www.iFourWinns.com

Last July I bought a 1998 Vista 258 . This past fall as I winterized the boat I noticed the previous owner was using a 7.5A fuse for the fresh water pump and it was labeled for 5A . I thought he must have been out of 5A fuses and used his next largest fuse . I replaced with a 5A and found out this weekend that the fuse blows each time it pumps up . The 7.5A works perfectly . How big a deal is it to use a 7.5 in place of a 5A fuse . thanks for any advice .

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1998 VISTA 258

You really need to have the proper size fuse in any given situation. Now, if the pump was upgraded in GPH etc...from the OEM pump, it may require a larger fuse due to current draw. If you can confirm that its the OEM or at least the identical replacement...its time to figure out why its drawing more than its rated/intended power.

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Current Boat:
2004 Sea Ray 320 Sundancer "Nauti Luvin'"

Previous Boats:
1999 298 Vista "Seas The Day"
2008 H200SS "Nauti Luv"
2006 Tahoe Q4

I agree with Nauti.. if it's OEM you need to check for shorts/grounds, if not, check the power rating of the pump and see what it draws. Fuse size will not hurt your fuse block, but can create issues if oversized for your equipment.

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Lubbs

Hudsonville, MI
1999 240 Horizon 5.7L GSi/SX

All depends on the wire size, you dont want the wiring to the load to become the fuse

My guess is the wire size is large enough for a 7.5a fuse, as mentioned if the pump was replaced to something a little larger or if FW switched suppliers and didnt remark the fuse panel that could be the cause. Myself I wouldnt be scared of a 7.5a fuse if everything was working fine, if it took a 20a to get it to work I'd be concerned..

Will said!!

Also, check the filter. On my other boats the fuse never popped but if the motor were to strain it would pull more to pop that 5 amp fuse. I am new to FW, but just a thought.

+1

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Jeff

'14 Cruisers 380 Express "Simon Sez"
Merc 8.2 Mag MPI 380
DTS B3X, (x2) Axius Premier


(SOLD)
'08 V318
Merc 350 Mag MPI 300
DTS Seacore, B3 (x2)

probably there's not always a "rocket-science" behind a slightly oversized fuse...yesterday without having read this topic I changed the 5A blown fuse of the horn on my 268, I had only a 7.5A and that's what I used for replacing...

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2006-288 Vista
"Drogue One" - a starboard story -
2 x Volvo Penta D3 - 160 HP

previous boats:
2001 -FW 268 Vista
1998 FW 258 Vista
2003 Saver 690 Cabin Sport

thanks a bunch guys , I'll check the pump , the filter , and I'll check and see if the wire's getting hot while the pump is running . I should have thought of all that stuff without bothering you guys .

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1998 VISTA 258

It's never a bother to ask. Better safe than sorry.

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-Tony
2016 Robalo R200 w/Yahama 200!

Previous boats:
2003 Four Winns 248 Vista - sold
1994 Sunbird Corsair 200 - sold
1980 Checkmate Predictor - sold

It looks like there has already been a lot of good advice on this topic but I'll throw this in too. Fuses as used in automotive and boat applications perform two functions. One, Short Circuit Protection and two, Overload Protection. Changing an ATC or ATM fuse (most common vehicle fuses) from the smallest continuous current rating to the largest will rarely have any effect on short circuit protection. In this case, your fuse blew due to an overload and not a short circuit anyway.

The engineering that goes into sizing fuses requires a study of several components. The wire size, the length of the wire in the circuit, the thermal capabilities of the wire's insulation, the fuse or breaker size upstream that the fuse in question must coordinate with, and the continuous current capabilities of the equipment and electrical connectors in the circuit all have to be evaluated. Also important is the failure mode of whatever equipment is in the circuit and any secondary protection built in to the downstream equipment. A major handicap that all vehicle electrical system engineers face is that fuses are only available in standardizes current ratings. Also remember manufacturers are financially motivated to keep fuse ratings as small as possible. Well, actually they are motivated to keep the wire size as small as possible to reduce costs. Generally speaking, to properly protect a smaller wire means a smaller fuse.

Where boat and automotive designs are different is that automotive engineers have much more control over what components get used and the specification of those components. Boat electrical systems are not so much designed as they are integrated. If you think about it, almost every electrical component used in a boat is mass produced for the entire marine marketplace and not specific to any one boat manufacturer. This is even true for critical components like engine controls. I think this difference leaves the boat designer more open to making mistakes that could create problems like the one described in the original post. I also would wager that significantly less pre-production testing is done on boat electrical system than for automotive applications.

