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Would you use a multiple wire ciruit (three circuits run together with ballast connected to alternating phase with a 3 pole circuit breaker) for fluorescent lighting instead of a one phase circuit? A specific situation would be rows of strip lights in a store. (At 277V) one circuit would serve two rows. A three phase circuit would serve 6 or so rows. If the multi wire circuit were used, should the neutral be oversized because of possible harmonics due to the elecronic ballast?

At first glance I would not see a problem

Basically a design issue, based on your input. Downside may be IF you have a fault...3 circuits 'trip' as opposed to one. Harmonics, with today's ballasts should be a non-issue. See Scott35's harmonics comments within another thread here.

the 08 requirement to handle tie the breakers for multiwire circuits could be a problem if one circuit had a fault you would loose all three circuits which could leave you in the dark.

3 phases feeding a factory-wired strip assembly ( with five conductor Molex snaps ) is standard for West Coast Safeway Stores.

Savings on the neutral wiring...

EE sizes the string such that field wiring of #10 mates to factory stranded #12...

Neutral not oversized since the bulk of the return is just the harmonics: the phases are balanced enough for this to be true.

The only trip-outs will be due to collision or original installation miss-wire.

These days the circuit normally passes through a smart controller racked right into the distribution boards. Cutler-Hammer, Square D, GE, et. al. are building these solutions as a canned package.

Circuit fault concerns are deemed inconsequential relative to the benefits and energy savings.

For what it's worth.

cgw;

Check out this Discussion Thread:

Introducing Harmonic Currents

*** NOTE ***
Click on the underlined text above, to open that page.

Thread located in the Electrical Theory and Applications Section.

Scott

The last lights I installed had a caution notice printed inside them addressing this very issue - that you need to be wary of harmonics issues.

IMO, there is merit to oversizing the neutral, at least through the first row of lights.

This does complicate your installation technique. The insulation-piercing connectors are designed for use with #12 wires. The same limitation arises with Wagos. Nor am I very happy connecting tiny ballast wires to a #10 with a wire nut.

Another possibility is to run a separate neutral to each set of lights, joining these smaller wires to a #10 at the start of the row. This would allow for the use of 'easier' connectors.

I have planned a few European commercial lighting systems, and we'd always run 3-phase circuits to feed the lights, but the ballast manufacturers (we mostly specified Osram) gave out leaflets with strict tables telling us how many fixtures we could connect to any given circuit, a number considerably lower than it would be expected were the lights resistive loads.