Breaker Sizing

thinwater · May 21, 2011

FourPoints said:
I'm trying to size the breakers for the new electricial panel, right now on the old panel everything just has 10A fuses.

Here's what I'm thinking, please tell me if any of this seems wrong.

10A - Cabin Lights (all LED but the head)
3A - GPS (Garmin GPSMap 540s with dual frequency sounder attached)
10A - VHF (basic no frills, but good shape standard horizon, has a 6A inline fuse that will stay)
5A - Nav Lights (All LED)
10A - Steaming Light (festoon bulb)
5A - Anchor Light (LED)
15A - 12v "cigarette lighter" receptacle
15A - Inverter (haven't bought one yet, going for something small around 500w)
5A - Spreader Lights (LED)
10A - Stereo
3A - Bilge (3A is manufacturer spec)

When sizing breakers, you are protecting the wire, not the equipment. You want a short to fail safe and not overheat a hidden wire. Since the wire will be 16 AWG minimum, 10 amps is common.

Certain items--compass lights, GPS--may have small leads, and often small in-line fuses are speced to protect those small leads. They are generally installed where the wire tapers down. Sail mag just had an artical railing against these, because they can be poorly located and be a trouble shooting problem. True enough, but that is up to the installer. I'm always careful to make them very easy to reach and hang a tag on each.

The down side of small breakers is that if you ever wish to add to the circut you will need to upgrade, by which time they may have stopped making the gutts to the breaker your looking for. Been there. You may add more electronics and wish you could branch off the GPS wire.

I can see no reason to go down on the nav lights; there is no lead to protect, and if you ever went back to regular (burn out a bulb on a cruise) it won't work.

I think the 10 amp ratings make sense for most people. The bilge pump is a separate issue. Often bilge pumps are wired straight to the battery with a separate fuse or breaker and a switch, rather than placing them on the main panel, where they will be turned off by the battery switch. I don't know your arangment.

Just a few thoughts.

bria46 · May 22, 2011

Protecting Wire? Thats wrong! You are protecting your equipment. Why are there so many size breakers on the market then?

After reading Clark Beek's article on Up grading Fuse Blocks (Clark is a marine electrician) I quote from the article published in SAIL Magazine-May 2011. "Many electronic devices require circuit protection as low as 1 Amp, sometime even half an amp. The smallest circuit breakers available for standard panels are rated at 5 amps, which is too high to adequalely protect sensitive electronics."

Roger Long · May 22, 2011

bria46 said:
Protecting Wire? Thats wrong!

No, you are completely wrong about this and it's an ignorance that could cost you your boat or even your life. There is a lot of information about the subject available with some Google searches. I highly recommend you spend some time seeking it out.

Both houses and boats are frequently full of violations of the basic principles which make the subject a bit confusing.

KD3PC · May 22, 2011

bria46 said:
Protecting Wire? Thats wrong! You are protecting your equipment. Why are there so many size breakers on the market then?

I think you will find that prevailing wisdom and objective science will point to the poster above you, actually being correct. Fusing and circuit breakers are in fact there to protect the circuit, especially for over current which causes copious amounts of heating which leads to fire.

Please check an electrician's NEC code book or NFPA (latest version)
http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=70&cookie_test=1; or one of the manufacturer's of overcurrent protection devices like cutler, siemens.

A side effect of those protection devices, is that you can power down that circuit to do work on gear, without affecting the rest of the power distribution system and those systems it may support. But that is certainly not the primary or only reason.

If you look at failed gear, there is absolutely no indication that any down line fusing protected the gear, as is evidenced by smoke, burned traces/components/etc.

Please be careful with your advice, as many here count on it to be accurate - yours is not.

Failure to understand what these devices do, can cause more damage than you may want...and in some case cause your insurance to be null and void.

BTW, I am a licensed electrician.

thinwater · May 22, 2011

Before you all explode, I suggested that fusing the wires to the wires' rating by the OEM made sense. I also suggested smaller fuses for electronic equipment as needed. It boils down to the probability of adding load later. kd3pc is right in that equipment also needs protection. I worded that poorly. What I meant is that the protection can be located further down the branch rather than at the main panel.

One hazard I frequently see, both in boats and in refinery settings, are small leads that would have been safe properly arranged in a box, either stuffed under the ceiling liner or otherwise miss located. This is part of "protecting the wire." Generally it is equipment that was meant to be mounted in an enclosure or on a proper panel misinstalled. Instructions are so useful.

Yes, it is certainly safe use small breakers and run every item on an isolated circuit. Often it's good practice. However, there are many good reasons it is not the only practice. Yup, got the NEC on the shelf, read parts now and then.