I recently started blowing the 10 amp fuses in my DuoProp's trim pump circuit when using it for normal operation. I am assuming it is caused by winding to winding faults in the motor which would increase the running current of the motor. I have heard the Volvo's are known for faulty trim pump motors and mine might be about to go. I checked the wire size, relay current ratings, etc and decided to put a 15 amp fuse in instead. No blown fuse issues to date with about 10 hours on the 15 amp fuse. If it blows one time, then I'm going to replace the pump motor. I guess my point here is that you should not upsize a fuse without some due diligence to make sure you are not creating a fire hazard. You should also not assume that upsizing a fuse will automatically create a hazard. With that said, I have an auto fire extinguishing system in my engine compartment and another hand held extinguisher on board. I also have five spare fuses of each rating on board just in case. Best to be prepared.

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Jim
Richmond, Virginia
2005 Horizon 230 w/ Volvo 5.7GXI Duoprop
Towed by: 2007 Chevy Tahoe 4x4 LTZ

I am sorry!! I don't understand your statement above. All fuses (electrical not thermal) will open/blow upon a short circuit. At lest all the ones I have ever seen, not to put foot in mouth. I just installed a new radio, on the DC panel is a fuse (some boats have a breakers), why? If it shorts out, the current will go so high, that with out a fuse or breaker, the wire will get hot and cause a fire. If I misunderstand you, sorry. I bring this out more for the other boaters.

I believe you might have misunderstood me. I was trying to say that the current rating of a fuse does not have much to do with the short circuit protection it provides. I think you are saying the same thing.

As long as you are not changing the type (frame size) of fuse, then your fuse will blow for a short circuit in almost every case and will prevent the possibility of a fire. The fuse's continuous current rating does have an impact on the overload protection it provides. Overloads can also cause wires to get hot and in extreme cases can also cause fires.

To oversimplify the process of sizing fuses you should:
1. Determine the running current during normal operation of whatever the fuse is protecting.
2. Select the appropriate fuse current rating by picking the next higher standard fuse size.
3. Use a wire size capable of handling the full fuse current rating on a continuous basis based on the wire manufacturer's data. This is a function of the insulation's thermal properties and this information is available from wire manufacturers.

In a lot of cases (and certainly in the case of your radio), the fuse you are installing is ONLY providing short circuit protection. This is because the device already has a built in method of providing thermal (overload) protection; usually in the form of an inline AGC fuse. In this case, your fuse is only protecting the wire feeding the device from short circuit because any overload condition will blow the fuse the device's manufacturer provided. I just installed a VHF radio in my new boat and the Cobra radio I bought came with an inline 10A fuse built in to the radio's wiring harness. I chose to put a 15 amp ATC fuse in the circuit feeding the radio to protect it from short circuit. If I had used a 10 amp fuse, then I would have run the risk of blowing the ATC fuse in my dash because of the differences in fuse current curves of time delayed AGC fuses and ATC fuses. The way I did it, the AGC fuse will always blow for an overload the way the manufacturer intended and the ATC fuse will always blow for a short circuit in the wiring to the radio which provides complete protection of the circuit. I also used wire capable of carrying the full 15 amps of the ATC fuse on a continuous basis even though all the circuit can ever flow for long periods of time is 10 amps due to the inline fuse from the manufacturer.

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Jim
Richmond, Virginia
2005 Horizon 230 w/ Volvo 5.7GXI Duoprop
Towed by: 2007 Chevy Tahoe 4x4 LTZ

OK, I see what you are saying!! Yes, I agree with you!

Thank you for your understanding.

Similar thing with me last weekend. My blower wasn't working, checked the fuse and it was blown. 5 amp I believe. I replaced it and it blew again. Replaced with a 10 and no problem. What could be causing the 5 amp to blow all of a sudden with no prior issues?

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Steve
2007 Fourwinns Horizon 240
VolvoPenta 5.7L DP GL 280 hp

You should NOT just replace a fuse with a higher-rated one! NEVER. Otherwise you risk the added current going through the wire causing it to overheat and CATCH FIRE.

When a motor driven circuit blows a fuse it's often because the motor is going bad. It's working harder than it's supposed to and that causes it to draw too much current. This blows the fuse. The solution is to replace the motor. Blowers are relatively cheap, certainly a LOT cheaper than risking a fire.

If it's not the motor then it's possible there's corrosion, either inside the wire insulation or at the terminals. Corrosion prevents the wire from carrying it's rated load. The device on the circuit tries to draw more current but the wire can't do it. This causes the wire to overheat.

One way to tell if there's a problem is to check the voltage on the line when the device is pulling it's full load. Under normal circumstances there won't be much of a drop in voltage. But if the device is pulling an excessive load you'll often see a voltage drop at the device end of the circuit. If you have an ammeter you can measure just how many amps are being pulled through the circuit. You can compare what the device claims to consume against what the ammeter detects. If it's a big difference then the device may be starting to fail.

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-Bill Kearney, 2005 348 Vista