Association Forum - Inline Fuse Size?

Assn Members Area · Join

Home.

Association Forum

Ships Store

Cruising

Racing

Technical Tips

Photo Gallery - New

Boat Search - Updated

Manuals & Brochures

Swap Meet

Links

Officer Flag Line & Staff

Bylaws & Constitution

Members Area

Join the Association

Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.

Association Forum

Username:	Password:
Save Password
Forgot your Password?

All Forums

Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Inline Fuse Size?

New Topic

Topic Locked

Printer Friendly

Author

Topic

wmuchmore
1st Mate

Member Avatar

USA
56 Posts

Initially Posted - 08/07/2010 : 21:09:40

Can any of you electrically savvy folks provide some advice on the size of fuse and type of in line fuse holders to use for my depth finder, marine radio, and gps? I thought this would be simple but was overwhelmed by all the options at West Marine. Thanks.
Mike Muchmore
2083 TR/FK

Edited by - on

sweetcraft
Admiral

Members Avatar

USA
816 Posts

Response Posted - 08/07/2010 : 22:17:32

Wire size dictates the max size fuse but each unit has own requirment for protection. Use wire size for the circuit and an inline size for each unit as specified. Placed for easy access for checking and replacing. There is a chart for amps to wire size.

Edited by - on

Voyager
Master Marine Consultant

Members Avatar

USA
5371 Posts

Response Posted - 08/08/2010 : 19:37:02

Here's a kludgey but practical way to determine what you need. Start with the smallest fuse you have, like a 5A fuse.
Plug it in and turn on the device full blast. If it's a VHF, key the mike. If the fuse blows, double it using a 10A.
Even if the 5A doesn't blow, replace it with a 10A fuse anyway.
If that blows go up to 20A (don't even waste time with a 15A).
If a 20A fuse blows, you're in trouble, and recheck your circuit for a short.

Another set of approaches you can use is:
(1) Find the recommended fuse in the instruction booklet or online (if you have the make/model)

(2) Read the Amps requirement on the back panel of the unit. If you have a Watts measure instead, divide by 12. For example, a 50W unit will use 50/12 amps, or about 4 Amps.
In this case, use a fuse that's the next one or two sizes up from that or 10A. If it needs 12 Amps, install a 20A fuse.

(3) Put an ammeter in place of the fuse (the ammeter has to be able to read 10-20A, and not all ammeters will do this and could damage your meter).
Read the Amps needed, so if it uses 8 Amps, install a 15A fuse.

(4) Use the klugey approach above (start small and keep replacing fuses until it doesn't blow, and then use the next one or two sizes up.)

You can get an assortment of fuses for under $20 in an auto store.
Here is an example, not that I recommend this supplier, but you get the idea.
http://www.china-tonytool.com/admin/upload/imgb/200999031435623.jpg

Edited by - on

wmuchmore
1st Mate

Members Avatar

USA
56 Posts

Response Posted - 08/09/2010 : 07:03:26

Thanks, Bruce. Very helpful advice. I'll print it and keep a copy with my boat papers for reference.
Mike Muchmore
2083 TR/FK

Edited by - on

Stu Jackson C34
Admiral

Members Avatar

844 Posts

Response Posted - 08/09/2010 : 14:03:22

Mike, Bruce is close, but please add this: do BOTH, a fuse sized for the wire near the power source, and a fuse sized for the wattage of the equipment at the equipment. One protects the wire, the other protects the equipment and are usually very different in size. Just look at any stereo installation guide and you'll see.

Edited by - on

skrenz
Captain

Members Avatar

USA
351 Posts

Response Posted - 08/09/2010 : 15:28:13

This is the old "what does the fuse protect" discussion. The fuse on the breaker panel protects the wire. I suspect you have 10 amp and 15 amp breakers. However, I think you will find that each device vendor wants its power lead protected by a much smaller amp fuse. (My fish finder specified a 5 amp fuse). If you are feeding all of your devices from a single circuit, between that circuit feed wire and each device you should install a second fuse rated at what the product specifies.

Edited by - on

Voyager
Master Marine Consultant

Members Avatar

USA
5371 Posts

Response Posted - 08/09/2010 : 20:31:02

These are good points. My approach was intended to protect the wire. Many boat fires result from unfused, unprotected cables.

I have one line from the battery to the panel with a 30 or 40A fuse next to the battery (for the wire), and each circuit with its own fuse in the panel (for the leads delivering power out to each piece of equipment or light).
Cabin lights use a 25A or 30A,
Anchor light uses a 10A,
Steaming light uses a 10A,
Deck lights use a 20A (this supplies the stereo),
Running lights use a 10A,
Accessory uses a 15A which powers the VHF and depth finder.

