So the question is kinda part 2 of my question about the DC Output

Today I went to Hellweg (It's like an Electronics shop in Germany/Europe). To buy a Circuit Breaker or Fuse (idk what I am looking for) for my solar system because I saw this pictures below:

From https://www.windynation.com/jzv/inf/how-properly-fuse-solar-pv-system


enter image description here

Now My question is: What Fuse/Circuit size breaker do I buy? Because I went to Hellweg and there are like 1000 of them with different Apmps, Voltage, etc.

Example below of Hellweg stuff:

enter image description here

I have a 100 Watts Solar Panel, 50A Controller, Battery, etc. I read using a wrong circuit breaker and fuse will cause a fire.

What size do I buy to make the my Solar Power System like the diagram?

Updated with Specs:

1) Inverter: Aukey 1000 W 2) Solar Controller: Here 3) Battery: Solar battery 100 Ah C100 4) Solar Panels: One 100W PET Panel

  • you're asking for product recommendation; those are off-topic here. Ask the employees at Hellweg; they're paid to actually help you buy what you need. The way you ask this indicates you have no understanding of even what part of your system you need that circuit breaker for – maybe you should ask the folks installing your solar system? They'll typically deliver a safe system, so chances are you don't need anything external. Jul 13, 2019 at 16:30
  • No I don't want product recommendation! I want product type and that's different! I'm building it myself and brought all the parts myself.
    – Graham Miranda
    Jul 13, 2019 at 16:31
  • You need to know the max current flow in each circuit so that you can buy a circuit breaker which is just above that max value. So if the circuit is 40A, then I would get a 50A breaker.
    – Solar Mike
    Jul 13, 2019 at 17:14
  • 1
    Asking for what to buy is off topic, to ask for "how do I size the breaker" is not. It's all how you ask, read the help center for recommendations on asking questions if you don't want it to be closed Jul 13, 2019 at 17:23
  • OKay i've added size :)
    – Graham Miranda
    Jul 13, 2019 at 18:54

3 Answers 3


You'll need to read the specs of those breakers to see if any of them can play with DC. For instance of many lines of breaker used in North America , precious few do (e.g. QO, but those only fit QO panelboards, they are not standard DIN rail like Euro panels). Speaking of DIN rail, there are loads of designed-for-DC breakers, just at EE/design type electronics shops like Mouser, not home improvement stores (except for the odd nuts like QO).

Also given the loads you want to run, you should really seek ways to run these direct on 12V DC. Inverting 12V DC to mains merely to power a wall-wart that makes 12V DC isn't even stupid. For instance if your TV can't take 12v direct, loads of other TVs can... get one of those.

  • There are QOU breakers that are basically DIN rail QOs, but they don't fit IEC distribution boards. Some IEC breakers are indeed DC rated, though -- for instance, Eaton FAZ-NAs Jul 14, 2019 at 2:53
  • Interesting @ThreePhaseEel. I am starting to think IEC is how I should go for my other project... Jul 14, 2019 at 2:56
  • ABB S200 family is rated to 10kA at 60VDC. The Schneider versions (iC60N) are good to 72V at I think the same fault current. Jul 14, 2019 at 12:39

Some answers in here:

  1. None of those Circuit Breakers are useful for this application, because they are from AC loads, not for DC loads. You should use DC fuses which are common, or DC Breakers which are less common.

  2. You have 12 AWG and 4 AWG, which have Allowable Ampacities close to 20A and 70A respectively, which would be a good starting idea for the fuses limits, for protecting the cables (only).

  3. The Panel Fuses at the user end should be calculated according the circuits loads you are planning to install. Just like any Panel. If you want three circuits each with 5A each, you should then put three Fuses for 5A. And you should consider most of the design criteria you apply for designing AC Panels in here (which ones?).

  4. The Inverter converts the DC into AC, which is not what you are showing in the diagram. I am actually not clear if you plan to supply DC or AC loads. I see you don't have that issue clarified either.

  5. As for any Panel, for those current levels, you will require specific component for interconnecting the equipment and protections. Also I see you have not questioning about this. Remember the specs for AC should not be necessarily the same for DC. For 1W AC there are specific requirements.

As a final comment: Those current levels, without any experience, are like a suicide. This requires minimum electrical knowledge in order to not killing yourself or anybody close to your system. Your system omits all protection design. It is like an open energized wire ready to be touched.

  • 1
    It's an AC System I'm trying to build (For my laptop charging, TV, etc) Jul 14, 2019 at 0:55
  • I wouldn't worry about the fuses values. I would worry about the rest.
    – Brethlosze
    Jul 14, 2019 at 1:05
  • @GrahamMiranda The breakers are still on the DC side of the system, before the inverter, so they need to be rated for DC. Jul 14, 2019 at 12:40

Pay attention closely to breaker specifications

As it turns out, you don't need a fuse in the solar panel wiring provided you use adequately sized wire from the solar panel to the charge controller. This is because solar panels are inherently current limited sources; in your case, your panel specifies an Isc of just under 6A, so it won't put more than that out, no matter what happens, meaning that 1.5mm2 wire is plenty adequate for the panel connections.

However, the battery wires are a different story. A fully-charged lead acid battery can put out somewhere between 1000 and 5000A of short-circuit current, and you will need breakers or fuses that can handle such a fault at 12VDC. This means that you will need to check the specifications for the breakers you want to use; not only will you need a 50A and a 100A breaker, these breakers will need to have a minimum of a 5kA interrupting rating at >16VDC. Some IEC-style breakers are DC rated, but not all, so you must check the specifications for the breakers you want to use.

As to wire sizing, you'll need some fairly thick wires for the charge controller and the inverter. 10mm2 is a reasonable size for the wiring from the charge controller to the battery; however, you'll want to increase that all the way to 35mm2 for the wiring from the battery to the inverter as the inverter can pull much more current than the charge controller provides. You also may need to use fine stranded wire for the connections to the battery to avoid putting mechanical strain on the battery posts, which requires its own precautions for making good connections (such as using compression lugs instead of mechanical setscrews). You'll also want to connect the negative post of your battery to an earth ground stake, or use two-pole breakers if you want to leave it floating.

Don't get gassed!

A vented-type lead-acid battery, like yours likely is, releases highly flammable hydrogen gas during the charging process. This means that you will need to make sure that the battery lives in a quite well-vented space so that hydrogen can't accumulate and ignite.

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