Trying to install a new panel and very frustrated

[john61ct]

Yes, but that is the maximum it supports.

You should size the wire for the maximum current the devices you plan to run off it will draw at a time.

Maybe "show your work" here for feedback.

[Cthoops]

Originally Posted by john61ct

Yes, but that is the maximum it supports.

You should size the wire for the maximum current the devices you plan to run off it will draw at a time.

Maybe "show your work" here for feedback.

Thanks, John. I'll do that. Heading home soon.

[Cthoops]

O.k. I'm home now. Adding up the amps at any given time, I calculate 24.25 (we have all LED lights for interior and exterior which helps a lot). I assume I can bump it up to 30 to account for things we may want to buy that we haven't thought of yet?

Using the Blue Seas circuit wizard, that gives me 6 awg wire for our run which is approximately 25 feet round trip. Since it's a single wire, we should use a 125amp ami or midi fuse in a fuse block.

Sound good? I think I'm almost there!

[hellosailor]

ct-
As John said, show your work. That's the only way to really check for an error. If the panel can support 100A service, there's nothing wrong with wiring it up to do that. But you may need to either put on a more substantial primary connection point (tap a hole for a larger screw) or just use a pigtail on the supply wires. If you have a 6" piece of 10AWG or something similar to make the connection? The impact will be negligible on voltage drop, and normally negligible of safety as well.

[Larry Florida]

Originally Posted by Cthoops

O.k. I'm home now. Adding up the amps at any given time, I calculate 24.25 (we have all LED lights for interior and exterior which helps a lot). I assume I can bump it up to 30 to account for things we may want to buy that we haven't thought of yet?

Using the Blue Seas circuit wizard, that gives me 6 awg wire for our run which is approximately 25 feet round trip. Since it's a single wire, we should use a 125amp ami or midi fuse in a fuse block.

Sound good? I think I'm almost there!

I have little electrical knowledge. Nevertheless, why would you use round trip in the calculation, which I assumes doubles the wire length. The run is from battery to distribution panel yes? One way?

Maybe someone can comment. Thanks

[Cthoops]

Showing our work:

Chartplotter - .99A
Wind Instrument/Screen - 1A
Radar (to be installed) - 1.5A when active
Interior LED lights - 7 @.3 amps each = 2.1A
LED deck light - 1.08A
Nav lights - 3 @ .2A each = .6
Tri color (to be installed) - .54 A max draw
Nature's Head - .16A
Hella Fans (to be installed) - 3 @ .54A = 1.62A
AIS (to be installed) - .16A
VHF - 8A at max power
Charging iPad and other toys - 5A
Compass light - estimating .5A (the website says it uses a 1A fuse)

Total = 23.25A

23.25A at a 25 foot round trip run = 6 AWG wire. Since it's a single wire, we should use a 125amp ami or midi fuse in a fuse block.

We have simple systems (Origo stove, no fridge, manual windlass to be installed) so I don't think I've forgotten anything. How does that look?

[Sailmonkey]

Originally Posted by Larry Florida

I have little electrical knowledge. Nevertheless, why would you use round trip in the calculation, which I assumes doubles the wire length. The run is from battery to distribution panel yes? One way?



Maybe someone can comment. Thanks

The electrons make the round trip. They don't just vaporize at the end of the wire.

[sailorlink]

When you supply your panel, you wire the larger feed to the panel bus that feeds all the breakers.
You use much smaller wire from each breaker to its load, so you end up running a lot of wires from the panel to various locations in the boat.
Cheers!

[Jd1]

If I might add a minor point .... if it is a panel that supports 100A, I would wire it up as that. What happens if later on you decide to put extra loads on. Will you pull the wire to the battery and put in new wire ? Whatever you decide, make sure you put a properly sized fuse at the battery. It must be sized for the wire run and not the panel.
Just looked it up and #6 gauge is good for 120A, the panel is good for 100A, I would use anything in the 120A to 100A fuse for that setup.

