fuse versus breaker

[bigsallysmom]

Been looking at many diagrams to get a solar build solid in my head.  I'm looking for more understanding of one -- a 200W system.  On the positive line they put a 30A fuse between panels and charge controller, but then put a 40A breaker after the charge controller.  Then put an 80A breaker between 4 six volt batteries and 1000W inverter. 
When should I use fuses and when should I use breakers?  Should I just stick with fuses?

 

[Trebor English]

I stick with fuses.  Breakers are complicated and have moving parts and can fail.  When a breaker fails that means there is an over current and it doesn't open the circuit.  Fuses are quite reliable in that regard.  

Breakers have more voltage drop than fuses.  

Breakers are more expensive than fuses.  

Fuses are available in slow blow, fast blow, and medium too.  Breakers are, for the most part, slow.  

It doesn't matter much in a van but breakers are heavier.  

Sometimes people want to use a breaker to use it like a switch.  Before you do that look up the specification about how many times the breaker can be used to turn off the load.  Switches are usually rated for many more cycles than breakers.  

There is one case where I recommend using a breaker.  If you can't trust the user to replace a fuse with the correct size then use a breaker.  

I don't like fusible links but you didn't ask about them.

 

[Reducto]

I've never had a fuse blow on my solar system. There really isn't a reason it should happen unless you're using the wrong size fuse or a wire shorts out. If a wire does short, you'll want whatever blows fastest.

For the inverter I can see using a breaker since it could see brief spikes over 80A but a fuse is just fine especially if you aren't running anything big like an air conditioner or table saw.

 

[Trebor English]

For an inverter it is typical to use a much fatter than necessary wire to reduce voltage drop.  A fuse rated according to the oversized wire is not likely to be a problem.  

A high current load like an inverter is exactly where you don't want a higher voltage drop breaker.  If you want slow blow you don't have to settle for a breaker to get slow blow.

 

[Weight]

I know there is disagreement with this; If the proper size wires are used with the solar, then the only place a fuse is needed is at the battery positive terminal where the charge controller connects. If using three or more panels in parallel, a fuse is needed on each panel. Of course every load such as inverters need to be fused at the battery positive. At or very near the battery. Breakers are not good choices for high draw direct current devices. There does needs to be a way to disconnect the solar panels from the controller. Keep in mind, every fuse, every switch adds a bit of resistance and so voltage drop to the system. Larger fuses and heavier rated switches are better. Size all fuses to the wire AWG rating.

 

[Boyntonstu]

I stick with fuses.  Breakers are complicated and have moving parts and can fail.  When a breaker fails that means there is an over current and it doesn't open the circuit.  Fuses are quite reliable in that regard.  

Breakers have more voltage drop than fuses.  

Breakers are more expensive than fuses.  

Fuses are available in slow blow, fast blow, and medium too.  Breakers are, for the most part, slow.  

It doesn't matter much in a van but breakers are heavier.  

Sometimes people want to use a breaker to use it like a switch.  Before you do that look up the specification about how many times the breaker can be used to turn off the load.  Switches are usually rated for many more cycles than breakers.  

There is one case where I recommend using a breaker.  If you can't trust the user to replace a fuse with the correct size then use a breaker.  

I don't like fusible links but you didn't ask about them.

https://www.hillerelectric.com/circuit-breakers-vs-fuses-for-your-home/

Circuit Breaker Pros and Cons
Pros:

• Very easy to reset if tripped
  
• Useable with a GFCI-style breaker
  
• Does not need to be replaced like a fuse once tripped
  
• Is often more compatible with modern electricity needs

Cons:

• In some cases, not as sensitive as fuses; slower to react to surges
  
• More sensitive to sudden movement and/or vibration than fuses 

Fuse Pros and Cons
Pros:

• More sensitive than circuit breakers, which can be useful for sensitive devices
  
• Cheap—fuses are very inexpensive at any hardware store
  
• Perfectly viable if they’re rated with the proper amperage

Cons:

• Aforementioned sensitivity can cause frequently-blown fuses in some situations
  
• It’s possible to use an oversized fuse; a 30 amp fuse can fit in a 20 amp circuit, which is a dangerous fire hazard
  
• More difficult to replace in the dark
  
• Often more difficult for the average homeowner to maintain

 

[Trebor English]

The original post was a question about a 200 watt solar and battery system.  That would not be a typical home system.  

