Electric wiring question

[Riley1840]

Here I am again. Just finished installing a newer and bigger on board charger. There is an inline fuse on both positive and negative wires. To each of the three batteries. This is not something I am use to. Can someone explain why this is?

 

[Grub54891]

Protecting the wiring/charger. That’s what fuses do to prevent fires.

 

[Riley1840]

Understand what you would use a fuse, I use them all the time. I just put them on the positive side i have never put them on the negative side.

 

[Grub54891]

Well, the charge is hooked to 120 volts. I’m not sure why it’s on the negative side unless you accidentally hooked it up backwards and fired it up. I’ve seen them like that also. I looked it up: Edit
A boat battery charger has fuses on the negative cable to protect the wiring from overcurrent situations, particularly in the event of a short circuit between the positive wire and the boat's metal hull (effectively acting as a ground), as the negative cable is typically connected to the boat's ground; this fuse can help prevent damage to the charger and the electrical system in case of a fault.

 

[Riley1840]

No did not hook up backwards. Charger came with inline fuses premade. I hooked pos to pos neg to neg. Charger working just fine. I was only wonder why a fuse on the negative wires.

 

[Scott Danforth]

Charger working just fine. I was only wonder why a fuse on the negative wires.

Poorly designed charger, or designed to blow when someone wires it wrong

 

[Riley1840]

It’s a pro mariner. The one that came with boat was wired the same. The possibility of wiring wrong makes some sense.

 

[Kosmofreeze]

Belt AND Suspenders? If it comes from the factory that way, I'd be interested in what their engineering minds have to say. I'm not sure about the 'wrong wiring' scenario ... fuses take too long to blow - the damage will be done before the fuse "opens" the circuit.

 

[mike_i]

I'm curious why you say " fuses take too long to blow - the damage will be done before the fuse "opens" the circuit." If the proper capacity fuse is installed why would there be damage done before the fuse blows.

Belt AND Suspenders? If it comes from the factory that way, I'd be interested in what their engineering minds have to say. I'm not sure about the 'wrong wiring' scenario ... fuses take too long to blow - the damage will be done before the fuse "opens" the circuit.

 

[cyclops222]

mOST NORMAL FUSES HAVE A 300 % CAPACITY FOR QUITE A WHILE. fUSES / CIRCUITBREAKERS ARE NORMALLY SIZED TO PROTECT THE WIRES FEEDING POWER TO THE DEVICE. However a lower current fuse or circuit breaker can be used to give more protection to a sensitive device. Look at all fish finders and their supplied protective fuses. The wire is tiny and so is the fuse.

 

[cyclops222]

The Electrical Code is now very dangerous when D C and AC equipment are being fused in either POSITIVE line or NEGATIVE line.
With also 120 vac grounds from the 120 vac charger wires and neutrals being tied to them. Not a safe practice if the Non Positive fuses blow open. If the Negative fuses blow ? Then it is possible the metal case can rise up to 120 vac. If the device has that capability.
Why no fuses or breakers are allowed in equipment except in the highest input voltage wires.
The new code is dangerous.

 

[Kosmofreeze]

I'm curious why you say " fuses take too long to blow - the damage will be done before the fuse "opens" the circuit." If the proper capacity fuse is installed why would there be damage done before the fuse blows.

Generally in vehicles - cars, boats, airplanes, etc - fuses are used to protect the wires, not the appliances. Depending on the wire type, they can tolerate an over-current fault for a short time (on the order of seconds or more) while they heat up to their maximum temperature rating. Electronic components (semiconductor devices, small capacitors, etc) will FRY in an instant - think static spark. Fuses just don't respond in an instant - see Time/Current curves in any fuse data sheet.

 

[cyclops222]

The electrical code DOES ALLOW a fuse smaller than the size protecting the wire. Common sense wins in that case. 14 gauge wire can have a 1 amp fuse as the protection.