Breaker Switches vs Fuses

[Squanderbucks]

Squander Bucks is over 50 yrs old and originally had a main AC circuit breaker and then two panels for the AC individual circuits that had the old round screw in fuses. A second 30 AMP system was added as well for additional draw for the A/C and cooking systems. The DC system used the larger glass fuses (I forget their size numbers) for all of the 12 volt equipment items with no master fuse only a on/off breaker switch.
It took me a month os so to switch it all over - all the AC stuff to Circuit breakers with a new panel and threw out the old screw in fuse boxes and then to install a whole new DC Master panel and switch anything with 5AMP requirements to the circuit breakers. Then several smaller DC sub-panels were mounted close to the equipment they served were switched over to the ATO fuse panels.

[exMaggieDrum]

The OP started out asking about a DC panel. The comment above about needing dual (hot and neutral) breakers is entirely correct. I would consider it absolutely mandatory. It is a safety (as in saving a life) deal.

Also, glass plug fuses are a danger on a boat, as they are in a house. Many a house has burnt down when these fuses have failed. Might as well put in post wiring while you are at it.

Regarding using fuses for a windlass, I would never do that, personally. There are times when you need to get the anchor up Right Now and finding and changing a fuse could be catastrophic. From what I have seen with windlasses, the CB may trip when the motor is overloaded which can lead to overheating. A momentary pause, along with correction of how you are trying to bring up the anchor, will usually solve this, and later, you can troubleshoot the issue. If it is a major short, a CB will do that, and you don't need a super quick acting fuse. Of course, the CB has to be correctly sized and rated.

One the things that has not been brought up is what to do when a fuse, or a breaker, keeps tripping. I repaired a panel fire (wood burnt, wire insulation melted) when an owner kept resetting an AC breaker. So when a breaker, or fuse, keeps tripping or blowing, it is time to stop trying to use that circuit and investigate the cause - in my experience is most often wiring, terminals, and good connections. There are other reasons too.

If a bilge pump keeps tripping or blowing, it is critically important to investigate and fix. Motors can start a fire when locked up. However, a locked up motor doesn't always trip the breaker or blow the fuse, so the bilge has to be kept clear of debris and its wiring has to be kept better than all the wiring in the rest of the boat (except for AC).

And, the comment about small breakers for sensitive equipment is spot on. You can't (usually) find small amp breakers. In those cases, I still put the circuit on a breaker to protect the wiring and a small amp fuse close to the device, as recommended by most electronics manufacturers. This small fuse is to protect the device, not the wiring, although it would certainly do that too.

I greatly prefer the use of the automotive style ATC/ATO blade type fuses. They are much easier to replace and last longer, especially the ones with water resistant caps. For a lot of small amp circuits, like for battery monitors, radios, etc. I like the multi-position ATO fuse blocks. They can be placed close to the battery if necessary and you have one spot to go find the fuse. The wire to the fuse block should be fused as well unless it is very close to the battery, to protect that wire.

One of the very best upgrades for an older boat is to replace the fuse panel, or lack of a fuse panel, with modern fuses and marine rated wiring (tinned). It is more expensive, but the corrosion you get with regular copper wire is fast and insidious. Solid copper wire should NEVER be on a boat.

This is a digression from the original OP question, but the subject of protecting the wiring, and the boat, with fuses/breakers is only part of the overall electrical system for a boat.

Also, if you do have fuses you should have a minimum of three of the same rating/kind for every circuit with a fuse. Often the replacement fuse will blow when replaced since there was a reason for it to blow in the first place and owners tend to just replace the fuse first. So I keep a kit onboard for the fuses I do have where I only have to go one place to find a replacement. In addition, for critical circuits, I wire tie one of the ATC/ATO fuses to the wire right at the fuse holder to make it faster and more convenient to replace it the first time.

Another reason to use the ATO fuses is they are easy to identify by amp rating (color and number right on the top). The little barrel fuses are incredibly hard to read for the rating on one end. And, as noted above, the barrel fuses, and their holders, do seem to develop a bad connection between the fuse and the holder contacts. The holder contacts are almost impossible to clean without a very small wire brush, smaller than readily available. Someone may have a better idea for this but I am not aware of it. If you do have barrel holders, it is best to have the water resistant/proof ones to help delay or prevent the corrosion.

