Fuses Needed to Comply with ABYC Rules

[macbeth]

My battery combiner outputs are connected to the #1 and #2 battery posts on my Off-1-Both-2 battery switch. The two cables used from the combiner to the two posts are 4 gauge.

Also connected to the #1 & #2 battery posts on the switch are 2/0 cables which run back to the respective batteries.

The common post on the switch holds two cables: one going to the starter, the other going to the alternator. Both cables are 2/0. The distance from the batteries to the engine is 16'.

Where do I need fuses to comply with the ABYC 7" rule ?

My guess is 300amp (one each battery) near the actual +ve battery posts, and 100 amp on the ends of the combiner wires BEFORE they are connected to the switch posts. Wrong/Right ?

[macbeth]

No ABYC experts out there ???!!!!

[nigelmercier]

Originally Posted by macbeth

No ABYC experts out there ???!!!!

Perhaps if you told us what the ABYC 7" rule was, someone could help.

[smurphny]

The way I interpreted the fusing requirements was that anything coming off a battery needed to be fused within X inches (I forget the exact distance). When rewiring my battery banks, all line side wiring, including starter circuits, were fused very close, with 300a. ANL fuses on both house and starter with a small subpanel to distribute all house circuits. This way, a dead short anywhere will blow a fuse. I really like the idea of this close fusing. The old method of just draping 1/0 cable long distances with no fusing was very dangerous indeed. By the way, even in conditions of maximum strain on the starter, I have had no problems with blowing the large ANL fuses. That said, I keep a set of jumper cables within reach right by the batteries should a fuse blow and I need to have the starter fast.

[cuthbert]

I'm going to post this from memory without referring to any reference material, E.11.10 says power sources have to fused with 7", hence just fuse at the batteries. You can move the fuse up to 72" if the cables are contained in a conduit or similar. Practically (and off the top of my head again without referring to any reference material or getting an exact schematic of what the circuit is) you have a 1v volt drop on 16ft of cable assuming your starter is around 1kw. 300 amp fuse is approx correct.

[Lars_L]

For thing that use much current and you need to get all the power the equipment can give, it is stated that the voltage drop could be max 3%. There exist a lot of tables that shows the size but if you are used to SI measurement, you can count it in your head.

Take the distance from the battery to the user (one way) in meter. Multiply bye the current that goes true the cable in ampere. Dividing the result by 10 and you have the cable area in mm². This will give a cable with 3% voltage drop. Remember that the plus and minus cable need to have the same area (ore greater).

[GordMay]

Check out the ABYC Cct Protection diagrams:

➥ DC Circuit Protection - ABYC Section E-9 Figure 11 Battery Supply Circuit Protection. See also Figure 12 These are essentially the same as the new Figure 15, in revised Section E-11. Cruisers & Sailing Photo Gallery

➥ DC Circuit Protection (2) - ABYC E-9, Figure 12 (see also Fig. 11) Cruisers & Sailing Photo Gallery

➥ ABYC Section E-11 ~ Table 15 - Location of Overcurrent Devices in DC Circuits, per New Electrical Section E-11 (effective 2004) Cruisers & Sailing Photo Gallery

[smurphny]

Originally Posted by GordMay

Check out the ABYC Cct Protection diagrams:

If I'm reading these schematics right, the starter wire can be any length with no fusing under ABYC guidelines. The way I read the USCG specs. before redoing the wiring on Philyria, was that ALL load side circuits from battery, not just house circuits, need to be fused within 7". It does not make much sense to me to leave a large, unlimited length cable vulnerable to a dead short with absolutely no fusing. That's a recipe for meltdown/fire. Once a large 1 or 2/0 wire burns off the insulation, it will likely touch off an explosion of battery gasses as it melts through the battery plastic at well above the flash point of battery gasses. I have had this happen in vehicles and would not want to deal with the mess it would make in the enclosed space of a boat.

[GordMay]

ABYC E-11.10.1.1.1 Overcurrent Protection Device Location - Ungrounded conductors shall be provided with overcurrent protection within a distance of seven inches (175mm) of the point at which the conductor is connected to the source of power measured along the conductor. (See FIGURE 15.)

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 (1.83m) ...

[smurphny]

The installation of ANL fuses or fuse blocks within a few inches of batteries is not a difficult/overly expensive endeavor and imo, is common sense regardless of requirements.

[CharlieJ]

ANL fuses and their fuse holders provide the required protection but...there are two connections to the fuse holders. Two crimps. Two ring terminals.

IMHO the better solution is the use of the Marine Rated Battery Fuses (MRBF) by Cooper-Bussman and repackaged by Blue Sea Systems. These small footprint fuse holders are bolted directly to a battery terminal or to a bus bar. A single crimp is made on the load side conductor and bolted to the fuse holder, sandwiching the fuse between the ring terminal and the fuse holder. Capacity to 300 A and an AIC rating of 10,000 A!

Fuses: Terminal Fuses (MRBF - Marine Rated Battery Fuse) - Blue Sea Systems
Fuse holder, single: Terminal Fuse Block, 1 Terminal Stud - PN 5191 - Blue Sea Systems
Fuse holder, double: Terminal Fuse Block, 2 Terminal Studs - PN 2151 - Blue Sea Systems

Charlie

[waterdancer]

One word of caution about fusing. I had a secondary 500gph bilge pump that was fused with a 10 amp fuse. I had a fire on the boat at 2:30 in the morning because the pump jammed, and drew 8 amps istead of the regular 2-4. The winding heated up so much that the plastic caught on fire. When I opened up the floorboards there was a 3 inch high crown of fire around the pump, licking the floorboards. It was a lucky thing that we had cancelled our plans to go and stay at some friends. Rule actually sent me a free pump and offered to pay for all the repairs. So make sure that the fuses are not too big.

Here is the Related blog page

[smurphny]

I did look at those in catalogs Charlie but wasn't near anywhere to actually pick one up to look at. You're absolutely right about there being one less connection to fail. The ANL fuse blocks worked out really well and are a great improvement over the 8' of unfused wire that was originally in the boat. I have them mounted within about 4" of terminals, very accessible. They would be quick to change in a pinch.

[Lars_L]

The size of the fuse to the start motor can be too big. According to the performance diagram, my start motor have a stall current of 370 A. If I then have a fuse on 400 A, it will never blow, not even if the motor is blocked. It could be that when the motor starts to burn, the internal resistance will go lower and therefore the fuse will blow. But that’s a little late. A small consolation compared white if I hade no fuse at all is that then even the cables to the motor had start to burn.

[smurphny]

Originally Posted by Lars_L

The size of the fuse to the start motor can be too big. According to the performance diagram, my start motor have a stall current of 370 A. If I then have a fuse on 400 A, it will never blow, not even if the motor is blocked. It could be that when the motor starts to burn, the internal resistance will go lower and therefore the fuse will blow. But that’s a little late. A small consolation compared white if I hade no fuse at all is that then even the cables to the motor had start to burn.

That's a good point. There could be a build up of heat if the battery wire is not large enough to take the maximum amperage of the starter. I've seen many boats with very small battery wires. That's the reason to make sure to use 1/0 or 2/0 cable. I think the basic safety idea though is to eliminate a quick meltdown after a dead short somewhere. My concern is that the rather long battery cable somehow gets sliced open or pinched somehow and causes the insulation to burn off almost instantaneously, causing a fire. Fire in a car is one thing, in a boat it is right up there among worst things that can happen. In a dead short case, almost any fuse you could find would open up the circuit in microseconds.