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Old 01-12-2020, 07:12   #1
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Dumb Electrical Question

Why don’t we use normal circuit breakers and fuses?

I’ve always assumed the BlueSea or Paneltronics marine power distribution panels as a given. Never gave it a second thought.

But I wonder why we don’t use fuses and switches. Or standard circuit breakers and switches.
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Old 01-12-2020, 07:22   #2
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Re: Dumb Electrical Question

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Originally Posted by Chotu View Post
Why donít we use normal circuit breakers and fuses?

Iíve always assumed the BlueSea or Paneltronics marine power distribution panels as a given. Never gave it a second thought.

But I wonder why we donít use fuses and switches. Or standard circuit breakers and switches.

'Normal' as opposed to what? The top-level answer is that many normal (aka used on land) components are more prone to corrosion and failure in a marine environment.
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Old 01-12-2020, 07:25   #3
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Re: Dumb Electrical Question

Some people do, at least as to fuses. For switches, breakers, and disconnects it’s all about the DC rating. AC voltage goes to zero many times a second (not giving a number because some of us use different frequencies than others). When you open a switch/breaker/disconnect with AC it is at most a few milliseconds until voltage goes to zero. This quenches any potential arc.

DC is a whole different animal. Voltage remains constant. Thus an open switch needs a much bigger gap to prevent an arc from forming. The size of the gap required depends on the voltage - higher voltage = bigger gap.

That’s the short version (there are lots of nuances and many construction techniques to provide “gap” or its equivalent) the bottom line is you need DC rated switching equipment. That is available many places other than the marine market, but not generally in the household electrical aisle at Home Depot.

[Edit] look up Carling Switch, they actually make many/most of the low voltage DC switches and breakers sold in the marine market. You can usually find them for less money at a non-marine place, or look at the industrial automation suppliers, where 24VDC is more common than coffee at breakfast
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Old 01-12-2020, 07:30   #4
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Re: Dumb Electrical Question

Higher end bilge pumps and most electronics come with automotive type in-line fuses. The real problem with relying on them alone is inconvenience. Trying to find the fuse, figure out what size it is and keep a stock of non-corroded spares is a treat. Home type panels are too big and corrode too quickly for most boats.
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Old 01-12-2020, 07:38   #5
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Re: Dumb Electrical Question

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Originally Posted by Chotu View Post
Why don’t we use normal circuit breakers and fuses?

I’ve always assumed the BlueSea or Paneltronics marine power distribution panels as a given. Never gave it a second thought.

But I wonder why we don’t use fuses and switches. Or standard circuit breakers and switches.

..and what is the question here? Not sure what you mean by "normal" or "standard".

Most larger distribution panels use magnetic single or double pull circuit breakers for both AC and DC. These magnetic pulls are similar to land breakers (unless you have a very old box w/the screw in fuses).
On some smaller older boats they had fuses and toggle switches for smaller panels.
All comes down to expense and sometimes not needed on smaller boats w/simpler electrical systems/needs.
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Old 01-12-2020, 08:27   #6
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Re: Dumb Electrical Question

These are some great answers. Thank you. I guess what I mean by normal is standard land based AC breakers, or DC breakers.

That would be one type of set up.

Another type might be to use a fuse block. Not for AC. But for DC. A standard fuse block like you might see in an automotive sense. And then use switches apart from that fuse block to control the systems.

I find it hard to imagine the makers maker of these power distribution panel is is using anything other than standard parts. Especially like mentioned above for the DC switches/circuit breakers.
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Old 01-12-2020, 08:40   #7
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Re: Dumb Electrical Question

My boat has a combination of breakers and fuse blocks. For the helm electronics, for example, there are 2 power buses (a vestigial feature of the original electrical architecture). Each one is fed from a breaker in the main DC panel to a fuse block under the helm. Then each device is individually fused on those blocks and power is distributed from there.


In general, the marine breaker panels and associated parts are more compact than most home AC breaker panels. And a lot of the marine breakers are rated for both AC and DC use, which helps parts commonality throughout the electrical system.
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Old 01-12-2020, 08:56   #8
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Re: Dumb Electrical Question

Who says we donít?

I donít have a single DC breaker onboard, I do have a fuse block and normal carling switch toggles.
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Old 01-12-2020, 09:12   #9
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Re: Dumb Electrical Question

Quote:
Originally Posted by Chotu View Post
Why donít we use normal circuit breakers and fuses?

Iíve always assumed the BlueSea or Paneltronics marine power distribution panels as a given. Never gave it a second thought.

