Wiring problem

[Seahorse]

I was adding LED lights on boat.
put the lights in, then opened up box that housed the switch panel.

just as I opened the panel, i could see smoke on the earth wire on motor. I dissconnected battery straight away.

this wire is only about 6 or 8 inches long and is heavy guage.

is goes from aluminium pplate to motor frame.

it had plastic over it but burnt the plastic, leaving the wire only. Its a really heavy stainless steel looking wire.

The prob was , that i later saw a slit in the earth wire from battery to switch and it must have touched part of the boat when i opened the box.

The motor is fine. Starts, power and trim works.

should i replace the wire ? Its just got a screw on either end.

whats it for?


cheers
greg

[Seahorse]

Pic of wire

[Spaniard_King]

It's a bonding wire to connect the aluminium of the engine to the anode so that the anode corrodes and not your engine. If it's still in tact leave it.

Make sure you protect the positive circuit from the hull at all times, do you have a battery isolator?

[Seahorse]

Hi Garry
wire is still in tack, just missing plastic on outside.
i dont have an isolater switch.
I have now run my switch panel to a separate battery, thats not connected to the main battery.
Do ii need an isolater switch between that battery and panel switch?
My main battery is now only used for starting.

may have been an overkil for the separate battery, but i feel safer.

thanks a lot Garry, i was worried i had done damage somewhere.

cheers Mate
greg

[scottar]

As Gary has already touched on, you need to make sure the positive never comes in contact with the hull as it is a Negative via the outboard. Best way to do this is disconnect the battery via a switch or removal of terminals any time you are doing work. Unfortunately the manufacturers of some of the switch panels dont tend to leave a heap of room around the exposed positive connections so it is almost inevitable that you will bump the alloy in the process of getting it out.

[Fed]

Your fuse should have blown.

[davo]

You refer to an "earth" wire on the boat. You should only have a positive and negative on the boat and no connection to the alloy hull. Your outboard negative is connected to the outboard frame but that is it. Earth the alloy hull with the wiring and you will cause electrolysis to the hull.

[Reel Hard]

Davo is correct. You need to run everything above ground. Ie, run an earth wire back to the battery and run all your accessories via this and not the hull. And make sure you use a thermal breaker at the battery and fuses at the switchboard.

[Seahorse]

I havnt earthed to the hull. I have a 4 switch panel, with fuses on each switch.
The positive wires go to each switch and the negative wires to a common post inside panel.
i then run another wire from that neg post to neg on the battery.
I then run the pos wires from each fuse to a common post and then run a wire from that pos post to the pos on battery, with a in line fuse with 20 amp fuse.
no fuses blew today.
what is a thermal breaker.

[scottar]

Your fuse will do the same job. There are two schools of thought with the "earthing" of a hull. You should definately not use the hull of a boat as an accessory earth/negative as the flow of current will cause electrolysis. This has brought about the thinking that "earthing" the hull is a bad thing. The other thinking is that the hull should have a single heavy negative connection to provide an "earth" for situations exactly such as has occured. The hull is effectively connected to negative anyway through the motor but due to paint/sealant Seahorse's motor has electrical resistance between itself and the hull sufficent to prevent the fuse blowing. If there had been a negative link to the hull, there would have been a spark, the fuse would have blown and that would be that.

An ex client I ran into the other day has just had something similar happen in a Sailfish Cat. His vessel however has inboard diesels that are isolated via flexible engine mounts. When the positive touched the hull, the only return path it could find was via a gauge clamp/bracket behind the dash and it consequently melted the negative to the gauges. Once again, had there been a negative to the hull, the fuse would have blown.

[Seahorse]

I think i have the problem all solved now. I saw a split in the neg wire from battery to switch. I could see the wire through the plastic.

I think this wire touched the hull as i open the box and moved the neg wire.

up till then all the accessories were working fine.

as i said before, i now run all access and panel swith to a separate battery that is a stand alone battery.

i will just trickle feed this battery after each use.

i think i prefer it this way because if something does happen then it wont go through the main battery and back into the motor.

maybe a little extra work with charging after each trip, but i condider safer.

thanks everyone


Cheers
greg

[Fed]

I then run the pos wires from each fuse to a common post and then run a wire from that pos post to the pos on battery, with a in line fuse with 20 amp fuse.
no fuses blew today.
If it's wired as you described then it should have blown the 20A fuse, it takes far more than 20A to melt the insulation off one of those grounding straps.
Did the wire heat up along its length or was the heat concentrated at one end?


is goes from aluminium pplate to motor frame.
Where exactly is each end of that burnt wire connected to?
Does the wire look original or does it look like an add on?
What motor is it?

It's important that you find out what happened, why it happened and how the boat is wired.

Here's a question....
Why didn't the current which had to be well in excess of 20A flowing through that wire blow the 20A fuse?

Ground the hull separately or ground it through the motor, you're damned if you do & you're damned if you don't?
It does raise an interesting point though, grounding the hull through the motor means the main accessory fuse should be in keeping with the size of the motor ground strap between the transom bracket & the engine block.

