Results 1 to 14 of 14

Thread: Fusing Bilge Pump

  1. #1
    Join Date
    Jan 2007
    Location
    Brewer, Maine
    Posts
    124

    Default Fusing Bilge Pump

    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

  2. #2
    Join Date
    Jan 2005
    Location
    Deepest Darkest Wales
    Posts
    24,678

    Default Re: Fusing Bilge Pump

    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.
    I'd much rather lay in my bunk all freakin day lookin at Youtube videos .

  3. #3
    Join Date
    Mar 2007
    Location
    East Quogue,NY
    Posts
    24,665

    Default Re: Fusing Bilge Pump

    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
    Last edited by Breakaway; 01-21-2022 at 03:11 PM.
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  4. #4
    Join Date
    Jan 2003
    Location
    Southern Maine
    Posts
    21,935

    Default Re: Fusing Bilge Pump

    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.

  5. #5
    Join Date
    Oct 2009
    Location
    South Puget Sound/summer Eastern carib./winter
    Posts
    21,045

    Default Re: Fusing Bilge Pump

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

  6. #6
    Join Date
    Apr 2005
    Location
    Hills of Vermont, USA
    Posts
    44,176

    Default Re: Fusing Bilge Pump

    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.
    "If it ain't broke, you're not trying." - Red Green

  7. #7
    Join Date
    Apr 2013
    Location
    Pittwater, NSW, Oz
    Posts
    135

    Default Re: Fusing Bilge Pump

    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.)

  8. #8
    Join Date
    Apr 2005
    Location
    Hills of Vermont, USA
    Posts
    44,176

    Default Re: Fusing Bilge Pump

    Quote Originally Posted by Corella View Post
    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.
    "If it ain't broke, you're not trying." - Red Green

  9. #9
    Join Date
    Apr 2013
    Location
    Pittwater, NSW, Oz
    Posts
    135

    Default Re: Fusing Bilge Pump

    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.....

  10. #10
    Join Date
    Apr 2005
    Location
    Hills of Vermont, USA
    Posts
    44,176

    Default Re: Fusing Bilge Pump

    Quote Originally Posted by Corella View Post
    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.
    "If it ain't broke, you're not trying." - Red Green

  11. #11
    Join Date
    Mar 2007
    Location
    East Quogue,NY
    Posts
    24,665

    Default Fusing Bilge Pump

    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
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  12. #12
    Join Date
    Apr 2013
    Location
    Pittwater, NSW, Oz
    Posts
    135

    Default Re: Fusing Bilge Pump

    Quote Originally Posted by Garret View Post
    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.

  13. #13
    Join Date
    Apr 2005
    Location
    Hills of Vermont, USA
    Posts
    44,176

    Default Re: Fusing Bilge Pump

    Quote Originally Posted by Corella View Post
    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!
    "If it ain't broke, you're not trying." - Red Green

  14. #14
    Join Date
    Jan 2007
    Location
    Brewer, Maine
    Posts
    124

    Default Re: Fusing Bilge Pump

    got my question answered, and then some!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •