Big Block Street

[cobrakiwi]

Morris
I understand why your grounding the fuel thank but why the cap?
That car is a aluminum body right?

[Gaz64]

Originally Posted by cobrakiwi

Morris
I understand why your grounding the fuel thank but why the cap?
That car is a aluminum body right?

The filler neck needs to be grounded, because while it is not grounded it is a point of static electricity conduction. Placing a fuel hose into the neck creates the loop, and we have fuel vapour right at the point of the spark path.

All late model cars with plastic tanks have a ground strap at the filler neck.

Some cars I have worked on needed to have a strap added as a rework.

Gary

[cobrakiwi]

Hey Gary
So how does touching the fuel cap or the cap neck with the pump nozzle make any difference if the cap has a ground strap or not?

[patrickt]

Originally Posted by cobrakiwi

Hey Gary
So how does touching the fuel cap or the cap neck with the pump nozzle make any difference if the cap has a ground strap or not?

A cap with a wiggly hinge on it might not meet the "less than one ohm" test. If it doesn't, then touching it with your hands, after rubbing your butt on the leather seats while wearing wool pants, would be just like shuffling your feet across the carpet and then touching the doorknob on your wooden door. You can get a spark if the planets are aligned just right.

[patrickt]

FWIW, my tank and inlet are grounded, but my cap does not have a separate bond to ground. The ERA fuel inlet though, below the lemans cap, has a twist off gas cap below it, so fumes are presumably vented out below the car via the vent tubing.

[patrickt]

[cobrakiwi]

Originally Posted by patrickt

A cap with a wiggly hinge on it might not meet the "less than one ohm" test. If it doesn't, then touching it with your hands, after rubbing your butt on the leather seats while wearing wool pants, would be just like shuffling your feet across the carpet and then touching the doorknob on your wooden door. You can get a spark if the planets are aligned just right.

Yes I agree with that, so what? You will touch the cap to open the cap to fill the car right, I still don't see how that is any different if the cap has a strap to any place on the car or not.

[patrickt]

Originally Posted by cobrakiwi

Yes I agree with that, so what? You will touch the cap to open the cap to fill the car right, I still don't see how that is any different if the cap has a strap to any place on the car or not.

I don't see not running a ground wire to the cap as being a large risk. In theory, there's bound to be some goofy way that the charge on the cap could be different than the potential of the rest of the car. Probably because air passes over it or some such reasoning. I wouldn't worry about it though and my cap has no ground wire and I don't plan on installing one. But my fuel inlet certainly is grounded with a bonding wire. Of course, my body is plastic. At least my car's body is.

[Gaz64]

Originally Posted by cobrakiwi

Hey Gary
So how does touching the fuel cap or the cap neck with the pump nozzle make any difference if the cap has a ground strap or not?

It is the filler neck that needs to be grounded.
The filler neck metal is nearly always isolated from the car body/chassis.
The amount of volatility that occurs at pump delivery is higher and more likely to combust from a spark, as can be seen by that woman in the video above.

[cobrakiwi]

The video in post 95,
I think this shows the risk at the fuel pump, it makes no difference if your fuel neck is grounded to the cars ground side or not.

[patrickt]

Originally Posted by cobrakiwi

The video in post 95,
I think this shows the risk at the fuel pump, it makes no difference if your fuel neck is grounded to the cars ground side or not.

Remember, the goal is to keep the potential of the different objects involved in fueling all the same, because any one particular object can develop a charge that is different than another from a million different ways. You do that by bonding each component to one another so no particular object is isolated. That means all metal pieces (even the fuel cap since we're talking theory) are wired together and your hand never leaves the pump handle, and the pump nozzle is always in contact with the filler neck. If any are, or become, isolated from the others then you have the potential for a static buildup that arcs over to a neighboring object of different potential. That's really happening all the time in your life, you just don't know it because it's at level that is low. But it's really no different, in theory at least, from a bolt of lightning that comes down and blows an office building apart. A static electricity fueling accident is pretty rare, as is a grain silo explosion, but if you can lessen the threat by just running a little wire, it's hard not to do it. I remember about 35 years ago we had one particular employee who could not use our dinosaur computer system without first putting on a wrist strap that was grounded to the keyboard. If he tried to use the keyboard without grounding himself he locked up that particular dumb terminal. That's the only person I have ever seen where that happened, but it happened repeatedly and I saw it with my own eyes time after time. We even had him strip down to make sure it wasn't his shoes or clothes or something causing it. But nope, it was him. You probably couldn't do that today. I hadn't thought of that in decades.

[Gaz64]

Originally Posted by cobrakiwi

The video in post 95,
I think this shows the risk at the fuel pump, it makes no difference if your fuel neck is grounded to the cars ground side or not.

It does make a difference.

I have seen many fires in one make of car that did not have a filler neck ground strap.

As Pat has said, it is about making all metal at the same potential.

[cobrakiwi]

Originally Posted by Gaz64

It does make a difference.

I have seen many fires in one make of car that did not have a filler neck ground strap.

As Pat has said, it is about making all metal at the same potential.

What make of car have you seen this happen with?

Cheers.