AC/DC power panels

[Terry Cox]

Interested in the pros and cons of various types of panel switches when located inside the boat cabin. Reviewing the BlueSea Systems site there are rocker, Flat Rocker, toggles, push buttons etc... All appear to be tailored to the interest of the buyer like fishing lures.

So when used on a boat have you found one better than another? And why.

Thanks for your insight.
John

Hi John, my experience is limited to Paneltronics power panels: https://www.paneltronics.com/Power_Distribution_Panels.asp?op=Standard-Electrical-Panel

Our current boat has a large panel that they made for both AC and DC distribution. I like them because of the lighted toggle type white switch; easy to use with visual indication of whether on or off. Panel is hinged so it can be opened up for easy back-panel access.

 

[Johnb]

Ron I'm not disagreeing with you. But you and Stu are ignoring (his!) original question, which I answered.

'Not sure I understand the value of ONLY all 15A breakers'

They do this because the breakers are there to protect the boat by protecting the wire that runs out of them, rated at 15A. No need to have smaller. BSS, who knows a bit about boat wiring and AYBC, does this for a good reason.

Simple and done.

If yours are smaller on a per-load basis, fine. But there is no need to have that, and certainly no need to swap them out on a panel that came full of 15A breakers because of that very reason.

If the panel feeds a wire that has less than 15 amps ampacity then you need to have a commensurately lower amperage circuit breaker.
I am willing to believe that the standard may be to require all wires to be at least #16 for mechanical reasons but if you have an existing wire that is smaller then you need to put in a lower amperage breaker.

 

[dlochner]

BSS has a very practical reason for installing only 15 amp breakers in a production panel, it is a lot easier to manufacture a consistent panel. If all the breakers are 15 amp, then no one in the factory can screw up and install a 10 amp where a 5 amp should be. Also make managing the supply chain easier, just keep 15 amp breakers in stock.

And then there are the paid installers who get to boost their profit margin by swapping breakers.

 

[jssailem]

Thanks Terry and Ron
I have my options open. Currently
the DC panel(on left) has 6 toggle breakers, an Off/1/2/both switch and an analog meter.

The AC has a 30amp main breaker and 5 AC sub circuits.

While the 5 AC circuits appears to be ok in the refit I think I want to add more DC options so I can have fewer combined circuits (i.e. lights and propane sniffer on same circuit). These are so old the lights are difficult to identify if they are on or off. I think I like the toggle in that it is easy to identify on or off condition.

 

[Jackdaw]

;^)

Some of you guys should read some more about basic electronics. Even very small gauge wire can handle more amperage than you can imagine, the voltage just drops and it might get warm. Its not designed for 15A, but the breaker will trip before the wire fails in any way.

Do you think you're the first person that thought this out? Maybe the BSS and the AYBC guys did the calculations before agreeing that this was an OK idea?

 

[Bill Roosa]

Not to be disagreeable Jackdaw but what if a 15 amp thermal breaker was installed and you used it to power a seatalk instrument (no auto pilot) set. You would have to install the recommended 5 amp in line fuse to protect the circuit and probably do it behind the panel where it would be very inconvenient to check. So I'd be thinking of installing a panel mount fuse instead of the breaker and probably save some bucks in the process.
So it is not about protecting the wiring only but also the load
Thoughts?

 

[Jackdaw]

Not to be disagreeable Jackdaw but what if a 15 amp thermal breaker was installed and you used it to power a seatalk instrument (no auto pilot) set. You would have to install the recommended 5 amp in line fuse to protect the circuit and probably do it behind the panel where it would be very inconvenient to check. So I'd be thinking of installing a panel mount fuse instead of the breaker and probably save some bucks in the process.
So it is not about protecting the wiring only but also the load
Thoughts?

Bill, Good question. But if you have a 5A breaker and no fuse, a short circuit will trip the breaker but your instrument will still fry!

At the end of the day if need both you have to have both. Having a breaker at the rated fuse level will not save the device.

Think of your aforementioned VHF, or any other electronic device. The makers all know they will be on a breaker, but they ARE ALL FUSED in-line. For that exact reason.

 

[Bill Roosa]

My point was that I don't need a breaker at all in some cases.

 

[Jackdaw]

My point was that I don't need a breaker at all in some cases.

Maybe. So you use a fuse as a breaker. But think about how devices are fused. How close the fuse is to the device. There is reason for that. The wire between the fuse and the device is unprotected, so they minimize that. If the short happens in the wire between your suggested fuse/breaker and your device, your device will likely fry. So mmost are like this harness. The fuse is 3 inches from the radio.

 

[Bill Roosa]

If the wires short the current will flow between the battery side of the short not the load side. The wires on the battery side will fry using the OEM recommended location. If the load shorts (internal) then the unit is fried already and no fuse will help. If you put the fuse at the panel then the wires and load are protected.