Of course, some circuits require quick fuses and these are only in the barrel style as far as I have seen, so you might have a few of those, usually only for electronics. The manual for each device will tell you what type and rating of fuse you need.

Just my two cents. Everyone makes their own decisions for their own boats.

[Cadence]

Originally Posted by mitiempo

AC should have breakers, not fuses. Double pole for the main, single for circuits.

He was speaking of finding fuses common in the forties and fifties. Seems a penny could be put in the socked and the blown fuse screwed in if you didn't have a replacement. A sure fire starter.

[rwidman]

Originally Posted by TooCoys

This may be the dumbest question you read all day...

What's the difference between a breaker switch, and a fuse panel switch?

I'm assuming that a breaker switch is an all-in-one switch, whereas a fuse panel switch has a separate rocker switch and fuse.

You have been given a lot of information, some of it correct, much of it incorrect and much of it off topic.

You didn't post why you wanted the answer, but if you want the correct answer to your question, you'll do far better looking for definitions of each on the Internet. Or, buy a book on boat wiring.

The simple answer to your question is that most circuit breakers can also be used as switches so you have overcurrent protection and a switch in one unit. A switch is just that, a switch. It provides no overcurrent protection.

[Colin A]

Originally Posted by noelex 77

I think Mitiempo has a good point. The IC rating is an important factor. Unfortunatly it is a complicated subject. To correctly calculate the minimum IC rating depends on factors such as the battery capacity and wire size.

I slightly disagree with the suggestion that: "It is expensive to find breakers that have the interrupt capacity of MRBF or T class fuses". I think it is more accurate to suggest "It is difficult (or impossible) to find marine breakers that have the interrupt capacity of MRBF or T class fuses". If you switch to industrial CB often even the smallest models have IC that are similar to T class fuses. These are not expensive. Larger models do even better if you need extra headroom.

This is just one of reasons are why commercial boats use this type CB rather than "marine CB" for general circuit protection. I think many pleasure boats could follow their example, although for most circuits marine CB have more than adequate IC. (Inverters are often an exception).

There are more significant advantages of industrial CB such as easy replacement and longer life.

Carling switches which are common in the US boat market offers some high AIC breakers.

The A series which is the most common has either a 3,000 or 5,000 AIC rating depending on configuration.

The C series which is pretty common as a main breaker goes up to 10,000 as a UL489 version

The F series get's you up to 50,000

Also not sure of the others but the A series is rated for 10,000 actuation's. In practice at work we find people calling to replace them some where between 20-25 years old.

Here is a link to the site.
Carling Technologies Hydraulic Magnetic Circuit Breakers

Some times we also use industrial DIN rail mount breakers.

As an example Altech UL489 rating have a 10,000 AIC rating and a 6,000 actuation life span

http://www.altechcorp.com/PDFS/Altec...ction(all).pdf


Or like we use for many larger ship's Square D/ Schnieder breakers
http://www.schneider-electric.us/en/...load-pdf/60103

You will also run into QOB breakers which are similar to home breakers but with an industrial bolt on mounting in some commercial marine applications.

[Cadence]

Originally Posted by rwidman

You have been given a lot of information, some of it correct, much of it incorrect and much of it off topic.

You didn't post why you wanted the answer, but if you want the correct answer to your question, you'll do far better looking for definitions of each on the Internet. Or, buy a book on boat wiring.

The simple answer to your question is that most circuit breakers can also be used as switches so you have overcurrent protection and a switch in one unit. A switch is just that, a switch. It provides no overcurrent protection.

Ron, the problem with using a breaker as a switch is they have a duty cycle. It may not be significant if switching isn't a regular thing.

[TooCoys]

Originally Posted by rwidman

You didn't post why you wanted the answer, but if you want the correct answer to your question, you'll do far better looking for definitions of each on the Internet.

Post #8


I want to rewire the boat completely so that I know where everything is, and how its wired.

