Wire size for bilge pump installation.

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fredrussell

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I’ve finally got round to purchasing an electric bilge pump. I’ve always been somewhat baffled by wire sizing. Pump (Rule 2000) uses 8.4 amps at 12v. They suggest using a 15 amp fuse in supply.

Can anyone suggest a wire/cable size guide online, or a calculation to work out mm2 of wire fog this and other boat projects?
 
For most normal runs you could get away with 1.5mm cable at this current (rated to approx 15 amps).

Personally, for bilge pumps I would over-rate and use 2.5mm cable for no other reason that I just don't want issues with bilge pumps.

Usual caveats about waterproof connectors, plenty of extra length in the cable to allow for cutting back the 'dead ends' eventually, etc, etc...
 
Moodysailor said:
For most normal runs you could get away with 1.5mm cable at this current (rated to approx 15 amps).

Personally, for bilge pumps I would over-rate and use 2.5mm cable for no other reason that I just don't want issues with bilge pumps.

Usual caveats about waterproof connectors, plenty of extra length in the cable to allow for cutting back the 'dead ends' eventually, etc, etc...
Click to expand...

That’s great idea to leave some spare So you can cut back when it gets corroded , I’ve re joined so many bilge pumps with failed connections and ended up stripping back loads to get to something that resembles copper wire, I’ve got to install extra bilge pumps in my boat , so will def leave some extra ?
 
Restoration man said:
That’s great idea to leave some spare So you can cut back when it gets corroded , I’ve re joined so many bilge pumps with failed connections and ended up stripping back loads to get to something that resembles copper wire, I’ve got to install extra bilge pumps in my boat , so will def leave some extra ?
Click to expand...

Yep, always leave a bit extra for davy-jones ;-)

What I did on our previous boat that had a deep encapsulated keel was to install a connection box high up in the engine compartment, then ran a 'sacrificial' length from this to the bilge pump. So that even if the wire corroded all the way back to the terminal box it wouldn't mean running a new length all through the boat (again). That, and having the connections routed as high up as possible out of the wet area means it should be good for many years for the new owner.
 
Sizing wires by what amperage they will 'carry' (or rated) isn't the best technique for low voltage DC. You also need to make sure the voltage drop along the length of cable is acceptable for the item you're fitting. Why buy a pump of a set capacity if you then provide it with power at a less than optimum voltage so it can't work as advertised? Traditionally incandescent bulbs were tolerent of a 10% voltage drop, but for most other things, the cables were sized at a 3% drop. HF SSB transmitters even less than that.

The 12v Planet calculator does a good job of calculating voltage drop. You just need to know the length of cable run from supply to pump including any extra you want to leave for alterations later. For calculators using metric sizes the convention is to use the one way distance, but for American calculators, they usually need the combined distance there and back!
 
fredrussell said:
I’ve finally got round to purchasing an electric bilge pump. I’ve always been somewhat baffled by wire sizing. Pump (Rule 2000) uses 8.4 amps at 12v. They suggest using a 15 amp fuse in supply.

Can anyone suggest a wire/cable size guide online, or a calculation to work out mm2 of wire fog this and other boat projects?
Click to expand...

The instructions for 12 volt Rule 2000 bilge pumps say

1642505889727.png

14 gauge ( AWG) is 2.1mm², The nearest sizes listed by 12 Volt Planet are 2.0mm² in plain copper and 2.5mm² in tinned copper

12 gauge (AWG) is 3.3mm². The nearest sizes listed by 12 Volt Planet are 3.0mm² in plain copper and 4.0mm² in tinned copper

.
 
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