12/2 NM with undersized ground for ceiling lights on 20 amp circuit

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  #1  
Old 08-21-17, 07:35 AM
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12/2 NM with undersized ground for ceiling lights on 20 amp circuit

I want to replace ceiling light fixtures in my dining room. When I opened up the current fixtures the first thing I noticed was an odd ground wire. Through more research I've learned that the wire to the light fixtures is 12/2 nm which is not generally used for lighting but is Ok on a 15 amp circuit. But this circuit is on a 20 amp breaker.

There is BX coming into the switch with no evident ground and then it is the 12/2 NM from the switch to the fixtures. Since this is all preexisting (and has not given me any trouble in the 2 years I've owned this house) I'm looking to get some advice. Is this just a disaster waiting to happen? Or can I just replace the fixtures with the wiring as it is and carry on happily?

I have attached photos of the light wiring and an angle on the switch wiring.

Thanks!
 
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Old 08-21-17, 02:44 PM
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So I may have figured out the answer to most of my confusing question. For whatever reason the circuit is on a 20 amp breaker. The cable from the switch to the light fixtures is 12/2 which is fine on a 20 amp circuit. And, therefore, the cable from the 20 amp breaker to the switch is almost certainly 12/2.

Which brings me back to my initial concern. The 12/2 NM from the switch to the fixtures has a very light gauge, covered ground wire that can be seen looping in the photo. As far as I can tell it is 16 gauge. Is that something I should be concerned about?
 
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Old 08-21-17, 04:03 PM
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Older NM when they first started including grounds use an undersized ground. Older style BX cable with no bonding strip is not considered a reliable ground but since this is a light and grandfathered there no issue code wise and safety is only slightly less than with a grounded circuit.

Is that second picture supposed to be the ceiling box for the light?
 
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Old 08-21-17, 07:09 PM
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That is actually the old light fixture itself (see pic). It has its own incorporated junction box. I am planning to pull both light fixtures and replace them with proper ceiling boxes and new light fixtures.
 
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Old 08-21-17, 08:50 PM
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When you make the replacement.... the grounds get connected to the box and to each other..... inside the box. That wiring method was very popular years ago but is no longer used now.
 
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Old 08-22-17, 07:41 AM
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There is a very good chance that the new fixtures will require 90 degree C rated insulation . You do not have that . Your wiring is too old.
 
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Old 08-23-17, 06:47 AM
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Can you explain that to me? Other than the 18 gauge ground all other aspects of the cable seem standard. There is certainly older cable in this house than that! Are you suggesting that I need to have the house rewired so I can put in new light fixtures? Very recently I had quite a bit of permitted work done by an electrician (new circuits, new sub panel, etc) and he made no mention of any wiring that needed to be replaced. And I'm not sure why new standard fixtures would be functionally different from what's already there.

I feel I have a good grasp of basic wiring (and know my limitations) but this is a very new concept to me.

Thanks.....
 
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Old 08-23-17, 07:12 AM
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Light fixtures with incandescent bulbs produce a lot of heat.* That heat can damage insulation over time so the insulation was changed some years ago. Most light fixtures are now made based on the heat rating now used on wires.

Just using LEDs isn't a work around if someone else could later install an incandescent light bulb so you either have to take the wires up into an attic and splice 90 cable to the original cable in an always accessible box or replace the cable back to the switch.

However with either of the two methods you may violate code that states an ungrounded circuit can't be extended. It is debatable if old style BX cable is an adequate ground.
 
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Old 08-23-17, 12:17 PM
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Now I understand the issue and I see that it is an ongoing issue on many message boards across the internet. Like everyone else I didn't initially realize the heat issue wasn't from the wire but from the bulb itself.

I just looked at some of the fixtures I installed recently in the house and none of them warn that 90C insulation is required. I also looked at some light fixtures at Home Depot that I would consider installing and those don't mention it, either. But that doesn't cover want someone might do down the road.

Unfortunately this is on the first floor so I can't run up to the attic for a splice. The BX to the switch comes up from the basement but it ties into a junction box with a bunch of other BX cables so I'm not sure there's a solution to the ground issue there. So it looks like I'd have to rewire the house to replace two light fixtures that are probably less safe than what I would be putting in!

I know that code changes affect new construction and substantial alterations. I'm thinking that removing two old light fixtures with incorporated junction boxes and replacing them with new ceiling boxes and light fixtures is not a substantial alteration. I know I am very prone to overthinking things and I'm really wondering if that's what is happening here. I would mark the new boxes to signify that the wiring is not NM-B so I don't mislead anyone down the road.

Am I off base here? If I were a completely helpless homeowner what would a reputable, licensed electrician do?
 
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Old 08-23-17, 01:51 PM
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I'm thinking that removing two old light fixtures with incorporated junction boxes and replacing them with new ceiling boxes and light fixtures is not a substantial alteration.
That is correct. It is only when you add new cable that lack of ground is a problem. That is because the new cable must meet current code which requires a ground.

The reason old style BX with no bonding strip is unreliable as a ground is because the joints of the spiral can be to high resistance due to age and corrosion. The purpose of the ground is to trip the breaker in case of a fault but there have been some reports of BX armour glowing red hot without tripping a breaker.

You are allowed to add a single ground wire following what ever path is easiest. Under old code the wire must be fastened within five feet of the panel to the main panel ground. The latest code allows you to go to the nearest correctly installed ground such as a grounded receptacle.
 
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