Blown 15 amp inline fuse on freshwater pressure pump

Merry Christmas everyone. The other day we found there was no running water in the galley and discovered a blown 15 amp inline fuze on freshwater pressure pump. I replaced it and water pressure returned but I noticed yesterday that the fuze had blown again. A colleague suspects it's a load issue which suggests the pump is the issue. The system groans when the pump is operating. Are there other possible causes for this? I do have a spare pump, BTW.

Jim, Sent from my iPad using Trawler

Your pump is probably binding due to trash in the impeller, bad bearing, ? and is pulling enough current to blow the fuse. Pull the pump and replace and it should be fine.

David

Check your filter(s)- they could be clogged enough to cause this.

Good suggestions from David.
It also could be the pressure switch, the pump should shut off b/4 it draws more than 10-12 amps. If it "groans" just b/4 shutting off but not while the water tap is full on, I would say pressure switch. Some are adjustable, some not, If adjustable lower the shut-off pressure (CCW on the screw or nut) in the pressure switch.

Thanks so much. I'm a newbie boat owner and am continuing on my learning curve. Is the pressure switch on the pump or elsewhere in the system?

Jim, Sent from my iPad using Trawler

Usually it's on the pump, depending on the manufacturer.

If replacing the pump solves the problem, you might be able to rebuild the old pump economically and use it as your spare.

Jim

Depending upon the sound insulation in your Krogen 42 you may not be able to hear the fresh water pump running. Before you replace the pump, replace the fuse once more and then listen to whether or not it turns off or is it running 24/7. If it is running then you either have a malfunctioning pressure switch or an air leak.


Marty

also check your wiring..... too small wire in the system or corrosion could be the culprit by increasing the amperage draw....

Fuses come in many styles , some are ,slow blow, that will allow a slight overload as a motor starts, some are very fast blow , to protect delicate electronics .

Slow blow for motors is worth the effort, although I would measure the pressure at the faucet to see if its normal..

Small wires and corroded connections equal high resistance and high resistance in a DC system means lower voltage and current.

Too small cross section of wire and a corroded connection gets hot because the power per unit of area may be very high, not because the amount of power has increased.

Increasing resistance in order to reduce voltage and current is the oldest method of controlling the speed and power of brushed DC motors. When you increase resistance you decrease voltage and that reduces the speed the motor turns. The slower it turns the less power it produces and the less current it draws.

If the load on the motor increases (say it's a positive displacement pump and the discharge is blocked) and voltage remains the same, then yes, the current will increase and the fuse may blow.

But, when electrical input to the motor is decreased by resistance, the current required to run the motor is also decreased and the fuse will not blow.

RickB said:

Small wires and corroded connections equal high resistance and high resistance in a DC system means lower voltage and current.

Too small cross section of wire and a corroded connection gets hot because the power per unit of area may be very high, not because the amount of power has increased.

Increasing resistance in order to reduce voltage and current is the oldest method of controlling the speed and power of brushed DC motors. When you increase resistance you decrease voltage and that reduces the speed the motor turns. The slower it turns the less power it produces and the less current it draws.

If the load on the motor increases (say it's a positive displacement pump and the discharge is blocked) and voltage remains the same, then yes, the current will increase and the fuse may blow.

But, when electrical input to the motor is decreased by resistance, the current required to run the motor is also decreased and the fuse will not blow.

Click to expand...

Thanks for the explanation....

Good advise from psneed and RickB! Spot on!
I suggest this book or one like it for anyone not understanding all the systems on their boat. After teaching electrical and diesel and a career in the automotive industry I am amazed at the myths of electricity that are given as gospel by even experienced cruisers.

Boatowner's Mechanical and Electrical Manual : How to Maintain, Repair, and Improve Your Boat's Essential Systems: How to Maintain, Repair, and Improve Your Boat's Essential Systems, Edition 3
Nigel Calder - May 31, 2005
McGraw Hill Professional - Publisher
$49.95 $27.47 Buy Goolge play store

Hope this Helps
S

Thanks again all. I've got the e version of Calder's book on my iPad and have even reviewing this section on water pumps etc. it seems the pump may or may not have the switch. This will be a. Winter project.

Jim, Sent from my iPad using Trawler

Which water pump mfgr & model and maybe you will get more specific answers? Maybe not but usually it helps us help you.

Why not start with the simple things first? Check the strainer or filter on the inlet side of the pump. Make sure it's not partially clogged. Clean it and reinstall it.

Is the fuse that's blowing the correct fuse for the pump? Check the installation instructions or the manufacturer's website. A previous owner may have used the incorrect fuse. Something like a pump would do well with a "slow blow" fuse because of the current surge when the pump starts up.

Why is there an inline fuse in the first place? Isn't the circuit protected by a circuit breaker (or fuse) in the electrical panel?

I haven't been back to the boat since Christmas Eve so cannot comment further to you questions, except to say that I don't know why this is protected by an inline fuse.

I am concerned however that I may have either drain the water tanks prior to working on this pump or have a bung (or two) at the ready to control the water flow while I work on the pump. I'm worried the system will siphon otherwise. I don't believe there is a shutoff on the tank side of the pump.

Jim, Sent from my iPad using Trawler

You need a fuse/breaker for the circuit and you should have one for the device, hence the inline.

Xsbank said:

You need a fuse/breaker for the circuit and you should have one for the device, hence the inline.

Click to expand...

