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Water pump replacement
I just replaced our original 2008 Shurflo 5.7 Extreme with a Revolution 4008 that I've been carrying as a spare. The swap went well, but now I'm wondering about the extra inline fuse that was on the Extreme pump. It was on the hot lead of the original pump. It was rated at 15 amps.

The Extreme pumps calls for a 15 amp fuse on the motor label.
The 4008 calls for a 10 amp fuse on the motor label.

Do I need an additional 10 amp inline fuse on the 4008?

Do i need to change the converter panel fuse to a 10 amp?

Thanks everyone,

Larry
Larry in Monument, CO
2008 24' FD
Re: Water pump replacement
Reply #1 –
Larry-

I forget if there were other loads on the water pump circuit that originates on the DC panel. If the pump is by itself, I would omit the inline fuse and reduce the DC panel fuse to 10A. If there are other loads, then you need to consider whether or not those loads will draw current when the pump runs.

Dropping the panel fuse to 10A should not harm anything. You'll know soon enough if you need to go back to a 15A fuse, and after that if an inline fuse for the pump is warranted.

Mark H.
Former owner, 31-foot gas Class A
Former owner, 1997-8 mid-bath
Re: Water pump replacement
Reply #2 –
Thank you, Mark. It looks as though the water pump is on its own dedicated circuit which is what the Shurflo installation sheet recommends. I'll give it a try with the 10 amp fuse, and as you say, I'll know soon enough if it works.

Larry
Larry in Monument, CO
2008 24' FD
Re: Water pump replacement
Reply #3 –
Some basics - A fuse is sized so that ALL the wiring served by said fuse is protected and will not overheat.  Wiring should be thought of in two ways - to and from the pump, and in the pump. 

The formula is V=IR where V is volts, I is amps and R is resistance.  The pump has a set amount of resistance, and the voltage is a set amount, thus the amps are limited.  If resistance is reduced, say by a coil in the pump shorting from damaged or faulty insulation, the amps would increase, and the wiring remaining could overheat. 

The Revolution pump, needing only a 10 amp fuse, MAY have lighter wiring than the Extreme at 15 amps, OR the Revolution may simply pull less, allowing use of a smaller fuse.  The wiring from the fuse panel to the pump is not changing.  It is rated for at least 15 amps, so using either a 10 or a 15 amp fuse will adequately protect the wiring to the pump.  If, however, the Revolution has lighter gauge wiring inside, a 15 amp fuse may not adequately protect the pump because it will allow more amps into those wires than they might be able to handle.  As long as the pump is working well and has no internal faults, insulation breakdown, etc., the pump will draw less than 10 amps and a 15 amp fuse or a 50 amp fuse would work, but if there is anything that happens inside the pump that reduces the pump's internal resistance, too heavy a fuse will allow excess heat in the wiring and could cause a fire.  The 10 amp fuse is what ShurFlo recommends, and that is what I would use.

Now, as Mark said, if there are other components on that same circuit, you might have a problem with a 10 amp fuse but assuming that the pump is on its own circuit, go with 10 amp, not 15.

Ken F in WY

'08 MB
Re: Water pump replacement
Reply #4 –
I would leave all the fuses as they are. The wiring is already sized to handle 15A, so replacing the fuses would be a waste of time with no improvement in safety.

Steve
2004 FL
2013 Honda Fit
Re: Water pump replacement
Reply #5 –
Steve, the feed wiring is sized to work with a 15 amp fuse, but the wiring in the new pump may not be.  The manufacturer recommends 10 amp.  That is what should be used.

Ken F in WY
'08 MB
Re: Water pump replacement
Reply #7 –
"Steve, the feed wiring is sized to work with a 15 amp fuse, but the wiring in the new pump may not be.  The manufacturer recommends 10 amp.  That is what should be used."

I agree.  If the circuit is dedicated to the pump, the 10 amp fuse recommended by the manufacturer is the right fuse to protect their equipment, and provides greater protection for the wiring than the 15 amp would.  If by chance the circuit were to feed other devices, then an inline 10 amp fuse to the pump would be the right way to protect it.
Bill
2003 -- 23' FL
 
Re: Water pump replacement
Reply #8 –
Thanks everyone. Ken your review of basic E&E takes me back to Radio school in the Navy ( in a good way!) Also my Dad was an EE and he tried to raise me right, but I always wind up needing to double and triple check when working with electricity. So, I'll try the 10 amp fuse because, Joan, I reread my copy of the instructions and the first bullet under electrical connections says to use a fuse as specified on the motor label. That's not verbatim, but it's close.

Larry
Larry in Monument, CO
2008 24' FD