How to wire a DC breaker?

[12VoltInstalls]

panel string is protected with an appropriate fuse" "The" meaning only one PV string? Normally we don't use a fuse in that case.

Sorry. I should have been more clear.

I have 8 100W panels 4S2P and have two dual 10A breakers as a shutoff, one for each string. Around 88V VOC and 5.6A each string. 10A fuses on panel pos(+), 60A fuse at battery from charge controller. Charge controller is AN50, 6AWG feed.

I’m tempted to buy an extra and pull a “AvE” on it by dissecting it. LOL

 

[Tecnodave]

Midnight carries breakers manufactured by Carling. Midnight obtained UL listing for them covering conditions for solar use that aren't covered by Carling's listing. Same hardware, different paperwork.

@Hedges,

You might want to check that, boB and Robin tell me that they do not recertify the Carling breakers, but the CBI breakers that are sold as Midnight MNPV have been recertified to 150 volts DC and that is why they have a 120 volt rating and a sticker with the Midnight 150 volt recertification lable.

The Carling breakers are certified by Carling technologies to 120 VAC and 150 VDC

 

[Hedges]

That sounds correct. I remember looking up CBI specs.
I mixed things up in my head; didn't realize they similar range of breakers from two vendors.

 

[Hedges]

Sorry. I should have been more clear.

I have 8 100W panels 4S2P and have two dual 10A breakers as a shutoff, one for each string. Around 88V VOC and 5.6A each string. 10A fuses on panel pos(+), 60A fuse at battery from charge controller. Charge controller is AN50, 6AWG feed.

I’m tempted to buy an extra and pull a “AvE” on it by dissecting it. LOL

2s, 5.6A per string and 10A breakers, won't have a problem with tripping due to backfeed. OCP not required.
The only thing I could imagine going wrong is if one string was shorted, other backfeeding into it, and you manually opened the breaker being backfed. It might sustain an arc.

 

[Tecnodave]

That sounds correct. I remember looking up CBI specs.
I mixed things up in my head; didn't realize they similar range of breakers from two vendors.

Cant remember every thing in the right place....

The Carling breakers are panel mount and are used in the DC-15 distribution box as well as others
The CBI breakers are din rail and used in all the combiners and the baby boxes and big baby’s both PV and AC breakers

The CBI breakers allow you to put string breakers and AC breakers in the same box.

 

[12VoltInstalls]

OCP not required.

the fuse at the strings pos(+) makes me feel warm and fuzzy, though

The only thing I could imagine going wrong is if one string was shorted, other backfeeding into it, and you manually opened the breaker being backfed. It might sustain an arc.

Point taken.
I suppose if there was a short like that and I opened the breaker I’d think it would be noticeable and at least I’d be standing right there.

 

[Hedges]

the fuse at the strings pos(+) makes me feel warm and fuzzy, though

2-pole disconnect is good to make it safe before working on.
I turn off rotary DC switch at GT inverter, lift touch-safe fuse holders and/or unplug MC cables at array.
I use DMM to check voltage before and after each step, observing it goes from Vmp to Voc, so I know I've interrupted current and then made the circuit cold.

Point taken.
I suppose if there was a short like that and I opened the breaker I’d think it would be noticeable and at least I’d be standing right there.

Let go and turn off the other breaker!

 

[Keith Moreau]

Sorry I may have posted this same question a couple times. I currently have the huge Carlling / Midnite Solar MNDC Panel Mount breakers mentioned here. Is a breaker on both the positive and negative battery terminals recommended or just optional, I've seen builds with a single pole and double pole breakers. Thanks much!

 

[HRTKD]

Sorry I may have posted this same question a couple times. I currently have the huge Carlling / Midnite Solar MNDC Panel Mount breakers mentioned here. Is a breaker on both the positive and negative battery terminals recommended or just optional, I've seen builds with a single pole and double pole breakers. Thanks much!

Optional. Most installs seen here on the forum have OCP only on the positive leg. This is for between the solar charge controller and the common bus bar as well as between the common bus bar and the battery.

Dual pole breakers are common between the PV and the solar charge controller. Necessary? I don't know, but that's what I'm using.

 

[Tecnodave]

On the hot side only, no need to disconnect the grounded side.

 

[Keith Moreau]

On the hot side only, no need to disconnect the grounded side.

Well, I don't think I have a 'grounded' side, I haven't grounded the negative bus bar to anything. It's a stationary set of batteries. So I guess it is 'floating'. Is that OK?

 

[Tecnodave]

Well, just what code set are you working under?

The NEC clearly says that the return line is to be grounded. Period.

That is the DC side as well as the AC side.

Only the hot side needs to be switched, breakered, fused....

