Pins 13, 14, and 15 on the D-SUB connecter will be connected to 120AC line voltage when their respective relays are on. I can imagine a situation where line is shorted to neutral (dirty connector, bent pins, etc) and I'd like to get ahead of that issue. Can I simply add a fuse, maybe with a fuse holder between line and relay common?
Per the accepted answer. I decided to use 4 panel mounted NEMA 5-15 outlets and just plug the pump, fans, etc into the outlets.
I'd not put mains on a DSUB-xx (and I've been putting mains on things for 50+ years :-) ).
EXCEPT, back of brain says that you can (or may be able to) get ones with mains rated shrouded contacts - these (if they exist) are super rare and no standard.
For a prototype, unless you need the "all connect together aspects" of a single connector, I'd use two connectors, or some other connector. It's doable, but "hairy".
The safest way of ensuring mains does not get out of control people-wise is to use an earth leak circuit breaker (ELCB) / ground fault interrupter (GFI).
That saves lives but NOT equipment - a person will feel a shock* but the mains will be interrupted fast enough to (almost always) not be killed. (*Ask me how I know :-) ).
BUT equipment will usually be damaged.
A fuse will also open the circuit - but will not usually save lives or equipment downstream of the fault.
A polyfuse protected circuit will limit current, but still kill you.
GFI/ELCB for life protection and maybe a tranzorb for energy absorption MAY prevent damage.
A large range of subminiature connectors with various add in contacts - usually aimed at high current or coaxial here
Not what you want, but shows what people do ...
And ...
(I have no involvement whatsoever with "Signal Origin" - they just seemed to have parts worth using as examples.)