[hellosailor]

"Total = 23.25A

23.25A at a 25 foot round trip run = 6 AWG wire. Since it's a single wire, we should use a 125amp ami or midi fuse in a fuse block. "

Eh, not quite. While the 6AWG cable is sufficient for a 25-30A load in a 25' round trip (which is how you measure it) according to
Amps and Wire Gauge - 12V Circuit

that also means you would FUSE that cable at 30A, or the next step above. (40A or 50A) Yes, the wire can safely carry more current, but with questionable voltage drop. So I'd use the voltage drop, not the safe carrying ampacity, as the limiting factor.


You want the fuse to be just above the maximum current you will be pulling if everything is turned on, which in your case means you would use a 30A fuse, being conservative and knowing that your 23A of equipment NEVER would need more than a 30A fuse unless there was a problem. And when there's a problem, it doesn't matter if it is the wires or the loads, you want a fuse to kill the power quickly.

Pick a suitable fuse type for the service, and get a couple of spares, as well as a couple of higher capacity fuses for use at a later date, when and if you add more loads to the panel.

At 30A, you could also consider using a 12V breaker as a "master off" for the panel as well, instead of fuses. Of course, that can be problematic if you add too many more loads and push it past levels you can replace the breaker for. And of course, if you exceed 30A in the future...that 6AWG cable becomes problematic again as well, having too much voltage drop.

[sailorboy1]

use the 6 awg and fuse/breaker for 50 amp and stop stressing about it

[hellosailor]

There's never a quantum physicist around when you need one.

Actually I was told decades ago that the conventional "electrons flowing" business is totally wrong 1950's physics. And that by the 60's they had figured out that electrons don't flow from the negative terminal, but "electron acceptance holes" or some such thing flow from the positive terminal...I don't even try to remember what the deal is, but just that 'electricity' flows the opposite of the way we were all taught (and still are taught) in school. Unless you're in an EE program or working on the Large Hadron Collider.

You could take a "round trip length" chart, cut all the numbers in half, and make a "one way length" chart out of it. Sure. Doesn't matter, just READ THE CHART and make sure to apply apples to apples.

(I don't care what is flowing which way in those wires, I just want the light bulbs to work.)

[StuM]

Originally Posted by Cthoops

Ah yes, I'm sorry - I don't have the paper with my calculations in front of me. I believe it was actually approximately 65 amps (maybe a bit less) over a 24 hour period running all of the instruments, radar, lights several hours a night, charging the iPads, etc.

First thing is you need to learnt the difference between Amps and Amp hours.

This is a classic situation were misunderstanding basic units gives you the wrong answer.

Please read this before going any further

http://www.cruisersforum.com/forums/...ml#post1933764


(And they wonder why I get so picky about people using the wrong units )

[john61ct]

30A over 50' is fine safety wise with AWG 10.

But keeping voltage drop to 3% means #3 wire.

Per Blue Sea's app.

[Cthoops]

Originally Posted by hellosailor

"Total = 23.25A

23.25A at a 25 foot round trip run = 6 AWG wire. Since it's a single wire, we should use a 125amp ami or midi fuse in a fuse block. "

Eh, not quite. While the 6AWG cable is sufficient for a 25-30A load in a 25' round trip (which is how you measure it) according to
Amps and Wire Gauge - 12V Circuit

that also means you would FUSE that cable at 30A, or the next step above. (40A or 50A) Yes, the wire can safely carry more current, but with questionable voltage drop. So I'd use the voltage drop, not the safe carrying ampacity, as the limiting factor.


You want the fuse to be just above the maximum current you will be pulling if everything is turned on, which in your case means you would use a 30A fuse, being conservative and knowing that your 23A of equipment NEVER would need more than a 30A fuse unless there was a problem. And when there's a problem, it doesn't matter if it is the wires or the loads, you want a fuse to kill the power quickly.

Pick a suitable fuse type for the service, and get a couple of spares, as well as a couple of higher capacity fuses for use at a later date, when and if you add more loads to the panel.

At 30A, you could also consider using a 12V breaker as a "master off" for the panel as well, instead of fuses. Of course, that can be problematic if you add too many more loads and push it past levels you can replace the breaker for. And of course, if you exceed 30A in the future...that 6AWG cable becomes problematic again as well, having too much voltage drop.

Thank you. Fusing at 30 (or 40) does make more sense than 125 now that you point it out.