Both of the lines that are lit up are flexible aluminum couplings. They're required in some areas as the final connections to the appliances. They're in line with cast iron gas pipe and fittings. They are much more thin and way better at conducting heat.

Source: former HVAC tech

[–] [email protected] 10 points 1 month ago* (last edited 1 month ago) (2 children)

Thanks for the clarification, pipes look like copper but might be cast iron.

Still doesn't fit with the explanation, aluminum has more resistance than copper, but not that much more. The resistance of cast iron is an order of magnitude higher than aluminum. So it would still be the lowest resistance in the circuit and thus the coolest part.

And cast iron is pretty good at conducting heat. Not as good as copper or aluminum, but still pretty good. We've been using the material to make pans and pots for cooking because of it's thermal properties. So the heat wouldn't just stop at the fitting, but continue on at least some ways.

Moreover it's physically impossible to get aluminum hot enough to glow like this and still keep its shape. It melts at 600 degrees C, well below the point where something gets red hot, let alone yellow like this. If the aluminum were to be this hot, it would be in a puddle and at risk of burning.

[–] ghterve 8 points 1 month ago* (last edited 1 month ago)

Sorry, I meant to type higher resistance. On my water heater, the equivalent part that is glowing in the picture is a really thin flexible corrugated gas pipe that surely can carry much much less current than the iron gas pipe feeding it before it went really high resistance. I could totally see it glowing like this with enough current. But if it is aluminum (not sure if it is), what you said makes sense.

My gas pipe to the house comes out of the ground inside a plastic protective pipe sleeve, so I can imagine it possibly not having enough of a low resistance path to earth to trip one of the cutout fuses on the primary distribution line. Granted, mine also has a big ground wire bonding it to the house ground, which I would think would help here...

/shrug I was just sharing what I read. It was supposedly the explanation as to why local breakers on the house didn't trip.

[–] [email protected] 8 points 1 month ago

The flexible pipes are normally stainless steel. The main gas line is steel with thick walls so this seems plausible to me. Stainless steel has higher resistance than steel and is so much thinner.