[mitiempo]

Originally Posted by Cadence

Ron, the problem with using a breaker as a switch is they have a duty cycle. It may not be significant if switching isn't a regular thing.

Blue Seas A series breakers (made by Carling) are rated for 10,000 switching cycles.

[mitiempo]

Originally Posted by Colin A

Carling switches which are common in the US boat market offers some high AIC breakers.

The A series which is the most common has either a 3,000 or 5,000 AIC rating depending on configuration.

The C series which is pretty common as a main breaker goes up to 10,000 as a UL489 version

The F series get's you up to 50,000

Also not sure of the others but the A series is rated for 10,000 actuation's. In practice at work we find people calling to replace them some where between 20-25 years old.

Here is a link to the site.
Carling Technologies Hydraulic Magnetic Circuit Breakers

Some times we also use industrial DIN rail mount breakers.

As an example Altech UL489 rating have a 10,000 AIC rating and a 6,000 actuation life span

http://www.altechcorp.com/PDFS/Altec...ction(all).pdf


Or like we use for many larger ship's Square D/ Schnieder breakers
http://www.schneider-electric.us/en/...load-pdf/60103

You will also run into QOB breakers which are similar to home breakers but with an industrial bolt on mounting in some commercial marine applications.

The breakers used for heavy loads - windlass, davits, or bow thruster can have issues with AIC. Blue Seas 187 series breakers have an AIC of only 5000 @ 12 volts. That is not high enough if you have a house bank larger than a few group 31 batteries. Blue Seas used to have a paper about this on their site but I can't find it. Blue Seas 285 series have an AIC of only 3000 amps.

Fuses commonly available and rated for marine use are ANL - 6000 @ 32 volts, MRBF terminal fuses - 10,000 @ 14 volts, and Class T - 20,000 @ 160 volts. These are the fuses that are appropriate for high current loads and are what I would choose instead of breakers.

[HankOnthewater]

I noticed there are a lot of acronyms used in this thread, and not all readers may know what they stand for.

AIC Ampere Interruption Capacity
IC Interruption Capacity (of current), same as above
MRBF Mean Rounds Before Failure
ANL type/brand? of fuse; it seems sometimes being labelled as current limiter (bottom left image)
Class T fuse fast acting type of fuse for large amperage and high AIC (bottom right image)
CB Circuit Breaker
ATO Range of blade style of fuses see wikipedia here: https://en.wikipedia.org/wiki/Fuse_(automotive)

I also added some images borrowed from the net; as they say "a picture is worth......."
And yes, there are many more types of fuses and breakers, each with their own specifications, being an advantage or disadvantage.

[mitiempo]

Originally Posted by HankOnthewater

I noticed there are a lot of acronyms used in this thread, and not all readers may know what they stand for.


MRBF Mean Rounds Before Failure

MRBF stands for Marine Rated Battery Fuse. They are a good choice for main battery fuses as well as high load items like windlasses. They have a high AIC - 10,000 @ 14 volts. They save running a wire from the post of the battery to a fuse.

https://www.bluesea.com/products/cat..._Battery_Fuses

[HankOnthewater]

Originally Posted by mitiempo

MRBF stands for Marine Rated Battery Fuse. They are a good choice for main battery fuses as well as high load items like windlasses. They have a high AIC - 10,000 @ 14 volts. They save running a wire from the post of the battery to a fuse.

Obviously I got it wrong here, thanks Mitiempo for the correction. However it shows, that it is important that a poster explains an acronym, the first time that is used in a thread. I will keep on learning, and the day that I don't.... time to give up.

[noelex 77]

Originally Posted by Colin A

Carling switches which are common in the US boat market offers some high AIC breakers.

The A series which is the most common has either a 3,000 or 5,000 AIC rating depending on configuration.

The C series which is pretty common as a main breaker goes up to 10,000 as a UL489 version

The F series get's you up to 50,000

Also not sure of the others but the A series is rated for 10,000 actuation's. In practice at work we find people calling to replace them some where between 20-25 years old.

