Inline fuses

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katana750

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Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Hi again

I had a quick question about inline fuses. Does it matter where in a circut I mount an inline fuse? I currently have my wiring going to a Blue sea spade type panel (just like Sums), but in order to protect the devises I need to use a smaller glass fuse type. My wiring is all 12 awg. It will be protected by 15 amp spade fuses. I normally see an inline fuse close to the devise it is protecting, but I was wondering if I could place it near the Blue sea panel and then I keep all my fuses in neat little area That I can clearly label and not in all different parts of the boat.

Too me it seems like a good idea, but there may be a good reason not to do this.

Thanks for all the previous help with my shopping list.

Dave
 
Tom J

Tom J

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Sep 30, 2008
2,319
Catalina 310 Quincy, MA
Your idea to install the fuses in one area, clearly labeled, sounds good. A lot of inline fuses are installed near the device for the convenience of the person installing the device. Might be a good idea to install a fuse panel, or even better, a circuit breaker panel. Lots of sizes and types out there.
 
Sumner

Sumner

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Jan 31, 2009
5,254
Macgregor & Endeavour 26S and 37 Utah's Canyon Country
It is a little hard to answer the question without more knowledge but here are a couple things.

The fuse is normally there to make sure the wiring in the circuit does not get hot enough to cause a fire. For that reason it is usually placed near the source of the power. If you say had a long wire from the battery to a device and the fuse was at the device and the wire shorted before the device (say it wore through) then the fuse would never blow and the wire between the battery and the short might burn up.

For this reason you want a fuse at the battery sized for the run to the Blue Sea panel. Then the fuses in the panel are sized to the wire leaving the panel on each circuit to a load or loads on that circuit.

In my case I had a heavy wire running to above the sink area that was protected by the fuse in the distribution panel. Then above the sink at the end of that wire I used smaller wiring to different loads and fused those wires with smaller...



...glass fuses that are sized for the smaller wire. Above I had the same situation at the computer area and used glass fuses (top arrow above) on smaller wiring to different components.

If I wanted and I did I could put in a smaller fuse that would protect the device at that point. So if you have number 12 wire going from the panel to say one device that you want to use a small fuse on then put the small spade fuse in at the panel. If you have other items on the circuit that would blow that fuse then put a smaller one at the item or the wire to it.

Hope some of that makes sense,

Sum

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K

katana750

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Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Thanks Sum

It makes perfect sense. Sorry I didn't provide more detail I was just trying to keep my question short. I am basically copying what you have done. Heavy wire to the distribution box protected by the battery fuse. From the distribution box (15 amp breakers) I have run individual 12 guage wire to every devise. This is probably over kill, but I don't have ton of electronics so I bought two spools of red and black 100' wire and every devise has a home run of wire. I have mounted the distribution panel on some plywood under the sink. I have a negative buss also screwed to plywood. After running my wires I noticed I still had room to add a fuse box for the glass type fuses. Obviously most wires to the devises are much smaller than the 12 gage that I have used. Can I put the glass fuse on the 12 gauge wire to protect the 16 gauge wire at the other end that goes to the devise? Is the inline fuse there to protect the devise or the wire. I just wanted to put the fuses on the plywood because it would be tidy, but was unsure if that was ok. It kind of made sense that with a devise that requires a 1 amp fuse if more than 1 amp was being pulled through the 12 gauge wire it would blow protecting the wire/devise but after you said

If you say had a long wire from the battery to a device and the fuse was at the device and the wire shorted before the device (say it wore through) then the fuse would never blow and the wire between the battery and the short might burn up

my idea doesn't sound very clever or maybe it is. Maybe the best place to put the inline fuse IS closest to the distribution box. It would be like protecting the whole run from the distribution box to the devise with 1 amp. Does the amperage draw stay the same along the entire run or can it change there by constantly causing nuisance tripping.

Sorry but this is probably just basic electrical knowledge, but if I don't ask I can't learn,

Thanks again

Dave
 
Sumner

Sumner

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Jan 31, 2009
5,254
Macgregor & Endeavour 26S and 37 Utah's Canyon Country
Hey I hope to learn something new everyday that I can, so ask away. I'll bet your asking helps someone that won't ask.

The short answer in my opinion is that if you have one fused circuit with the #12 wire and one device on it you could put any fuse from your 15 amp (the wire will take more than that even) down to 1 or 2 if you want. This is if the smaller wire size you mentioned at the device is very short. If you are just going say a foot with the smaller wire to connect to the #12 I personally wouldn't worry about it. That would be if you stayed with the larger fuse at the panel. If you used a 1 or 2 amp fuse at the panel then I wouldn't worry how long the small wire at the end is as long as it was 18 or larger.

With your #12 wire and a device with low power you will have no real voltage drop (resistance) on the run. If they say to put a 2 amp fuse on it then that is what I'd use at the distribution box,

Sum

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K

katana750

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Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Thanks.....I thought what I was planning would be ok, but then I had a case of secondthoughtitis. I thought it would be best to ask somebody that knew for sure. Much safer than me assuming.

Back to the boat

Thanks again

Dave
 
K

katana750

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Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Sum

I could but I am pretty happy with your answer, it makes sense.....besides Canada isn't as sue happy as the states....and the pay outs are way less:D

I was going to try goggle but I wasn't quite sure how to pose the question. I guess it would be prudent though. I'll try tonight.

Thanks

Dave
 
Sailvayu

Sailvayu

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Jul 25, 2007
320
-Irwin -Citation 40 Wilmington, NC
The small in line fuse is to protect the piece of equipment and should be as close to the unit it is protecting as possible. The fuse or breaker in the panel is to protect the conductor. Placing the fuse at the panel my seem to make sense but will offer less protection from a short or surge. This is why most equipment comes with the fuse pre installed on the equipment end.

