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Old 27 June 2011, 00:00   #1
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Grounding fuel tank

Hey,

I'm installing a stainless steel fuel tank, and wondering if I should run a grounding wire from one of the tank's brackets back to the -ve battery?

The tank itself has a wema fuel sender (model SSS on Fuel Tank Senders, Gas Tank Senders, Water Tank Senders, Holding Tank Senders by WEMA USA, Inc.)... this sender has a return to ground wire, and the sensor is screwed/bolted to the tank... so am I ok in presuming this sender and the fact it's screwed into the tank will offer any grounding requirements of the tank itself (e.g. during filling etc).

Happy to put an extra cable from tank bracket to -ve terminal if it's worth it...

Thanks
Rob
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Old 28 June 2011, 15:47   #2
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Hate to bump a thread (sorry), but any thoughts?

Thanks
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Old 28 June 2011, 15:52   #3
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Would "earthing" to the battery, provide any advantage from a static spark which is presumably part of your concern during filling?
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Old 28 June 2011, 15:55   #4
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Quote:
Originally Posted by Polwart View Post
Would "earthing" to the battery, provide any advantage from a static spark which is presumably part of your concern during filling?
I have no idea... my sparky skills are rather limited...

I presume then it wouldn't provide much advantage... so in that case, how/where would one ground a fuel tank to, on a fibeglass and pvc boat?!
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Old 28 June 2011, 16:26   #5
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Ground the tank to earth. Preferably direct from the tank to one of the lower outboard mounting bolts.
Also electrically bond the filler to the tank.
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Old 28 June 2011, 16:38   #6
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Thanks for the reply.

Running a grounding wire from the tank to the outboard mounting bolts would be pretty tricky unfortunately... also would mean any such grounding cable is pretty much guaranteed to get soaked everytime the boat gets wet and would be exposed... would that not be a problem?

re 'electrically bond filler to tank' -- run a ground cable from the tank to the filler cap? The filler pipe is a woven matting type stuff, with cable running through it - it's only the cap itself which is metal...

Thanks for your patience in my lack of electricalness!

Cheers
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Old 28 June 2011, 16:42   #7
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Trying to think about this logically I'm not sure grounding it would actually be a good idea. I presume the principal risk is from static building up in the tank and then suddenly discharging when you bring the pump nozzle to the fill pipe. The likelihood is that you have a rubber fill pipe so there is going to be no two metal parts close enough to each other to create a spark risk. If you do ground it to a proper ground then I would have thought there is a small risk that if there is a fault in your boat wiring or with the sender then there is an immediate discharge point which may actually induce a spark rather than prevent one. It is possibly a bit like equipotential bonding in a bathroom. You don't connect a metal bath to the earth circuit because a fault in that circuit would electrocute anyone in the bath at the time.
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Old 28 June 2011, 16:47   #8
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Thanks Erin, that does make sense...

The fill pipe is a woven matting with metal cabling through it, which is exposed at the ends (because it's been cut).

Would this change the scenario in that there could be two metal parts close enough?
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Old 28 June 2011, 16:56   #9
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I suppose there is a slight chance of continuity. I don't know enough about static electricity to know the risks, nor for that matter how petrol pump nozzles at fuel stations cope with it as static can be created by flow of liquids particularly in plastic materials.

There is a great bit of footage of a woman in America getting out of her SUV while on her cellphone and starting to fill her car up. There is an almighty explosion and ever since they have banned using phones at petrol stations. Someone tried to explain that being on the phone was just coincidence and not the cause. They had a convincing argument too which I can't fully remember.

Your best bet would be to read up on the Lloyds or USCG guidance for fuel tanks. That will state best practice.
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Old 28 June 2011, 17:13   #10
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Just a few things to consider that most of us don't think about.

As had been mentioned before, static discharge during refueling is an issue.

Grounding all metal objects together in a boat provides protection during lightning strikes by providing a path for the lightning to go into the water without arcing between metal objects or you. This is especially important on yachts with masts but when you are out at sea, chances are your boat will be the tallest object around during a lightning storm.

Grounding is also meant to deal with galvanic corrosion for boats that spend a lot of time in the water.

You have a stainless tank and if you have an aluminum boat, you have dissimilar metals. Some salt water sitting under your tank or even some dried salt that is back in solution thanks to some rain water will complete the reaction. The aluminum will in time be eaten away unless the tank is electrically isolated from the boat. It will be in an area (under the tank presumably) where you are not likely to see it until it is too late. If you can't put something non metal in between to isolate it, use a product like Duralac to stop the electrolytic corrosion.

Electrolytic corrosion is why even motor vehicles now all have negative earth.

In short, make sure you don't have dissimilar metals touching and use a decent size grounding wire on everything metal in your boat if you want to do things according to the book.

As for your tank, if you have positive and negative from the sender, it will work without an extra ground wire.
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