Matching wire size to panel connector

[$tingy Sailor]

I purchased a replacement breaker panel that has six breakers: 2x20A, 2x15A, and 2x5A or 80A total. However, it only has male spade type connectors and the largest crimp-on connectors that I've found are 10-12 AWG.

What's the best way to wire up this panel since it should be fed with 4 AWG cable (< 20')? Mount a post near the panel, connect the battery to it with a 4 AWG ring terminal and then run a short 10 AWG conductor with a female disconnect to the panel? Or just run 10 AWG the whole way from the battery and downsize the MBRF fuse to 30A and not connect too large of devices?

The connected loads are all small (< 10A total): LEDs, small autohelm, stereo, etc., no big motors. But I'd like to build the system able to safely handle full capacity.

 

[$tingy Sailor]

I think I can answer my own question. When I looked up the wire size, I did a quick Google search for the ABYC table and rather than scroll through the whole document, I looked at this table on the Blue Sea Systems website, figuring they would be the same.

Not. If I look at the actual table X in ABYC E-11 2009, I see 80A round trip in 10' is 10 AWG and an easy connection.

So the question then becomes, what the heck is the Blue Sea Systems table about

 

[Maine Sail]

Ideally, if you want yo wire the panel for max capability, you would wire the main feeder to an 80A DC main breaker first. You would also ideally not use a panel with friction fit connectors because they are anything but reliable in the marine environment.

You are confusing max ampacity for over current protection with voltage drop.. The max ampacity 105C marine wire can be fused for is 60A but you would never run 10GA at anywhere near 60A. Not the same things. All critical circuits should be sized for no less than 3% voltage drop and if the main panel feeder is undersized you won't be able to feed critical circuits such as nav lights the right voltage..

 

[$tingy Sailor]

I agree with what you're saying and that was my understanding. But I wasn't really concerned about ampacity since I will use 105C wiring throughout. Are you saying that the Blue Sea table is listing max ampacity and not voltage drop? I want to understand this correctly.

Let's consider two example scenarios for this panel with the same <10' max feeders:

A. Ideal Max Capability
Battery>80A MBRF>10 AWG>80A main breaker>10 AWG>20A panel breaker>16 AWG>device(5A @ 15' or less)>16 AWG>neg bus>10 AWG>Battery

What role does the main breaker play? Feeder protection in case of a short of the feeder at the panel connection (upstream of the circuit breakers)? Doesn't the MBRF fuse do that? Or is it more for convenience to de-energize the panel for maintenance without disconnecting the battery?

B. My Real World (<10A total loads)
Battery>60A MBRF (existing)>10 AWG>5A panel breaker>16 AWG>LED nav light>16 AWG>neg bus>10 AWG>Battery

Where is the deficient link? If the light shorts, the breaker will trip. If the breaker shorts, the fuse will blow. Right? Or will the 10 AWG overheat first and I should reduce the battery fuse to 30A?

Thanks for your help. I appreciate it.

 

[Maine Sail]

I agree with what you're saying and that was my understanding. But I wasn't really concerned about ampacity since I will use 105C wiring throughout. Are you saying that the Blue Sea table is listing max ampacity and not voltage drop? I want to understand this correctly.

Let's consider two example scenarios for this panel with the same <10' max feeders:

A. Ideal Max Capability
Battery>80A MBRF>10 AWG>80A main breaker>10 AWG>20A panel breaker>16 AWG>device(5A @ 15' or less)>16 AWG>neg bus>10 AWG>Battery

You should not protect 10GA wire with an 80A fuse. 60A is the max safe recommendation for over current protection for 10GA 105C wire and this is not bundled and outside an engine space... There are exceptions where you could exceed the max ampacity but this would not really qualify for going above the 60A max ampacity standard....

10' 10GA feeders at 80A results in approx a 14% voltage drop. The most allowed is 10%.. I recognize you will never exceed 10A but you said you wanted to wire it for the max capability of the panel, and if you want to do that, you'd need larger wire.

What role does the main breaker play? Feeder protection in case of a short of the feeder at the panel connection (upstream of the circuit breakers)? Doesn't the MBRF fuse do that? Or is it more for convenience to de-energize the panel for maintenance without disconnecting the battery?

It serves as a main switch and a place to wire the larger gauge wire to because they normally have a 1/4 X 20 stud like the Blue Sea C-Series 80A. The problem is your panel is simply not well designed for the breaker loads mounted into it. I won't even install friction fit breaker panels, I have been asked. I refuse because I can't stand behind the product. I simply ask the customer to sell it on eBay and get a quality DC panel.. It is a simple "get what you pay for" type of panel. A quality panel would have sufficient busbars to wire ring terminals to for the proper size wiring.

A main breaker is not 100% necessary but is certainly nice to have.

B. My Real World (<10A total loads)
Battery>60A MBRF (existing)>10 AWG>5A panel breaker>16 AWG>LED nav light>16 AWG>neg bus>10 AWG>Battery

Where is the deficient link? If the light shorts, the breaker will trip. If the breaker shorts, the fuse will blow. Right? Or will the 10 AWG overheat first and I should reduce the battery fuse to 30A?

That is the proper sized fuse for 10GA wire. You will never have 80A on that panel sol I would advise keeping the OCP at 60A that way cou can't overload the 10GA wire. Never hurts to reduce fuse size UNLESS you have motor starting loads that need to be accounted for...

Approx six of the friction fit connectors on this panel were failing to pass current. Two of them had physically fallen off. The breakers that had been replaced used screw terminals and they worked fine. I see this over, and over, and over..... Last week I was working on a center console that had three of the six friction fits fall off the breakers.. Not uncommon...

This one cost the owner over $600.00 in towing plus my time to diagnose and fix it...

Friction fit connectors can not always be avoided on boats, but one should really try to avoid them......

 

[$tingy Sailor]

Got it. And you confirm what I suspected about the panel design: low mfg cost and consumer convenience. The panel it's replacing (WM) did have #10 ring terminal bus bars but disconnects for the bus bars to the breakers and load connections and they were about as badly corroded as your example. The rest of the wiring is a trainwreck too so I'm going to replace it all as I go.

What's your opinion about putting (dielectric?) sealant on the disconnects to discourage corrosion?

Thanks again, Main Sail. Theory from books is fine but getting practical wisdom from real world applications of the theory is even better.