The best advise is that this sort of thread doesn't work on a forum; there are too many details and textbooks are better suited to this.

Maine Sail · May 22, 2011

The breaker is there to protect the circuit and wire. If a sensitive electronic device needs a small fuse for protection then an additional in-line can be installed as close to the equipment as possible. In certain cases primary OCP can be sized at up to 150% of the wires ampacity rating taken from table VI in the current ABYC E-11 standards. I usually prefer to stay at 100% or less but sometimes the wiring builders used forces you to go over the Table VI ampacity rating. Individual circuit wiring is based on voltage drop, wire temp rating, distance round trip, wire gauge and max amps flowing through the circuit. Most all critical circuits, such as nav lights and the panel feed, should be sized for a max of 3% VD.

For nav stations etc. I often use the Blue Seas ST Glass fuse blocks for distribution to multiple devices off one breaker rated for the entire load of devices running of the sub fuse block..

I much prefer the glass ST holder as I can mix and match fast blow or slow blow based on manufacturers specs.

I use one of those in my own nav station. It powers - 12V outlets, stereo, cell phone amp, secondary plotter, fan & iPod.

Blue Seas no longer offers any toggle breakers at less than 5A though they are available out there if you know what to look for. These "World Series" breakers are all made by Carling anyway but built to the "World Breaker" spec. Blue Seas now offers 5A, 8A, 10A, 15A, 20A, 30A, 40A, 50A etc....

While there is technically nothing wrong with installing a CB smaller than the wire size it drastically limits you're circuit to that breakers limit. I run across a number of devices that use sub 1A fast blow fuses and you're certainly not going to find that in a breaker.

JohnShannon · May 22, 2011

I dabble in electronics, and in my experience by the time the device is drawing enough current to blow a fuse the damage is done.

Works as follows everything OK, circuit draws normal current fuse is OK too.
Then something in the circuit goes BANG, now the circuit draws high current.
Fuse blows.
Change the fuse the next one blows too cause the device it is protecting is dead.

Far more to the point as far as protection is concerned would be surge suppressors like MOV's that prevent nasty overvoltages from destroying sensitive equipment. Ideally these are placed right next to the device to be protected.

With this scenario the overvoltage is converted to a high current which then might blow the fuse prior to any other damage.

mitiempo · May 25, 2011

The above posters are correct, the breaker is designed to protect the wire, not the device. But you are over thinking the sizes in my opinion, especially for the lights. Blue Seas breaker panels for example are all shipped with 15 amp breakers. The common wires on a boat are 14 awg and sometimes 12 awg for most circuits. 15 amps works well to protect these gauges. Yes, you can go smaller but then as posted there may be a problem when the circuit is added to or an LED bulb is changed to incandescent in an emergency situation. I usually stick to 15 amp for normal circuits. Some items such as the refrigeration system that was part of a recent wiring job received a 40 amp breaker and 10 awg wire as that was called for by the manufacturer. On the same job the autopilot received a larger breaker and 10 awg wire. For electronics I like the fuse block Maine Sail showed as they are usually (should be) easier to access than in-line fuses located all over the place.

Your inverter at 15 amps will not work with an inverter rated at 500 watts. A 500 watt inverter at max output will use over 40 amps. An of that size is probably best wired to the positive bus with a dedicated fuse of the proper size and wire of the proper gauge to handle it - 8.4 amps per 100 watts of inverter output minimum. For a 500 watt inverter I would suggest wiring of at least 8 awg and a fuse of 50 amps. I would use 6 awg for this, mostly because neither of my crimpers does 8 gauge so I avoid it.

philwsailz · Jun 2, 2011

Gents-

The U.S. Coast Guard provides documentation that outlines the law as it relates to new boat production... CFR 33 Subpart I speaks specifically to electrical systems. You can find everything required by law detailed here: http://www.uscgboating.org/regulations/boatbuilder_s_handbook/electrical_contents.aspx

I am paraphrasing, to make reading easier, but here is the las as stated in CFR33, subpart I, section 183.455:
In general terms, primary power distribution cable shall have an over-current device, with a trip current up to 150% of either the total fused load on the circuit or up to 150% of the current rating for the cable, generally whichever is lower. This primary over-current device is required to be within 7" of the battery or battery switch, otherwise known as a voltage source. Current rating for conductors is tied to the thermal capabilities of the insulating jacket of the cable. You can find values in figure 5 within section 183.425.

