Re-wiring 17-footer

Electrical and electronic topics for small boats
mdizzl
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Joined: Sun Sep 13, 2020 8:07 am

Re-wiring 17-footer

Postby mdizzl » Thu Oct 08, 2020 4:24 pm

[Moved to SMALL BOAT ELECTRICAL for discussion]

I've recently moved the battery [on my 17-foot center console boat from the stern at the transom] to be located inside the console, and I am working on re-wiring the boat.

Is a fuse or circuit breaker needed between the battery and the battery switch?

Is a fuse or circuit breaker needed between the battery switch and the power distribution fuse panel?

I plan on mounting a Perko-brand battery switch under the console, even though I'm only using one battery for now, so that all loads can be disconnected from the battery when the boat is not in use.

I have a Blue Sea Systems fused power distribution panel. All electrical loads [except the engine] will be powered from this panel.

I have a six-switch load control panel. This panel three 15-Ampere fuse. Each fuse protects two circuits.

Thanks--Matt

rcapriola
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Re: Rewiring Montauk

Postby rcapriola » Thu Oct 08, 2020 9:34 pm

My 1985 MONTAUK 17 was re-wired for two batteries. A Blue Sea Systems battery switch that could separate the engine and house loads was used.

[The boat was wired to] keep house loads separated from the engine starting battery.

I moved both batteries into the console. The batteries cannot sit on the plywood shelf. The battery must sit on the deck and in a hole cut in the plywood. The power cables run to the engine should be extra heavy.

No duses or circuit breakers are needed between the battery and the switch/ All of the smaller wires going out from the battery switch to the house items should have their own fuses. I am not sure if the engine circuit should or should not need a fuse. I never fused this circuit in my systems. See the diagrams with the Blue Sea Systems switches.

[Removed link which was supposed to point to a diagram but did not.--Moderator]
1980 Revenge V-22 Sterndrive

jimh
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Re: Re-wiring 17-footer

Postby jimh » Fri Oct 09, 2020 12:36 am

For general advice on power distribution on a small boat, see the article on that topic at

Boat Electrical Circuits and Wiring Practices
http://continuouswave.com/whaler/reference/boatWiring.html

For advice on the necessary battery cable conductor size for longer than normal distance between the battery and the engine, see

General Advice on Moving Engine Battery to Console from Transom and Extending Battery Cables
http://continuouswave.com/forum/viewtopic.php?f=9&t=5111

The conductor between the battery and the battery switch is usually not fused because the distance is usually very short, and the conductor is usually heavy and in a protected area.

The engine load is typically not fused.

The conductor from the primary power distribution point to a secondary power distribution panel is normally protected by a circuit breaker.

Primary and secondary power distribution using two batteries and an isolated battery switch is shown and discussed in an article at

Primary Power Distribution
http://continuouswave.com/forum/viewtopic.php?f=9&t=4329

Dual-circuit battery switches are discussed in an article at

Dual-circuit Battery Switches
http://continuouswave.com/forum/viewtopic.php?f=9&t=2627

USE OF TWO BATTERIES ON 17-FOOT BOAT
Use of isolated HOUSE and ENGINE loads and use of two batteries on a 17-foot boat is unusual. Generally on a 17-foot boat the HOUSE loads will be minimal and one battery can easily provide power for both engine starting and running minimal other loads. The most critical electrical load is the propulsion engine starter motor. If the engine cannot be easily starting with pull-starting, having two batteries available for engine cranking is a prudent precaution against a single battery going dead. However, adding a second battery just as a back-up for engine starting may not be necessary. A smaller Lithium-Ion jump-start battery pack can be carried aboard as a method to assist in engine cranking in the event of a deeply discharged engine starting battery.

If use of dual batteries is anticipated for the future, then it would be prudent to use a dual-circuit battery switch for the re-wiring, even though there is only one battery. The single battery could be initially wired to both poles of the dual-circuit battery switch, and later, when a second battery is added, the second battery would be be easily wired in to replace the temporary connection of the first battery to the second pole of the dual circuit switch.

For a good discussion on adding a second battery to isolate house loads, see

Adding a House Battery
http://continuouswave.com/forum/viewtopic.php?f=9&t=2027

For discussion of the proper gauge wire to use when engine battery cables are lengthened, see

Selecting Proper Wire Size: Engine Starting
http://continuouswave.com/forum/viewtopic.php?f=9&t=4992

For advice on updating 12-Volt DC power distribution wiring, see my article at

DC Power Distribution Updating
http://continuouswave.com/forum/viewtopic.php?f=9&t=3233

For advice on secondary power distribution refurbishment, see

Secondary Power Distribution Refurbished on c.1990 Whaler
http://continuouswave.com/ubb/Forum6/HTML/003179.html

mdizzl
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Joined: Sun Sep 13, 2020 8:07 am

Re: Re-wiring 17-footer

Postby mdizzl » Fri Oct 09, 2020 12:38 pm

Jim,
Thanks for the thorough response. I've read your articles and they've been very helpful as well. Forgive my lay understanding of circuitry jargon, but to be clear I think your answer is here:

"The conductor from the primary power distribution point to a secondary power distribution panel is normally protected by a circuit breaker."

Translating this for my set-up, there should be a circuit breaker between the Perko and the Blue Sea fuse box...right?

In the article viewtopic.php?f=9&t=4329 there is a "Aft Sec. positive fused bus" that is not served by the 50amp breaker. How is it different than the "house load fused panel" in terms of needing the protection?

Also, what scenario allows for tripping of that breaker? In other words, what load are we protecting the system from?

And finally, would you mind giving your opinion as to why mine and many others' aren't wired with one? Were they negligent or has standard changed?

For anyone else reading this, after a long time reading Jim's electrical information I ended up using 17 feet of 2 AWG cable between my Honda BF90 and the battery in the console.

Thanks again Jim for your dedication to helping us all! Matt

jimh
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Re: Re-wiring 17-footer

Postby jimh » Sun Oct 25, 2020 10:54 am

MATT--I apologize for the late reply. I just now came across your October 9, 2020 post with some questions.

...should [there] be a circuit breaker between the [battery switch] and the Blue Sea fuse box[?]


Let me answer this in a general way. Power distribution wiring is the method of distributing electrical power. In electrical power distribution there are three fundamental elements:
  • the source of electrical power
  • the loads that will consume the electrical power
  • over-current protection devices, usually a fuse or a resettable circuit breaker, that will protect the wiring that connects the sources to the loads

In a small boat, the source of power can be considered to be the positive terminal of the boat battery. There are, of course, the negative terminal and all the negative circuits, but we can ignore them because of two reasons:
  • there are never any fuses or circuit breakers in the negative circuit
  • all loads share a common negative circuit

The wiring path from the battery positive looks like this:

BATTERY (+) ----unprotected short CONDUCTOR-A----main battery ON-OFF switch COMMON

A short unprotected conductor is allowed because the battery switch is usually within a foot or so of the battery terminal, the wire size is very large, and the conductor is often enclosed in a protective sheath. All of these factors tend to minimize the possibility that there could be a short circuit from this conductor to the battery negative. If the battery switch is more than about a foot or perhaps more than 18-inches away, there may be regulations or suggested practices that would prefer to see a fuse at the battery to protect this conductor. But in a small boat the battery switch is typically right next to the battery, so CONDUCTOR-A is not protected by any overcurrent device.

The next step in the wiring path will be

Battery Switch POLE--->unprotected CONDUCTOR-B ---> PRIMARY POSITIVE BUS

Again we have a wiring segment CONDUCTOR B that is not protected for over-current, and this is allowed for the same reasons as above for CONDUCTOR A. In some instances in a small boat there really is no separate BUS bar, and the terminal post on the battery switch itself performs the function of the PRIMARY POSITIVE BUS.

