400W mercs run on 3.25A, what would be the chain supply current (and not 6.6A; I guess they do not use special lamps)

I thought 400w mercury lamps operate at 3.2A? Anyway, they actually operate on series isolation ballasts that convert 6.6A into the voltage/current required by the lamps. Due to the high voltage of the series circuits, the isolation ballasts are remote from the fixtures in the pole transformer bases.

@Silverliner: You are correct, i messed it up somehow, is is corrected now...
But what is the advantage of series connection, if each lantern has to have it's own ballast? Why not to use e.g. 244V parallel supply and serial reactor ballast instead (it would be lighter, more reliable and safer to relamp, i guess)?

@ silverliner, Series ballasts are not always remote mounted. When we had series MV lighting here in Buffalo, the Westinghouse, Line Materials, and GE M-400 and M-400A1 replacement luminaires had the transformers fixture mounted. In fact, the M-400A luminaires with the series ballasts were housing mounted.

What a beautiful sight to see all those mercs steadfastly lighting the roadway! I love driving through an area lit by mercs...it reminds me of the 70s, when many mercs were still in service.

Dave, is this the area where you showed me in Google Maps with those OV-20s?

@Medved, it seems there was a big infrastructure for series systems here in Southern California, most of the remaining incandescent and mercury lights are series.

@NiMo, there are some cobraheads with integral series isolation ballasts on wooden utility poles in LA. I was just referring to underground wiring and freestanding metal light poles, I should have been a little clearer in my description.

@GullWhiz, no this is a different area.

Our HPS and some MV and incandescent lighting in Frederick MD are in series!

There's a post office in New Kensington that has series wired mercury vapor lights.