FUSES??

[benzu]

Looking at this diagram posted several years ago for fuses I now have a question wiring my trailer.

It seems a little on the high side for fuse for a couple of things.

Water pump 20amp fuse.
My shurflo at home draws a max of 7amps and it states on the pump to use a 10amp fuse, why the 20amp fuse?

Roof Vent and Fan 20amp fuse.
My fantastic fans draws a max of 3amps on high, which I will probably never use. Wouldn't a 5amp fuse work or maybe just a 10amp just to be safe?

I'm thinking of putting the dome lights and exterior light on one circut, I could see putting these on a 20amp just to be safe. But on this chart it shows a 15amp for just the dome lights and 15 for the porch lights and a 15amp for the reading lights. It seems to be a bit too much for everything.

Thanks for your help.

Mike

[Jiminsav]

Mike, I think thats metric power...

[Miriam C.]

Mike use the size fuse your appliances call for. You can add them up to see the max. You really don't want to have them too high. The goal is for the fuse to blow before the wire burns or the appliance.

[Arne]

I ran only one wire, so will fuse it at the battery, probably 15 amp. I will run fantastic vent, dome light, reading lights. And, a power receptacle for charging cell phones, etc.

I went nutty with a marine switch bank on tear no. 1... now, only switch will be dome light.. all others have built in switches.

All wiring has been tested and it buried in the ceiling... if I have a real problem, I'll be SOL.. as they say. But all joints are soldered and wire nutted... so I feel confident it will be just fine..

[Sonetpro]

Fuses do not protect appliances. They protect the wires going to them. Fuse it according to the size of wire on the circuit.

22awg => 8A

20awg => 10A

18awg => 15A

16awg => 19A

14awg => 25a

[brian_bp]

I agree with Sonetpro... in that the fuses are sized to the circuit, not the end device.

In your house, there can be a dozen receptacles or light fixtures on a circuit, and all the stuff plugged in might need only one amp or might (if all turned on at the same time) need 100 amps... you don't know. The circuit breaker is sized to prevent the wires from carrying too much current.

If an appliance needs a fuse matched to it, that fuse should be in the appliance.

Having said that, as other topics here have discussed, there is a lack of consensus about the capacity of a given gauge of wire. Personally, I would vote for lower currents than listed above, such as those used in household wiring:

18 ga - 7 A
16 ga - 10 A
14 ga - 15 A
12 ga - 20 A
10 ga - 30 A
8 ga - 40 A
6 ga - 55 A

(these values from the most conservative National Electrical Code "ampacity" listed the Wikipedia page for American Wire Gauge)

That's just my opinion; higher values may well be appropriate in specific conditions.

... and I don't have the patience to deal with 22 ga wire. I don't tie fishing flies, either.

[benzu]

Thank you to everyone, I understand it now.

Mike

[Mike C.]

Water pump 20amp fuse.
My shurflo at home draws a max of 7amps and it states on the pump to use a 10amp fuse, why the 20amp fuse?

Roof Vent and Fan 20amp fuse.
My fantastic fans draws a max of 3amps on high, which I will probably never use. Wouldn't a 5amp fuse work or maybe just a 10amp just to be safe?

Mike....

I've worked with AC electricity for 33 years and I am assuming that DC would work the same. On any motor load you have what is known as inrush current that saturates the windings and starts the motor to turning.
In most cases, this inrush current can be from 6 to 10 times the full load current of the device. So in your case a 3 amp load could see 18 to 30amps for 2 to 3 cycles. Now on DC, I am assuming that a motor works the same and if you are using fast acting, fast blo fuses, they might not deal with the inrush, if they are too small. Just my 2 cents worth.

[angib]

I've worked with AC electricity for 33 years and I am assuming that DC would work the same. On any motor load you have what is known as inrush current that saturates the windings and starts the motor to turning.

Nope (to working the same). DC has only impedance, and not inductance, so it's all much simpler. A motor will still draw a bit more current at start-up, because it can generate more torque then, but DC doesn't have the same short-term effects.

Andrew