Wiring question for behind-helm fuse block(s)

I'm actually thinking of putting another CB back by the battery for the Windless wire. While the one up front works nice as a master switch for the windless, I'm more concerned about any shorts between the battery and the CB at the helm. I need to look closer at the main wire then going to the fuse block. There are actually two bus'es (Fuse blocks) in the berth behind the helm, with electronics and lights. I don't imagine there is a lot of draw, the most amperage coming from VHF transmissions and the radar. Otherwise the GPS, two VHF radios while not transmitting, Fish finder, radar and lights probably don't pull more than 10 amps combined. But suppose I should hook up an ampmeter and see what I'm really drawing.
 
It may be more than you want to wade through, but there was some good discussion of main breaker size and wire/loads to helm in my "Mystery electrical problem" thread started last fall.

Upshot was to figure out your max loads, size the wire appropriately (for round-trip run), and then size the fuse for the wire. I had a 30 amp main fuse and a (IIRC) 12 gauge main helm feed wire, which was basically appropriate for the boat as outfitted (simple/low tech). I calculated my known future loads, plus added a bit of fudge factor for those "little extras," and decided to upgrade to a #6 helm feed wire and a larger fuse (which I say vaguely as I cannot remember right now if I decided to go with 50 or 60 amp fuse after calculating - I'm not with the boat right now).

I've just received most of my new "goodies" and am looking forward to improving things forward of the lazarette :thup I also ordered a windlass (it did come with its own breaker and the main wiring will be the balance of the rolls of #6 cabling I ordered). Whee, project time!
 
Hi Sunbeam, yeah I remember that thread...and had followed it somewhat. I did end up ordering some 6 gauge marine wire off of Ebay for a good price. Even if I don't need to replace the wire that is already on the boat, I may still decide to run another line and keep those two fuse blocks separated.

Bob, regarding the voltage drop, is the drop relative to the amperage, or is the drop constant? Thanks. Colby
 
colbysmith":31ukeix1 said:
Hi Sunbeam, yeah I remember that thread...and had followed it somewhat. I did end up ordering some 6 gauge marine wire off of Ebay for a good price. Even if I don't need to replace the wire that is already on the boat, I may still decide to run another line and keep those two fuse blocks separated.

Bob, regarding the voltage drop, is the drop relative to the amperage, or is the drop constant? Thanks. Colby
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The voltage drop is amperage dependent. The wire is simply another resistor in the circuit and the resistance depends on the length (longer = more resistance) and the diameter (bigger diameter = less resistance). So the more current you put through, the bigger the voltage drop (DeltaV=I*R where R is the resistance of the wire).
 
Captains Cat":3aixzqbq said:
Bob, if you use the breaker for a switch, how do you reverse it?

Charlie
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The breaker or an "on" switch is put near the helm in many power boat applications with large amperage draw to prevent accidental use.--and there needs to be fuse or breaker protection near the battery. Examples are bow thrusters and windlass. Bow thruster, you don't want someone accidentally hitting the thruster (often many stations) when you are docking.

The windlass is perhaps even more serious--you don't want someone hitting the up or down switch when some one is near the windlass, and mangling an extremity.

In the case of the C dory, the up and down functions are done by remote switch at the helm toggle switch (often to a reversing relay) or on the deck with foot switches.

Roger gives an excellent explanation of the resistance of wire, as part of the circuit. You always must figure the "round trip"--length of positive and negative wire. So if it is 15 feet of wire from the battery to the bus bar behind the helm console, figure the total run of 30 feet.
 
2 days in a row of 40 degree weather, but back into ice and cold tomorrow....so anyway I opened the cover a bit and crawled on board my C-22. A few weeks ago I ordered and received some marine 6 gauge "battery cable". Looking today at what was factory, sure looks like 10 gauge wire to me. The Anchor windless is probably 6 gauge (but not quite as heavy as the cable I just bought...probably just sheathing size.) The thermal CB back at the battery is 50 amp. The anchor wire is not fused until just behind the helm seat, where it also has a switchable thermal 50 amp CB. I also bought a 50 amp CB that I will put in the anchor wiring by the battery. Ok, back to the 10 gauge that is factory installed. As of yet, I have had no problems running these items, not necessarily all at once, but many times several at once (including all electronics at night underway....) 2 VHF radios, Radar, Garmin GPSMAP, Navman Fish Finder, and then of course you have the nav lights, cabin lights and bilge pumps. I suppose I could take the time to figure out current draw, but if it ain't broke, why fix it? Yeah, I know.... anyway I'm still rewiring with the 6 gauge cable between the 50 amp thermal CB and the fuse blocks. The boat has the set up with two fuse blocks, so I'll also replace the smaller jumper with the 6 gauge. FWIW, the 6 gauge is pretty thick stuff. (Probably why it's referred to as battery cable! ;-) I got the wire ran in the boat today, but out of time so will finish the project next time we get some more warm weather...
 
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