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cliffdykes · 31-10-2010, 08:00

Ok, so here's my stupid question of the day.

I'm fitting instruments on the helm. There are none at present. The cable run is about 12 feet from a suitable internal switch panel. The instruments are from the Nasa Clipper range - Easylog, wind, depth and compass.
Is there any reason why I can't run a single power cable to a busbar in the instrument panel and then run individual cables to each instrument, as long as I size the single cable for the combined current for all 4 instruments?

Sorry but electrics makes my head hurt!

Cheers
Cliff

rebel heart · 31-10-2010, 08:30

It's six vs. half a dozen on running individual power lines. The only thing I'd be wary of is putting a bus bar in an area that isn't *very* sealed off from the weather. If you run individual lines, you shouldn't have a single piece of exposed metal anywhere outside of the bus bars in the battery compartment.

If you run one big line to the helm, you'll need to have a bus in a potentially not-so-well-sealed-up environment.

If the place where the bus bar is won't ever see a drop of water or a droplet of sea spray, go for it.

The only other thing is that you can get wire sprawl if you do too much of it. Make a few decisions like that and you'll have buses and breakers all over the boat rather than confined to a single area.

It's not the end of the world though.

Mambo · 31-10-2010, 08:38

Can't you "daisy chain" them?

That would allow you to jump one to the next and avoid both multiple feeds and the bus you are proposing. I would think this would be covered in the install instructions or on the NASA Instruments website. If not, try an email to the company tech support.

sailvayu · 31-10-2010, 08:47

Yes nothing wrong with the buss bar, Fuse/Breaker the main feed line within 7" of the power source. If you are coming off a main house panel just add a breaker, if you are coming off the battery switch add a in-line fuse big enough. Sorry Mambo but I do not recommend daisy chain approach. places the full load on the first instrument, if one connection fails it will take out everything behind it and you would have to run one lager wire to the first instrument.

goboatingnow · 31-10-2010, 13:12

Given that these instruments draw little current daisy chaining is fine

Dave

CharlieJ · 31-10-2010, 13:20

Daisy chaining anything is inserting the possibility for an additional single point failure mode into a system with no real gains. I do not recommend this practice.

Charlie

capt_douglas · 31-10-2010, 14:03

While I see no reason you couldn't daisy chain them, and save a circuit breaker for another use, you might want to consider which one(s) you're going to want on 24/7. I tend to turn off all but depth when I'm on the hook or moored. If I had wind sensors then I might turn them on when the weather piped up, but I don't see the need to have speed on when at the dock or on the hook or mooring.

cliffdykes · 01-11-2010, 02:27

Sorry but I don't understand this - surely if the instruments are daisy chained from a switch panel then they are either all on or all off?

The new panel by the way is pretty well sealed with just a small hole down into the box below so the bus bar is an option which could work.

Information on the Nasa website is sketchy to say the least but I'll try an email.

Cheers
Cliff

Privilege · 03-11-2010, 17:40

Running a single bus bar does make sense. (You will also need one for the negative returns). Each of the positive feeds from the bus to each instrument can then have it's own on/off switch if you want one or you can have one on/off switch for the whole lot before the bus. You are correct that a daisy chain is either all on or all off. Make sure that your fuse or breaker is sized to suit all of the instruments being on at the same time.

**David M** · 03-11-2010, 17:55

Nooooo! Do not daisy chain them. You cannot wire loads like this in series. You will have a significant voltage drop if you do this. Each instrument power wire must be wired in parallel to the source...in this case the bus, that I think you should install.

Remember to twist all your DC wires so there is less magnetic influence on your compass.

I like the idea of running some larger gauge wire up to the instruments and creating a bus. You will need to know sum of the draw of all your instruments, need to know the length of the run and then size the wire for a 3% drop at most.

sailvayu · 04-11-2010, 04:03

Voltage drop may not be a big issue here but the main issue is that if you have a connection failure then us lose everything behind the failure not just one instrument. Also you need each instrument to have its own fuse or breaker. A very simple solution is to install a 4-6 fuse block. Run your main power to that (fused at the source of course) and then just attach each instrument to a single fuse. Get a fuse block with more fuses than you need that way you can add more stuff (not that we ever add more stuff) Use a larger feed line than you need so that you have the size to cover expansion. This really is fairly simple and straight forward no need to over think it and make it harder than it needs to be. What I suggest is standard practice and done all the time and works

jannw · 04-11-2010, 04:35

for water tightness you can mount the busbar into some tupperware, with tight holes slopped with silicone sealer for the in and out cables ... makes a watertight but accessible and mountable enclosure for cheap

cliffdykes · 04-11-2010, 06:10

Thanks for all the contributions. I do like the idea of running to two busbars and then a fuse block to each instrument. It will be much easier to run two slightly larger cables than eight smaller, especially as they need to run through a 31mm armoured cable glassed under the bridgedeck which will also have to contain the data cables for wind, compass and depth, as well as the cable for the RAM mic linking to my VHF in the starboard hull.
It's going to be pretty tight!

Cheers
Cliff