Here is a link to the site.
Carling Technologies Hydraulic Magnetic Circuit Breakers

Some times we also use industrial DIN rail mount breakers.

As an example Altech UL489 rating have a 10,000 AIC rating and a 6,000 actuation life span

http://www.altechcorp.com/PDFS/Altec...ction(all).pdf


Or like we use for many larger ship's Square D/ Schnieder breakers
http://www.schneider-electric.us/en/...load-pdf/60103

You will also run into QOB breakers which are similar to home breakers but with an industrial bolt on mounting in some commercial marine applications.

Colin, I am pleased to see someone looking into the specifications in a detailed way .

It is very difficult to compare specifications of circuit breakers. The specifications such as interupt capacity varies significantly with voltage. The specifications for marine circuit breakers at first glance appear to be better because they are quoted at relatively low voltages, because this is how they are most commonly used.

The very popular Blue Seas"A" series toggle circuit breakers that are seen on the main circuit board of many boats are often quoted as having an interrupt capacity of 7,500A. This is correct, but it is at under 65v. Most of the DIN industrial MCB have an interrupt capacity of 6000A (or 10,000A depending on the standard), which looks similar or even slightly worse, but this is for 230V.

The Blue seas circuit breakers do actually list the interrupt capacity for higher voltages and it 1,500 A for 250V

Finding the interrupt capacity of the DIN industrial circuit breakers for lower DC voltages is difficult, but it can be found. For the circuit breakers fitted to my new boat it is 20,000A at 60VDC.

So looking at interrupt capacity:

Lower voltages:
Blue Seas 7,500A
Industrial 20,000A (some are 15,000A)

Higher voltages:
Blue Seas 1,500A
Industrial 6,000A

So the interrupt capacity of the Din industrial models is generally higher.


Cycle life is even more fraught with difficulty comparing specifications. It will vary significantly with voltage and is worse for DC rather than AC.

The Blue Seas circuit breakers are rated at 10,000 operations, at rated specification and voltage, but it is not clear which specification they are refering to. It will be lower for DC that AC. Most industrial circuit breakers have a similar rating, but once again it not entirely clear if you are comparing like with like. The circuit breakers I am fitting have a cycle life of 20,000 operations below 32A and 10,000 operations at 64A. This is not unusual for the better industrial circuit breakers.


If you want to use the industrial circuit breakers and want a higher interrupt capacity there are some models that go higher. Most companies offer a range of products some designed for very high powered systems. Unfortunately these breakers become physically larger so are not suitable for the main circuit board. Even the "small" industrial circuit breakers I am suggesting above are quite a bit larger than the marine equivalents.

The main advantage of the industrial circuit breakers is not their greater interrupt capacity, but rather they are very easily replaced and are available from many manufacturers in very similar models. The Din rail standard is very common. If marine circuit breakers fail they can be difficult to replace especially if the model concerned has been discontinued.

I should also note I think the Blue Seas products are excellent. Many marine breakers are simple thermal breakers that are not the same quality as the Blue Seas products, but if are refitting a boat with a new electrical system the Din rail industrial circuit breakers are worth considering.

[exMaggieDrum]

The discussion of interrupt ratings is certainly useful but will certainly just be right over the tops of the average cruiser's head. I have worked on hundreds and hundreds of boat electrical systems and I can't recall any major problems (fires, etc.) from using the run of the mill (good) breakers, such as the Class A's from Blue Sea. I am just completing my new BS DC panel and finished my AC panel previously and I have no concerns about them.

DIN mounts are great but the parts and breakers are not easily found by the average boater in the US nor is the expertise to design and install them. They are far more common in European boats. I have mostly seen them on the very large high-end boats who had commissioned electrician engineers on the specification and design team.

Just my observations in the field.

[rwidman]

Originally Posted by Cadence

Ron, the problem with using a breaker as a switch is they have a duty cycle. It may not be significant if switching isn't a regular thing.

I wouldn't use one for the cabin lights or even navigation lights, but a breaker switch is fine for things like a refrigerator or the automatic water pump.

The OP never said why he wanted to know the difference, but as a practical matter, the boat manufacturer usually installs the appropriate device.