Floating an Array
I just got the biggest shock of my PV career last Summer. As my installation partner and I were laying down panels on a rack, he was shocked. ANY SHOCK CAN KILL YOU. EVEN THE "LOW" AMPS IN PV PANELS ARE 1000'S MORE AMPS THEN NEEDED TO STOP AND SEIZE YOUR HEART MUSCLES.
We analyzed the situation until we could figure out why he was shocked.
I checked online.
I checked with other experts. (Wiles included)
I found that ?floating an array? is key to installer safety.I was surprised to find I never heard the term "floating" before. Nor was I ever taught the practice. (I won't detail my experience, but it's lengthy)
I WANT TO SHARE WHAT I LEARNED AS PART OF MY NEW YEAR'S SAFETY RESOLUTION.
Basically: BEFORE installing PV panels, remove the GFDI fuse or otherwise disconnect the grounded conductor (usually negative) from ground (usually in the inverter). This simple action could be a lifesaver.
The Handbook states: " (GFDI) Devices meeting 690.5 are intended to prevent fires in DC PV circuits due to ground faults." That means that the fuse will not protect life.
Background: NEC 690.5 requires that most PV systems be GFI protected. If you land all wires in DC disconnects and inverters before installing panels, then the GFDI fuse links PV negative (usually, sometimes positive) to ground. (And, landing wires BEFORE energizing them (adding PV PANELS) is a best practice.) That means all metal racking on the roof, all conduit and grounding wire every where is effectively charged (usually negative) - and exposed to the touch. Like one big, exposed and charged bus bar. All I need to do in order to get hurt is to accidentally contact PV positive. I am all but guaranteed to be simultaneously in contact with racking, grounding wire or a module frame by holding, leaning, or sitting on a grounded component, like a rail, i.e. negative. Maximum potential would then exist between the positive wire I accidentally touch and the exposed - negatively charged - metal of anything. Between the two.... my body would be the connection!
Is this unlikely? I used to think so.
Yet....this just happened to my partner on a rooftop. ( I also had a buddy shocked through the seat of his pants while sitting on a rail and wiring an array.) While tightening the set-screw in the bonding lay-in-lug on the underside of the module frame with his screw-driver, and laying the #10 bare copper grounding conductor into it, his screwdriver must have slipped into the MC Connector of the positive lead of the module! He was shocked and yelled.
However, if you remove the GFDI fuse then both polarities should be separately derived from ground - and thus the racking. Potential - in my understanding - should really exist only between the two polarities. If you manage to connect these two with your body, then ....well..... you are talented.
Anyways, just my two cents.
tip #2 Wear gloves. Gorilla brand neoprene fit like a secondskin for me. So I actually wear them!
tip #3 Use insulated screwdrivers. Even when grounding! (as we were)
tip #4 Remove pointy drill bits and pointy tools from toolbelts while installing panels. (MC Connectors are ?touch safe?, only to adegree - but not when handling pointy drill bits and screwdrivers. When handling 100's of modules it is just a matter of time before something slips inside the MC Connector or you crush or nick a wire)