Fuse question

[Fred Koehlmann]

John,

Ours was 1602 (I know its later tan your) and like Roc's we also had a breaker under nav station just like below. So in your situation you only have one breaker? Maybe you can add a second, if there is room?

[Roc]

Yes, mine is just like Fred's picture. 

[John Langford]

Thanks for all the help and advice.  I just installed a 150 amp Blue Sea block fuse at the battery bank end of the positive cable from the house bank (4 Trojan T105s) to the battery switch and DC electrical panel and a 30 amp inline fuse in the #10 gauge wire from the battery switch common terminal to the various DC panel circuits. I use the start battery so rarely (like never) that I have left the 0/1 cable from its positive terminal unprotected. 

[KWKloeber]

John

  When you say "in line" fuse, what's the configuration? Is it a crimp on blade type fuse holder (ATC) or a barrel fuse? Do you want Ensure that the connections are good because any voltage loss there just travels down the line.

If it's a butt crimp-on fuse holder, make sure the fuse wire size is as large as the jumper.

Since the jumper is # 10 fusing should more likely be the wire capacity which is 60 amp in this application.  It would really be worthwhile upping that wire size, # 8 would be good to cut voltage lost considerably.   In fact if you'd like to do that, I'd be happy to mail you a jumper made up n/c.

Ken

[mainesail]

Thanks for all the help and advice.  I just installed a 150 amp Blue Sea block fuse at the battery bank end of the positive cable from the house bank (4 Trojan T105s) to the battery switch and DC electrical panel and a 30 amp inline fuse in the #10 gauge wire from the battery switch common terminal to the various DC panel circuits. I use the start battery so rarely (like never) that I have left the 0/1 cable from its positive terminal unprotected.

A 150A fuse for starting may eventually nuisance trip on you..... You just hope this does not occur when you really need the engine... For any bank that can be used to start engines I usually recommend using a 250A to 300A main battery fuse. These fuses also need to meet the AIC requirements of the bank so Class T, ANL or MRBF are the three go-to fuse types for bank protection..

Course Catalina used 4GA wire on many boats, max ampacity of about 160A with 105C wire with no derating factored in, and no fuse at all. A fuse is always going safer than no fuse at all, unless it nuisance trips.

[John Langford]

Thanks very much to both of you for the follow up.

The 30 amp blade fuse holder came with short 10 gauge tails so I crimped the appropriate fittings on either end and used it to replace the existing unprotected 10 gauge connector from the common terminal to the panel circuits. My calculations suggest that I would have to have every pump, the frig, all the electronics and every light running at the same time to get anywhere near 30 amps. My crimps are done with a professional crimped and my system has run successfully for 18 years with a 10 gauge wire so I should be ok. Thanks very much for the advice and the offer Ken.

The Blue Sea terminal block fuse is a MBRF, the wire gauge is 1/0 and the run length one way must be all of 20 feet from the battery bank under the starboard settee to the battery switch on the electrical panel and then to the engine. I will buy a more robust cube fuse on your advice, MS. Apologies, but I don't know your name.

[KWKloeber]

 I have a boxfull of 10 gauge ATO/ATC capped (weathertight) fuse holders if anyone else wants to make their  distribution panel safer and add a fuse to their (10 gauge) panel feed, or a fuse to their cockpit panel feed wire (my "Universsl" pet peeve.)   Looking for a new home, here for the asking.


If you want it with an M8 starter lug to fit the starter solenoid post it would be slightly more than "free".


kk

[J_Sail]

MaineSail's name is Rod, but mostly we just call him MaineSail; he doesn't seem to have taken offense yet.

Double-check your calcs and keep a spare fuse or two onboard, just in case, but you may well be just fine. If at some point you ever decide to fuse the #10 a bit higher, BlueSea does make an inline fuse holder that can take Maxi fuses as large as 60A (although the holder is rated at 48A continuous, so I would not fuse it above 50A). It has #6 pigtails, but could be readily spliced to your #10.
https://www.bluesea.com/products/5068/MAXI_In-Line_Fuse_Holder

I would encourage you to fuse your reserve battery too. It doesn't matter if it's almost never used, the concern is something somehow causing a short in its cable. That could occur from something hitting, cutting, or chafing the insulation somewhere or from a careless moment during servicing, with potentially catastrophic results. Unless you are severely limited on vertical height, it's trivial to add a BlueSea MRBF/holder right to the battery terminal.
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

If you have not yet read MaineSail's article, it (and all his others) are a valuable resource.
http://www.pbase.com/mainecruising/battery_fusing

Enjoy,
Jeremy

[KWKloeber]

Jeremy, Maxis are also available in 8 gauge which makes butting a bit easier,


I'd have to hunt back and locate my source for them if anyone is interested.


kk

[John Langford]

Jeremy's prudent advice re fuse protection for the cable from the start battery to the battery switch sent me back to take another hard look at the wiring of my electrical panel. Almost everything on the panel is powered from the common terminal on the battery switch and thus protected by the 30 amp in line fuse I have just put into the 10 gauge connection between the common terminal and the panel circuits. The significant exception is the power for the electric bilge pump that comes directly from the house battery terminal of the battery switch. Should that connection be independently protected by its own inline fuse or, since the bilge pump is the only potential power draw on that connection, is the protection provide by the bilge pump breaker on the panel enough?

PS by way of explanation, the bilge pump is powered directly from the house battery terminal on the battery switch because the automatic bilge pump must have access to power even when the battery switch is off and I am not around to turn it on.

[J_Sail]

The short answer is a definite YES.

The primary purpose of fusing is to prevent the wiring from becoming a fire hazard in the event of an overload. The cause of such overload can be a failure in a device or a short circuit in the wiring (due to a breach in the insulation). Thus the wire to the bilge pump needs protection even though the only intended load is the pump. What if something like either a loose anchor or a sharp edge of a screw shorts the bilge pump supply wire to ground? In that scenario, the small normal draw of the bilge pump is no longer a factor, and the unprotected wire rapidly overheats and potentially starts a fire.

Thus the advice to size fuses/breakers (aka over-current protection or OCP) to protect the wire, not the load. The largest allowed amp value is a function of the gauge of the wire, the temperature rating of the wire's insulation, how many wires are bundled together, and whether the pathway includes an engine room or not. It is not a function of what the load normally draws. Those guidelines also allow one to slightly oversize the fuse in certain circumstances.

HOWEVER, there are limited cases where one MAY choose to undersize the OCP. One of those is for motor loads, where it might be nice to have a breaker that trips when the motor becomes temporarily overloaded due to something jamming it. In that case, there is a point of view that having a breaker that trips and can be conveniently/quickly reset may be better than risking the motor overheating and burning out. Some bilge pump manufacturers  provide a spec for such a breaker. In that case you may want to use a breaker that is smaller than the rating of the wire. If it's a fuse rather than a breaker, then I would probably not undersize it, as a blown fuse is almost as bad as a blown motor if you can't quickly find and replace the fuse.