Split Bus Fuse Block

Electrical and electronic topics for small boats
skistler
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Split Bus Fuse Block

Postby skistler » Mon Apr 04, 2016 11:28 am

I'm rewiring my 1981 Montauk. I plan to add a DC subpanel under the console to power all of the house electrical system, connected directly to the battery (which is located in the stern). I would like to have a switched partition of the block that powers all of the electronics (stereo, VHF, and GPS/sounder combo) so that I can turn them all on and off with a single switch. I'm using Cole Hersee push/pull switched just because I'd like to retain the original look.

Given the limited space in the console, I was thinking of using a Blue Sea split bus fuse block (https://www.bluesea.com/products/5032/ST_Blade_Split_Bus_Fuse_Block), with one bank wired directly to the battery for lights/bilge pump/horn/etc. and the other bank for the electronics controlled via a switched relay. The total draw of the electronics I have (Fusion RA-50 stereo, ICOM M-304 VHF, and a circa 1982 Datamarine depth finder that will be replaced with a combo GPS/sounder when funds allow) looks to be less than 30 amps peak.

So here's my question - could I power fuse bank "B" (electronics) from a 30 amp fused circuit from bank "A," or should I power each bank from a separate bus bar that draws from the battery?

So the first option for getting power to the electronics bank would look like

Battery ----> fuse bank A ----> 30 amp fuse on bank A ----> relay ----> bank B ----> individual bank B circuits for each device

And the second option would be

Battery ----> 3-terminal bus with lines feeding bank A and to relay ----> relay to bank B ----> individual bank B circuits for each device

Appreciate any help/advice anyone can provide (other than "why on earth do you want to separately a switched electronics circuit?").

In case it matters, the boat has a single battery for house and starting/engine systems and is powered by the original 1982 Evinrude 90, which only has about 300 hours on it (as does the entire boat, for that matter). Wiring has aged, though, and needs to be replaced. A bad negative battery cable already helped me to fry the starter and solenoid, so I"m replacing all of the cable that I can at this point. I also have to replace the steering cable as the jacket has cracked, and am installing a new NFB helm. I've just about gutted the console and am ready to start reassembly.

FWIW, I posted the same question over on The Hull Truth, and all I got was a recommendation to add a battery switch and a fuse at the battery (I was planning on a terminal fuse block at the battery for the house system, anyway).

Sorry for the long post, and many thanks in advance for any advice proffered,

-Steve in VA

jimh
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Re: Split Bus Fuse Block

Postby jimh » Mon Apr 04, 2016 12:20 pm

My approach to your electrical power distribution would be like this:

The single battery on the boat will feed the secondary split power distribution panel via 8-AWG conductors, probably via a main power switch and perhaps a bus bar. A circuit breaker (or fuse) about 50-Ampere rating will be located as close to the battery as possible in the positive circuit to protect this feed to the secondary panel from the primary bus or source. If the boat has an open transom and the battery is at the transom, protect the circuit breaker or fuse from weather and splash.

At the secondary split power distribution panel, the black or yellow insulation color 8-AWG conductor for the negative circuit connects to the (-) bus main connection post. The red insulation color 8-AWG conductor connects to the A+ terminal post.

Assuming the relay which will be used to control power to the B bus of the split secondary power distribution panel is located close-by, a red insulation color 10-AWG conductor connects the A+ terminal post to the relay's COM contact. Another red-with-violet-stripe insulation color 10-AWG conductor connects the relay's N.O. contact to the B+ terminal post of the split secondary power distribution panel. (Don't worry if you can't find red-with-violet stripe wire; just use red.)

