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Old 10-12-2017, 03:26 PM   #1
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Big fuses

Hi All,

My 40 year old trawler has every kind of wiring you can imagine, bad routing, good routing, bad hookups, good hookups, you name it, it's there.

What I see that I want to fix first is I have a couple of old fashion fuses on a bulkhead. One rather large fuse is from the battery to the charger/inverter. I should be able to remove that and put a large amperage fuse right on a battery post, no? Those fuses sitting on the wall bug me.

Dave
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Old 10-12-2017, 04:25 PM   #2
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Fuses mounted on a wall or bulkhead are no problem. In fact with big wire, 2/0 probably, to your inverter you need a Class T fuse to have enough short circuit current breaking capacity. If a small terminal mounted fuse blows, but the arc continues because the current being supplied from the battery is huge, a lot of damage can result.

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Old 10-12-2017, 04:49 PM   #3
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Originally Posted by djmarchand View Post
Fuses mounted on a wall or bulkhead are no problem. In fact with big wire, 2/0 probably, to your inverter you need a Class T fuse to have enough short circuit current breaking capacity. If a small terminal mounted fuse blows, but the arc continues because the current being supplied from the battery is huge, a lot of damage can result.

David
I did not know that. Thank you.
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Old 10-13-2017, 06:53 AM   #4
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Class "T" fuses in their proper holder are safest at stopping large DC current flows.

The worry is not an inverter taking too much juice ,

the worry is the feed wire falling off and creating enough heat to start a fire , before the fuse blows.

Any brand will work.


Blue Sea 5119 Fuse A3T (Class T) 300 Amp

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Old 10-13-2017, 08:40 AM   #5
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There is nothing wrong with the factory wiring. You are more dangerous with your ignorance than the 40 year old boat is. If you have a problem hire a real boat electrician. I am trying to save you from yourself.
no insult intended.
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Old 10-13-2017, 08:51 AM   #6
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Quote:
Originally Posted by Cliff Meima View Post
There is nothing wrong with the factory wiring. You are more dangerous with your ignorance than the 40 year old boat is. If you have a problem hire a real boat electrician. I am trying to save you from yourself.
no insult intended.
Quite the assumptions.....

Especially that the factory wiring still exists untouched. On a 40 year old boat.....

That the inverter wiring was a factory option on a 40 year old boat.....

That by asking questions, a handyman cant install things better than a pro......

He wasnt tryingvto remove fuses, just move then off the bulkhead which is not dangerous..... in fact it may be safer if closer to the battery.
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Old 10-13-2017, 11:11 AM   #7
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Quote:
Originally Posted by Cliff Meima View Post
There is nothing wrong with the factory wiring. You are more dangerous with your ignorance than the 40 year old boat is. If you have a problem hire a real boat electrician. I am trying to save you from yourself.
no insult intended.
Hi Cliff, I won't take it as an insult, but you have no idea what my ignorance level is on the subject. The inverter charger is 10 years old on a 40 year old boat. I worked on boats for 5 years as a pro... never saw a big "old house" looking fuse on any boat I ever worked on. That's why I asked. But thanks.

Dave
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Old 10-13-2017, 11:45 AM   #8
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I've found the original wiring on our '84 boat to be well-done and mostly in fine condition. The insulation is still flexible (unlike, say, a 10 year old European car from the '60's or '70's) It's not the current tinned stuff. Places to worry about are those where the terminals are or have been damp.

Piece by piece, I am replacing everything that's newer, amateurish, or the wrong stuff.

Current Code/practice is to fuse the battery wiring close to the battery, both positive and negative(!?). I have yet to do that, but will. None of the big stuff on the boat was, or is, fused.
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Old 10-13-2017, 11:52 AM   #9
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Hi Dave!

