what gauge wire?

[1st grady]

I would like to run a new feed and replace the fuse block under the helm because I seem to have a voltage drop somewhere in the system.
What gauge wire will be required to supply 40 amps to the helm?
Is 40 amps adequate for the spreaders, FF, sonar, AMFM and VHF?
Do all the accessories also run off this main panel? (windshield wipers, washdown, fresh water system etc? )
I have a 95 Islander so I figured it was time for some electrical repair. While drifting, the FF shows low voltage and some systems shut down but the battery is strong. Last year I removed the fuses and the contacts were green so I cleaned them and replaced some of the fuses that looked corroded.
I don't plan on a total rewire job, just power to the fuse block and ground strip.

 

[Boats Rock]

When you cleaned the fuses did that correct the low voltage situation?

 

[seasick]

You should attempt to find the cause of the voltage drop. It could be a bad battery terminal or anything up the line to the electronics. Turn on some gear (motor not running) and measure the voltage at the battery positive terminal and ground. Should be about 12.5volts.
Now measure at the main feed of the fuse block. It will be lower but shouldn't be less that about 11 volts with all the gear on. If it's lower, you now need to determine if the drop is in the supply (positive) wiring or the return (ground) wiring. Using a piece of wire as an extension to the volt meter, measure the voltage from the negative battery terminal to a ground at the fuse block. There should be less than a few tenths of voltage. If you see more, the bad wire/connection is in the ground side. Otherwise it is in the positive side of the wiring.
If it's in the positive side, measure the voltage from the positive battery terminal to : The end of that battery cable, before and after the battery switch, the hand off to the accessory feed (a smaller gauge wire) etc.
As you move along you will see some voltage drop but not a lot. If you measure more than a few tenths, the problem is in the last section tested.

You can replace the accessory feed wire but there is a pretty good chance that it is not the problem.

With respect to wire gauge, the size depends on the length of the run and the current draw. There are many web sites that will help you size the cable. The old one should have markings and that is probably a good size. Going to a bigger (lower gauge) supply wire may not add anything if the return (ground wire) is a lower gauge.

Good luck

 

[1st grady]

Thanks seasick, that was some great info. I have saved the document and as soon as the weather breaks I will start checking the wiring.
After cleaning the fuse block, I still had low voltage to the electronics.

 

[Grog]

If you're going to run new wire, I'd run a #6 (tinned wire) and use a 50A fuse or breaker. It's a little overkill but better than not having it if you need it. Your voltage loss can be by the batteries, main breaker or at one of the crimps in the fuse panel. The factory wire isn't tinned and will corrode, especially at the crimps.

 

[SBLGFD]

I had a similar issue in my 96 Sail Fish – Bought it last spring and during the summer while trolling my voltage would start to tank – sometime below 10 volts showing on the Fish finder causing malfunctions of the electronics – if I would run both engines I could get my voltage back. Never seemed to effect the batteries – starting ect. So I set out to rewire and as I went discovered multiple ground issues – poor grounds or grounds not connected all resolved, I did not replace my helm feeds, switches or fuses. Only corrected the ground issues and rewired the electronics box. Added a fuse block and a ground bar there. Now no issues troll all day long and stay around 13+-.

SBLGFD

 

[1st grady]

I was looking at the Blue Sea Fuse and Grounding System. Maybe thats all it will take. I will probably change the E-box fuses as well. Thanks

 

[Boats Rock]

Don't forget to use dielectric grease on the connections.

 

[seasick]

Don't forget to use dielectric grease on the connections.

After you make the connections!
By it's nature, dielectric grease in non-conductive.

 

[plymouthgrady]

And don't forget to use heat shrink butt connects, ring terminals, spades, and heat shrink tubing.
IMHO, if you're not going to heat shrink your work, don't bother doing it because you'll be doing it over again next year. "do it once, do it right".

 

[seasick]

Look for Ancor adhesive lined heat shrink tubing. West Marine carries it as do many marine supply stores.

 

[BobP]

Grog, he can use the same 40A breaker with any larger size wire he wants, just can't make the wire size smaller.

Not that new wiring may help the problem.

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I had discovered an excessive voltage drop in the hardtop feed, way moe than it should have been from my calcs.

I disconnected both ends and abandoned the existing feed and found another route for a new feed, end of problem. What is wrong with the existing feed I may never know.

 

[Grog]

Grog, he can use the same 40A breaker with any larger size wire he wants, just can't make the wire size smaller.

Not that new wiring may help the problem.

-----------------------------------------------

I had discovered an excessive voltage drop in the hardtop feed, way moe than it should have been from my calcs.

I disconnected both ends and abandoned the existing feed and found another route for a new feed, end of problem. What is wrong with the existing feed I may never know.

It may be OK but it's also a 13 year old breaker that isn't in the best of enviorments.

 

[BobP]

true, then he shouldn't replace it with a button breaker like the existing one, no good back there, best to have one of the waterproof switchable types.

I'd still like to see the voltage drop test results on a diagram before dropping a dime since there is a problem. Easy enough to do.

My main feeders and everything at the stern has been replaced, so as not to have any mid season nuisances. Season is too short to begin with. All my cables are heavier than original, but main breaker stayed 40A. I even rewired totally the FW & SW pump and macerator pump feeds, the 16 AWG size originals just doesn't cut it for me. I think I went to 12 AWG or heavier.

 

[1st grady]

Seasick,
What you are saying is that the voltage drop may not be evident unless there is a load placed on the system. I did not fire everything up but did check V at the fuse block. 12.48V and the battery read 12.49V.
All electronics are off the boat for now so getting everything running would take some work.

Just a couple of notes for any battery Gurus:
AM/FM draw is listed as 10 A (on most of the time)
Wash down listed at 15 A (only during actual use)
GPS 7.5 A (on all the time)
VHF 5.5A (on all the time)
Sonar 1 A (on all the time)
39 A total

These loads are all off the same group 27 house battery. It seems like a large draw when everything is on.

I did notice that I had an unused 20 A line up in the E-box that is supposed to be for the VHF. I will be changing the VHF and AM/FM over to this line but it still feeds from the House battery.

 

[seasick]

Seasick,
What you are saying is that the voltage drop may not be evident unless there is a load placed on the system. I did not fire everything up but did check V at the fuse block. 12.48V and the battery read 12.49V.
All electronics are off the boat for now so getting everything running would take some work.

Just a couple of notes for any battery Gurus:
AM/FM draw is listed as 10 A (on most of the time)
Wash down listed at 15 A (only during actual use)
GPS 7.5 A (on all the time)
VHF 5.5A (on all the time)
Sonar 1 A (on all the time)
39 A total

These loads are all off the same group 27 house battery. It seems like a large draw when everything is on.

I did notice that I had an unused 20 A line up in the E-box that is supposed to be for the VHF. I will be changing the VHF and AM/FM over to this line but it still feeds from the House battery.

If there is no load, there won't be a voltage drop. if you have spreader lights, try turning them on, that might show an excessive drop. Those lights can draw significant current depending on the model.

Note that the current numbers you note seem to be higher that I would expect. You can't add up the fuses to get the draw. While it is true that you won't draw typically more than 80% of the fuse rating, almost all devices draw a lot less than the fuse size. The VFH radio for example, draws very little while receiving. It uses more when transmitting.

If your main breaker at the batteries is 40 amp, the maximum sustained load should be 32 amps or less (80%). Even though you may have 50,60 or more amps total in fuses at the fuse block, you still shouldn't draw more that 80% of the main breaker size.