Wire Size

[Project_Mayhem]

I don't think I understand this table, I'm assuming that an 18awg wire can handle 10amps at 75C, 20amps at 90C, and 20amps at 105C? I would have thought that the hotter the environment the less amps the wire could handle since it is unable to dump heat it generates. Or is it at 10amps an 18AWG wire will heat up to 75C and in an EngRm it only take 8amps to reach the same temp?

I thought the same thing when I first saw the table. Ambient temp in engine rooms is hotter so the insulation is already closer to it's melting point before current flows through it

This is so much easier, I've always used banana plugs for my DIY speaker connections since they have the pinch screws for the plug and receptacle, wire nuts would be way easier.....

You might like lever nuts. I've seen them used in industrial products. Great product but I'm guessing corrosion could get to it in harsh environments. It's all about the right product for the application

 

[Ralph Johnstone]

Regardless of temperature rating I would never attempt to push 20 amps through an 18 awg wire. It's too hot to handle even at 1500 watts

I'm curious as to how you came to this conclusion and the reference to 1500 watts ?

 

[Project_Mayhem]

I'm curious as to how you came to this conclusion and the reference to 1500 watts ?

I accidentally plugged a 1500 watt fog machine into an 18awg IEC cable. We smelled something funny two minutes later and then realized how hot the cable was. There's a reason why 12 guage is spec'd for 20 amp circuits in buildings

 

[Ralph Johnstone]

Interesting. When you say 1500 watts, I'm assuming this is supplied by a 120 volt AC supply.

The fog machine would have been using an amperage of 1500 watts ÷ 120 V = 12.5 A and not 20 A.

I would suspect a partially broken wire in the 18 AWG cable rather than a simple overload to produce that high a temperature.

From what I have seen with ABYC regs. they are extremely conservative and I just didn't think there would be any extreme temperature rise when a wire is run at full amp capacity.

 

[leo310]

My question is what are you doing? Are you rewiring the boat or are you adding new stuff? If your rewiring the look at length of run for each load then you can find what size you need based on the wire size table. What I found is yes this was a over kill but I use 10 gauge for all runs and each run has it own 20 amp breaker (breaker protects the wire not the devise ).

 

[Ralph Johnstone]

Why stop there ? Go bigger.

You're using a 20A breaker to protect a single 105° C marine wire with a rated ampacity of 60A. Have you got a special deal on electrical wiring which no one else knows about ? Share ?

 

[rlongfield]

Are you rewiring the boat or are you adding new stuff?

Yes! The wiring in the boat is well, bits and pieces. Literally (as my kids like to say ALL THE TIME) pieces, bits of wire here and there, a few loops of wire from somewhere. I'm going on the assumption that if any wire runs are still intact they don't (or soon won't) work.
I'd adding a few things, not much right now but I want to future proof myself and not have to come back later and do this all over again.

I use 10 gauge for all runs and each run has it own 20 amp breaker

I did some rough calculations and my highest load seems to be the Stereo at 10amps, the VHF at 6, and Bilge at 5. Now given I don't have these items in hand the load might change but if my research is accurate (and I added an amp to each rating I found) my total load for the boat with everything on at once is 40amps (rounded up)

(breaker protects the wire not the devise )

I watched a great video on this, it boiled down to 'A breaker's job is to prevent the wire from overheating and setting your house/boat/trailer on fire.' Also of interest was the fact that most extension cords are overrated and can't handle the load they say they can.

 

[leo310]

Like I said over kill but the cost on Amazon for ancor 10 gauge flat duplex was $20 cheaper than 12 gauge. Also the nice thing using this was, using a felt pen I could label what it was every few feet.

 

[Justin_NSA]

This is only a C22. 10ga up the mast may affect handling

I ran 16ga up my H30. Not because I needed the current capacity, the cable is physically stronger and can support it's own weight. It's clamped up on top.

 

[DayDreamer41]

@rlongfield I trust that you are planning to have a breaker for each device and not one breaker for all.....ie adding a Blue Seas breaker panel running a DC main to the bus bar on the breaker panel and then breaker(s) out to the devices.

 

[rlongfield]

I trust that you are planning to have a breaker for each device and not one breaker for all...