Here is that configuration as ASCII drawing (CB means circuit breaker):

Positive Circuit Power Distribution

BATTERY (+) source --> Fuse or CB ≅ 50-Ampere --> 8-AWG conductor --> Split panel A+ terminal
(red insulation)

Split panel A+ terminal --> 10-AWG conductor --> Relay COM
(red insulation)

Relay N.O. --> 10-AWG conductor --> Split panel B+
(red with violet stripe insulation)


It seems unlikely the total current load of the B segment of the split panel would reach 30-Amperes, unless you really like to listen to a very loud loudspeaker reproduction of music with that FUSION radio.

jimh
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Re: Split Bus Fuse Block

Postby jimh » Mon Apr 04, 2016 12:29 pm

The alternate approach suggested in the initial article of running separate feeds from the main 12-Volt source to both the A+ terminal and the Relay COM terminal is also a good method.

For a fuse near the battery or the main power switch, perhaps the Blue Sea Systems Maxi In-line Fuse Holder will work. It has a 6-AWG wire and is rated to 48-Amperes. Wire one side to the battery or switch terminal. Make an in-line butt splice to your 8-AWG feed to the secondary panel on the other side. See

https://www.bluesea.com/products/5068/M ... use_Holder

Or use a Maxi Fuse Block (rated to 80-Amperes) but add some weather and splash protection:

https://www.bluesea.com/products/5006/M ... _30_to_80A

Or use a waterproof fuse holder (but limited to 30-Amperes)

https://www.bluesea.com/products/5065/W ... use_holder

Or try to incorporate the fuses under the protection of the battery box cover (but not vented cover).

skistler
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Re: Split Bus Fuse Block

Postby skistler » Mon Apr 04, 2016 12:54 pm

Many thanks - sounds like I am more-or-less on the right track. I'll likely stick with the first option as it means one less wire from the transom to the console.

For the fuse at the batter, I was thinking of a termal fuse block like this one:

https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

But I'm not sure that it will fit within the battery box, so your inline suggestion may be better.

Also, thank you for all of the articles on boat wiring and such that you have posted to Continuouswave (including the one on VHF antenna selection). They have been an invaluable primer.

-Steve in VA

jimh
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Re: Split Bus Fuse Block

Postby jimh » Mon Apr 04, 2016 1:09 pm

Steve--thank you for the very kind words about my writing. They are most appreciated.

That marine-rated battery fuse or MRBF Terminal Fuse Block may be the best solution. However, the darn fuses are awfully expensive at about $17 each.

jimh
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Re: Split Bus Fuse Block

Postby jimh » Mon Apr 04, 2016 2:40 pm

Also--just thought of this: if the relay COM is fed from the A+ terminal post, you could use an in-line fuse there to give the B-bus its own fusing. You could just use a standard ATO or ATC fuse and holder with 12-AWG pigtails like this one:

https://www.bluesea.com/products/5064/I ... use_Holder

The 12-AWG will be sufficient for the very short distance the conductor will be run, as it looks like the fanned out wires are only a few inches. Of course, the relay will have to be very close to the secondary panel to use this without splices.

Also--what sort of relay are you going to use for the control of power to the B bus? I am curious to know what you have in mind.

skistler
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Re: Split Bus Fuse Block

Postby skistler » Mon Apr 04, 2016 3:45 pm

Well, that's why I was thinking of feeding the B+ terminal from one of the circuits on the A+ terminal - so that the whole B+ circuit would be fused just upstream of the relay (meaning the relay would then be fused with a lower amperage fuse than the terminal block, and closer).

In terms of a relay, I was just going to go with a simple Bosch SPST automotive relay:

http://www.amazon.com/HELLA-965400001-SPST-Relay-Bracket/dp/B004NIKVWC?ie=UTF8&psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00

It's perhaps not quite as waterproof as one might like, but then it's going to live in the console up near the top (I was planning to mount both it and the fuse block on the backing board for the shepherd's crook).

-Steve

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Re: Split Bus Fuse Block

Postby jimh » Mon Apr 04, 2016 4:25 pm

Try this relay for about $3.70

http://www.digikey.com/product-detail/e ... ND/1236843

It has a suppressor diode across the coil. I think you can use push-on terminal connectors to connect to the relay contacts, or perhaps use soldered connections for the power contacts. They made a $6 socket which actually costs more than the relay, and their push-on wire terminal connectors are expensive, too, about $0.66 each.

