I have a pulse start 400watt fixture, I just have been wondering, would it ever be possible to put a mercury vapour bulb of the same wattage in said fixture, or will that wreck the ballast or bulb?

Simply remove the ignitor before operating the mercury lamp.

Simply remove the ignitor before operating the mercury lamp.

Yes, that works. Leave capacitor on if came with ballast.

Got it, thanks

You don't even have to completely remove the ignitor, just disconnecting the white lead and capping it off will be enough.

Yeah removing and capping separately the ballast tap wire (usually blue or labelled x3) also works to disable 5h4 ignitor.

The capacitor isn't needed for lamp operation. He can connect the 400W MH lamp to his ballast without a capacitor and still get a full performance from the lamp.

The capacitor isn't needed for lamp operation. He can connect the 400W MH lamp to his ballast without a capacitor and still get a full performance from the lamp.

I wouldn't be so sure. A lot of PSMH ballasts I've seen above 150w tend to be S-CWA which requires the capacitor for correct ballast operation. And I've personally found with most multi tap HX, the ballast acts strange with the capacitor omitted. Best to consult the ballast spec sheet if available or even the ballast label before.

It is perfectly safe to run a 400w mercury vapor lamp on a North American 400w M135/M155 pulse start metal halide ballast because North American 400w M135/M155 pulse start metal halide lamps run at the same arc voltage and current as 400w mercury vapor lamps at 135v 3.25a. In fact, I have actually managed to run North American 400w M135/M155 pulse start metal halide lamps on 400w mercury vapor ballasts. I was able to successfully start and run North American 400w M135/M155 pulse start metal halide lamps on 400w mercury vapor ballasts by using a European 220-240v superimposed ignitor in the circuit. The reason that European 220-240v superimposed ignitors can work on 400w mercury vapor ballasts very nicely is because these ignitors do not require a ballast with a dedicated impulser ignitor tapping, which is not provided on most mercury vapor ballasts and that most 400w mercury vapor ballasts have the right OCV for these ignitors to work properly, which is between 190 and 270v. The reason that European superimposed ignitors are able to reliably ignite pulse start metal halide lamps
is because they use an internal pulse transformer to provide high voltage pulses of up to 4.5kV, which is necessary for the ignition of such metal halide lamps.

ONE IMPORTANT THING TO DO BEFORE RUNNING MERCURY VAPOR LAMPS ON PULSE START METAL HALIDE BALLASTS IS TO DISCONNECT THE IGNITOR.