I'm undecided whether to go with 2 fused switch panels or un-fused and a separate breaker panel.

My plan (as it stands right now) is to have a main switch panel that controls 6 circuits,
1 - Cabin interior (feeds to a sub-switch panel)
2 - Instruments, VHF, Depth Finder (future), Auto Pilot (future)
3 - Aux, Raspberry Pi (future), Wifi (future, maybe moved to AC)
4 - Nav Lights, bow and stern
5 - Anchor light
6 - Steaming light

Sub-Switch panel (cabin interior)
1 - Cabin Lights (3 overhead LEDs, 2 LED strips)
2 - Stereo
3 - Cabin Fans
4 - DC Power Outlets (USB and Socket)

The sub-switch panel accounts for nearly half my load at about 17amps (2amps added as buffer). I don't know if on fused switch panel if a fuse/breaker are 20amps or if they can be changed out. Outside of circuit #1 the highest load on a circuit I have is 9 amps.

 

[Justin_NSA]

I think you are overcomplicating this. You only need one panel where the C/Bs are the switches. Standard on most boats.

 

[Ralph Johnstone]

I think you are overcomplicating this.

I would go one step further to say you are waaaaaaaaaaaaaay over complicating this.

Interior lighting would be about 1.0A. Each LED light will be 0.1A.
Circuit #3 comes off the interior lights.

Sub panel ? Not on a system that small.

This is my original DC panel for far more equipment and even several of these are not necessary. They just "look nice."

Think about WHAT you want the breaker to do.

 

[rlongfield]

I do tend to over think things. I just did some checking and it seems the panel I want (I like the look of the classic switch panel) has a panel max of 37A and a circuit max of 10A.
Soooooo, sub panel gone. If I do some re-arranging I can fit everything on one panel (except the Wi-Fi which I'd likely only use in a marina?)

Switch Panel 1
1 - Cabin interior (LED Lights, Fans, DC Power Outlets, Rpi) = 9 amps
2 - Nav Lights = 2 amps
3 - Anchor Lights = 1 amp
4 - Steaming Lights = 1 amp
5 - Instruments (VHF, Depth Finder, Auto Pilot) = 9 amps
6 - Stereo = 10 amps
total amps = 32amps

I'm a bit worried that at 9 amps there isn't much overhead if something pulls more than spec. The stereo at 10 is at the panel's switch max. Also the DC power outlets are likely not fitting on Circuit 1, to much potential to overload there.

 

[Stu Jackson]

What kind of stereo do you intend to use? I have a Bluetooth car stereo, and with four speakers going at reasonasble levels I rarely see more than 3-4A. 10 seems awfully high. Care to comment?

 

[Ward H]

Not sure what panel you are looking out but most come with 15A breakers and some blank spots. (At least Blue Sea panels do) You can buy breakers from 5A up but remember, your sizing the breakers to protect the wire. IE: You may only draw 1 A on the anchor light but the charts may say if you run 14ga wire you can use a 15A breaker. Then you don't need to buy smaller breakers.

 

[MaryEllaRose]

If it were up to me, I’d break up circuit #2, putting the auto pilot on a circuit all its own. It’s a relatively higher current device that could blow the fuse if it were to mechanically jam or lock up. With my luck, you’d be left with no instruments, GPS, or depth gauge.
Tom G

 

[Ralph Johnstone]

Consider dumping all your tungsten lights and converting to LED's. Easy to compare to your old ones and inexpensive.

As far as stereos go, mine pulls 2.0A.

 

[rlongfield]

What kind of stereo do you intend to use? I have a Bluetooth car stereo, and with four speakers going at reasonasble levels I rarely see more than 3-4A. 10 seems awfully high. Care to comment?

I haven't picked out the stereo yet, the 10amps is the number I got from looking up the load of a few items I don't have yet. 10 seemed high to me but I wasn't sure, perhaps 10A is the max load of the stereo at full power?

 

[rlongfield]

If it were up to me, I’d break up circuit #2, putting the auto pilot on a circuit all its own. It’s a relatively higher current device that could blow the fuse if it were to mechanically jam or lock up. With my luck, you’d be left with no instruments, GPS, or depth gauge.
Tom G

Good point, I too have that string of luck. The Auto Pilot is a future add-on