Big fuses

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Dave_E

Dave_E

Senior Member
Joined
Sep 2, 2014
Messages
276
Location
USA
Vessel Name
Agnus Dei
Vessel Make
36' Shin Shing
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
 
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
 
djmarchand said:
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
Click to expand...

I did not know that. Thank you.
 
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


 
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.
 
Cliff Meima said:
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.
Click to expand...

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.
 
Last edited:
Cliff Meima said:
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.
Click to expand...

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
 
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.
 
Last edited:
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.
 
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.
 
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
 
DHeckrotte said:
............... Current Code/practice is to fuse the battery wiring close to the battery, both positive and negative(!?).
Click to expand...

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.
 
Cliff Meima said:
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.
Click to expand...
This makes WesK look polite.
 
The current interupting capacity of Blue sea battery terminal fuse is 10,000 amps at 14 VDC.
 
djmarchand said:
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
Click to expand...

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

Ken
 
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.
 
Last edited:
tiltrider1 said:
...............No mention of OCP on the ground side for DC current. (AC does often require OCP on the neutral side)............
Click to expand...

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.
 
My statement is correct and Wesk’s Statement is correct. This discussion was about DC. When you get to AC It gets more complicated as you go from 120 to 240. I can give you several senerios with 120/240 were a neutral needs COP to protect the wire.
 
Two clarifications/amplifications on #20:
1. The link in a double pole circuit breaker is internal to the circuit breaker. It is not the tie bar between the two toggles.
2. Branch circuits do not require double pole circuit breakers if the system is polarized, and there is a reverse polarity indicator or the system is fed from an isolation or polarization transformer.
 
psneeld said:
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.
Click to expand...

Yes, close is preferred as below from ABYC DC systems: The exceptions are given since the 7" spec is unfeasable in many installs. Especially when dealing with bolted in, Type T and other like fuses. And the fact that batteries are a maintenance item and best practice is to limit the connection complexity at the battery posts. And, I would add, to further the distance away from a hydrogen gas source.

E-9.10. DC POWER SOURCES
a. Overcurrent Protection Device Location - Ungrounded conductors other than cranking motor
conductors shall be provided with overcurrent protection within a distance of 7" of the point at
which the conductor is connected to the source of power measured along the conductor. (See
Figure 11.)
EXCEPTIONS: 1. If the conductor is connected directly to the battery tenninal the 7 inch distance
may be increased up to 72 inches.
2. If the conductor is between the source of power, other than the battery terminal,
and the required overcurrent protection device, and is contained
throughout its entire distance in a sheath or enclosure such as a conduit,
junction box, control box or enclosed panel, the 7 inch distance may be increased
up to 40 inches.
 
diver dave said:
Yes, close is preferred as below from ABYC DC systems: The exceptions are given since the 7" spec is unfeasable in many installs. Especially when dealing with bolted in, Type T and other like fuses. And the fact that batteries are a maintenance item and best practice is to limit the connection complexity at the battery posts. And, I would add, to further the distance away from a hydrogen gas source.

E-9.10. DC POWER SOURCES
a. Overcurrent Protection Device Location - Ungrounded conductors other than cranking motor
conductors shall be provided with overcurrent protection within a distance of 7" of the point at
which the conductor is connected to the source of power measured along the conductor. (See
Figure 11.)
EXCEPTIONS: 1. If the conductor is connected directly to the battery tenninal the 7 inch distance
may be increased up to 72 inches.
2. If the conductor is between the source of power, other than the battery terminal,
and the required overcurrent protection device, and is contained
throughout its entire distance in a sheath or enclosure such as a conduit,
junction box, control box or enclosed panel, the 7 inch distance may be increased
up to 40 inches.
Click to expand...

You left out an important piece..

"ABYC E-11
11.10.1.1.2 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent protection within a distance of seven inches (178 mm) of the point at which the conductor is connected to the source of power measured along the conductor (see FIGURE 14).

EXCEPTIONS:
1. Cranking motor conductors.

2. If the conductor is connected directly to the battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box or enclosed panel, the overcurrent protection shall be placed as close as practicable to the battery, but not to exceed 72 inches (1.83 m).

3. If the conductor is connected to a source of power other than a battery terminal and is contained throughout its entire distance in a sheath or enclosure such as a conduit, junction box, control box or enclosed panel, the overcurrent protection shall be placed as close as practicable to the point of connection to the source of power, but not to exceed 40 inches (1.02 m).

4. Overcurrent protection is not required in conductors from self-limiting alternators with integral regulators if the conductor is less than 40 inches (1.02 m), is connected to a source of power other than the battery, and is contained throughout its entire distance in a sheath or enclosure.

5. Overcurrent protection is not required at an alternator if the ampacity of the conductor is equal to or greater than the rated output of the alternator

6. Pigtails less than 7 inches (178 mm) in length are exempt from overcurrent protection requirements."
 
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