Quick electrical wiring question...
I have my power distro set up with several L14-30 twist lock receptacles that I run to amp racks, stage snakes, etc.
My question is when I am working a gig where I am unable to do a proper tie in would it be possible to make some adapters to "pool" power together for the amp racks? Aka have two 15A edison plugs that then run into an L14-30 receptacle and share a common neutral and ground but each keep their separate hot poles? The idea would be to pull power from two separate circuits with standard edison receptacles and "merge" them together to power the amp rack.
Is this possible?
Possible, but a serious code violation to do so.
The first problem is that you can't guarantee that the two outlets you connect from will be on separate legs (phases) of the panel. If they're on the same phase, then instead of your neutral currents subtracting, they'll add together. So you can easily burn up a neutral wire. However, in your case the two 15-amp services could never draw more than the 30-amp capacity of your plug contacts and cable (assuming you're using 10 gauge wiring).
The second problem is that any circuit breakers feeding such a receptacle must be ganged together. That is, if one of the legs trips from over-current, the other leg must also trip. This is to prevent 240-volt loads from cross-feeding power from the "on breaker" to the loads connected to the "off breaker". That would create very bad and unsafe conditions for both the gear and the user.
If you do build one of these gadgets and an inspector sees it, he will almost certainly shut down your show. And he'll likely want to put a magnifying glass on your entire rig. Worse still, if there's a fire at your gig, even if it's not your fault", you'll have every lawyer within a hundred miles after you for liability. "It's always the sound guy's fault".
So the answer is this. While it could works in theory, there's too many practical and legal reasons not to do it. Hate to say it, but in these cases running heavy Edison extension cords around is the only good option. And if you're worried about ground-loop hum from multiple outlets, that's the best reason to have 1:1 audio isolation transformers on the inputs of your power amps.