Maybe this is the best deal: five relays with pigtails for $12:

http://www.amazon.com/dp/B017VDI0GY?psc=1

jimh
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Re: Split Bus Fuse Block

Postby jimh » Mon Apr 04, 2016 4:42 pm

Re providing the power to the relay contacts by using one of the fused circuits on the A-bus:

If you use one of the circuit of the A-bus to fuse the power to the relay you will have one less circuit available on the A-bus for other loads that are not switched by the relay. Don't forget you will have to power the relay coil from an un-switched source, which I assume will be from the A-bus. That means you have used two circuits of the A-bus just to power and operate the relay that energizes the B-bus.

What circuit do you plan to use to operate the relay coil? Perhaps the engine ignition ACCY circuit?

skistler
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Re: Split Bus Fuse Block

Postby skistler » Mon Apr 04, 2016 5:20 pm

Thanks for the Digikey link - that could save me some money. I was indeed just planing to use push-on connectors, but soldering on some pigtails is an option, too. All of the socket options I looked at seemed more trouble than they were worth (although I must admit I do like the way they limit the exposure of the connections).

In terms of setting up the fuse block, here's what I was thinking of:

A+
1. Lights (running/anchor/instruments)
2. Horn
3. Bilge pump
4. Accessory outlet (cigar-lighter style)
5. Power to relay coil (and in turn to B+)
6. Switch to operate relay

B+
1. VHF
2. Radio
3. Depth

I am going to use a simple Cole Hersee push/pull to switch the load. My ignition switch just has stop/run/start (plus push to choke).

Looking at my list again, I think I might move the accessory plug to B+, leaving me with a free circuit on A+ and two on the switched bank. It's a small boat, so I don't anticipate adding anything much electrical in the future, anyway.

-Steve

jimh
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Re: Split Bus Fuse Block

Postby jimh » Tue Apr 05, 2016 1:24 pm

Aside: I never noticed that split bus distribution panel before. It is a handy wiring accessory. It is marked as a NEW item on the website. The people at BLUE SEA SYSTEMS seem to be very well tuned-in to the marine electrical market's needs. They make all the right stuff.

Beerspitnight
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Re: Split Bus Fuse Block

Postby Beerspitnight » Tue Apr 05, 2016 10:47 pm

Good Evening. This thread is very helpful as I am planning to re-wire my 1989 Montauk 17 this summer, which I have indicated in a preview thread. I have spent the last two weeks searching the site for threads that discuss approaches to wiring the boat, and reading the many articles that Jimh has written. Jimh’s articles on boat wiring are indeed very helpful, as are many of the posts found on this site. I have also spent a good amount of time asking a co-worker (he is a Science teacher) for help as I wade through the vernacular of electrical systems, and the properties that guide those systems.

I would like to piggyback on Steve’s original post, as I have a few clarifying questions to ask that will help me as I plan to rewire my boat. I will keep these questions as general as possible as I will ask more specific questions on my own thread.

Steve, your approach to rewiring your boat appears to be straightforward and concise, which is what I am looking for as I plan out my rewire. I have also decided to move my battery to the stern, so your system is even more relevant for my goals.

Jimh: You mention the "Positive Circuit Power Distribution". Does this imply that there is a negative circuit power distribution that needs to be considered? Or would using BLUE SEA SYSTEM Split fuse block 5032 complete the negative flow of the current?

Also, what is the purpose of using a relay in this scenario? I did some research on relays, and I understand their purpose, but I am unsure why one is necessary in Steve’s setup.
Positive Circuit Power Distribution

BATTERY (+) source --> Fuse or CB ≅ 50-Ampere --> 8-AWG conductor --> Split panel A+ terminal
(red insulation)

Split panel A+ terminal --> 10-AWG conductor --> Relay COM
(red insulation)

Relay N.O. --> 10-AWG conductor --> Split panel B+
(red with violet stripe insulation)


Will utilizing the aforementioned BLUE SEA SYSTEM split fuse block 5032 eliminate the need for a bus bar in the console?