Subsequent smaller conductors then, where taken from a single large conductor treat the larger single conductor as the voltage source, so they similarly shall each have over-current protection within 7" of their connection to the large conductor. This is where the distributed fuse block comes into play, and it provides the distribution within the required 7". These smaller conductors then similarly shall be provided with individual over-current protection at either up 150% of the total summed fusing of any individual components on that circuit or up to 150% of the current rating of the smaller current carrying cable.

NOTE: there are exceptions, including cranking motor circuits

The A.B.Y.C and the NMMA promulgate their own requirements for member boat building companies. Over-current iprotection is outlined under E-11.10.1 in ABYC's Standards and Technical Information Reports for Small Craft, but know it toes the line with the law set forth by the U.S. Coast Guard. These guidelines and law requirements are put into place in order to prevent the wires or conductors from becoming an ignition source in the event of a short circuit.

Beyond these requirements, it is advisable to provide over-current protection for the load device. There are many factors that have to come into play and at smaller loads it does get interesting... For example, a bilge pump wired directly to the battery might include and/or require a 3A fuse to prevent the pump in the event that debris lodges in the impeller and sticks the motor. That fuse will often be located right at the pump. If located at the pump, you would want to install up to a 4.5A fuse within 7" of the battery terminal to protect the wiring in the even of a short, but knowing a 5A fuse is common, you are scratching your head... 5A is outside the law based on the recommended fusing for the pump. It is then relevant to go to Table 5 and see that for even the lowest thermal rating 16AWG conductor, (60C) we can run up to 15A, so using the 5A fuse on a bilge pump for primary over-current protection is acceptable.

Hopefully my inclusion of the link above will be of invaluable assistance in helping you guys choose conductors and over-current protection properly. Know sometimes you get what looks like a broken link, (afterall, it is the government) but if you go back and then click a link again, it will usually pop up. I have all of subpart I saved as a PDF and it is small enough to e-mail so if anyone wats a copy, feel free to PM me with e-mail address, and I will get a copy out.

Phil

jfmid · Aug 8, 2011

Hello Again Maine,

How are you today? Thanks again for your help, we all owe you big time. Do you accept shipments of beer??? There must be a local watering hole that one could phone in a credit card # to buy you a round. Give it some thought.

I'm looking at running my bilge pump directly off the house bank as you have suggested. I will be using 14-3 bilge wire (25 ft run one way) and connecting to a Rule 1000 GPH 12 V drawing 2.9A. From what I can glean from this thread it seems that I should have CB/Fuse protection at the source (the house bank terminal) to protect the wire and then I "could" have an additional fuse close to the pump to protect the pump itself. Am I getting the jist of this concept? I have tried to read the ABYC tables and honestly I'm embarrased that I cant determine this for myself. If I'm reading correctly Table X seems to say that I would need wire size 10 for a 5A circuit of 50 ft to have a 3% voltage drop. For a 10% drop it shows 16. So I should be okay with 14-3. This will be switched for manual/auto use.
So my question is what size Fuse at the house bank and then what size fuse at the pump if I even put a 2nd fuse at the pump?

In the what we cant see wont hurt us dept. the previous wire for the pump was what looks like 18 or 22 guage with wire nut connections.

mitiempo · Aug 8, 2011

Your numbers are correct. Here's the wire sizing calc I use http://boatstuff.awardspace.com/awgcalc.html
Just plug in the numbers and it is easier to use than a chart.

You want to fuse it above the pump's amperage and below the wires capacity (ampacity). 14 awg has an ampacity of 35 outside engine spaces and just under 30 in engine spaces. I would use a 15 amp fuse. Most wiring on a boat your size is 14 awg and for that reason companies like Blue Seas ship their panels with 15 amp breakers, suitable for most applications. The fuse will go before the wire gets too warm and that is the goal.

Are you using a bilge pump switch like the Rule with auto/manual/off and a built-in fuse holder? If so I would install the 15 amp fuse at the battery and the size fuse recommended for your pump in the switch.

Maine Sail · Aug 8, 2011

mitiempo said:
Are you using a bilge pump switch like the Rule with auto/manual/off and a built-in fuse holder? If so I would install the 15 amp fuse at the battery and the size fuse recommended for your pump in the switch.

This is the MOST important aspect of bilge pump fuse protection. Do not use a fuse bigger than what Rule says to use. The fuse sizes recommended by the manufacturer are intended to prevent the pump from catching on fire and will blow before that happens. 15A is fine at the battery but the bilge switch should be no bigger than what Rule suggests.

jviss · Aug 10, 2011

mitiempo said:
Most wiring on a boat your size is 14 awg ....

Not so in my experience. I don't think there was any 14g wire other than the battery cables, alternator output and starter wire in my C36 before I rewired it. Most was 16g or less, and not even marine grade.

