Breaker sizing (Amps) in breaker panel

[smac999]

I think some of you are mixing house code and abyc code... 18awg isn't even allowed for power wires in a boat.

16 is min. I would run everything at 14 min

To answer question. Yes you size breakers to loads and what the device calls for in its manual . They can always be swapped later if you need to add a small load device down the road.

[KP44]

Originally Posted by smac999

I think some of you are mixing house code and abyc code... 18awg isn't even allowed for power wires in a boat.

16 is min. I would run everything at 14 min

To answer question. Yes you size breakers to loads and what the device calls for in its manual . They can always be swapped later if you need to add a small load device down the road.

The question was about 18 gauge wire, and wire that small needs a low-amp fuse or breaker. I would use 5 amp - if I had any wire that small. I normally use 14 ga minimum size.

Breakers are to prevent overcurrent heat and fires. Over half of all boat fires are electrical, and fire is the most dangerous situation on a boat. Breakers must be sized to protect the wires, without regard to load. If a device needs a smaller breaker because a short can cause a fire within that device, then size the breaker to the device.
If you have 14 ga throughout your boat, your standard 15 amp breakers are correct unless an electronic device demands a smaller fuse (breaker).

[masonc]

OCPD (breakers) are not designed to protect equipment, they are designed and rated to protect the conductors.

[a64pilot]

Originally Posted by masonc

OCPD (breakers) are not designed to protect equipment, they are designed and rated to protect the conductors.

That is correct, but
For example I have a circuit I added last weekend, a 16ga wire running to the cockpit to power two LED lights on my Bimini, the LED's will draw less than 1 amp, the 16 ga wire can safely carry 25 amps (according to Blue seas circuit wizard app).
I used a 5 amp CB, cause if for any reason I draw more than that, I want it to trip and alert me that something is wrong.
I don't know maybe the light shorted out internally and could set the Bimini on fire?
There is logic to sizing the CB to the load and not just the conductor

[Cadence]

Originally Posted by a64pilot

That is correct, but
For example I have a circuit I added last weekend, a 16ga wire running to the cockpit to power two LED lights on my Bimini, the LED's will draw less than 1 amp, the 16 ga wire can safely carry 25 amps (according to Blue seas circuit wizard app).
I used a 5 amp CB, cause if for any reason I draw more than that, I want it to trip and alert me that something is wrong.
I don't know maybe the light shorted out internally and could set the Bimini on fire?
There is logic to sizing the CB to the load and not just the conductor

Absolutely! :thumb : A smoldering component is not going to worth a damn just because the wire was larger than required an was fused for the wire rating.
Don't take me wrong, I am a proponent of over sized wire if for nothing but line lose on a long run.

[GordMay]

Originally Posted by a64pilot

... There is logic to sizing the CB to the load and not just the conductor

There is logic to DOWN-sizing the CB to the load and not just the conductor.

[Tasso]

Originally Posted by Cadence

That's an excellent comment. You don't want the smallest wire to be the fuse.

I installed an in-line fuse with each of my LED fixtures as the pigtails on these were about 22ga. On older boats - lighting circuits had 15 amp breakers - with LED lighting you can reduce this if you like - as the current is reduced by 90%...

Wire size determines protection. Wire needs to be big enough to power connected equipment.

I often oversize wiring on circuits that run constantly - as on my 25 amp solar system I used 10ga and some 6ga wire to reduce loss... No need to increase the breaker size on these.

[Bleemus]

I often fuse the load as close to the load as possible in addition to the appropriate sized CB or fuse for the wire at the source end. Works for me.

[masonc]

Originally Posted by Bleemus

I often fuse the load as close to the load as possible in addition to the appropriate sized CB or fuse for the wire at the source end. Works for me.

What's the point? If equipment needs fusing, it will have an equipment fuse.

[Colin A]

A breaker can be a equipment protection device. The Thermal and Hydraulic Magnetic breakers used in boats are very similar to the same devices used as equipment protection devices in telecom equipment for instance.

Not all equipment that needs a protection device comes with it (many smaller pumps for instance).

Here is a breaker selection article from one of the marine breaker builders
http://airpax.sensata.com/pdfs/guidetoprotection.pdf
and another from the biggest marine breaker builder
http://www.carlingtech.com/sites/def...Protection.pdf

Both are technical but interesting.

[Bleemus]

Originally Posted by masonc

What's the point? If equipment needs fusing, it will have an equipment fuse.

True. Some things come with a fuse. Some dont. If they dont I will fuse it in relation to its draw as measured in use.

[smac999]

Originally Posted by Bleemus

I often fuse the load as close to the load as possible in addition to the appropriate sized CB or fuse for the wire at the source end. Works for me.

That is a trouble shooting nightmare. Don't double fuse.

[Tasso]

Originally Posted by smac999

That is a trouble shooting nightmare. Don't double fuse.

Not sure how you'd install a nav system properly without doing this. I have a single breaker for "Nav" that goes to a sub-fuse panel holding individual fuses for each display, my GPS antenna and the NMEA 2000 backbone... These fuses will never fail unless something has gone seriously wrong. I also giggle the fuses from time to time to fight corrosion.

[Frankly]

Originally Posted by smac999

That is a trouble shooting nightmare. Don't double fuse.

Quite the contrary. One of the often overlooked functions of multiple object electrical systems is that of selectivity (isolating a problem electrical appliance when it develops trouble and leaving the remaining equipment operational). If I run a circuit up to my steering pedestal and then tap it for my AP, radar, and chartplotter, a problem with the AP trips the feeding breaker and I loose power to all three. Can always hand steer clear of the oncoming Aircraft Carrier. Three independent fuses at the pedestal solves this problem. Obviously three independent circuits would provide a similar function just a lot more wiring.

[Bleemus]

Originally Posted by Frankly

Quite the contrary. One of the often overlooked functions of multiple object electrical systems is that of selectivity (isolating a problem electrical appliance when it develops trouble and leaving the remaining equipment operational). If I run a circuit up to my steering pedestal and then tap it for my AP, radar, and chartplotter, a problem with the AP trips the feeding breaker and I loose power to all three. Can always hand steer clear of the oncoming Aircraft Carrier. Three independent fuses at the pedestal solves this problem. Obviously three independent circuits would provide a similar function just a lot more wiring.

Exactly.