Capt. Wayne Canning, AMS
www.projectboatzen.com
 
K

katana750

.
Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Sailvayu said:
The small in line fuse is to protect the piece of equipment and should be as close to the unit it is protecting as possible. The fuse or breaker in the panel is to protect the conductor. Placing the fuse at the panel my seem to make sense but will offer less protection from a short or surge. This is why most equipment comes with the fuse pre installed on the equipment end.

Capt. Wayne Canning, AMS
www.projectboatzen.com
Click to expand


Too bad, I was hoping this was not the case, however it does explain why you see things wired in such a manner all the time. l

Thanks

Dave
 
Sumner

Sumner

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Jan 31, 2009
5,254
Macgregor & Endeavour 26S and 37 Utah's Canyon Country
Sailvayu said:
The small in line fuse is to protect the piece of equipment and should be as close to the unit it is protecting as possible. The fuse or breaker in the panel is to protect the conductor. Placing the fuse at the panel my seem to make sense but will offer less protection from a short or surge. This is why most equipment comes with the fuse pre installed on the equipment end.

Capt. Wayne Canning, AMS
www.projectboatzen.com
Click to expand
I'm not sure that I can see how more than 2 amps is going to get to an item if you have a 2 amp fuse at the panel?

I think one reason you see those fuses on items is that people tend to wire them direct to batteries or other sources that might not be fused properly,

Sum

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K

katana750

.
Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
OK I did a little research....maybe my question isn't as cut and dry as I first thought.

seems to be quite a few opinions ranging from get rid of them, they cause too many problems, to you must have them and close to the devise.

I found this comment

[FONT=Verdana, Arial][FONT=Verdana, Arial]The in-line fuse protects the individual device and is chosen with a rating to match the device. The fuse at the power distribution panel protects the branch circuit and is usually chosen to have a rating in proportion to the wire size used in the branch circuit. If there is only one device on each branch circuit, then the fuses become redundant, and you could eliminate the in-line fuse.[/FONT][/FONT]

My wiring is done in this manor but I still think it makes sense to have an inline fuse, just for the fact I don't think spade fuses come in anything less than 5amps (I have to look into this) How does the inline fuse protect the devise better when it is closer to the devise. I mean it kind of makes sense, but in what kind of circumstance would the 1 or 2 amp inline fuse not protect the devise/smaller gauge wire if it was located near the distribution panel . For example a bilge pump....wouldn't it be better to keep the inline fuse in a relatively dry spot compared to a damp bilge?
 
K

katana750

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Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Sumner said:
I'm not sure that I can see how more than 2 amps is going to get to an item if you have a 2 amp fuse at the panel?

I think one reason you see those fuses on items is that people tend to wire them direct to batteries or other sources that might not be fused properly,

Sum
Click to expand
Sumner said:
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I totally agree with you, but my complete knowledge of 12v electrical wiring is from the internet and this site. I would think both are very good resources but my electrical knowledge is still pretty basic...although growing. Certainly not at a point were I can start breaking from the normal procedure.

Dave
Click to expand
 
Sumner

Sumner

.
Jan 31, 2009
5,254
Macgregor & Endeavour 26S and 37 Utah's Canyon Country
katana750 said:
....I found this comment

[FONT=Verdana, Arial][FONT=Verdana, Arial]The in-line fuse protects the individual device and is chosen with a rating to match the device. The fuse at the power distribution panel protects the branch circuit and is usually chosen to have a rating in proportion to the wire size used in the branch circuit. If there is only one device on each branch circuit, then the fuses become redundant, and you could eliminate the in-line fuse.[/FONT][/FONT]
Click to expand
I agree with that. With the small fuse you want to use on the circuit the wire due to its size is never going to be in danger. The small fuse in the panel will protect the device to its amperage rating and also protect the wire to the device should it become shorted since it is on the power end of the wire.

We bought our fuses here and they have them down to 1 amp...

http://www.defender.com/category.jsp?path=-1|328|296553&id=336270

Sum

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Our Endeavour 37

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K

katana750

.
Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
We bought our fuses here and they have them down to 1 amp...

http://www.defender.com/category.jsp?path=-1|328|296553&id=336270

Sum

[FONT=Arial, sans-serif]============================[/FONT]

It looks like my shopping list was incomplete. I always thought I could pick up my fuses here. If they make 1 amp spade fuses it would seem I should be able to ditch the inline fuses all together.

I did buy things from defender when I went on my spree. Even contacted them in person....they were quite helpful.

Another place that had good prices was

www.thechandleryonline.com/ I was also quite happy with their service

Thanks

Dave
 
K

katana750

.
Sep 30, 2012
224
macgregor 26s 1993 cranbrook bc
Just in case somebody also had the same question. After a bit more reading I am pretty convinced the only reason you would need and inline fuse would be:

you have a distribution panel for argument sake with 15 amp breakers. From that panel you run a 12 gauge wire. This wire branches off into three different devices each having their separate safe draw requirements.

I thought it would simpler to trouble shoot in the future if each devise had its own circuit. After running my wires and thinking about what I was doing I came to the conclusion if my electrical needs where more complex. I would need a few miles of wire but in my case I only have about 14 items. I don't need an inline fuse because I can adjust the fuse in the breaker box according to the devises needs.

I hope I have it straight now. It seems quite simple really,, but doubt and second guessing can muddle things in my mind it seems.

Thanks for your help
Dave

now back to the boat to hook things up......
 
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