And, speaking of bus bars, or power distribution busbar, there is one located aft in my boat where the all-around white light connects for power. Perhaps I am mistaken, but I also believe that the bow navigation lights connect there as well. Is this considered a negative bus bar, a positive bus bar, or just a bus bar?

Thank you in advance for your responses.

Also, please note that the BLUE SEA SYSTEM split fuse block 5032 can be purchased from http://www.ceshowroom.com/for $47.24. Economy shipping will cost between $6 to $9.
1989 MONTAUK 17

jimh
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Re: Split Bus Fuse Block

Postby jimh » Wed Apr 06, 2016 8:38 am

In my ASCII drawing, the label "positive circuit power distribution" is used because my drawing shows ONLY the positive circuit.

In distribution of direct-current power there are always two circuits involved, the positive circuit and the negative circuit. Usually all control elements such as fuses, circuit breakers, switches, relays, and so on, are put in the positive circuit, and the negative circuit has none of those devices. Thus the negative circuit becomes just a common circuit among all primary, secondary, and branch circuits.

A good general description of power distribution on small boats is given in

Boat Electrical Circuits and Wiring Practices
This article presents recommendations for small boat 12-Volt direct-current (VDC) electrical circuits and how they should be wired and installed. Electrical 12-VDC circuits on a small boat can be considered in three segments: primary power distribution, secondary power distribution, and branch circuits.
http://continuouswave.com/whaler/refere ... iring.html

One often finds on smaller Boston Whaler boats that a TERMINAL STRIP near the stern is used a wiring point for the navigation lighting circuit. The terminal strip has both the positive and negative circuits connected to it. A terminal strip consists of individual two-pole wiring points, and is not a bus bar. Terminal strips just serve as convenient wiring points in which various conductors of a circuit elements can be connected together. Terminal strips with multiple wiring points can have multiple circuits wired at that terminal strip. There is no mandate that all connections are part of one common circuit.

A BUS BAR is typically a wiring accessory with two or more terminal posts connected in common by a large flat conductor or bar, so that all connections to the bus bar are in common. The bus bar is used as a common connection point in power distribution wiring and can be in the positive or negative circuit.

A RELAY is an electro-mechanical device that permits a low-voltage, low-current circuit to operate the coil of the relay while the contacts of the relay control the flow of current in another circuit. Usually the other circuit has a different voltage or current than the relay coil circuit. The general reason to use a relay is to avoid bringing the conductors of the main circuit to the location where the relay coil control circuit will be switched. Usually the current in the controlled circuit is much higher than in the relay coil circuit. For example, a relay might control a circuit with 40-Amperes while the coil of the relay only uses 0.05-Amperes.

It is unusual in wiring the power distribution in a small boat to employ any relays. This thread is discussing such an arrangement, but one should not make the inference from this discussion that use of a relay is common in small boat power distribution control. It is actually somewhat unusual, in my opinion.

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Re: Split Bus Fuse Block

Postby jimh » Wed Apr 06, 2016 8:44 am

Will utilizing [a] BLUE SEA SYSTEM split fuse block 5032 eliminate the need for a bus bar in the console?


The panel is a secondary power distribution panel with provision for 12 fused circuits. It is not the equivalent of a bus bar. The panel provides 12 fused circuits for the positive power and one unfused and in-common circuit for the negative circuit, but with 12 wiring points. The panel is designed to distribute fused power to branch circuits from power supplied to it from the main power circuit.

jimh
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Re: Split Bus Fuse Block

Postby jimh » Wed Apr 06, 2016 8:56 am

The secondary power distribution panel being discussed in this thread is unusual. It has two separate six-circuit fused power distribution panels combined into one assembly. As the manufacturer notes, the panel is intended for applications in which one segment of the panel will have six fused circuits to which the power can be supplied on a different basis than for the other segment of six circuits. A common use for such a panel is to have one segment be always supplied with power while the other segment may have power applied only when needed.