But I wonder why we donít use fuses and switches. Or standard circuit breakers and switches.
Some boats use standard industrial Din rail circuit breakers. In my opinion this is a great solution. The biggest advantage is that these breakers are available from a multitude of manufacturers and are very easy to replace. They just clip into place. If you are using circuit breakers as switches (as most users do) circuit breakers do fail. Easy replacement with no risk that that the particular sized model will be no longer available is helpful and din rail breakers provide this.

There are scores of din rail breakers available, but in general with care you can source equipment with better specifications (such as permitted voltage, interrupt current etc) than the standard marine options. It is also more feasible to install enough breakers to have a dedicated function for each breaker.

The biggest drawback is they are bulkier and look ďindustrialĒ which does not match some boat interiors.

This is the circuit board in our new boat:
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Old 01-12-2020, 09:24   #10
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Re: Dumb Electrical Question

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Originally Posted by Dsanduril View Post
Some people do, at least as to fuses. For switches, breakers, and disconnects itís all about the DC rating. AC voltage goes to zero many times a second (not giving a number because some of us use different frequencies than others). When you open a switch/breaker/disconnect with AC it is at most a few milliseconds until voltage goes to zero. This quenches any potential arc.

DC is a whole different animal. Voltage remains constant. Thus an open switch needs a much bigger gap to prevent an arc from forming. The size of the gap required depends on the voltage - higher voltage = bigger gap.

Thatís the short version (there are lots of nuances and many construction techniques to provide ďgapĒ or its equivalent) the bottom line is you need DC rated switching equipment. That is available many places other than the marine market, but not generally in the household electrical aisle at Home Depot.

[Edit] look up Carling Switch, they actually make many/most of the low voltage DC switches and breakers sold in the marine market. You can usually find them for less money at a non-marine place, or look at the industrial automation suppliers, where 24VDC is more common than coffee at breakfast
I use the Carling G series a lot. They are readily available from Mouser, DigiKey and all the other typical suppliers. Good price and work very well.
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Old 01-12-2020, 11:30   #11
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Re: Dumb Electrical Question

These are interesting answers. I’m not the ones I would have expected. I will have an electrical closet. It’s a closed area that you open up containing all of the stuff. Inverter, charge controllers, breakers, so it’s hidden out of sight. Some items will be on display outside the electrical closet. The battery monitor, controllers for the inverter. Things like that. However, all of the major components will be inside the closet.One of the many parallel things I am looking at at the same time right now to plan out. I appreciate these posts. Interesting reading.
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Old 01-12-2020, 11:41   #12
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Re: Dumb Electrical Question

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Originally Posted by noelex 77 View Post

The biggest drawback is they are bulkier and look ďindustrialĒ which does not match some boat interiors.

This is the circuit board in our new boat:
I noticed that all your breakers are 2pole. Are these +ve and -ve DC breakers or are you in a split phase AC market? My limited understanding is that breakers are typically only on a single Active line in a single phase circuit.

Thanks
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Old 01-12-2020, 11:57   #13
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Re: Dumb Electrical Question

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But I wonder why we don’t use fuses and switches. Or standard circuit breakers and switches.
When I completely rewired my boat a few years ago I did exactly that.

BlueSea makes ATO/ATC fuse blocks for good reason.

Here was my thought process when I rewired my boat....
1. Many CB panels are small and end up becoming a rats nest of wires over time as systems are added (or they are huge, and still overloaded).
2. Many circuit breakers have way too many wires (devices) connected to a single CB.
3. Many people use the CB's as switches (often to make power available to a device that also uses a switch to turn on/off)
4. CB can fail over time (esp. the more they are cycled)
5. It is damn hard (nearly impossible to find low amperage CB (e.g. 1 amp) for sensitive electronics which is why most electronics have...yep...IN LINE FUSES!!!
6. If a fuse (or CB) blows...there is a problem. Fuses can react slower then a CB...so if a CB blows because of a power surge....it is a likely indicator of a faulty CB, if a fuse blows due to power surge you like have a fast blow fuse instead of a slow blow fuse.
7. Powerwerx makes "resettable" fuses....so ignore the CB reset argument.
8. Many CB are oversized for the circuits they are protecting.
9. I designed my electrical system so each device is protected by a single fuse. If a fuse blows...I know exactly what device caused the failure.
10. Lights are fused by zone. (Forward berth, head, saloon, etc). If turning on a light in that zone fails, I try another one...if 2 lights fail to turn on...I probably have a blown fuse, if the second light turns on...I need to replace the failing LED light fixture.
11. There is a single remote switch to power off all DC loads (except refer, bilge pumps) if I leave the boat for any length of time. When I get to boat I push the BlueSea 7700 remote battery switch to make power available to all circuits.
12. I added a small LED light panel at my nav station that will lite to show me if a fuse to a critical circuit blows (e.g. water pumps, refer, bilge & sump pumps).
13. If a fuse blows...I have spare fuses separated by size in a box that is securely affixed to the inside of the fuse panel door. I don't have to search for fuses, and they certainly take up no additional usable space.
14. I've never experienced a problem with corrosion (but my boat is dry, and I use Boeshield T-9 on ALL electrical connections).
15. I eliminated all inline barrel fuses (which do tend to corrode over time).
16. All navigation / safety lights (nav, anchor tri-color, steaming, deck/spreader, cockpit, aft flood etc) are controlled by switches, not by CBs used as switches. (All other devices have their own built in power on/off switches.)