 

[Keith Moreau]

@Tecnodave NEC 2017 code for now which is the California 2019 Electrical Code. Let me look at the code again but yes if negative is grounded then that makes sense to just have the breaker/disconnect on the positive. Thanks for the input.

 

[Tecnodave]

One of the reasons for grounding is that takes unusual voltages to ground. If you do not have a ground reference then your whole system could float at any voltage above ground. What would happen if say a 23,000 volt power line fell on your solar array. If you were not grounded anything you touch would be at 23,000 volts and you get to see bright lights in one big flash then its all over. That is the whole reasoning in grounding. Yes if you are grounded and that power line fell there will be damages to your system, It would be totaled but the grounding has just given you another chance at seeing the sun one more day. Power company insurance will buy you a new whatever they destroyed but it will not buy you a new life!!

Others on this forum have stated that the solar system does not need to be grounded. If my inspectors were to visit that persons house it would be red tagged and you will not be allowed on that property until the violations are cleared, if you are adamant, a court order will keep you off your property until a licensed, bonded, insured contractor removes all out of compliance items. At your cost, and no the items will not be returned to you, they will be destroyed.

 

[Drizzt321]

Hope it's OK to resurrect this thread, I'm also facing a bit of confusion with these DC circuit breakers. They're basically straight-through if I consider it to be a "straight through" continuous wire for pos/neg to from the Source (higher potential) to the Load (lower potential). So assuming breaker has a '-' neg on the left, and '+' pos on the right, run the neg (black) wire from the PV or BATT into the top left, and out the bottom left to the neg input on the SCC, and the pos (red) wire on the right side of the breaker.

Also, would it be OK to "flip" it upside down (so source input is on the bottom) to make it easier to run wiring? I have a good label maker so plan on labeling everything quite well.

So from PV to charge controller, this would be correct

- PV +
-    +
-    +
-    +
-    +
------
|    |
| CB |
|    |
------
-    +
-    +
-    +
-    +
 SCC

And for the Battery, this would be correct

-BATT+
-    +
-    +
-    +
-    +
------
|    |
| CB |
|    |
------
-    +
-    +
-    +
-    +
BUS BAR

 

[timselectric]

Hope it's OK to resurrect this thread, I'm also facing a bit of confusion with these DC circuit breakers. They're basically straight-through if I consider it to be a "straight through" continuous wire for pos/neg to from the Source (higher potential) to the Load (lower potential). So assuming breaker has a '-' neg on the left, and '+' pos on the right, run the neg (black) wire from the PV or BATT into the top left, and out the bottom left to the neg input on the SCC, and the pos (red) wire on the right side of the breaker.

Also, would it be OK to "flip" it upside down (so source input is on the bottom) to make it easier to run wiring? I have a good label maker so plan on labeling everything quite well.

So from PV to charge controller, this would be correct

- PV +
-    +
-    +
-    +
-    +
------
|    |
| CB |
|    |
------
-    +
-    +
-    +
-    +
 SCC

And for the Battery, this would be correct

-BATT+
-    +
-    +
-    +
-    +
------
|    |
| CB |
|    |
------
-    +
-    +
-    +
-    +
BUS BAR

Yes

 

[timselectric]

Also, would it be OK to "flip" it upside down

I would not recommend this. Unless you are sure that you will be the only person to ever need to shut it down, in an emergency.

 

[Drizzt321]

Finally, the light bulb goes on! Thanks!

I would not recommend this. Unless you are sure that you will be the only person to ever need to shut it down, in an emergency.

Hm.. That's a fair point. Probably would only ever be me, and I do have a higher rated Class-T fuse for at the battery as a juuuust in case. But I'll have to think about it more, you make a good point.

 

[Hedges]

Polarity +/- marks on a DC circuit breaker are important; they relate to which direction of current flow it can interrupt successfully.
I wouldn't rely on an ASCII schematic to document it. Better start with a picture of the actual breaker.

You can get non-polarized breakers. Some have AIC ratings suitable for batteries. Voltage requirements for the PV side can be pretty high, depending on your array.

 

[Drizzt321]

Polarity +/- marks on a DC circuit breaker are important; they relate to which direction of current flow it can interrupt successfully.
I wouldn't rely on an ASCII schematic to document it. Better start with a picture of the actual breaker.

You can get non-polarized breakers. Some have AIC ratings suitable for batteries. Voltage requirements for the PV side can be pretty high, depending on your array.

What I was having trouble realizing, for a bit, was that it was really "straight through" on either side, I saw pictures with - + and then + - on the bottom, which was confusing to me.

The breakers are just like pretty much all the rest of the pictures I've seen here,

https://imgur.com/o2Q4hVk