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Fuel Tank, Earthed?
The Baron - 9/7/07 at 08:47 PM

Dumb question for the day,

Does my Ally fuel tank need to be earthed to the chassis?

Cheers in Advance.

The Baron

dave r - 9/7/07 at 08:49 PM

mine is
the sender unit will be if you have one...
more likely to cause problems if some things are not down to earth

DRC INDY 7 - 9/7/07 at 08:52 PM

Mine has a little eath lead from the fuel sender to the chassis

If you do not have a petrol gauge then no you dont need the earth

Litemoth - 9/7/07 at 09:02 PM

Simply drill a hole in the bottom of the tank and use a nut and bolt. Use a self-tapper if you can't get your fingers down the neck.

Seriously though, there must be good safety reasons for doing this? Aren't metal tanks supposed to be mechanically insulated with rubber or neoprene from their mounts so would always need earthing?
I can't remember seeing earths on production cars but they must have them.

Ian D - 9/7/07 at 09:12 PM

As the fuel is combustible you need to keep the fuel tank at the same potential as the chassis so there is not the possibility of a potentail between the two and a spark.

In practice highly unlikley but better safe than sorry.

MkIndy7 - 9/7/07 at 10:39 PM

"As the fuel is combustible you need to keep the fuel tank at the same potential as the chassis so there is not the possibility of a potential between the two and a spark"

As the cars are -ve earth Doesn't that mean any stray +ve wires could then ARC to the Fuel tank?.... if anything to stop it Arc'ing wouldn't you make it +ve or better still have totally isolatedinsulated, or if anything those rubber earthing strips down to the ground to prevent static.

All a bit overkill really.

dave_vic_ozz - 10/7/07 at 09:04 AM

This topic has had me thinking before. From what I have seen the +ve is connected to the sender, the sender connected to the resistor on one side the the other side of the resistor connected to earth. This way the wiring (read in theory) will not have a large potencial to chassis. The tank should be connected to the chassis so when you fill the tank (yes most have a rubber / plastic hose) the chassis and tank have the same potencial (as written above) so to minimize static sparks. Nylon clothing and the seats etc. The car is on rubber but when you fill the tank you most likely will have touched the car first. More cars are coming out with plastic tanks. Great insulation and good in a crash but real trouble for Clubman builders.

dave d.

DaveFJ - 10/7/07 at 10:03 AM

My fuel system is fully earthed, filler neck to tank to lp pump to hp pump to swirl pot to metal hp filter and all to chassis. better safe than sorry...

MkIndy7 - 10/7/07 at 12:04 PM

quote:
Originally posted by dave_vic_ozz
This topic has had me thinking before. From what I have seen the +ve is connected to the sender, the sender connected to the resistor on one side the the other side of the resistor connected to earth. dave d.


No quite, the +ve goes nowhere near the tank, the +ve feed only goes to the dial.

The sender is earthed to the tank and the float resists/moderates this earth to effectively give 0v for empty 6v for 1/2 full and 12v for full and supposedly quite analogue imbetween.

There is no +12 and -12v in the tank to either ARC accross, or to short and make the resistor hot.. unless there's a poor connection or problem with the guage.

[Edited on 10/7/07 by MkIndy7]

dave_vic_ozz - 11/7/07 at 09:15 AM

Right on the money.

Got gauge and sender termanology mixed up.

+ve (+12Vdc) to gauge,
>
Gauge signal to sender (variable resistor)
>
Sender to chassis -ve (0 Vdc)

1000 appologies.