Essentially...if a fuse or CB blows...there is a problem that needs to be investigated. Simply resetting a CB could be hiding a bigger problem. I use quick disconnect terminals on all devices (no barrel connectors) or ring terminals in watertight terminal boxes below the cabin sole, so if a fuse were to blow...I would disconnect the device, and begin troubleshooting the problem. Fortunately...in 7+ years...I've never had a fuse blow. Also, in re-wiring my boat...I replaced all the old corroded bare copper wire with tinned wire of the appropriate size.

I have a single switch that applies power to all circuits (except bilge and refer which are always on) and a handful of switches for nav/safety lights and AIS on/off & AIS xmit on/off at the nav station. Engine room exhaust fan is fused and comes on when I start the engine and shuts off 1 hour after stopping the engine using a Powerwerx APS-12 power switch/timer...no need to remember to throw a switch or CB.

And I should mention that my AC circuits use circuit breakers (1 Master and 5 zones).

In the time since I rewired my boat I have found one minor issue with the fuse block solution. I don't run my water maker these days to refill my forward water tank because I am mostly stuck at a marina. My deck wash down pump is plumbed to my forward tank (maybe a bad setup on my part). When it ran dry while out for a weekend...the pump continued to run until I removed the fuse. It was a little inconvenient...but that will teach me to make sure I fill the forward tank before heading out when i'm not running my water maker daily.

The other downside to fuse blocks is that they are hidden, so I don't have that really impressive looking circuit breaker panel that will impress my guests.

So, IMHO...the debate over fuse blocks vs. cb panels is really a mute point. Of course the zealots won't let it go.
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Old 01-12-2020, 12:36   #14
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Re: Dumb Electrical Question

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Originally Posted by GoneDiving View Post
I noticed that all your breakers are 2pole. Are these +ve and -ve DC breakers or are you in a split phase AC market? My limited understanding is that breakers are typically only on a single Active line in a single phase circuit.

Thanks
Yes, they are all double pole circuit breakers on the DC supply. Most circuit breakers and switches cut only the positive supply. This leaves the negative still applied to the the appliance. Strange, given that the electrons and current actually flows from negative to the positive.


A short between a high power positive cable from say an anchor windlass to a low power negative cable such a lighting circuit creates a potential hazard with a single pole circuit breaker or fuse. The fuse or circuit breaker will not trip in an over current situation. A dual pole breaker eliminates this potential fire hazard and also reduces stray current corrosion problems.

Particularly to reduce the latter problem the better aluminium boats use double pole circuit breakers. They are overkill for most fibreglass boats, but some commercial standards require at least some dual pole protection on certified boats.
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Old 01-12-2020, 12:53   #15
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Re: Dumb Electrical Question

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The other downside to fuse blocks is that they are hidden, so I don't have that really impressive looking circuit breaker panel that will impress my guests.

So, IMHO...the debate over fuse blocks vs. cb panels is really a mute point. Of course the zealots won't let it go.
A switch and fuse adds a number of extra connections that are not needed if a circuit breaker is used. Less connections is more reliability.

The other obvious problem is fuses take some time to replace. The re-setable ATO/ATC-Style “fuses” that you refer too are really mininiture circuit breakers, but they are very simple thermal circuit breakers with a relatively low IC and no switch function. They have their uses but they are not an ideal replacment for genuine magnetic/thermal circuit breakers in most applications.

I think some of your concerns are valid, but they centre on not having enough circuit breakers. The answer is generally more circuit breakers, not installing switches and fuses. Most modern boats have only a small number of circuit breakers to reduce costs.

It is more economical to employ fuses to protect secondary circuits and this is resonable providing the circuit breakers are not reduced to the absolute minimium.
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