Feed/Ground Conductor size for 6 Gang fused and lit Swith Panel

[Dave0963]

Good afternoon,

I just purchased a Victory 6 Gang fused Switch Panel, with on/off lights for each circuit (part #AA10067). I've attached a photo of the backside of the panel.

My question is; can a 6 branch circuit (15 amps/ea, as per Victory packaging) panel be safely fed with 1- 16 awg conductor? I believe a 16 awg conductor max fuse rating is 25amps (21 in engine compartment).

Each branch circuit in the panel is fed with a 16 awg conductor, each having a max 15 amp fuse rating, which makes sense. What I can't get my head around is how the entire panel (6 circuits, 15 amp each) can be safely fed with 1 - 16 awg, 25 amp rated conductor.

If the loads were known and didn't exceed 25 amps, then the 16 awg feed may be acceptable.

What am I missing?

 

[dlochner]

To do this safely with a 16 ga wire feeding the panel, the total load on the panel cannot exceed the ampacity rating of the wire, which is 25 amps. With six switches, one combination would be 1 15a circuit and 5 2a circuits, or 6 4a circuits, and so forth.

The other concern with a small wire is voltage drop. With the power source (battery) 5 feet away there would be a 10% voltage drop between the battery and the panel. And then there would be additional voltage drop between the panel and the device being powered. If your battery is up under the V-berth, there would be close to an additional 10% drop between the panel and the stern navigation light if 16 gauge wire was used, that 12.5V you started with is now down about 10 V.

 

[Foswick]

If you don't know about Blue Sea's Circuit Wizard, check out: Circuit Wizard - Blue Sea Systems Super helpful.

There is a tricky thing, though, about doing what you are proposing. Ideally, everything would be sized appropriate. That is, if you have 6x15A fuses, then you would feed the panel with a conductor capable of 90A (something like AWG 6). Strictly speaking, you don't have to. But, then you have to manage each of these circuits to ensure your total load doesn't exceed the capacity of your feed conductor. And ... you should use circuit protection that protects that conductor.

That is, if the conductor feeding your panel is only capable of ... say ... 35A, it should be protected by a 35A (or smaller) fuse/breaker because your distribution panel would happily allow you to almost triple that, almost certainly ending in catastrophic failure.

So, in short, you can feed your panel with whatever you calculate will be sufficient at your system's voltage and length of wire. But, you should protect that conductor with proportionately-sized circuit protection so your panel does not overwhelm your main feed wire. It is often a good idea to size that wire according to what the system might draw, some day, rather than what it should draw today. That wire is usually a short run from the battery and so you might as well make it big and future-proof your system.

Or, but another way, you can pretty much use any wire you want for any purpose, provided you protect it. Whether the wire is adequate for the loads on it then becomes a performance issue and not a safety issue. That is, you "could" wire in a 60A winch on a AWG 18 wire protected by a 20A fuse/breaker. It won't be enough to run the winch, but it won't blow up.

That said, assuming your system is 12V, you are probably looking at AWG 14, at least, to feed your panel with 25A. AWG 16 would just barely do it for a short run - very marginal and depending on the details.

 

[CYQK]

the bigger the better for wiresize

 

[sailme88]

Ever have your internet slowed down? It's about the flow...Ground and feeds need to be sized for the potential loads.

 

[Project_Mayhem]

There are many variables that go into how much a particular wire can handle. I use AC amperage ratings as a general rule of thumb because I have that memorized but I will look it up if I know I'm close to capacity, temperature is an issue or I have a bundle going through conduit. For 16 gauge the general capacity is 13amps. They will handle more but they will get warm. The general capacity for 18awg is considered 10amps but don't like to put that much power through a wire that small. Most space heaters use use around 1200-1500 watts and come with a 16awg, high temp power cord. For 25amps I'd run at least 12awg, preferably 10. For 60A I'd run 6 or 4awg. Use the amperage chart that @Foswick posted. While I'm leaning on the more conservative size for wiring, he really knows his stuff. However, you need to know all the variables in order to know what you can get away with.
For example, when I used to race RC cars, the short runs of 16awg silicone wires would get too hot to touch. Clearly we were pushing far more than 13amps through them but they held up because they had silicone insulation. If they weren't, the insulation would've melted, a short would've occured and something would've self destructed or caught on fire. I was young and didn't realize how much voltage drop was occurring. Had I known my little car would've gone faster with bigger wires, I would've upgraded in a heart beat.

 

[Dave0963]

Thank you for everyones input. I believe my understanding of the conductor current carrying capacity, voltage drop and use of overcurrent devices (OCD) is sound/correct.

I have come to the conclusion that I simply bought the wrong product or rather a product that needs to be reconfigured. My combined loads will likely exceed the 25 amp threshold under intermittent periods. As a work around, I'll feed a fuse block (100 amp and adjacent to the swith panel) with #8 awg conductors (protected by 30 amp OCD) and feed each individual circuit/switch with #16 awg, from a suitably rated fuse. The switches in the panel are rated for 15 amps.

I understand that the circuits will have 2 OCD's in series.

I wonder how many of these panels have been installed incorrectly, excessive loads and or no OCD's.

Again, thank you for your thoughts and helping me sort this out.