Hey everybody, just looking for opinions on using a 7.5uF cap. instead of a 7uF cap on an advance CWA mercury vapor ballast?

Your using it to change the power factor, expect a change to the current crest factor, but not by much with only a 0.5 uf change, have you measured it to see which way the tolerance is on the cap some can have very large swings + or - for all intense purposes it might be close enough...   

On constant wattage ballasts the capacitor also provides some current limitation to the lamp. A higher value capacitor will allow more current to flow in the lamp, but also in the ballast, making it run hotter. At the extreme the ballast burns to a crisp, as I've seen in a high bay fixture once. Though in that case the ballast (a 347V CWA) originally used a 18.5uF, while I found a 24uF inside the fixture next to the original cap that was left disconnected.

Though in your case the difference isn't that big, and certainly not enough to cause damage in the short term. To be extra sure you can measure the current consumption and see if it matches the spec (if there's one).

0.5 shouldn't make much difference. When caps age I'm sure they vary in rating over time slightly

Or not so slightly. From what i seen F96T12 HO Rapid Start ballasts for 230V/50Hz stop working when the capacitor is at or around 1/2 its rated value

With CWA the current regulation mechanism is capable to "swallow" quite large tolerance into its regulation range (7uF vs 7.5uF is quite large tolerance for a current definition component), so very likely it will work.

The 500nF difference is also commonly within the manufacturing tolerance range.

Any luck with it ggillis, did it work or did you get the right cap ?

IMO, I wouldn't use the 7.5uF on that ballast (even with MV). Is the capacitor in series of that lamp?

The capacitors are spec'd at +/- 3% on CWA ballasts, so the acceptable range is 6.79 to 7.21uF.
Typically, capacitance decreases as the capacitor ages.

I work on CWA 1KW MH pole lights on a regular basis and capacitors are critical to proper light output
and lamp life. These fixtures use 24uF caps and they get replaced when they read 22 or less.

I would use two caps in parralel ( many times lighting caps tend be out of my price range) 3 uF and 4 uF
Caps together.  Amrad makes good caps and they
Give 5 year warrenty as soon u purchase them

http://m.ebay.com/itm/4-MFD-x-370-440-VAC-Oval-Run-Capacitor-AmRad-USA2028-Made-in-the-USA-/181736127547?hash=item2a50513c3b%3Ag%3AVXkAAOSwBLlVSOLB&_trkparms=pageci%253A3b48be4f-4925-11e7-b029-74dbd1801ace%257Cparentrq%253A732daa0815c0ab6af75f39a0ffff7617%257Ciid%253A16

Also this together

http://m.ebay.com/itm/OEM-Amrad-Run-Capacitor-3-3-0-uf-MFD-370-440-Volt-VA2000-37-305-Made-in-USA-/371622240482?hash=item56866960e2%3Ag%3Alb8AAOSw2x1XMMo9&_trkparms=pageci%253A023f9eb2-4929-11e7-87ee-74dbd18013e0%257Cparentrq%253A73466b2315c0aca4b4bab184fffedbcb%257Ciid%253A20

I never had any problem runing motor caps
Also u can call Amrad up they can make any size cap type of cap u need