fuse size for accessory plug?

[rebars1]

Is there a recommended fuse size for an accessory plug. I would be using it for a variety of things like cell phone, inflatables blower, etc.

 

[imported_Curmudgeon]

Re: fuse size for accessory plug?

Use a fuse that will support the largest amp load you invision having ... and know that stuff with lesser loads will not be well protected. Nature of the animal.

 

[vipzach]

Re: fuse size for accessory plug?

The other thing to consider is wire size. Example: Don't put a 25A fuse in if you have 18g wire.

 

[DangerDan]

Re: fuse size for accessory plug?

If it were me I would use 10ga. wire and a fuse that suits the rating of the receptacle/plug like say 25 to 30amp if this were the case.

 

[Paul Moir]

Re: fuse size for accessory plug?

I think those sockets are rated for 15 or 20 amps, so fuse it to that if the wiring supports it.<br /><br />(I'm sure I rember seeing connectors speced at 15 amps, but I'm also sure I remember replacing 20A fuses for car's ligter sockets.)

 

[rebars1]

Re: fuse size for accessory plug?

I just found some fine print on the package saying "for 15 amp applications or less only" so I guess it's 15 amp fuse with a 12ga or 14ga wire?<br /><br />Speaking of wire guage, are auto wire guages different from boat wire guages? The wire sizes for auto look smaller than the "boat wire" for the same guages on the packages. Thicker insulation?

 

[jlinder]

Re: fuse size for accessory plug?

You need the fuse to be no larger than the rating of the weakest link in the circuit.<br /><br />If the plug is rated for 20 amps, and the wire is good for 20 amps (12ga.), use a 20 amp fuse. If it is wired with 16ga. wire, use a 10 amp fuse.<br /><br />Accessories with plugs commonly have a fuse somewhere to protect what it is wired for. Many cig. lighter plugs have a fuse in them or there may be an inline fuse in the wiring.<br /><br />Fuse the accessory plug for the most you can (based on the weakest link). Make sure what you plug in has it's own protection.

 

[rebars1]

Re: fuse size for accessory plug?

Thanks Jack L, and others. <br /><br />Any insight on the wire guage v wire size/type question>

 

[jhebert]

Re: fuse size for accessory plug?

The rated current a conductor can carry varies depending on a number of factors, including who is issuing the rating. The variables include:<br /><br />--type of insulation<br />--single conductor or in bundles with other conductors<br />--application, e.g., industrial, home, hospital, marine, etc.<br />--temperature ambient<br />--environment, e.g., dry, wet, oil<br /><br />The outside diameter of an insulated conductor will vary, of course, depending on the type of insulation and what service it has been designed for.

 

[jlinder]

Re: fuse size for accessory plug?

While all those are factors, the most important is the size of the wire.<br /><br />Here is a simple rule of thumb:<br /><br />12 ga will carry 20 amps<br />14 ga will carry 15 amps<br /><br />Every time you go down 4 gauges you double the current capacity. Every time you go up 4 gauges you cut the capacity in half<br /><br /> 6 ga - 60 amps<br /> 8 ga - 40 amps<br />10 ga - 30 amps<br />12 ga - 20 amps<br />14 ga - 15 amps<br />16 ga - 10 amps<br />18 ga - 7.5 amps<br /><br />you get the idea.<br /><br />Again, there can be other factors. For example, you derate to 80% if there will be a constant high current rate like you would experience with electric heaters. <br /><br />You also derate if the wires are bundled, as you would see in an electical conduit with a lot of wires all carrying current.<br /><br />After you talk about how much current you can carry without burning up the wire, you have to be concerned with what is referred to as the voltage drop. Anytime you deliver power through wires (as opposed to what?) you lose some power in the wires. The result is that the voltage delivered to the destination is lower than that as the source. This drop is considered as a percentage of the source voltage.<br /><br />In house wiring you want a maximum of 2% voltage drop. In 12volt systems people talk about 3% to 10% voltage drops, or up to a 1.2 volt drop in the wire.<br /><br />There are calculators on web sites. Just search the forum for voltage drop and calculator and you will find some links.<br /><br />This may be overkill. If you go by the maximum current, then if the run is long (front of boat to back) you might just go down one or more gauges for some headroom.<br /><br />Hope that is not too much information.