Grounding fuel tank

rjbathgate · 27 June 2011, 04:00

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

rjbathgate · 28 June 2011, 19:47

Hate to bump a thread (sorry), but any thoughts?

Thanks

Poly · 28 June 2011, 19:52

Would "earthing" to the battery, provide any advantage from a static spark which is presumably part of your concern during filling?

rjbathgate · 28 June 2011, 19:55

Quote:

Originally Posted by Polwart

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?!

Searider · 28 June 2011, 20:26

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.

rjbathgate · 28 June 2011, 20:38

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

Erin · 28 June 2011, 20:42

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.

rjbathgate · 28 June 2011, 20:47

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?

Erin · 28 June 2011, 20:56

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.

kubcat · 28 June 2011, 21:13

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.

rjbathgate · 28 June 2011, 21:19

Thanks - this makes interesting reading: New Boatbuilders Home Page - Everything Boat Building - Fuel Systems

I think I'm going to go and find an expert, and talk to my local boat builder.

Don't want to blow myself up.

rjbathgate · 28 June 2011, 21:25

Hi Kubcat...

I have a stainless steel tank, sitting on a Fibreglass hull, and have used stainless screws and brackets around the tank for that reason, to prevent dissimilar metals.

The only dissimilar metals would be the metal in the fuel filter and fuel filter fittings, which are close to the tank. Cause of issue?

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

So, does that mean I don't need to worry about anything? I indeed have in and out cables from the sender... what about any connections to the filler cap etc...

This image has extra grounding for tank and filler cap: http://newboatbuilders.com/images/Fuel_Tank.jpg

Thanks

martini · 28 June 2011, 21:52

Halmatic fitted my boat with stainless tanks which, along with the outboards, are connected to an anode. There is also a cable between the tanks and their metal filler necks.

They've been building boats for a while now, I'm happy to take their word on the subject...

rjbathgate · 28 June 2011, 21:58

Ok, having spoke to Marine Electrician:

ground cable from filler cap to tank
ground cable from tank to engine block
less than 1ohm resistance across the lot

I might do it all, and then take it in to show them to get the tick of approval.

really not tempted to blow myself up.

Searider/martini, looks like you were on the ball...

Thanks all

kubcat · 28 June 2011, 22:10

rjbathgate,

Grounding the filler cap to the tank, the tank to the engine and the engine is obviously to the battery negative, so you have a complete loop for lightning and for static discharge while refuelling and as you have a fibreglass boat, no problem with dissimilar metals. No need to worry about fuel filter as they are not connected to dissimilar metals and too small to attract lightning. Even your sender is stainless and you are using stainless fixing screws, so no issues.

Enjoy.

It is nice to use heat shrink or liquid electrical tape on the ends of the wires to stop them going green and eventually failing.

rjbathgate · 28 June 2011, 22:22

Thanks kubcat...

So I now need to run a cable from tank (bow) to engine... not going to be a fun afternoon.

Anyone got a well trained mouse?

kubcat · 29 June 2011, 02:34

You are already running a wire from your tank to your gauge, just make sure it is twin wire, one to the gauge and one to a negative somewhere in your console. The negative in your console will be attached to your engine so you don't have to do it again.

You can then use the mouse to turn a wheel that is attached to a generator that keeps your battery charged ..... hahaha

rjbathgate · 29 June 2011, 02:37

Quote:

Originally Posted by kubcat

You are already running a wire from your tank to your gauge, just make sure it is twin wire, one to the gauge and one to a negative somewhere in your console. The negative in your console will be attached to your engine so you don't have to do it again.

You can then use the mouse to turn a wheel that is attached to a generator that keeps your battery charged ..... hahaha

My negatives in my console run to the -ve on the battery (also in the console) so any quickest route would be to battery, rather than out to engine... does that matter? Can I just bang the tank ground to that? Won't that just give me the same as grounding it directly to -ve post?

My cat keeps on killing the mice... no wonder my battery goes dead over winter!

kubcat · 29 June 2011, 08:13

Quote:

Originally Posted by rjbathgate

My negatives in my console run to the -ve on the battery (also in the console) so any quickest route would be to battery, rather than out to engine... does that matter? Can I just bang the tank ground to that? Won't that just give me the same as grounding it directly to -ve post?

My cat keeps on killing the mice... no wonder my battery goes dead over winter!

I won't bore you with the theory, just bang the tank ground to the battery -ve, that will be fine.

Erin · 29 June 2011, 12:10

The negative post on the battery is not a true 'ground'. To achieve this you would need a proper ground plate fitted to the hull to allow static discharge to the sea. Connecting everything together and linking to the neg post on the battery will not earth the items and may also create corrosion. As Martini stated, his is connected to an anode which will limit corrosion and also act as a partial ground.

Depending on your sender type, the two wires running to it may also not be connected to 12v or 0v but may be just a loop out of the gauge sensing resistance.