Are 15-amp circuit breakers adequate?

[skipjack27]

I'm in the process of replacing my old fuse panel with a new circuit breaker panel. This panel controls 6 items of equipment (e.g., radio, bilge pump, wipers, sounder, etc). The original panel featured fuses varying from 5 to 15 amps, depending on the particular item. The new panel, however, has fixed-value 15 amp circuit breakers for all 6 items.

I understand (please correct me if I'm wrong) that such panels are principally intended to protect wiring, rather than equipment - and that equipment connected to these panels should be separately fused if a value lower than 15 amps is required. I have two questions that I would very much appreciate comment on:

1. Are 15 amp breakers likely to be appropriate for the protection of the boat wiring? My boat (Australian Riviera 27) is a highly regarded make and is known for the quality of its construction. I'm guessing, therefore, that all equipment wiring should be able to carry currents well in excess of 15 amps. Is this a reasonable assumption?

2. How necessary is it to separately fuse such items as, for example, bilge pumps or radios if they come with lower ratings than 15 amps (e.g., 5 or 10 amps)? I can appreciate that current flows above these lower ratings may very well damage said equipment - but how would such flows arise from a 12v battery? I can only imagine that such flows would arise from some kind of short-circuit in the equipment itself - in which case there wouldn't be much point in having a 5 amp fuse instead of a 15 amp fuse (or breaker). The particular item of equipment would already be pretty much u/s, and the only critical consideration would be to prevent the short-circuit from allowing current flows that could set the wiring on fire. And (assuming (1) above), the 15 amp circuit breakers should take care of that.

These are quite critical matters, as you can appreciate, and I'd very much appreciate any advice.

Jeff

 

[midcarolina]

Verification of wire size ( gauge ) is the only way to know for sure......... But unless someone in the past messed with the wiring it would be reasonable to assume the original 5 amp circuits do not have wire capable of carrying 15 amps.........

You are correct the fuses/breakers at power distribution point job is to protect the wiring from becoming a toaster element...................

Say for example you have a device that pulls 3 amps on a 15 amp breaker, the breaker is now basically a power disconnect switch and not a over current protection........

 

[Georgesalmon]

I would disagree that breakers and fuses are only for wire protection. For example, if a motor draws 3 amps when operating correctly and 20 amps if the shaft is stopped, such as debris in a bulge pump. A 5 amp protection fuse (or breaker) would blow before the motor was damaged where a 15 amp might allow the motor to be ruined. In the case of the 5 amp protection you only need to clean the debris out. In the 15 amp case you need a new piece of equipment instead of a 50 cent fuse or a free breaker reset. This type of scenario would be applicable for other equipment also. Most things come with a recommendation for fuse size. In my case I used inline fuses after the panel when the breakers were bigger than the manufacturer suggested for their equipment. To your battery question; 12V batteries are quite capable of delivering current flow into the hundreds of amps. Think about how much your starter motor draws. 12V batteries can even be used for welding in an emergency. JMHO

 

[midcarolina]

Breakers/fuses located at the power distribution IE breaker panel are over current protection for the wiring........... If you have a 15 amp breaker you must have wire that can handle 15 amps The gauge wire will depend on how long the run is..............

As long as the wire leaving the breaker matches or exceeds the breaker rating you can run multiple items off that individual circuit provided you have appropriately sized fuses at each device..........And the combined amperage does not exceed the breaker/fuse at the panel

 

[Silvertip]

As was pointed out in a couple of different ways, a 15 amp breaker requires 14 gauge wire on the line and load side to prevent current draw in excess of 15 amps from burning up the wiring. If you wire the loads with 14 gauge wire, at some point there will be a transition from 14 gauge to whatever gauge the wires the device has. In most cases, it will not be 14 gauge but rather a size applicable to the maximum current draw of the device. A stereo or fish finder for example will not have a 14 gauge power and ground wire so it makes sense to include an in-line fuse. The argument against that is the likelihood of a problem between that transition and the device is small but nevertheless, an ever present danger. As for too much amperage for a device: You cannot "force" more than 5 amps into a device that is designed to run on 5 amps maximum. Devices draw what they need and no more. You are correct when you say that if a device causes a fuse to pop, that device is probably toast anyway so again, the fuse protects the wiring.

 

[UncleWillie]

I would disagree that breakers and fuses are only for wire protection. For example, if a motor draws 3 amps when operating correctly and 20 amps if the shaft is stopped, such as debris in a bulge pump. A 5 amp protection fuse (or breaker) would blow before the motor was damaged where a 15 amp might allow the motor to be ruined. In the case of the 5 amp protection you only need to clean the debris out. In the 15 amp case you need a new piece of equipment instead of a 50 cent fuse or a free breaker reset. This type of scenario would be applicable for other equipment also. Most things come with a recommendation for fuse size. In my case I used in-line fuses after the panel when the breakers were bigger than the manufacturer suggested for their equipment. To your battery question; 12V batteries are quite capable of delivering current flow into the hundreds of amps. Think about how much your starter motor draws. 12V batteries can even be used for welding in an emergency. JMHO

The Fuse is there to protect the wiring.
It is acceptable and common practice to reduce the fuse size to also protect the equipment but that is a secondary consideration.
The device should have its own fuse to protect itself. They often do not.
The wiring after most boats fuse panel is 16 gauge and is good for 10 amps Max.
If the OP is planning to install 15 amp breakers, he needs to confirm that all wire after the breakers is 14 AWG or larger.
Any existing 16 gauge will need to be replaced.
14 gauge to a Nav Light is way overkill; which is why the original panel had 5 amp fuses in it.

In the example above, the faulty circuit drawing 20 amps would not only smoke the pump,
it would smoke the wiring to the pump if it were the normal 16 AWG or smaller.

 

[H20Rat]

As was pointed out in a couple of different ways, a 15 amp breaker requires 14 gauge wire on the line and load side to prevent current draw in excess of 15 amps from burning up the wiring. If you wire the loads with 14 gauge wire, at some point there will be a transition from 14 gauge to whatever gauge the wires the device has. In most cases, it will not be 14 gauge but rather a size applicable to the maximum current draw of the device.

You must be thinking of 120v AC stuff... 14/2 solid wire is the minimum spec for a household 15 amp circuit.

Low voltage DC current has some different rules to play by. It depends heavily on how far your wire run in. 18 gauge stranded is perfectly capable of carrying 15 amps of dc current, if the run is short. (actually 16 amps is the max on 18 gauge). 14 gauge stranded is rated up to 32 amps of DC 12v power. On the other hand, if you want acceptable performance with a 30 ft run (say 15 ft of positive and 15 ft ground), you need a minimum of 6 gauge for 15 amps. Using 18 gauge for a 15 amp 30 ft run would not pose a risk, but the voltage drop would be unacceptable.

 

[Silvertip]

Let's not overlook the physical strength of the wire. 18 gauge is pretty fragile.

 

[ssobol]

You can always change the breakers in the panel to ones more closely associated with the expected load (easily done) or you can add the right size fuse inline after the breaker. In that case the fuse is the protection and the breaker is just a switch.