Do solar panel setups need fuses or breakers

Re: Do solar panel setups need fuses or breakers

Some form of over-current protection is required on each circuit. A few (very few) units, particularly inverters, may have built-in protection, but don't count on it.

Panels will require a fuse or breaker each if there are more than two in parallel. Additional protection on the array as a whole is not necessary electrically but may be needed to meet local inspection or a breaker can be used as a convenient array disconnect.

Charge controller output to battery must have fuse or breaker on it, rated according to wiring & expected current.

Battery to each and every load (including inverter) must have appropriate protection as well.

Re: Do solar panel setups need fuses or breakers

PNjunction wrote: »

The reason for having fuses between the panels and the controller is to protect the wiring if one of the say paralelled panel wires shorts, and all the others dump their load into that short instead of going to the controller. That way, your panel wires don't become fusible links.

Nope.
Fuse/breaker between panels and controller does nothing. All that wiring should be sized for the Isc of the entire array. Thus there is no way an over-current condition can exist here, even if the controller input becomes a dead short.

The fuses/breakers on individual panel strings is to protect against a panel short where it goes from being a power source to being a conductor. Thus the other panels can put their full Isc into it, which may exceed the maximum current it was meant to handle as a conductor (maximum series fuse rating).

Re: Do solar panel setups need fuses or breakers

Plowman wrote: »

I'm not clear on the reason for this. If the CC short circuits, wouldn't a fuse on/near the battery terminal be preferable?

For function the placement of the over-current protection within the circuit is not relevant. It can even be on the negative wiring. Wiring convention places it on the positive lead, and it is safest to have it as close as possible to the power source (reduces the amount of 'live' wire if something happens) but it is not always practical.

The circuit in question is described as "charge controller output to battery" but that does not mean the fuse or breaker needs to be at the controller.

Re: Do solar panel setups need fuses or breakers

Plowman wrote: »

Maybe my understanding of short circuits is wrong (very possible), but I thought that the current will travel from the battery to the shorted CC. The closer the fuse/breaker is to the battery, the less chance you have of burning up your wires and having a fire on your hands.

Correct. That is what I said.

With that understanding (maybe wrong) I put a 40-amp circuit breaker as close to the positive terminal as possible (2-3")---this is connected to my bus bar, to which my CC is connected. I have no fuse on the wire between the CC and batteries.

Incorrect, because you have bus bars. That means the charge controller and inverter (as well as any other DC loads) connect to the bus bars. The breaker on the battery will protect output to everything, but not to the individual circuits that branch off from the bus bars. The correct sizing here is that the breaker on the battery should be able to handle the maximum current draw of all DC loads combined. Since an inverter typically draws much more current than a charge controller puts out, if you have it sized for that the controller circuit is not protected.

With this arrangement there are in fact three circuits that need protection: battery to bus bar, bus bar to inverter, charge controller to bus bar.

An example of correct wiring:

BATTERY --00 AWG--> BUS BAR (200 Amp circuit, requires appropriate fuse/breaker)
BUS BAR --00 AWG--> INVERTER (200 Amp circuit, requires appropriate fuse/breaker)
BUS BAR --10 AWG--> CHARGE CONTROLLER (30 Amp circuit, requires appropriate fuse/breaker)

Re: Do solar panel setups need fuses or breakers

767mrN#13 wrote: »

How does all this change due to my temporary setup? I did a poor job of asking the question. These panels will be on a stand. They will be moved out in the morning and taken in at night. When they are inside, they will not be connected to the battery. How does this affect the answer?

It doesn't.
When the system is active if something goes wrong you want fuses to blow or breakers to trip. Problems do not occur on systems that are shut down anyway. So whether it is a permanent installation or a mobile one there needs to be protection against faults.

Re: Do solar panel setups need fuses or breakers

Some inverters have built-in fuses. Most do not. The reason makers 'leave them out' is because every system is different; they can't know in advance exactly how their unit will be used. They do, however, supply a set of instructions with recommendations.

Plowman wrote: »

Cariboocoot, sorry if I'm just dense. I'm just trying to understand the theory behind putting an additional fuse/breaker between the CC and bus bar. Where would the current come from if not the batteries? Wouldn't a battery breaker be sufficient to protect the wires in the CC-bus bar circuit?

Here's the thing: you have one breaker protecting two circuits.

Let's say they are identical in current potential (which is highly unlikely). Charge controller shorts, breaker trips, invert goes down as well. Now that may be interpreted as a good thing because you've just been alerted that something is wrong by the sudden outage. You won't know what, though, and resetting the breaker will only cause it to trip again. Now suppose it is the inverter that shorts and kills all power. Again you don't know where, but this time you have the added disadvantage that the charge controller is no longer working either; the batteries that just got hit with a massive current demand that cause the breaker to trip are depleted and not getting better.

Now most of the time the inverter current will be much higher than the controller current, with different size wires. With one breaker if the controller shorts the wires to it can heat up and burn before the breaker trips because the breaker has to supply full inverter current; it is much larger than the current on the controller circuit. Again if the inverter shorts the breaker trips and everything goes down. This problem is exacerbated with additional DC loads.

We view the bus bars as an extension of the battery posts, and every circuit connected to them has its own proper sized wiring and circuit protection. But this leaves the wire from the battery to the bus bars unprotected, so an additional fuse/breaker is installed as close to the battery as possible in case the short occurs at the bus bars for example. This will be of a large enough capacity to handle all loads on the battery. Disconnecting said fuse/breaker kills all power to everything, which makes it safer for diagnosis and repair.

Things do get confusing when circuits branch off. Think of it like this: your household outlet has a breaker on it at the main box. You plug multiple items into that outlet. Each of those may have circuit protection within them. Why? Because the current demand for that particular item is <15 Amps and the wire to it reflects this. If something goes wrong you only want that one device disconnected, you don't want it taking out the whole circuit and you certainly don't want it setting its wires alight. This is in fact the #1 cause of household fires; overloaded extension cords that go up in flames before the circuit breaker is strained (because the cords are 18 AWG and people put >10 Amps of load on them; no problem for the breaker but a real problem for the small wire).

Re: Do solar panel setups need fuses or breakers

767mrN#13 wrote: »

So if I've got it, I'll be one between the panels and controller and between the controller and invertor. And, yes, I'll be checking with the hosts of this site as their sponsorship needs to be supported!

It should be one between the controller and battery, then one between battery and inverter.
Panels to controller is the circuit least likely to need any kind of over-current protection.