Im not sure what NEC says about it, it could just as well forbid it anyway ("lighting in home is required to be 120V only" sort of stuff)

But you can connect the lights through a receptacle, just like highbays are, at least here (do they connect HID highbays through receptacle and plug over there too ?)

Then question remains whether it is ok to cut only 1 side of a 240V receptacle with the switch

the high bats are in fact plugged into outlets. They are twist lock 277 volt for most high bay merc vapor installations for easy removal and repair of fixtures. As for the cutting of only one side, I'd just be better off using two SPST or DPST switch.

Our codes here require DPST for some stuff, specifically the water heater tank. That means interrupting both Phase and Neutral. I think it is for maximum safety during maintenance (what could be otherwise achieved by a receptacle/plug disconnect)

However, it has one side effect advantage too : If the heating element goes shorted to Earth, then even with the Phase off, a section of the heater remains connected between Neutral and Earth. If there are a couple of volts on the Neutral, this will start tripping the GFCI (here the GFCI is in the panel and is main for the entire house, there no unprotected circuits), and if the switch cut only the Phase the user can't get it to stop without actually disconnecting the wiring. When the switch opens both sides, you won't have random GFCI trips as long as you dont switch the damaged heater on

One more thing from our code, if the heaater unit is installed in a location common to few appartments (roof top, attic, basement etc of an apartment block) then there is a requirement to install a second identical DPST switch next to the unit. The purpose is, that you can switch off the switch in the apartment and then go and accidentally start working on the neighbors unit while that is powered on. With the switch at the unit you can make sure the power is really off to the one you are working on

But those codes are there to protect who is doing maintenance. In normal use (so switching it on/off and touching the metal body from outside) all you need is a proper Earth, the insides can remain energized - this is no different from any other appliance that stays plugged in at all times like a fridge or a washing machine....

We also have special GFCI breakers that controls the outlets for the bathrooms and the hot tub and hot tub room. The rest are normal circuit breakers.

For what i know you dont have the heater on GFCI. only circuits with receptacles, and only specific ones. Here there is no distinction made, the GFCI is connected straight after the main breaker and protects everything

I'll post a picture of what I was talking about soon.

I have a five pack of 4-6-8 ballasts for240 volt and a single f40 ballast I am watching. Would the 4-6-8 ballasts work since the bulbs are so small they may start without starters.

If they are 240V ballasts then yep they will work on 240V

If they are 120V ballasts you can try 2 in series on 240V, that would be pretty close. Then on the 2 series ballasts you can power either 1 or 2 series lamps, i dont think it makes much diffference with so low arc voltages (esp for the 4w)

If they are 240V ballasts you can try 2 in parallel on 120V

Anyway for 4-6-8 use the lowest voltage starter possible, that would be i think FS-2, unless there is lower one which i dont know

And for the "how to get the 240V for experiments":
I would really stick with a 120->240V transformer, preferably an insulating one. Connecting to a dryer or washer outlet is technically feasible, but really dangerous.
The danger come mainly from the arc energy (short circuit current, 240V, time it takes for the breaker to interrupt the current) in case a short circuit happens, with those installation it becomes really high.
For the purpose of an experiment, it does not make any difference, if the experimental setup is operated from such transformer, or directly from the 240V high power connection. Just the first is way safer, mainly when something "decides" to fail.

I'm just thinking of doing it for an experiment. I haven't bought anything yet and am waiting until after I grt back from vacation to monkey around with it.

A lower value breaker or fuse can be connected downstream from the dryer socket, and long cable can be used for added source impedance

I'll probably add a couple in line fuses since I have some holders.

Good idea.

Yep. From RadioShack clearance sales.

Funny, I got a bunch of fuses and holders from the RS clearance sale too!

I also got of e10 and BA9s indicator lamps just to keep for future projects.