Fusing Bilge Pump

[Bruce Brown]

I've designed my electrical system so that the bilge pump circuits are protected from excessive amperage upstream of the pump but what if the pump's rotors lock and send 5X pump amps out into the circuit? Where do I put a fuse to protect the wiring against that eventuality if the source of the over-amperage is the pump itself?

Bruce

[P.I. Stazzer-Newt]

The pump is not a generator

In locked or stalled condition a typical DC motor will draw a high current from the supply - battery/ alternator or whatever - one fuse should suffice and it should be sized to protect the cable.

[Breakaway]

Locked rotors are a tough one, and a common cause of fires aboard boats.

When a pump's rotor locks, heat is created by the incoming voltage. This increases resistance.

With voltage is constant, and with increased resistance, the amperage goes down ( Ohm's Law)--often below the rating of the fuse--so that voltage keeps flowing and heat keeps rising until the pump melts or catches fire.

This is especially common with bilge pumps, since they are usually wired to automatic switches, and thus operate when nobody is around, or when nobody is really monitoring what is going on (as opposed to, say, when running a deck washdown pump or a head macerator.)

We can do several things.

1. Fuse according to the pump maker's spec/ don't over-fuse
2. Keep a clean bilge.
3. Have a cage or strum box or other screen that prevents the pump from ingesting debris.

Kevin

[Hwyl]

Most people hardwire their bilge pump to the battery with an inline fuse in the circuit. I like a breaker in that circuit too, but you have to put it somewhere where you can be hyper vigilant that it’s not turned off.

[wizbang 13]

I use the breaker as the switch.
is that messed up?
no automatic float thingy

[Garret]

I have a breaker (in-line) for my bilge pump. One time the pump did jam up & burn out - but the breaker tripped. I had some water in the bilge, but no fire. So - IMO - definitely put protection in.

[Corella]

A breaker protects the circuitry (wiring), a fuse protects the device.
(All good advice above to size the breaker and fuse according to the wiring and the load. If you're still concerned about the pump overheating, easy enough to install a (manual) thermal cutout switch on the motor - a few $$ from any electrical store.)

[Garret]

A breaker protects the circuitry (wiring), a fuse protects the device.
(All good advice above to size the breaker and fuse according to the wiring and the load. If you're still concerned about the pump overheating, easy enough to install a (manual) thermal cutout switch on the motor - a few $$ from any electrical store.)

Wouldn't what is protected be affected by where the fuse or breaker is? After all, a breaker is functionally no more than a re settable fuse.

[Corella]

Its common practice to have multiple loads on a breaker(several lights or several instruments, etc), so it will serve all these loads. Difficult to get breakers rated low enough to protect many loads (electronics, etc). The wiring must be sized to cope with all loads on at once.
Each load should have its own fuse to protect it (often next to the load for convenience). If it didn't then if that load shorted, the currnent would surge, and one hopes the breaker would trip before the wiring overheated.....

[Garret]

Its common practice to have multiple loads on a breaker(several lights or several instruments, etc), so it will serve all these loads. Difficult to get breakers rated low enough to protect many loads (electronics, etc). The wiring must be sized to cope with all loads on at once.
Each load should have its own fuse to protect it (often next to the load for convenience). If it didn't then if that load shorted, the currnent would surge, and one hopes the breaker would trip before the wiring overheated.....

For sure that's common - but I wouldn't consider a bilge pump on a shared circuit. A bilge pump should be on its own dedicated circuit at the least - I prefer direct from the battery with an in-line breaker.

[Breakaway]

Much depends on location of the circuit protection. Most breakers are not ignition protected ( they spark when operated) and are not waterproof ( like a fuse in a WP holder.) Both points make a fuse a better choice if the circuit protection is in the bilge.

So, it depends.

Kevin


Sent from my iPhone using Tapatalk Pro

[Corella]

For sure that's common - but I wouldn't consider a bilge pump on a shared circuit. A bilge pump should be on its own dedicated circuit at the least - I prefer direct from the battery with an in-line breaker.

Absolutely, bilge pumps should be on their own circuits, preferably bypassing the main breaker panel and wired essentially directly to a battery, still protected by their own breaker(s) and fuse(s).
My comments were general ones on breakers vs fuses.

[Garret]

Absolutely, bilge pumps should be on their own circuits, preferably bypassing the main breaker panel and wired essentially directly to a battery, still protected by their own breaker(s) and fuse(s).
My comments were general ones on breakers vs fuses.

Gotcha!

[Bruce Brown]

got my question answered, and then some!