot enough, it could start to burn.

  2. If anybody touches the box, or anything connected to the box, they could be electrocuted. For example, you know those little screws that screw the switchplate over the switch? You know what they screw into? That's right, they screw into the box. So if the box is hot, then those little screws are hot too.

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If you're that worried about it, put an Arc Fault (AFCI) breaker on the circuit (or any circuit). Those greatly reduce house fires by detecting what starts the fire -- arcing.

If the circuit is also protected somehow by a GFCI, that will largely remove the risk of electrocution.

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