Proper Grounding or Bonding of Gas Cap/Fuel Tank

BatDaddy1887

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Jan 18, 2009
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While cleaning and inspecting the back of the boat I noticed that the previous owner had attached a ground wire from the fuel fill cap down to the aluminum trim at the edge of the floor near the engine. I don't believe this is good ground. Though I have never had an explosion from filling the tank with gas, you just never know. How is the filler cap/tank supposed to be grounded? How is yours grounded?

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bruceb58

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Mar 5, 2006
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It's likely fine since the frame is likely already bonded to the battery negative. You can always get a meter out and check.
 

MinUph

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It's likely fine since the frame is likely already bonded to the battery negative. You can always get a meter out and check.
Is this true? I never thought this would be a good thing.
 

bruceb58

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Is this true? I never thought this would be a good thing.

You are just bonding it. Doesn't mean you are running current through it which you definitely should not.

For example, your metal toaster is bonded to ground. Doesn't mean you are running current through it.
 

mla2ofus

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Dec 30, 2008
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The biggest danger is not from the battery but from a static spark.
Mike
 

Silvertip

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The instant you bolt an engine onto an aluminum hull you have a hull connection to the negative terminal of the battery. Don't believe it? An ohm meter will prove it.The negative terminal of the battery is connected to the engine block via the negative battery cable. The bolts that mount the engine to the boat therefore creates the bond between engine and hull. No! You do not connect the negative lead of any accessory to the hull. You run that wire directly to the battery or via a ground buss to the battery.
 

BatDaddy1887

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The instant you bolt an engine onto an aluminum hull you have a hull connection to the negative terminal of the battery. Don't believe it? An ohm meter will prove it.The negative terminal of the battery is connected to the engine block via the negative battery cable. The bolts that mount the engine to the boat therefore creates the bond between engine and hull. No! You do not connect the negative lead of any accessory to the hull. You run that wire directly to the battery or via a ground buss to the battery.

OK, that all sounds reasonable. But my transom is wood encased in fiberglass. Do you think bonding still occurs?

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bruceb58

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OK, that all sounds reasonable. But my transom is wood encased in fiberglass. Do you think bonding still occurs?
Get out your meter and measure ohms from the fuel fill neck to your negative post of the battery.
 

midcarolina

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Jul 16, 2013
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Here is what the USCG say's about bonding fuel systems, there is no mention on bonding portable tanks, as the law is clear that all portable tanks are to be filled ashore. [h=3]Manufacturer Requirements[/h]
FEDERAL LAW
183.572 - Grounding
Each metallic component of the fuel fill system and fuel tank which is in contact with fuel must be statically grounded so that the resistance between the ground and each metallic component of the fuel fill system and fuel tank is less than 100 ohms.

Fuel flowing from the dispensing nozzle into a fuel tank is a potential source of a static electric charge which could cause a spark between the dispensing nozzle and metal component of the fuel tank fill system. To prevent such a spark from occurring, metallic components of the fuel tank fill system and metallic fuel tanks must be grounded.
Grounding or bonding may be accomplished by connecting the metallic components electrically by running a wire from one component to the next, and so forth to the boat’s ground. Grounding can usually be accomplished by a connection to the common bonding conductor or the engine negative terminal.
If the fuel tank deck fill fitting is nonmetallic, and nonconductive hose is used as a fill pipe, there is no need for grounding the fill fitting. Chrome-plated plastic fill fittings are treated the same as metallic fittings.
NOTES:

  1. If a metal hose attachment fitting is used, it must be grounded.
  2. Fill cap retaining chains need not be grounded.
FIGURE 36 - Fuel Fill System Grounding
CAUTION
BONDING WIRES PUT UNDER THE END OF A HOSE COULD CAUSE A FUEL LEAK. The bonding wire should be a "bolted connection" on the tank’s ground tab. At the deck plate the bonding wire may be securely connected to a ground fitting provided on the deck plate, or securely connected to a deck fill plate bolt.

TO COMPLY WITH THE LAW
  • Are metallic components of the fuel tank fill system and the metallic fuel tank grounded?
  • Is the resistance between each of these metallic components, including the metallic fuel tank and ground less than 100 ohms?
 
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