Second try with reduced image:

 

   There are other possibilities- AVgas is nonconductive as far I could tell by testing with a megohmeter. I have seen electrical fuel senders with coils and wipers that are directly exposed to fuel.

 

  Sloshing around in a fiberglass tank, I believe the fuel could build a static charge on the surface. Fuel plumbing would normally be submerged so wouldn’t help by wicking off any buildup. An isolated metal object such as the filler neck could collect the charge.

 

  Normally this wouldn’t be a problem as the fuel tank is filled with such a high concentration of fuel vapor that it’s too rich for combustion. I used to be a firefighter, eventually fire chief and this is what we were taught.

 

  During the filling process concentrated fumes are displaced by fuel- the danger zone is the interface between the concentrated fumes and the outside air where the mixture becomes combustible. When the nozzle first touches the filler neck it would most likely be inside the noncombustible zone and would remain that way until fueling was finished. Cars aren’t grounded and yet they usually don’t catch fire when being fueled. Even so, touching the cap with the ground wire before opening wouldn’t hurt. Fuel nozzles are grounded so once a connection was made static should no longer be a problem.

 

  OTOH, I figure better safe than sorry. I thought about this quite a bit while building the Velocity and the picture shows my solution for the IV-P. Rather than try to ground the entire tank I made a cylinder of expanded copper mesh, sewed with copper wire and soldered. The lead formed is attached to the filler neck and also to the cap, using a braided ground strap to the adjusting nut. That connection isn’t perfect but it also serves to keep the cap from falling off the wing. The mesh not only collects any charge but prevents trash from going into the tank- I’ve heard of people sticking wrappers etc. into fuel tanks during airshows. The mesh was attached to the tank with Jeffco and slightly compressed when the tank was closed up.

 

  In use, the procedure would be to touch the ground wire to the cap before opening, and I’ll placard the filler. A ground wire could also be connected to the cap lead once it was open. In addition, I think Pete Cavitt’s method to remove surface static makes a lot of sense.  -Bill Wade