netstorm
I would definitely find a way to ground your PR511s. At first, I didn't ground mine and discovered that 1) they didn't work as expected, 2) one of them burned out multiple bulbs. Since I grounded the one that was burning out bulbs, I haven't had any issues with it.
I don't know if where you live you have lightning storms, but grounding them could also prevent a fire and extensive damage to the rest of your wiring or appliances connected to the same wiring.
I am aware that in most of Latin America, the grounding concept is almost nonexistent, but you can create your own by digging a hole in the ground close to the house and sticking a metal stick about 1 meter deep. Then, with a bracket, attach high-power bare wire. Then, you can run a 14 gage wire to the "ground" lead on the PR511s from the bare wire. The metal stick could be what's called "cabilla" in Spanish, which is used as reinforcement in concrete construction.
I'm no electrician, but I've seen people do that in parts of Latin America when grounding is needed.
I hope this helps.