 

[LeslieTroyer]

Circuit breakers and fuses are apples and oranges. Both are fruits that react to over current situations. How quickly or how long the over amp condition exists or or or all depending on the style of breaker or fuse.

If the autopilot calls for a specific 5 amp fuse that is what I will put in, even if the circuit is on a 5 amp breaker.

 

[Johnb]

;^)

Some of you guys should read some more about basic electronics. Even very small gauge wire can handle more amperage than you can imagine, the voltage just drops and it might get warm. Its not designed for 15A, but the breaker will trip before the wire fails in any way.

Do you think you're the first person that thought this out? Maybe the BSS and the AYBC guys did the calculations before agreeing that this was an OK idea?

Some of us guys are actually knowledgeable engineers. Proper practice is to size breakers according to the wire they protect.

 

[Scott T-Bird]

16 awg should be fine with 15A breaker. If my sailing instruments are on 18 awg, I'll probably change the wire. If the compass light wire is 18 awg and not easy to change, then I'll probably consider swapping a breaker because of the wire size.

 

[Ralph Johnstone]

16 awg should be fine with 15A breaker.

All ................. please recognize that breakers which protect your boat wiring are NOT based on opinion, the are based on the ABYC Ampacity Rating Table. Don't second guess it or you wind up with this:

 

[Scott T-Bird]

Well, you're right that the tables shouldn't be second guessed. I'm not sure I understand if you are condemning 16 awg in conjunction with 15A breaker or for what reason. A lot depends upon the insulation rating and bundling of the wires. 16 awg with 105 deg insulation should be fine, even if in a bundle outside the engine compartment. Obviously, the wires are already sized for the loads that they are connected to. The smallest gauges (16 awg) that I would consider for a 15A breaker would need to be 105 deg insulation rating for my comfort and typically installed in free air. I am a bit concerned about cabin lighting because the wires are probably16 awg but I don't recall the insulation rating and the wires are run in confined spaces, but not through the engine compartment. I've never changed out the existing wiring for cabin lights. I know that all wire that I have purchased for new installations has been 14 awg (min), 105 deg so I have no concerns with the considerable amount of new wiring that I have installed in the past. Table IV of ABYC encompasses a considerable amount of variation so blanket statements obviously don't necessarily apply. (The Blue Seas table attached in the post above does not encompass the entirety of the ABYC ampacity table IV)

 

[dlochner]

What is missing from this discussion is the margin of error that is acceptable. What is the current draw under normal conditions and what is maximum draw for safety?

If the device, say a VHF requires a 5 amp fuse the manufacturer is saying that the highest current draw will be less than 5 amps, a 16 ga wire can carry 15 amps, so there is a 10 amp margin. Anything that happened that caused the wire to draw more than 5 amps would likely be a direct short which should trip the breaker quickly.

The time to be concerned is when the maximum current draw on the circuit approaches the ampacity of the wire. If 3 devices each capable of drawing 5 amps is on the same circuit, the draw would be at wire's maximum and concerns about heat, accuracy of the breaker, and voltage drop would be a bigger concern. In this scenario, going to a 14 ga wire with a 15 amp breaker would make sense.

 

[Ralph Johnstone]

The smallest gauges (16 awg) that I would consider for a 15A breaker would need to be 105 deg insulation rating for my comfort and typically installed in free air.

You're exactly right in your choice of 16 AWG. Obviously you're designing and not guessing.

 

[Ralph Johnstone]

Anything that happened that caused the wire to draw more than 5 amps would likely be a direct short which should trip the breaker quickly.

And what if it were only a partial short ahead of the 5A fuse ? ? ? ?

What is the current draw under normal conditions and what is maximum draw for safety?

That's given in the table.

 

[Maine Sail]

Bill, Good question. But if you have a 5A breaker and no fuse, a short circuit will trip the breaker but your instrument will still fry!

There are very, very, very few instances, in electronics, where the fuses actually can or do protect it. Fuses are simply not fast enough to prevent transient damage, which is one of the major killers of electronics.. The fuses are almost always there to protect against fire.

Even in the realm of proper bilge pump fuse sizing, one area that folks grossly ignore, the fuse is sized at that rating to prevent a fire from occurring in a locked rotor situation. In a locked rotor case, with the correct fuse, the fuse will often save the pump if the rotor is locked. Its main purpose however is to prevent the pump from melting & starting a fire due to a locked rotor. Pumps are much more durable than electronics and I have seen numerous cases of fried electronics, with fuses perfectly intact. The idea that fuses protect your on-board electronics etc. is one that is more lore and urban legend than that of truth..

 

[dlochner]

And what if it were only a partial short ahead of the 5A fuse ? ? ? ?

I'm not sure what a partial short is. My understanding of a short circuit is a direct connection between the positive and ground. There is either a short or there is not, it is binary.

The other condition is an over current draw. Let's say that you have 4 lights that each draw 5 amps. So long as you have 3 or fewer lights on a 15 amp breaker should not trip, however, when that 4th light is turned on, the breaker will trip.