I'm looking at an industrial lighting retrofit project; will be replacing (139) 1000 Watt metal halide fixtures with (a) 4L T-5 or (b) 6L T-5 fixtures. Existing fixtures are spaced at approximately 40' on center. Would like to replace on a two for one ratio to achieve increased footcandles. Existing 20 Amp breakers have (9) 1000 watt fixtures per breaker. The 4L T-5 fixtures are 216 watts and the 6L T-5 fixtures are 324 watts.

I would prefer to replace the existing (9) 1000watt MH fixtures with either (17) or (18) 6L T-5 fixtures but according to my attached chart it seems that I will need to install the 4L T-5 fixtures or will exceed circuit load. Comments are appreciated..

Can you provide the length , width and height of the space?

Make and model number of the HB Fl fixture?

28 watt or 54 watt HB fixture?

Desired footcandles at what task height?

To answer your question in the title, a breaker cannot be loaded more than 80% of its rating, so 16 amps on a 20 amp CB.