Bilge Pump Disaster

[mick309]

I have not long ago purchased a second hand boat and today the wiring melted due to a short in the bilge pump. It was wrapped in a stocking and it got caught up inside. I am going to have to rewire and replace the bilge pump. So it goes but my question is.. Should the pump be wrapped in a stocking or is this a malpractice that nearly caused my boat to burn to the ground?

Edited December 10, 2006 by mick309

[johnno]

I think they had the stocking around it as a strainer

but think that might have been a easy quick fix

but to your horror now your fix.

I would recommend you put a strainer in the pump.

Rule have a Stainless stranier that fits in there pumps

[mick309]

and also, would installing an inline fuse stop such a meltdown again?

[offtap1]

For the wiring to start melting, there must not have been a fuse fitted , all electronic items must be fused to stop such a thing from happening. By having no fuse the short could have travelled back to ignition rendering boat inoperatable. Stocking is much to thin to have rapped around pump, could have wire fly screen which would not get sucked in. I have rule pumps which come with optional strainer which is a much better solution.

[johnno]

and also, would installing an inline fuse stop such a meltdown again?

Yes correct sorry never thought about that

[traysexy]

Maybe getting a little too serious, but you can install thermal fuses.. If the temperature of the cable exceeds a certain limit, then it cuts the power off, but definately safer to have a fuse in there for short circuit protection...

Just thought I should let people know about thermal fuses.. Very popular and very handy to have on some appliances..

Cheers,

Pete.

[Guest rzep]

I agree and Thermal Fuses are a great idea.

[Sammy0884]

Maybe getting a little too serious, but you can install thermal fuses.. If the temperature of the cable exceeds a certain limit, then it cuts the power off, but definately safer to have a fuse in there for short circuit protection...

Just thought I should let people know about thermal fuses.. Very popular and very handy to have on some appliances..

Cheers,

Pete.

Sorry to do this, but the above is mis-informed...

If a wire that is powering an appliance (bilge pump or other) is getting hot, or even warm, then the wire is far too small to deliver the required current, that is why it is getting hot... this "thermal fuse" you speak of, correctly termed a "thermocouple" is a 'circuit breaker' (fuses are things that blow) that will 'break' the flow of current when it exceeds the mandated capacity, it does this by passing the current through a switch that uses the heat generated by the current flow to activate the breaker, thus preventing the wires capacity being exceeded and preventing a fire... the benefit of a thermocouple is that they are very accurate with their tolerances, and they are able to be reset in situe..

Now the topic of fuses and wiring, first of all, to correctly wire a device you must first determine its peak current flow (we will assume it is a 1000GPH 12v Rule bilge pump) which is 4 amps.. Rule reccomends a 5 amp fuse be installed across the +ve, which is a 25% safety margin.... now an apropriate wire to connect the device with would require another 25-50% safety margin on top of the fuses capacity, which tells us that wire rated for 7.5 amps would be ample for this installation... what this all means is that if the bilge pump was to short out or fail, then the fuse would blow @ 5 amps, thus opening the circuit and a potential fire would be prevented, all because there is enough capacity in the wiring and enough safety margin in the installation.... the fuse must always be rated lower than the wiring, but higher than the device that is operating.

all make sense?

[Guest rzep]

That is right Sammy,

Although the problem with the wirring is not because the wire was not suitable for the job intended but due to the fact that the load placed on the pump due to the stocking being sucked into the pumps impellor caused the pump to draw more current through the wirring and that the wire was clearly not designed to cope with this much current or amperage.

So yes if there was a fuse installed then the fuse would of blown way before the wirring was placed under any stress.

Once a fuse blows then it needs to be replaced but on the other hand as you stated if a Thermal Fuse (Thermocouple) is tripped then it just needs to be reset once it cools down, but even then once you can reset it you still need to work out what caused it to trip in the first place. Or it would be likely to happen again.

[sluggo]

it pays to have a fire extinguisher on board as well...just in case

[traysexy]

Thermal fuses and thermocoplues are two totally different things..

Thermocouples reset themselves, where thermal fuses do not.

Alot safe to have a thermal fuse as it will completely asolate the issue in regards to heat tolerence.

[mick309]

More Problems!!!

I rewired the bilge today (with inline fuse and strainer) and found that the top of the battery has sustained some damage, there is a hole through to one of the cells, will this affect my battery?

[Guest rzep]

Short answer

Yes.

Replace you battery as it will likely fail on you.

[Guest johblow]

The right way to protect a cable is with a conventional wire fuse or circuit breaker that is wired in series with one of the conductors. Forget the thermal fuse, because to make it trip, the cable will need to be on fire. That is, their trip temperatures are very high, and much higher than regular cable insulation can stand.

Thermal fuses only work where there is good thermal coupling, and where the trip temperature of the fuse is suitable. In the case of boat wiring, neither of these are satisfied.

If this aint enough, consider this: if the wiring is hot enough to trip a thermal fuse or melt through insulation, then its hot enough to ignite petrol, or even worse melt through a tank.

So, as per the previous post, use appropriate size wire, and wire in a good old fashion fuse with some margin above the maximum current you expect.

[Guest Jewel]

Most appliences that have a thermal cut out do not use that in place of circuit protection, it is additional.

Thermal cutouts are generally used to physically protect a device (motors, trannys etc) independant of load on the cct. For example your 2400w bar heater is drawing its 10A on your standard 16A power cct........ it happily does this indefinately untill it cant dissapate the heat it produces and melts something/catches fire and then goes full short cct AND THEN finally trips your breaker but by this time your lounge room is on fire!

Additionally thermal cutouts are usually rated in degrees........... what temp is your pump going to be at when its drawing 5A?

Stick with conventional fuses as they require very little maintinence in a marine enviroment and are easy to check and replace, breakers have a internal mechanism which may corrode up out of sight and no longer work......... this you wont know untill its too late!

[Davemmm]

Part of the problem with wiring on boats (and cars) isnt so much the current carrying capacity of the individual wire but the manner in which it is installed.

As boat wiring is tucked up into tight spots and bundled into looms it reduces the amount of heat it can dissapate. If the stocking blocked the pump and overloaded the wiring it would blow a fuse ASAP but if it only slightly increases the load (which may happen if the pump keeps working with only a bit stuck in it) and the cabling is bundled up in the centre of a loom jammed against the side of a hot aluminium boat then that cables insulation will cook but a fuse may not blow untill it shorts out.

The best bet is to make sure any wiring you replace has a lot more capacity than the appliance uses but is still small enough to fit into any lug you are going to use.

Dave