For your home, building codes require breakers.  Do a search about Federal Pacific Electric, FPE.  The company went bankrupt because breakers didn't trip.  It costs one or two kilobucks to retrofit a home with a new breaker box.  You may have to do that to be able to get fire insurance.  Yay breakers!  

The last item, "Often more difficult for the average homeowner to maintain" is very true.  With the current state of education changing a light bulb is a challenge for the average homeowner.  Remember, half of the 10th grade students are below average.  That makes the average high school graduate the cream of the crop.

If you want to operate your own electric utility with multiple sources and a mixed 12 volt DC and 120 volt  AC distribution system you need to know stuff.  If you want to design and build your own you need to know stuff.  People who read cheaprvliving and apply the information available here to solving energy needs in mobile environments are above average.  They have taken control of their situation.

 

[Trebor English]

When should I use fuses and when should I use breakers?  Should I just stick with fuses?

They make breakers that are often used in vehicles that plug into fuse sockets.  It would seem that you could use a breaker then change your mind and switch to a fuse.  The problem is that the breakers have thicker contacts  The fuse socket contact gets bent by the thicker metal.  Then when you put in a fuse it is loose.  So, you can switch from fuse to breaker but not breaker to fuse.

 

[Boyntonstu]

The original post was a question about a 200 watt solar and battery system.  That would not be a typical home system.  

For your home, building codes require breakers.  Do a search about Federal Pacific Electric, FPE.  The company went bankrupt because breakers didn't trip.  It costs one or two kilobucks to retrofit a home with a new breaker box.  You may have to do that to be able to get fire insurance.  Yay breakers!  

The last item, "Often more difficult for the average homeowner to maintain" is very true.  With the current state of education changing a light bulb is a challenge for the average homeowner.  Remember, half of the 10th grade students are below average.  That makes the average high school graduate the cream of the crop.

If you want to operate your own electric utility with multiple sources and a mixed 12 volt DC and 120 volt  AC distribution system you need to know stuff.  If you want to design and build your own you need to know stuff.  People who read cheaprvliving and apply the information available here to solving energy needs in mobile environments are above average.  They have taken control of their situation.

You really need to update your information:

[font=Roboto, arial, sans-serif]If your home was built between 1950 and 1990 and is equipped with a [/font][font=Roboto, arial, sans-serif]Federal Pacific Electric[/font][font=Roboto, arial, sans-serif] ([/font][font=Roboto, arial, sans-serif]FPE[/font][font=Roboto, arial, sans-serif]) circuit breaker [/font][font=Roboto, arial, sans-serif]panel[/font][font=Roboto, arial, sans-serif] with Stab-Lok circuit breakers, you run a significant risk of breaker malfunction and fire.[/font]

[font=Roboto, arial, sans-serif]I am fairly confident that any panel available today will not have the malfunctioning parts.[/font]

 

[deadwood]

I use a combination of fuses and circuit breakers. My solar panel runs from the roof into a CB and then out to my charge controller. The wires from the charge controller then go into another circuit breaker and then to my battery. This way I can easily isolate the whole system if I need to do any work to it. By turning the breaker off I can kill power from the panel or from the controller or from both.

I also run through a circuit breaker before going into my blue sea fuse block which then has wires running to all of my electrical appliances or devices. This way every thing I use has it's own fuse but I can turn everything off quickly by switching the CB off. I also have a 60amp terminal fuse on my battery to kill all power if there is a surge or short in the system.

For the others that suggest using fuses because they are fast acting I totally agree. They will blow much quicker then a circuit breaker will which I think would be much safer. The circuit breakers can act as a back up but are really there to make it easier to work on the system. When I was adding some lights the other day to my fuse block it is handy to just turn the CB off killing power to that area so that I can safely work on them. My fuses are for safety and to protect the electrical system from some sort of fault. My circuit breakers are for my convenience to make it easy to work on my electrical.

 

[Boyntonstu]

I use a combination of fuses and circuit breakers. My solar panel runs from the roof into a CB and then out to my charge controller. The wires from the charge controller then go into another circuit breaker and then to my battery. This way I can easily isolate the whole system if I need to do any work to it. By turning the breaker off I can kill power from the panel or from the controller or from both.

