Last weekend I tried to replace a light fixture in my house, which I thought would be a quick fifteen minute job. However, when I took down the old fixture, I discovered there was no junction box. The wires simply came through the ceiling and were connected inside the canopy of the old fixture. What makes this more complex is that this is a 19th-century house, and the ceiling in this room is tin-style, likely on top of horsehair plaster & lath (though I don't know for sure what's behind the tin).

My question is whether this type of installation is dangerous? I know a junction box would be more proper, but with a metal canopy against a metal ceiling, there isn't any exposed combustible material adjacent to the wires. (I would be concerned about the wires chafing on the tin and cutting the insulation, but there is some type of ceramic (?) insulator around the wires, preventing that.)

There is enough room in the new fixture's canopy to do the wiring inside it just like the old one, but I don't know if that's a fire hazard or not. I'd just err on the safe side and cut the ceiling open to install a junction box, but my concern is that I don't know what the current mounting bar is screwed into. If it's screwed into a beam, I can put in a pancake box and be good, but if it's screwed into the lath, then once I break through that, there may not be anything nearby to screw into. My margin for error is very limited since I can't patch the tin once it's cut.

Help is appreciated! Here are pics:

Wires coming out of ceiling:


Old fixture:


New fixture (minus the fiberglass insulation that came inside the canopy):

 

If you've ever wanted a borescope, this would be the time as it would let you investigate the area above. They have gotten relatively inexpensive.

Lacking that, you should be able to poke around with a stiff wire and at least determine if there is framing nearby.

If there is framing next to it you could fasten the box to it or use a pancake box like you said. If there isn't you could install a fan mounting box that has a brace that you insert through the hole and expand by turning it until it expands against framing.

I would want some kind of box there, and more importantly, I would want to know for sure that the mounting bracket was secure enough to hold the fixture.

 

Junction boxes are required my code most jurisdictions.
Any way to get above through the attic to find out? How thick exactly is that tin roof?

 

Borescopes for cell phones are now under $20 in some cases.

 

You could use a surface mount box.

 

There may be a box behind the tin. Making sure the power is turned off.... check and see if a long thin screwdriver hits something.

Otherwise.... try carefully cutting the tin around the wiring to look in there.

 

Thanks, all. Sounds like I'll be cutting the ceiling open to put in a box. I hadn't seen those expandable arm fan boxes before. That'll be my backup if there's nothing nearby to screw into.

 

I'm also going to bet that based on the style of the new fixture, it requires 90C rated wiring, which you do not have. Newer flush and semi-flush fixtures get too hot for old wiring. You either have to choose a fixture that only requires 60C wiring or replace the wiring feeding the ceiling box.

 

I actually don't remember seeing any 90C warning on the instructions, but I'll take another look tonight. Thanks for the heads up. It will be a PITA if I do need to change the wiring since above this space is a finished attic room, and I really don't want to pull up those floor boards.

 

The heat factor is why the insulation was there. Look at the insulation and the tag on the wire for the 90° rating. The insulation is required for safety. I hope you still have it.

 

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That was my first thought too and that reminds me of something I have often wondered about. 30 to 35 years ago NM wiring wasn't rated 90C and fixtures back then didn't require 90C wiring. What has changed? Why is it today that the 90C wiring is required, but it wasn't back 35 years ago?