The segment with power always supplied is often called the "keep-alive" or "24-hour" segment. It occurs in some more complicated wiring arrangements that there is just such a need, that is, there are devices to which power should always be available without interruption, and those loads are connected to the "keep-alive" portion of the panel. Other devices whose power may be switched off from time to time are connected to the separate six-circuit segment of the panel.

Very similar versions of 12-circuit and 6-circuit power distribution panels exist without this feature of having a split, and use of those panels is much more common. Indeed, this split circuit panel was just invented and made available, so it probably has never ever been used before in a small boat in the history of boating. On that basis, readers should NOT assume that use of a split power distribution panel is common, recommended, necessary, desirable, mandatory, or unavoidable.

skistler
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Re: Split Bus Fuse Block

Postby skistler » Wed Apr 06, 2016 10:53 am

Jim is correct, there's really no need to wire things up the way I am proposing. I tend to overcomplicate things because, well, that's just the kind of person I am. As I mentioned in the first post in this thread, my setup is driven by my (arguably irrational) desire to have a subset of my electrical equipment/devices operated by a single switch (and an old-fashioned one, at that). This leads to the need for a separate positive fuse block/bus for those items, as well as the relay.

The simplest option (assuming one has roughly the same electrical/electronic "stuff" to operate) would be to use a single 12-slot fuse block and just switch the equipment on and off with the power switches on the devices (except for the lights and bilge pump, of course, which will need dash switches of some sort but not a separate fuse block). You could even scrap the fuse block altogether and rely on inline fuses, which is how yours may have been set up form the factory. Mine was a combination on inline fuses and glass tube fuses located adjacent to the relevant dash panel switches.

The relay is required in my set up because the load I am switching requires more power than the switch I am using is rated to carry. This is why I cannot just carry the positive straight through the switch to the bus that it's going to power. The relay is rated to carry way more load than my devices require, while the power required to operate (switch) the coil on the relay is well within what my switch can carry.

Also, I'm probably a bit of a fool for using the old-style, failure-prone Cole-Hersee switches rather than a nice new switch panel from BlueSea Systems. My boat is really original (about 300 hours total, no bottom paint, etc., etc.), so I'm aiming to improve the systems' performance and safety while keeping as much of the original look as possible. One elegant solution in a small boat like a Montauk is to use a panel like this one: https://www.bluesea.com/products/8053/6_Position-Slate_Gray

that includes both switches and fuses. This particular one uses glass fuses; some prefer the blade type for their easy availability etc., but I'm actually kind of agnostic on that front. There's a lot of good stuff available from BlueSea alone - in other words, you've got options. The best place to start is to evaluate what you need/want to operate and how, and then build out from there.

On fuse blocks and busses in general, note that there are BlueSea blocks available both with and without negative busses built in. The advantage to a combined fuse block/negative bus is that it takes up less space under the console, the disadvantage is that it ends up with a lot of wires coming in to a single, combined space and so can be fiddely to install/work on. A bus bar is positive or negative depending on which side of the circuit it is on. The positive side of a fuse block is actually a sort of bus itself wherein the circuits flowing from it are also fused.

As I understand them (and I'm certainly no expert on DC electrical systems), bus bars are simply a means of splitting out current paths that are much more solid and safe than pig tailing a bunch of wires together under a wire nut (or even worse, electrical tape). You can use them just about anywhere you need to make connections and/or branch circuits. If you employ a positive-only block, then you'll also need a simple strip bus to use for your negative wiring.

-Steve

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Re: Split Bus Fuse Block

Postby jimh » Thu Apr 07, 2016 10:50 am

I should have been clearer: I intended no criticism of Steve's wiring plan. It is a fine plan. And I, myself, have a relay on my boat that controls power in a particular circuit. But a reader, coming to this discussion to begin his learning and understanding of boat electrical power distribution and the electrical wiring devices, should be aware that using relays or using split power panels is not always necessary in a small boat's electrical power distribution system.