I also run through a circuit breaker before going into my blue sea fuse block which then has wires running to all of my electrical appliances or devices. This way every thing I use has it's own fuse but  I can turn everything off quickly by switching the CB off. I also have a 60amp terminal fuse on my battery to kill all power if there is a surge or short in the system.

For the others that suggest using fuses because they are fast acting I totally agree. They will blow much quicker then a circuit breaker will which I think would be much safer. The circuit breakers can act as a back up but are really there to make it easier to work on the system. When I was adding some lights the other day to my fuse block it is handy to just turn the CB off killing power to that area so that I can safely work on them. My fuses are for safety and to protect the electrical system from some sort of fault. My circuit breakers are for my convenience to make it easy to work on my electrical.

"[font=Verdana, Arial, sans-serif]For the others that suggest using fuses because they are fast acting I totally agree."[/font]

[font=Verdana, Arial, sans-serif]Except: [/font]

[font=Verdana, Arial, sans-serif][font=Helvetica, Arial, sans-serif]A slow blow fuse is different from a fast acting fuse in its capability to withstand transient pulse currents, i.e., it can withstand the surge current upon power-on/off, thus ensuring the equipment works normally. Therefore, slow blow fuses are often called time-delay fuses. Technically, a slow blow fuse features a higher I2t value, and it requires more energy to blow, so it is more capable of withstanding pulses compared with a fast acting fuse of same rated current.[/font]
[/font]
[font=Helvetica, Arial, sans-serif]When an overcurrent occurs in a circuit, the breaking time of a slow blow fuse takes longer than that of a fast acting fuse because of the larger I2t. Is it less protected this way as some people are worried? The answer is no. Once the circuit fails, the overcurrent will last and corresponding energy released will go beyond the I2t of the fuse until it blows out. The timing difference of slow blowing and fast acting is not significant to their protection. Slow blowing will affect the protection performance only when sensitive components existing in the protected circuit need to be protected.[/font]

[font=Helvetica, Arial, sans-serif]Due to the previous difference, slow blow and fast acting fuses are applied to different circuits. Fast acting fuses must be used in purely resistive circuits (no or fewer surges) or the circuits where IC and other sensitive components need to be protected, while slow blow fuses are preferably used in capacitive or sensitive circuits where surges occur upon power-on/off and power input/output. Apart from circuits for IC protection, most applications with fast acting fuses can be replaced with slow blow ones to enhance anti-surge capability. Contrarily, replacement of applications with slow blow fuses to fast acting ones may cause the fuse to break as soon as the equipment is switched on and fails to work.[/font]
[font=Verdana, Arial, sans-serif][font=Helvetica, Arial, sans-serif]Furthermore, economic consideration is also an indirect factor for selection because a slow blow fuse is much expensive than a fast acting one.[/font][/font]

 

[Trebor English]

You really need to update your information:

[font=Roboto, arial, sans-serif]If your home was built between 1950 and 1990 and is equipped with a [/font][font=Roboto, arial, sans-serif]Federal Pacific Electric[/font][font=Roboto, arial, sans-serif] ([/font][font=Roboto, arial, sans-serif]FPE[/font][font=Roboto, arial, sans-serif]) circuit breaker [/font][font=Roboto, arial, sans-serif]panel[/font][font=Roboto, arial, sans-serif] with Stab-Lok circuit breakers, you run a significant risk of breaker malfunction and fire.[/font]

[font=Roboto, arial, sans-serif]I am fairly confident that any panel available today will not have the malfunctioning parts.[/font]

I have one from 1979.  

I still think that fuses are simpler than breakers.  Breakers have moving parts that can jam.  Breakers have contacts that can weld, particularly if used often as a switch or in a DC circuit.  

The fact that FPE is bankrupt and gone doesn't convince me that breakers are better than fuses.  I see it as proof that bad breakers are possible and the market will punish.  

Any panel available today in the US will have been blessed by the Underwriter's Laboratories.  That involves design rules and inspections of product samples and factories, just like the FPE debacle.  When employees lie and hide facts (people misbehaving) bad things can happen.  

Square D management must understand that, like FPE, their entire business could get sued out of existence in an instant.  Even if they learned all the lessons and do everything right, actually achieve perfection, their breaker products could be as good as fuses.