We'll have to compare the "chicken coop wiring" on your 40 y.o. boat vs. my 30 y.o. BC-boat some time! That should be entertaining. End of J dock. I'll be on board next week, installing the rebuilt 24V alternator among other things.
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Old 10-13-2017, 12:17 PM   #10
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The inverter charger is a power source. ABYC says the fuse must be with in 40 inches of the inverter and 72 inches of the battery. If you use an un sheathed wire then 7 inches in all cases.
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Old 10-13-2017, 03:44 PM   #11
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I have discovered "Terminal Fuses" and they are great. Marine rated in sizes up to 300A. Available from Blue Seas and others.

https://www.bluesea.com/products/519...k_-_30_to_300A

Ken
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Old 10-13-2017, 05:37 PM   #12
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Ken:

Your reference does not include a short circuit current interrupt spec, but I will bet it isn't high enough. If you take a big battery bank, say two GC batteries, and a big conductor, say 2/0, and if it shorts to a serious ground, say the engine block, a whole lot of current will flow.

A Class T fuse has an interrupt rating of at least 10,000 amps which is what it takes to safely interrupt the situation described above. If the fuse isn't rated high enough the arc can continue until it melts the fuse block and could possible start a fire.

That is why you always want to use Class T fuses with big batteries and cables.

David
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Old 10-13-2017, 06:36 PM   #13
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............... Current Code/practice is to fuse the battery wiring close to the battery, both positive and negative(!?).
If that is code, I would like to see it in writing.

Fusing the negative lead is bad practice. If a fuse in the negative side of the circuit blows, the circuit will not operate but the entire circuit (including the negative portion on the "hot" side of the blown fuse) will still be hot.

The ABYC requires circuit protection within seven inches of the source with a few exceptions (distance, not protection). It does not require overcurrent protection in engine starting circuits.
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Old 10-13-2017, 06:59 PM   #14
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There is nothing wrong with the factory wiring. You are more dangerous with your ignorance than the 40 year old boat is. If you have a problem hire a real boat electrician. I am trying to save you from yourself.
no insult intended.
This makes WesK look polite.
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Old 10-13-2017, 07:07 PM   #15
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This makes WesK look polite.


LOL this is a good one!

@Wesk - No offense just find this one funny

L
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Old 10-13-2017, 07:18 PM   #16
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The current interupting capacity of Blue sea battery terminal fuse is 10,000 amps at 14 VDC.
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Old 10-13-2017, 07:50 PM   #17
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LOL this is a good one!

@Wesk - No offense just find this one funny

L
It's not that funny!
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Old 10-13-2017, 08:41 PM   #18
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Quote:
Originally Posted by djmarchand View Post
Ken:

Your reference does not include a short circuit current interrupt spec, but I will bet it isn't high enough. If you take a big battery bank, say two GC batteries, and a big conductor, say 2/0, and if it shorts to a serious ground, say the engine block, a whole lot of current will flow.

A Class T fuse has an interrupt rating of at least 10,000 amps which is what it takes to safely interrupt the situation described above. If the fuse isn't rated high enough the arc can continue until it melts the fuse block and could possible start a fire.

That is why you always want to use Class T fuses with big batteries and cables.

David
Yup. The terminal fuses do have the specs but it's buried. 10000 amps at 14v.

Ken
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Old 10-14-2017, 12:39 PM   #19
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ABYC says 7/40/72.

7 inches to over current protection if unsheathed wire is used.

40 inches to over current protection from a power source other than battery.

72 inches to over current protection from batteries.

Starting circuit is an exception, no over current protection (OCP) required.

There is a formula that takes battery and wire size to calculate the ECIP of the OCP.

No mention of OCP on the ground side for DC current. (AC does often require OCP on the neutral side)

WARNING: there are many other parts to this standard. Such as type of wire, type of crimp, type of support, routing standards, etc.
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Old 10-14-2017, 03:03 PM   #20
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...............No mention of OCP on the ground side for DC current. (AC does often require OCP on the neutral side)............
The Master circuit breaker for the AC panel must provide overcurrent protection and disconnect both the hot and neutral conductors simultaneously. This is done by linking two circuit breakers together mechanically so when one trips, the other trips at the same time. This is called a "double pole breaker".

The purpose is not to provide overcurrent protection to the neutral conductor, the current through either conductor is the same (unless there's a ground fault but that's a different matter). The purpose is to completely disconnect the boat from the power source in the case of a tripped (or turned off) breaker.

Branch circuits do not require double pole breakers.
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