300A T Fuse 12V

[Rjm st.petersburg]

The group is pouncing on my head pretty hard. I do understand that that the blown fuse is only a symptom. I do have a 25yr old son that has no problem pointing out my short comings, so I am used to it, not appreciated, but used to it.
Will Robinson

 

[Johann]

I did look on Amazon. The one you posted is 125v. The ones I saw were on back order. Grainger might have some, $180. At WM they were $45 with a procard.
My bilge pump is hooked up to the house batteries. I moved the fuse from the inverter to the house and it's working. I'll be ok, until I leave the dock.

I wouldn’t buy a Class T fuse off of Amazon. It maybe just as likely to start a fire as to prevent one.

Counterfeit Electrical Components - Just say no!

Fake look-a-like electrical components are flooding our shores. Buy Carefully.

marinehowto.com

 

[Rjm st.petersburg]

I did eventually find one and hour away and purchased it for $110. It is a Little Fuse made in the USA.

 

[Johann]

I did eventually find one and hour away and purchased it for $110. It is a Little Fuse made in the USA.

A bit steep, but it’s good you found one local. Bay Marine Supply is a reputable online store for your spares. Also it looks like defender has them back in stock now too.

Blue Sea Systems Class T Fuse

Blue Sea Systems Class T Fuse (5118) offers high interrupt capacity for large battery banks including Lithium-ion and TPPL batteries. Features: 20,000 Amp interrupt rating Extremely fast short-circuit response Only UL 248-15 listed fuse commo

defender.com

 

[Davidasailor26]

Before installing the new fuse I’d use a multimeter to check the resistance between the downstream side of the fuse holder and ground. The resistance you get should give an indication of the amount of current that will try to flow once the fuse is in place. The formula for that will be current = 12/Resistance. I’d expect R to be at least 1 ohm, which would lead to 12A of current through whatever circuits are turned on. 2 ohms or more is probably even more realistic. If it’s less than that beware that you might just blow your brand new $110 fuse again.

 

[Hello Below]

Good sourcing.
Out of curiosity, what size cable is this 300A fuse protecting? What is the length of this cable? What would be really nice is a DC wiring diagram for your boat.

 

[smokey73]

@Rjm st.petersburg Sorry if you felt we were "pouncing on your head." That was certainly not my intent nor I am sure, anyone else's. We didn't get a lot of info in the initial post and lacking that info had to make some assumptions. More info is always better than just a little information. With a blown 300 amp fuse, the potential for catastrophic damage is pretty high when the fuse is replaced and even if it doesn't blow when replaced, something might come on or some "intermitent short" might appear when you are heeled over have some shock (like hitting a wave). Depending on what was the cause, if it happens again the result might not be something you want to experience. Hence the "Danger Will Robinson" warning. Glad you found a fuse.

As a matter of caution. I am really surprised that whomever replaced your motor mounts, if that was the source, they did not alert you they shorted something out. Believe me, if they did it they knew it. Probably had to change their shorts after it happened. The spark probably left a burn mark on their metal tool or the thing that caused the short. And yes, I have welded a wrench to a fender so many of us speak from the screwups we did in the past.

 

[dlochner]

Maine Sail has a good article on circuit protection. It would be worth a read by all of us.

Battery Banks & Over Current Protection - Marine How To

Battery Banks & Over-Current Protection A 300A (MRBF)Battery Terminal Mounted Fuse by Blue Sea Systems In this article we will discuss fuse selection, fuse types, wire ampacity, Amperage Interrupt Capacity (AIC) and even potentially unsafe ABYC “exceptions to the rules”. In short,

marinehowto.com

 

[Rjm st.petersburg]

There wasn't any burn marks, melted wiring or insulation. As I removed the starter to be checked out, I noticed the ground was not installed correctly. So I cleaned it up, dielectric grease and properly grounded it to the engine block. The starter checked out fine. I believe the problem is solved. None of the connections heated up with the engine running, AC on, refrigeration on, lights on, microwave on, water pump running, windlass running even flushed the head a few times.
Next test is to make sure the shaft alignment is good. There is less than .004 between the flanges. Dock test first, then open water.

 

[dlochner]

The one you posted is 125v.

A fuse rated for a higher voltage is good for lower voltages, but not necessarily vice versa. Think of this it this way.
A fuse is like a bridge which has a weight limit. It really doesn't matter how fast you travel over the bridge, the bridge will break if you exceed the weight limit. For the fuse, the weight is the amperage and the speed is voltage. If the fuse will blow at 300a at 120v, it will also blow at 300a at 12 v or any voltage in-between. Thus it is only necessary to test at a higher voltage, because it will fail at all lower voltages with the same current. The testing determines the labeling, i.e., 120v 300a.