The next wiring path will be

PRIMARY POSITIVE BUS --->unprotected CONDUCTOR-C --->over-current device--->protected CONDUCTOR-D----> LOAD

The PRIMARY POSITIVE BUS typically will have a circuit breaker or fuse, located very close by, and unprotected CONDUCTOR-C connects them. The circuit breaker or fuse will protect the LOAD that is connected via protected CONDUCTOR-D.

Before going further, there is one important exemption from this practice: the propulsion engine electric starter motor. This load and the conductor connecting it to the PRIMARY POSITIVE BUS are not protected in most installations. The current anticipated to flow in this path is on the order of 300-Amperes or more at peak, so a fuse or circuit breaker is somewhat impractical. Also, the length of the conductor is anticipated to be short, a few feet at most, the conductor size is anticipated to be very large, and there is an expectation of some protection against damage to the conductor, such as very generous insulation covering the conductor and perhaps enclosure in a sheath. Finally, there is an expectation that there is a battery switch available to completely cut off current to this path if necessary in the event of a short circuit

All other LOADS should have over-current protection. A typical load on the PRIMARY POWER BUS will be a SECONDARY POWER DISTRIBUTION PANEL. (Now I am getting to your actual question.) This wiring path will be as mentioned above:

PRIMARY POSITIVE BUS --->unprotected CONDUCTOR-C --->over-current device--->protected CONDUCTOR-D----> SECONDARY POWER DISTRIBUTION PANEL

The length of protected CONDUCTOR-D may be quite long, perhaps more than 15-feet. The purpose of the over-current device is two-fold. First, the over-current device must protect against a short circuit of CONDUCTOR-D that might occur, so the value of the over-current device trip rating must be smaller than the rating of the conductor for maximum allowed current flow. For example, if an 8-AWG wire is used for CONDUCTOR-D, the wire itself is rated for a maximum current flow of 73-Amperes. (See the 'chassis wiring rating" in table at https://www.powerstream.com/Wire_Size.htm.) The over-current protection device should be rated for a lower trip curent. The second purpose is protect the power distribution panel itself. The panel should have a rating for maximum current. A typical panel is a Blue Sea Systems fused panel model 5026, which is rated for a very generous 100-Amperes. So the over-current device should be less than 100-Amperes. The over-current device in this example would then be chosen to be some value less than 73-Amperes, but large enough that the normal current demand of the secondary power panel loads won't cause a nuisance-trip, that is, won't trip in normal operation. This can be estimated by adding up the total loads connected to the panel by adding up the fused circuit values, but with an eye to which ones will be in use simultaneously. A typical figure for total fused loads expected at any one time might be 50-Amperes. So the overcurrent device is chosen to be 50-Amperes. Because fuses and circuit breakers are only available in particularly values, you often have to choose a bit higher or even a bit lower than the value you might calculate.

So there is the answer to your original question: yes, you should have an overcurrent device between battery and the Blue Sea System power distribution panel.

But let me hedge a bit on that recommendation. If on a small boat there is no PRIMARY POSITIVE BUS, and the battery switch terminal performs that function, and if the SECONDARY POWER DISTRIBUTION PANEL is only a foot or so away from the battery switch, and if the conductor connecting them is large and has generous insulation and is protected against damage, you might be able to consider that the power distribution panel is really the primary positive bus and omit that circuit breaker. In the case of recreational boats, it is your boat, you are not a boat builder trying to comply with ABYC recommendations, there really are no USCG recommendations that apply directly to this situation (that I know of), and you can more or less do what you want. I would use a circuit breaker.

jimh
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Re: Re-wiring 17-footer

Postby jimh » Sun Oct 25, 2020 1:17 pm

mdizzl wrote:In the article viewtopic.php?f=9&t=4329 there is a "Aft Sec. positive fused bus" that is not served by the 50amp breaker. How is it different than the "house load fused panel" in terms of needing the protection?


