Are these neons?

[dentaku]

I got this board from an old fax/copy machine. It has what looks like neons being used as some sort of fuse or something connected to an RJ45?
Is that what they are?

[mariush]

I think they're gas discharge tubes, to protect against lightning strikes and stuff like that.  A on the silkscreen could be short for arrestor, as in "surge Arrestor"

[T3sl4co1l]

Yes, sort of.  They probably glow bluish, though, and ignite at a fairly high voltage (200V+?).

Only one reason you'd find gas tubes near a phone connector: surge suppression.

If a high voltage surge appears on the phone line (usually induced from nearby lightning strike), the tubes spark over and shunt the surge to ground (there should be a ground connection on the machine to carry this current).

Tubes for this purpose are called Gas Discharge Tubes (GDTs).  They are used where high power handling and fast response time are required, and where a low power or otherwise current-limited source is present (the worst the phone line can do is 10s of mA and something like 80V, not a big deal).  They are unsuitable for unlimited sources and DC (because the arc will keep on burning until the device explodes).

Other protection devices are thyristor (similar behavior and application; slower; often used on phone lines as well), MOV (huge energy handling, sloppy voltage limiting; typically used for mains and automotive), TVS (fast, reasonable voltage limiting, typically used for surge and ESD protection on LV supplies and signals) and clamp diodes (ESD protection, when an LV supply is present).

Tim

[dentaku]

OK
I thought I remembered Dave explaining this in an old video.