[scottar]

It would probably be worth running a resistance check between the two components of the motor that that ground wire is connected to. If there is resistance there it may explain the heat.

[Seahorse]

Yes the wire goes from aluminium plate to motor.

the wire still in tack and look good except no plastic on outside.

it was the earth wire from the switch to the battery that caused it i feel.

That wire had a cut in it and wire was exposed.

I think it was this wire that touched the hull as i opened the box.

As i said there wasnt a problem till i moved the wires around.

Garry said that if wire still in tact, just leave it.

motor is 50 hp 4 stroke.

Iam now running a separate stand alone battery for all accessories. Nothing goes through main battery.

cheers
greg

[scottar]

A negative touching the hull shouldn't cause any dramas unless there is something else amiss. A positive definately will though. The hull should be at negative potential already through the motor.

[Seahorse]

Dont know Scottar.

i just thought it was the neg wire. Everything was ok till i opened the box and pull out the switch.

Maybe another wire touched somewhere.


Cheets
greg

[Noelm]

Not exactly sure I am on the same page here but.... normaly the bonding wires on the outboard do not have insulation on them in the first place, so not sure how the plastic melted off it? Even if for some reason it did, why did it melt when the motor is bolted to the Aluminium boat, with conductive bolts?, the fuses on the switches wouldn't blow because the short was before them (I think, if I am reading this right)

[scottar]

The circuit would have gone from the positive to the hull to the mount ,through the bonding wire to the outboard and back to negative. I have seen some of the bonding wires with a bit of plastic tube over them over the years. I don't know whether there are some sort of insulating bushes in the tilt tube assembly or whether it's just the grease - never pulled one apart. The fuse was the main 20 amp at the battery. Can only assume it didn't draw 20 amps. If the wire has a bit of resistance in it, it could certainly get hot with less.

[Fed]

Good point Scott could be special wire I know on my motor the wire is insulated and doesn't look or feel like copper.

[Seahorse]

Its like stainless wire

[Spaniard_King]

All bonding wires are stainless and most are coated in plastic.

taking a step back... you have an earth wire from the battery going to a switch? is this right. The problem you have had is consistant with the positive wire touching the hull and making a circuit back through the bonding wire through the negative battery lead to the battery.

[Reel Hard]

Thermal breakers are normally reset with a button, once the short is corrected of course.

I think Gary is onto it. But it should have blown that 20 amp fuse. Recheck the wiring.

[scottar]

If the cable and tilt tube assembly has as little as 0.7 ohms resistance the fuse will be borderline as to whether it will blow or not. If it has 1 ohm resistance(not much and it keeps the maths simple) it will only draw 12 amps at 12 volts. It will however be trying to disipate 144 watts of power that is being turned directly into heat. It will get hot rather quickly if that is the case but it wont blow the fuse. We used a one ohm 200 watt resistor for load testing autopilots on 12 volts and they would glow red if you left them long enough. I don't think Seahorse has a negative going to a switch - just a miscommunication. From his previous posts it goes to a post setup where the switch panel is located

[Seahorse]

I dont have a neg wire going to the switch. All the neg wires from the accesories go to a post bolt that i have sat inside the box that house the swich panel.I then ran a heavier guage wire from that same neg post bolt to the neg post on the battery.

The only wires that are attached to the switch panel are the pos wires from the accessories and the ones that are already there with attached fuses.

There is one positive wire that comes from the switch panel that is attached to the fuses.

i have put this wire on another post bolt. I then attached a heavier guage wire from that positive post and ran that to the positive on battery with an inline 20 amp fuse.

Hey Garry, do u think i have done any damage to motor. It all starts and power trim and everything works.

cheers
greg

[Spaniard_King]

I dont have a neg wire going to the switch. All the neg wires from the accesories go to a post bolt that i have sat inside the box that house the swich panel.I then ran a heavier guage wire from that same neg post bolt to the neg post on the battery.

The only wires that are attached to the switch panel are the pos wires from the accessories and the ones that are already there with attached fuses.

There is one positive wire that comes from the switch panel that is attached to the fuses.

i have put this wire on another post bolt. I then attached a heavier guage wire from that positive post and ran that to the positive on battery with an inline 20 amp fuse.

Hey Garry, do u think i have done any damage to motor. It all starts and power trim and everything works.

cheers
greg

No Greg your engine will be fine, no current has passed through any of the critical wiring.

The positive wire that has touched the hull must be before any fuse in the circuit hence no fuse has blown

[Fed]

The positive wire that has touched the hull must be before any fuse in the circuit hence no fuse has blown
Or as scottar said, the ground strap had some resistance in it that stopped the fuse blowing.

I've always been open as to grounding the hull separately or only grounding through the motor but I'm starting to feel swayed towards a separate ground strap now.

Maybe the Yanks & Quintrex have got it right after all, either way it's a can of worms.

Accurately measuring the resistance of the ground strap could answer a few questions.

[Seahorse]

Thanks Garry, much appreciated.

thanku scottar for ur help as well.

cheers
greg