Here is the illustration being referenced:
Image

The AFT SEC. POSITIVE FUSED BUS should be considered (in this instance) as the PRIMARY POSITIVE BUS. All the loads connected to it are protected by fuses or circuit breakers but the conductor from the battery switch (at L1) to the bus is not protected. Again this conductor is short, is a large wire not likely to be damaged, and this conductor only serves to get the power to the fuses and circuit breakers. It is inevitable that there MUST be some segment of wiring that connects a fuse or circuit breaker to a source of power that won't be protected; it will always take some length of wire to connect the fuse or circuit breaker. Note that the engine starting motor is connected at L2 on the battery switch; there is no over-current protection there, either.

The wiring from the AFT SEC. POSITIVE FUSED BUS to the HOUSE LOAD FUSE panel is a much longer wire, and this conductor is protected by the 50-Ampere circuit breaker shown. This is explained above in my first reply.

The fuse shown in the diagram at the AUX. CHG. OUTPUT is a little different than the others. The charging circuit is trying to push current into the battery, not draw current from the battery. So the fuse in that circuit is really to protect the charging circuit from damage if there were a big short circuit in the battery wiring. That fuse is a 50-Ampere fuse.

ASIDE: For my boat I installed an aft positive bus with several terminal posts because there are several loads right at the stern of the boat that need power, and instead of running power back from the forward secondary power panel to the stern for those devices, I just run them from this panel with fuses protecting them. An example of this is the sump pump I installed in the aft cockpit live well. The switch that controls this is in the stern, and the power for that circuit comes from this aft distribution bus. (My memory is a bit fuzzy on what else is connected there; I think there is a black-box SONAR unit that gets its power from that bus; that device has a separate power control wire that runs forward to the display unit to actually control the power.) The reason for the aft negative secondary bus is the same: to provide a negative circuit return for loads in the stern of the boat. The pump and SONAR I mentioned connect there, as does the lamp circuits for the white all-round navigation lamp; and there are a couple more I cannot think of right now.

jimh
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Re: Re-wiring 17-footer

Postby jimh » Sun Oct 25, 2020 1:39 pm

mdizzl wrote:...would you [give] your opinion as to why [my boat] and many other [boats] aren't wired with one? Were [the boat builders] negligent or has standard changed?

By "one" I think you are asking about having aft positive and negative power buses. As I mentioned, in many small boats the battery terminals themselves are used as the positive and negative primary power distribution bus by having more than one conductor connected to them. This brings up another consideration: how many terminal connectors should there be on one terminal post.

The ideal situation is to have only ONE terminal connector to each terminal post, or more practically, no more than TWO terminal connectors, which allows the terminal post to act as a junction point between the conductors. In some rather poor small boat wiring the number of terminal connectors attached to one terminal post will grow to four or five or more. This is a poor practice.

The greater the number of terminal connectors on one terminal post, the more prone an electrical failure will be. This is particularly true in situations where there is vibration. Five or six wires transmitting vibrations to a terminal post will result in a much higher chance of something working loose. Looking at the electrical path, some current will probably be flowing through a stack of terminal connectors instead of flowing from the post to each terminal conductor. The reason there are bus bars with multiple terminal posts is precisely to avoid having to stack up multiple terminal connectors on one post.

To end up with a lot of connections to a battery post on a boat is easy. The first set are for the propulsion engine. Then a second set for a 120-VAC battery charger; then connections for pump, lamps, a SONAR, a radio, and so on. Soon you have six or more terminals connected to each battery post.

The need for aft positive and negative buses can be overcome if all the circuits are wired to the forward distribution center. For me, it was simpler to install positive and negative aft buses than to run five or six positive wires and another five or six negative wires from the stern to the forward power distribution center. Not running all those wires saved a lot of expensive wire and also cut down on voltage drop because wire lengths were reduced.