If I need ~20A to power a device, but all the available circuits in the building are 15A tops, would I be able to power said device? Perhaps using a UPS and some tomfoolery?
Generally, nope. But...
Is this a commercial building, or in Chicago or a few other places? Most likely your wire is in conduit. Pull some 12AWG wire and breaker it properly.
Does the machine come in a 240V version? Is there a circuit in your building that you can knock out without falling below legally required minimum outlet and receptacle locations? Convert that circuit to 240V and use that. You will only need 10A at 240V.
Is it a machine capable of taking multiple power supply inputs? Many server-tier PCs or UPSs are capable of drawing from redundant power supplies, and current-limiting themselves. Internally they convert to DC onto a shared DC bus, which is the only electrical way to gang supply from multiple circuits.
Is it, or can it be broken into, several separate machines on a rack? Nobody cares if 2 servers on a rack are plugged into 2 different circuits.
Is it a welder? Special rules apply.
Is this an older air conditioner? Talk to your power company about whether they have an appliance upgrade program. Often they will buy you a new, efficient air conditioner because it will save X watts of power on the power grid, and that is actually cheaper than building X watts of additional power plant.
[Can I power a 20A load when available circuits are 15A]
There is no way to provide a continous 20A from one 15A circuit.
This is due to
- The principle of conservation of energy.
- Safety rules aimed at preventing your house/building burning down.
Even if I can pull from two separate 15A feeds?
In most jurisdictions, there is no legal way to combine circuits to provide more power to a single load.
The correct way to deal with this is to run a new circuit back to the main panel using wire sized for the load.
- How to combine in phase 120VAC 15A 60 Hz feeds on a pair of outdoor GFCI outlets?
- Can I substitute two wires for one heavier-gauge wire?
- Can two 30 ampere circuits be combined in an outlet?
All of which essentially say no.