Hi, This Intellivolt 4 lamp F54T5HO ballast has me confused. It says for 4 lamps on, S is on. What do they mean S? switch? For 4 Lamps on, which is what I desire, I connect the grey/red wire as well to Neutral or Hot?

Looks like : Connect S together with Phase or with Neutral - 4 lamps. Leave S alone disconnected - 2 lamps. So basically one switch controls the Phase in as with any light, and the other (optional) switch controls S

I guess this way it allows control the lamps separately as if there were 2 ballasts, without losing the efficiency of a 4 lamp ballast

I wonmder - What if S is on a 3way or an illuminated switch, which pass a leakage current ? Would this cause the ballast to flash between 2/4 lamps ?

Like Ash said (and the way I read it as well) 'S'/the red-gray can be connected to either hot or neutral for 4-lamp mode. :shock:
Interesting...on other versions of that I've seen, it was connected to hot.

The grey goes to the neutral, and it's normally run though a switch and depending how you wire it up you can have a few light options, don't wire it to the live line, probably won't hurt it but it won't work, basically just think of it like two ballasts in one box and your simply switching the second one by the neutral and both by the live wire..
Here is your options for wiring it up with a switch..

A. One light or three lights on,
B. Two lights or three lights on,
C. Two lights or Four lights on,
D  Just use a wire nut and have four on all the time..

Those are nice ballasts, programmed start, high frequency, nice power factor, EOL lamp protection, A sound rating, -28C starting temp, good stuff...    

The grey goes to the neutral, and it's normally run though a switch and depending how you wire it up you can have a few light options, don't wire it to the live line, probably won't hurt it but it won't work, basically just think of it like two ballasts in one box and your simply switching the second one by the neutral and both by the live wire..

Actually, the grey wire gets connected to the 'neutral' for 4-lamp operation is correct. However, you can connect it to either 'hot' wire when wired in a 208- or 240- volt single phase (U.S.) circuit. Back in late 2007, my company installed 120 6-lamp F54T5HO low bay lights in a retail building with 2 tenants. All had the first-gen Advance/Philips ICN- series ballasts with the push-in wiring connectors. It was a design-build project, meaning no job blueprints for the electrical other than the service panels and roof-top units. We opted to wire these fixtures on 208Volts after consulting with Advance. We were able to have up to 7 fixtures per circuit vs 4 fixtures per circuit (at 120 Volts), plus no neutral loading/harmonics. We still do maintenance on these fixtures due to height (13 to 17 feet off the floor) and have seen 25% ballast failure in the 10 years and most still have the original lamps. The stores are due for a blanket relamp (Philips F54T5HO/841) but the tenant is looking toward LED's (against my advice).

Pardon my late thank-you note! I've been too busy with work.

This ballast is too cool. I quickly installed 4 lamps, leaving the grey/red wire unconnected I get 2 lamps working only. Grey/red connected with the white/neutral I get all 4 lamps.

These 54watt T5s pack a lot of punch! Thanks again.