Most of the equipment came with its own inline fuse (VHF, depthfinder, stereo, etc), so I installed these as extra insurance. These handle the equipment's power requirements as Stu suggests.

But, if you are trying to keep things simple, run a single fused lead from the battery to the panel and select your panel fuses as described. There's nothing wrong with fusing the individual equipment as recommended by the manufacturer.

Edited by - on

wmuchmore
1st Mate

Members Avatar

USA
56 Posts

Response Posted - 08/10/2010 : 09:37:59

Many thanks to all for the electrical education.
However, the question remains in my mind why the lights require such large fuses compared to the accessories (anywhere from 10 to 30 amps depending on the circuit). Is it because the bulbs are almost dead shorts and accessories like a radio or GPS offer little resistance? (Household circuits are only 15 to 20 amps.)
My education continues ...

Edited by - on

redeye
Master Marine Consultant

Members Avatar

3476 Posts

Response Posted - 08/10/2010 : 10:06:23

<< Why lights require such large fuses? Is it because the bulbs are almost dead shorts and accessories like a radio or GPS offer little resistance? >>

Well the radio and other such are kinda small in what they draw little and can be damaged easily with excessive current. They want the fuse to go quick and with little amps. 1-5amp

The lights generally draw around 1 amp each and you might have 5-10 lights on a circuit. They don't really get "damaged" they get destroyed, but you can buy a new bulb easily.

The main concept is protect the wire but still allow the appropriate amps through. So the big 30 amp fuse is for the big wire from the battery to the panel.

The smaller 5-10 amp fuses are in the panel. Protecting the wire to the radio.

The even smaller 1-5 amp fuses are in the line to the radio and protect the radio, dept finder, etc.

Edited by - on

redeye
Master Marine Consultant

Members Avatar

3476 Posts

Response Posted - 08/10/2010 : 10:11:52

Now.. I'm only using the 5 to 7 amp fuses in my panel. May radio is not "fully" protected, nor is my wire to the panel from the battery.

If I had a short before the panel it could cause a fire.

If I had a short in the wire to the radio, the 5 amp would blow, but the radio would probably get damaged.

Shorts are not likely, but they do happen.

Edited by - on

skrenz
Captain

Members Avatar

USA
351 Posts

Response Posted - 08/10/2010 : 10:15:48

No, its not that a light bulb could become a dead short. The filament would dissolve long before the wire could be overloaded. It's that the lights draw a lot more amps when they are the typical incandescent type than your accessories.

When comparing to household circuitry you need to take the volts into consideration. Consider a 60 watt household light bulb. Watts = amps x volts. Your household circuit is running 110 volts. So to get 60 watts you need only ~.54 amps. Now consider if you could run that same bulb of 60 watts at only 12 volts. At 12 volts you need 5 amps to achieve the same wattage.

Wire sizes are rated to carry amperage over distance. Even so, I seriously doubt that you have a 30 amp circuit running your interior lighting. If you do, take a look at the wire on that circuit and make sure that ALL of it is sized correctly.

Again, the breaker is there to protect the wire.

Edited by - on

Voyager
Master Marine Consultant

Members Avatar

USA
5371 Posts

Response Posted - 08/10/2010 : 13:03:31

Ray, ... not to hijack the thread but ...
I'm glad you mentioned that your battery-to-panel wire is unprotected.
Like they used to say in school, "if one person says it, then several people are thinking it."

This is one of the most underrated fire safety issues on boats - unfused cabling.
While gasoline can burn and explode if mishandled, a major cause of boat fires is due to unfused electrical cables. This is more likely to happen when nobody's around, due to chafe.

A #10 AWG or #8 AWG cable can carry a lot of AMPs when shorting out a Group 24 battery (100s of amps), so it will heat up and catch the resin in the fibreglass on fire. As well it will ignite any wood, fabric or plastic it encounters. This is the kind of fire that can burn your boat right down to waterline.

Not to be an alarmist (oops too late), but anybody with unfused wires on their boat has a time bomb on board.

The safest approach is to place a fuse onto every circuit connected to the (+) terminal of the battery, within 1 foot of the battery connection, preferably right next to it.

This goes for your engine starter and alternator, your electrical panel, the memory wire for your radio, inverters and any solar chargers or conventional chargers you have wired into place connected to the battery.

