How to test bonding/grounding using a multimeter

[DaveChina]

I'd like to check bonding on the fuel fill tubes for my port and starboard tanks. I have a multimeter but am not sure where to touch the black probe to. I assume red goes to the fill tube, no?

I got a mild shock the other day fueling up at the marina fuel dock while I had the pump nozzle in one hand and I unscrewed the fill cap with my other. Marina says they had their electricians check all the pumps and found nothing. A mechanic I know said to check bonding on my fill tubes but I'm not sure how to do it properly.

Any assistance would be appreciated.

 

[rkhanso]

Checking for continuity (or lack thereof) doesn't matter what probe goes where. Set the DVM to a mid- to higher range. Make sure the probes aren't touching anything and the meter will show whatever it represents for infinity. Touch the two probes together and it will go to 0 ohms. This is a test to make sure the meter is reading correctly.

Now you can check your fill tube and ground of your boat.

I found this info online:
The green wire you are referring to is a grounding wire for the fuel fill. It is there to prevent a spark when you put the nozzle from the pump into the fill pipe. This wire is NOT part of your electric system but should be wired DIRECTLY to the negative bus bar or negative post of your starting battery with a minimum 14 ga. green wire.

 

[DaveChina]

So if I want to see whether the fill tube is grounded/bonded I touch one probe to the fill tube and the other probe goes where?

 

[flashback]

So if I want to see whether the fill tube is grounded/bonded I touch one probe to the fill tube and the other probe goes where?

Battery - post

 

[DaveChina]

 

[dingbat]

Marina says they had their electricians check all the pumps and found nothing.

Call their BS….there is a 99.99% probability it’s a grounding problem at the pump.

A mechanic I know said to check bonding on my fill tubes but I'm not sure how to do it properly.

The fact that you got shocked proves the bonding back to your battery is in tact

You got shocked because of a difference in ground potential (path of least resistance) between the pump and your boat.

If the pump would have been grounded properly it would not have happened

 

[DaveChina]

I've been told that by others too.

But ...

yeaterday afternoon I tested the fill tube/cap at my boat yesterday and if I'm using the multimeter correctly there's 3.2 volts coming off my fill cap on the starboard side while the port side shows 0.0.

This is with the battery switches both OFF.

 

[dingbat]

I've been told that by others too.

But ...

yeaterday afternoon I tested the fill tube/cap at my boat yesterday and if I'm using the multimeter correctly there's 3.2 volts coming off my fill cap on the starboard side while the port side shows 0.0.

This is with the battery switches both OFF.

Reverse the leads on the voltmeter and retake your reading. If you get negative -3.2 VDC you have a short (leak) to ground.

Locate and remove the power to the bilge pump. Typically wired directly to battery. If wired to switch, remove the positive cable to each battery and retest.

 

[mike_i]

If you got a shock while fueling I would measure voltage before I'd check for continuity. I would put the neg probe on the battery ground and the pos probe on whatever you were touching when you felt the shock. If your meter is on a resistance scale and you have a voltage across those two points your resistance reading will be irrelevant. Since for some reason your getting shocked I would either first check for voltage or disconnect the batteries if trying to measure resistance.

 

[DaveChina]

Had a marine electronics guy look at it. He said one of the fuel tanks was not grounded so since the welded grounding tab on top of the tank had broken (corroded) off he grounded to a fuel sender screw. He took readings and didn't find any voltage.

However, I fueled up afterward and I'm stll getting that tingly low-voltage sensation in my fingertips. On BOTH filter caps now!

Happened with batts OFF.