I don't think a second fuse is usually required...as long as the wire from a fused/breaker panel to the device is protected and the device doesn't need special protection (never had a pump that did)...no need that I know of.

http://www.shurflo.com/files/RV-Ins...qua King Mini - 911-733-C 1901-0003_0013_.pdf
.

unless there are other devices on that circuit.

I should have clarified. I understand the need for the fuze/breaker, but don't know why the pump wasn't wired into the breaker panel.

Jim, Sent from my iPad using Trawler

JDCAVE said:

I should have clarified. I understand the need for the fuze/breaker, but don't know why the pump wasn't wired into the breaker panel.

Jim, Sent from my iPad using Trawler

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some previous owners and even yard help are clueless/lazy.....do it in one of the many possible safe manners and move on...I'd go crazy if I dwelled on why my PO did to this poor boat.

JDCAVE said:

............I am concerned however that I may have either drain the water tanks prior to working on this pump or have a bung (or two) at the ready to control the water flow while I work on the pump. I'm worried the system will siphon otherwise. I don't believe there is a shutoff on the tank side of the pump.

Click to expand...

Take the hose off the inlet to the pump and raise it higher than the water level in the tanks. Or plug the end of the hose.

Sorry for the belated late response. I've only just got back to the boat to look at things. As mentioned, it has a 15 amp fuse. The unit is a Shurflo 5901-2212 (Extreme Pro-Blaster). The spec sheet says a 20 amp fuze is recommended. I'm concerned that if I go to a 20 amp fuze it might be too much for the wire. Also, it says this is for wash down applications. Spec sheet says it has a a sealed adjustable pressure switch that will be difficult to get at. There is no in-line strainer.

Would you recommend the installation of shutoff valves either side of the pump? Also is this the correct pump for my application? Spec sheet says.."Marine fresh or salt water wash down installation. Other uses may include 12V DC pressurized water system in cabins. This pump may be used for general water transfer."

Jim, Sent from my iPad using Trawler

...I should add that there is also breaker for the FW pump on the DC breaker panel, in addition to the in-line fuze.

Jim, Sent from my iPad using Trawler

We always get a deck wash down pump for house Fresh Water service.

Take a look and the motor is usually 2x as long.

This makes it longer lasting. A great idea if it can not be heard , and is not secured after each use.

Your CB on the panel should protect the existing wiring , the 20A fuse, the pump.

These units with a larger motor will start at a higher Amperage , but a CB is slow responding so should not pop.

Running they use about the same amps as the tiny motor style.

JDCAVE said:

...I should add that there is also breaker for the FW pump on the DC breaker panel, in addition to the in-line fuze.

Jim, Sent from my iPad using Trawler

Click to expand...

I'm assuming there is nothing else connected to the circuit the pump is connected to.

There's no reason to have two overcurrent protection devices on one circuit. Check the gauge of the wiring from the circuit breaker to the pump and back to negative. If it's #12, a 20 amp circuit breaker is appropriate, do away with the fuse. if it's #14 you need a 15 amp circuit breaker and the pump is designed for too much current for your wiring. Replace the wiring or the pump.

While your pump may work for a potable water system, you would be better off with one designed for that use. And you should install a filter just before the pump inlet.

JDCAVE said:

I should have clarified. I understand the need for the fuze/breaker, but don't know why the pump wasn't wired into the breaker panel.

Click to expand...

Maybe because the installer followed Shurflo's installation instructions to the letter without regard to existing wiring, or the existing breaker or wiring may not have been adequate for the new pump.

If the wiring and breaker are adequate, rewire it that way.

Pau Hana said:

Check your filter(s)- they could be clogged enough to cause this.

Click to expand...

I replaced the pump before i realized it was the filter.

>There's no reason to have two overcurrent protection devices on one circuit.>

There are frequently very good reasons to use 2 over current protections on one circuit.

The CB usually protects the wire , the fuse at the user protects the device.

A car radio can be fed with a 10G or 12Ga wire and proper CB , but all it may require is a 5A fuse , so an internal short (deck leak?) will pop the fuse rather than ignite the radio.

This also allows for more than one light user to be on a supply circuit and be protected.

Modern gear can easily be installed , radar used to be a big power draw , today almost minor.

The old heavy radar wiring can still be used to supply the new unit , IF the new unit has its own protection.

FF said:

The CB usually protects the wire m, the fuse at the user protects the device.

Click to expand...

If the distribution system has a breaker labeled "pump" then that that breaker protects the branch that supplies the pump. Since the wiring supplying the pump should be properly sized for current and voltage drop for that pump, there is no need to size the breaker for the wire. It should be sized to protect the pump.

Think about it for a moment ... if the pump draws 15 amps maximum it should be fused for around 20A or whatever the manufacturer specifies, the wire should be sized to handle more than 20A, considering the circuit is DC the wiring is probably "oversized" a bit to control voltage drop anyway. So, a fuse rated for the pump is all that is needed. A fault before the pump will pop the breaker and protect the wire, and a fault in the pump may pop the breaker and hopefully prevent a fire.

It is both uneconomical and pointless to have two differently sized circuit protection devices on a branch circuit that supplies one consumer. It is also foolish and dangerous to "steal" power by piggybacking on another branch circuit. That sort of thing is what leads to the light flickering and dimming and loss of electronic readouts (and damage) that we always read about here.

If the breaker on the switchboard or distribution panel says PUMP then that is all it should supply and it and the wire it feeds should be sized accordingly.