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Old 23-09-2020, 12:21   #1
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Identifying a wire on my diesel tank

Hi,

Due to Covid I'm not able to get to my new to me boat. Here's a pic of the diesel tank. This is my first boat with inboard diesel and I want to make sure I understand the connections. Bottom right is a plug that unscrews for so I can use the wooden dipstick visible in the pic. There's a red wire that connects to the tank also. I'm not sure what this is for. There's no fuel gauge, hence the dipstick, but I'm not sure what else this could be for. Grounding maybe? I would have thought it wouldn't be red. Suggestions?
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Old 23-09-2020, 12:29   #2
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Re: Identifying a wire on my diesel tank

Looks like a grounding wire because it looks like itís connected to a tab welded to the tank. Maybe whoever put it there just didnít have the correct color.
Where does the wire go?
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Old 23-09-2020, 12:54   #3
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Re: Identifying a wire on my diesel tank

It looks like a grounding wire (should be green). A gauge would be connected to a sender.
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Old 23-09-2020, 13:06   #4
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Re: Identifying a wire on my diesel tank

Hopefully I will soon be able to get to it. I don't know where it goes. Odd that the wrong colour was used as the PO was particular...though perhaps he was colour blind. Good point about what it's attached to so I guess grounding it is. So it's normal to ground a diesel tank?
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Old 23-09-2020, 13:08   #5
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Re: Identifying a wire on my diesel tank

Looks like it is strapped to the fill hose. My bet, if you trace it to the other end it is connected to the metal deck fill plate to allow static discharge from the nozzle when filling. Since the hose is non-conductive someone put in a conductor to connect the fill plate to the tank electrically.
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Old 24-09-2020, 09:45   #6
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Re: Identifying a wire on my diesel tank

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Originally Posted by Dsanduril View Post
Looks like it is strapped to the fill hose. My bet, if you trace it to the other end it is connected to the metal deck fill plate to allow static discharge from the nozzle when filling. Since the hose is non-conductive someone put in a conductor to connect the fill plate to the tank electrically.
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Old 24-09-2020, 10:15   #7
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Re: Identifying a wire on my diesel tank

Should a fuel tank also be grounded to the engine block?
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Old 24-09-2020, 10:26   #8
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Re: Identifying a wire on my diesel tank

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Should a fuel tank also be grounded to the engine block?
That would be my swag.
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Old 24-09-2020, 11:19   #9
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Re: Identifying a wire on my diesel tank

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Should a fuel tank also be grounded to the engine block?
Often pretty much everything metal is bonded together with the ideal of it all being protected by an anode that way.
Other school of thought is to isolate all the metal bits so that stray current canít get them all. Both schools seem to work.
Then there is the idea of bonding all metal bits as a part of a lighting protection scheme, who knows if thatís effective or not.

Iíd buy the bonding to prevent static discharge, except the way to do that is to bond the fuel filler to the vehicle being fueled, and Iíve never seen that on boats, or ground vehicles, only aircraft for some reason?

Real answer is to see where it goes, likely to the engine block eventually, but may go to other metal bits on the way. Often bonding is a series connection as opposed to each metal bit having its own bonding wire.
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Old 24-09-2020, 11:41   #10
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Re: Identifying a wire on my diesel tank

For gasoline boat fuel systems it is a federal requirement for boat builders that all metallic components of the fuel system and the tank be grounded. I don’t know if there is any such requirement for diesel systems.

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Old 24-09-2020, 11:54   #11
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Re: Identifying a wire on my diesel tank

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Should a fuel tank also be grounded to the engine block?
We have a black wire that goes from the deck filler to a bolt on the fuel tank inspection hatch before wandering off to a negative bus bar, which also joins the hull anode and engine block etc.

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Old 24-09-2020, 17:55   #12
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Re: Identifying a wire on my diesel tank

My surveyor wanted ( not unreasonably ) a wire from fuel fill to the tank. I only had red at the time so thatís what is there.
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Old 24-09-2020, 18:12   #13
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Re: Identifying a wire on my diesel tank

I had always assumed that when you buy fuel for your road vehicle, the fuel nozzle you insert makes metal to metal contact before any fuel flows. Presumably to prevent static discharge, which reduces the likelihood of an exciting day out. The fuel hose presumably has a secure and mandated internal wiring pathway to the fuel bowser earth.
So one would hope/expect the same thing for a boat. However! The fuel delivery company can't always be sure that there is an electrical connection to the tank and I have seen a fuel delivery company supply and use their own cable connection.
Also, many boats have long non metalic fuel hoses from the deck inlet to the tank and fuel flowing along these hoses may be prone to static charge build up during rapid fuel flow. Large diameter fuel hoses that meet safety standards do actually have internal metal spiral wires, but this is not a guarantee that the wires make contact with metal fittings at both ends. (Not applicable to outboard fuel tanks apparently.)
So if that red cable shown does not make it to the metal deck fitted fuel inlet, I would ensure that problem was addressed. Frankly, the colour is irrelevant, but the colour choice might have been the installer trying to imply that the cable is not an "earthing" connection (i.e. not connected to the engine negative earth) but rather a special wire for specifically connecting the metal tank to the inlet - although red seems a bit alarming... Maybe earthing a fuel tank might make it a "target" during a lightening strike?
The position becomes further blurred if the fuel tank is nonmetallic as many now are.
Fire outbreaks at fueling outlets are not uncommon so a thorough check might be in order. Ask your friendly local fuel delivery company what they expect/prefer. I asked around locally and the general comment was that it was not all that relevant on small boats - which wasn't much help at all.
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Old 24-09-2020, 18:16   #14
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Re: Identifying a wire on my diesel tank

Vent hose or fill or big red maybe ground small red...... Follow where it goes.
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Old 24-09-2020, 18:36   #15
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Re: Identifying a wire on my diesel tank

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Originally Posted by Dsanduril View Post
Looks like it is strapped to the fill hose. My bet, if you trace it to the other end it is connected to the metal deck fill plate to allow static discharge from the nozzle when filling. Since the hose is non-conductive someone put in a conductor to connect the fill plate to the tank electrically.
You are correct except that the most fuel fill hoses are wire re-inforced therefore conductive.
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