I would be shocked to see only 14g and up in an Oday 27. But, I am willing to be shocked.

jfmid · Aug 10, 2011

You would be "shocked" to see what wire was used on the bilge prior. It looked like 18g or even (dare I say it) 22G. Not sure as the wire stripper doesn't really fit on it because it's so thin.
Anyway you are correct as most of the other stuff I'm seeing is 16g. This correcting of wiring is really opening Pandora's box. Really scary stuff but kinda fun to do it correctly and take pride in ones work.

jfmid · Aug 10, 2011

Rule Pump Fuse size

Maine Sail said:
This is the MOST important aspect of bilge pump fuse protection. Do not use a fuse bigger than what Rule says to use. The fuse sizes recommended by the manufacturer are intended to prevent the pump from catching on fire and will blow before that happens. 15A is fine at the battery but the bilge switch should be no bigger than what Rule suggests.

Here is the link to the PDF for the Rule pumps manufactured by ITT. It is on page 20 of the pdf and lists the Fuse size required for each size pump
http://www.ittflowcontrol.com/files/itemdoc12431.pdf

jviss · Aug 10, 2011

Sub-panel

I did what Maine suggests, mounted a BSS ST glass fuse block as a sub-panel for the bilge pumps and a couple of other things, and powered this sub-panel via a 15A breaker on the main, with about a foot of 14/2. I mounted ON/OFF/AUTO switch for each pump in the main panel - BSS makes such switches that mount in the same locations as the breakers.

I then ran 16/3 or 14/3 (for pump plus float switch) to the loads depending on the rating of the load, and protected the circuits according to the load manufacturer's recommended fuse size.

I put a "toggle guard" on the sub-panel feed breaker. This is always on unless I turn off the main panel breaker.

Frankly, I think the ABYC is a bit overdone, and that we overdo it with breakers on boats. While in homes we protect circuits that may have many potential loads on them, on boats we often home-run and protect each load, which can add up to lots of breakers and wire and panel space. But, so be it, that's what I did.

Write down what you do! I have a couple of "mystery wires" that I'm sure I installed over the last 10 years since I redid the panel.

One thing I would do differently now is that I would have mounted terminal strips inside the panel cabinet (behind the panel, on the inside of the hull, on my C36), to terminate wires coming from the boat; and then jump them to the breakers with short pigtails. I saw it done this way on a new boat at a boat show, I think it may have been a Bavaria or a Tartan. It really makes things very neat, and allows you to change things or make additions without losing track of what a wire is for. My labels have invariably failed - faded permanent marker, disintegrated paper tags, fallen-off P-Touch labels, etc.

I would also have made a way of mounting some pluggable relays. For example, I want an ON/OFF/Auto switch for my refrigerator - auto would be only on when there's a charging source available. I could route the control line from my Pathmaker (which senses a charging source) to this.

Finally, don't forget a place to mount an NMEA multiplexor, and to patch and route signal wires for PC, GPS, autopilot, radar, sailing instruments, VHF (with DSC), AIS receiver, etc.

mitiempo · Aug 10, 2011

I meant "should be 14 awg." I never use wire smaller than 14 awg and have used 12 awg and even 10 awg on some boats depending on distance. On one 48' boat I used larger (#8 I think) from the panel to the terminal block for the mast wiring.

Terminal strips behind the panel are a good idea for groups of lights etc before wiring to the breaker. All negative wires are also best on terminal blocks to keep the panel neater. I run a light negative to the panel that is only used for the back lighting.

Items like nav lights can be on a separate switch panel and wired from one breaker unless there is an excess of breakers on the panel used.

As far as labels if you use P-Touch labels and cover them with clear heat shrink they won't fall off.

I don't think ABYC is overdone.

jfmid · Aug 11, 2011

mitiempo said:
On one 48' boat I used larger (#8 I think) from the panel to the terminal block for the mast wiring.

Just want to be sure I completely understand.

Are you saying that you can use #8 or #10 or whatever to a terminal strip and then step "down" to a #14 from there. I was under the impression that it needed to be #8 or #10 or #12 (whatever the tables and math calls for) for the whole circuit. From the batteries to the load and then back from the load (whatever that might be light, pump, windlass, etc.) Is the terminal strip becoming the defacto (power source) remote from the battery???
Thanks for the post

mitiempo · Aug 11, 2011

I ran heavy wire (#8 I think) to a terminal strip forward on the deckhead at the mast and lighter was used in the mast itself. It means less loss to the base of the mast. There were multiple lights on the mast - steaming, spreader, anchor, and trilight. Rare to run that heavy a wire up the mast but less loss to the mast itself.

Breaker Sizing

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