[End of soapbox speech]

Edited by - on

wmuchmore
1st Mate

Members Avatar

USA
56 Posts

Response Posted - 08/10/2010 : 18:50:16

In the many years I have been poking around on this website I don't recall such a thorough discussion of wiring and fuse requirements. Very interesting and much appreciated.
For those of you that may not have this information, here are Catalina wiring and bulb specifications from papers that were on my 1980 boat. Not sure what years they apply to though:

CABIN LIGHT, blue wire, 4-10W incandescent, 2 10W festoon, 1 8W Fluorescent
RUNNING LIGHTS, red wire, 3 10W festoon bulbs
BOW LIGHT, white wire, 1 10W festoon bulb
ANCHOR LIGHT, orange wire, 1 10W festoon bulb
DECK LIGHT, white wire, no bulb info shown

Above power supply wires are to be 14 gauge. Ground wires are to be 10 gauge. Ground wire for the mast fixtures is green, and black wire for all others.
(Actually the ground wires on my boat are definitely not 10 gauge ... probably 14 gauge.)
Hope this is helpful.
Mike Muchmore
1980 TR/FK

Edited by - on

redeye
Master Marine Consultant

Members Avatar

3476 Posts

Response Posted - 08/11/2010 : 06:28:29

Well they may have written up 14 gauge but they installed 16 on mine.

Somewhere between the design and application.

Edited by - on

redeye
Master Marine Consultant

Members Avatar

3476 Posts

Response Posted - 08/11/2010 : 07:13:46

Mike, I'm sorry to have been so short.

I think the wiring schematics are a design listed as an average application design, rather than a rule they follow. The actual application or install they build out depends on what they install. ( ie Microwave, TV, Heaters, Fans, who knows what)

So when they did the build out they may have used different gauge wire than what the schematics have listed for the design.

My boat originally only had 6 interior lights for instance.

Edited by - on

wmuchmore
1st Mate

Members Avatar

USA
56 Posts

Response Posted - 08/11/2010 : 07:50:38

Regarding wiring size, a sailor who's boat is a few slips from mine is a recently retired airline mechanic at JFK and instructor at Aviation HS in NY. He says 14 gauge should be used for 12 volt wiring with 16 as an absolute minimum. I have to admit to using 18 gauge years ago, not knowing any better.

Edited by - on

Voyager
Master Marine Consultant

Members Avatar

USA
5371 Posts

Response Posted - 08/11/2010 : 19:41:22

Don Casey, well known boat restorer, advises the same thing. 14 gauge tinned stranded wire is a good compromise for light duty cables.
He also says that 16 gauge is the thinnest practical cable recommended for only the lightest loads, as anything thinner or less robust may fail due to vibration causing the wire to repeatedly bend and fail by snapping internally.
There are two types of stranded cable available: (1) automotive - containing a few thick strands that are not tinned (covered with solder) and (2) marine - a lot of thinner strands that are tinned. The former are not recommended for marine use while the latter are.

Edit: you can continue to use the 18 gauge wire until it eventually fails, then replace it with 16 gauge.

Edited by - Voyager on 08/11/2010 19:44:09

skrenz
Captain

Members Avatar

USA
351 Posts

Response Posted - 08/12/2010 : 18:35:19

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Voyager
 
There are two types of stranded cable available: (1) automotive - containing a few thick strands that are not tinned (covered with solder) and (2) marine - a lot of thinner strands that are tinned. The former are not recommended for marine use while the latter are.

<hr height="1" noshade id="quote"></blockquote id="quote">

This statement about only tinned wire being acceptable in boats is not really true. I refer you to the July edition of Practical Sailor where they did actual comparisons for wires, connections, and anti-corrosion pastes. They compared Tinned Wire, Automotive Wire, and Machine Tool Wire. (Machine Tool Wire is that wire found at hardware stores and labeled as THHN stranded. Instead of having 26 strands in 16-gauge tinned and automotive wire, Machine Tool Wire has 19 strands).
Their conclusion: "this wire seems completely suitable for marine application except where tinned wire is needed in very damp locations and where high-frequency vibration is found in the engine room. It is approved by the NEC and Coast Guard for these applications."

Edited by - on

Voyager
Master Marine Consultant

Members Avatar

USA
5371 Posts

Response Posted - 08/12/2010 : 20:18:27

This is very good news, as THHN wire is much less expensive than marine cable, and available at most home improvement centers.

Edited by - on

Topic

New Topic

Topic Locked

Printer Friendly

Jump To:

Association Forum

Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.