Need Guidance on Solar Panel DC Breakers

[Henderson]

Hi all. I’m hoping for some guidance from this forum on the type of double pole breaker I should be using for my solar setup. I have 2x EG4 6500EX 48V inverters and will be using 32x 505W panels. The panels are being configured in 4x 8S strings, one string for each of the MPPTs of each EG4 inverter. The panels I am using have a Voc and Vmpp of 51.9V and 43V respectively. The panels also have Isc and Impp of 12.35A and 11.75A respectively.

Would a 500V breaker be sufficient given that the Vmpp is 43V, which times 8 would be 344V and the total VoC would be 415V? Where I live we don’t have winter so I don’t have to worry about cold temperatures and how that impacts voltage from the panels. I’m looking at the Taixi breakers from AliExpress. Here’s the link below- are these breakers suitable for my application? And if so, should I be selecting the 500V or 1000V breaker. And should I be using the 20A or a different current rating. Thanks in advance for your assistance.

https://www.aliexpress.com/item/100...artLeaderboard_6000504635794.1005002635067125

 

[OzSolar]

Would a 500V breaker be sufficient given that the Vmpp is 43V, which times 8 would be 344V and the total VoC would be 415V? Where I live we don’t have winter so I don’t have to worry about cold temperatures and how that impacts voltage from the panels.

Always use Voc when sizing breakers and inverters. 8 x 51.9 = ? Then you have to use your record cold temp, not your typical temp to calculate what your array Voc can get up to.

 

[ArkCabinMan]

I’m looking at the Taixi breakers from AliExpress. Here’s the link below- are these breakers suitable for my application?

Only use cheap breakers if/when:

1. You are very confident in the response time of your local fire department and,
2. Your homeowners insurance policy does not exclude coverage for fires started by solar equipment.

 

[On_The_Road]

I picked up some din mount IMO DC isolators.

I used to use breakers and now I know the way. Wonder what else I'm screwing up. ?

 

[TorC]

@ArkCabinMan If I had to be real cheap for a system I'd consider a cheap breaker in a place it couldn't ever be needed as more than a switch and a breaker mounted better than a true switch, but that's a risky road to start down.

 

[OffGridForGood]

I have 2x EG4 6500EX 48V inverters and will be using 32x 505W panels.

High power system, lots of expensive parts, don't go cheap on the Isolators/ Breakers/ Fuses/ Wire items.

 

[Henderson]

Thanks everyone for your input. Its very much appreciated. I'll look into some other options. In terms of one of the questions I asked, how should I size the breaker for the PV panels. My total voc for the panels would be 415.2v and isc of 12.35amps. What size breaker is best practice? Thanks.

 

[TorC]

I'd put in a 15A breaker. Only required if you have three parallel systems, but if you want resiliency in case of SCC failure, the breakers mean you could rearrange three SCCs with two strings to two SCCs with three strings for many systems, as long as you don't exceed the SCCs panel Isc rating.

 

[Henderson]

I'd put in a 15A breaker. Only required if you have three parallel systems, but if you want resiliency in case of SCC failure, the breakers mean you could rearrange three SCCs with two strings to two SCCs with three strings for many systems, as long as you don't exceed the SCCs panel Isc rating.

Thanks TorC but I'm not sure that I follow. Forgive, I'm still quite new to this. What I have is 2x EG4 6500EX inverters. Each inverter has 2 MPPTs so that's a total of 4 MPPTs. I will have each MPPT configured as a single string of 8 panels in series each.

 

[handinpalm]

Good practice is to derate your Vmax on breaker by at least 20% of the Voc, if operating below -40F, derate >25%. Here is a good guide from Eaton, see page 8.

Eaton Guide

 

[TorC]

@Henderson, in that case you don't actually need the breakers as breakers. The time breakers are required is when you have three or more strings wired in parallel. The blocking diodes in each panel are sufficient to hold against one other string in a fault condition, but not two strings. Thus the breakers to protect against that short.

With each string separately wired to its own MPPT input, only that string needs to be considered as regards a short in one of the panels.

 

[Henderson]

Good practice is to derate your Vmax on breaker by at least 20% of the Voc, if operating below -40F, derate >25%. Here is a good guide from Eaton, see page 8.

Eaton Guide

Awesome, thanks handinpalm.

 

[Henderson]

@Henderson, in that case you don't actually need the breakers as breakers. The time breakers are required is when you have three or more strings wired in parallel. The blocking diodes in each panel are sufficient to hold against one other string in a fault condition, but not two strings. Thus the breakers to protect against that short.

With each string separately wired to its own MPPT input, only that string needs to be considered as regards a short in one of the panels.

Ok thanks TorC. Appreciate the guidance.

 

[OffGridForGood]

Required or not, I recommend a fused disconnect on each string between the PV and the inverters. When you want to do some work on the system during sunlight hours, you can easily (and safely) shut down the incoming DC from the PV stings by opening the disconnect. By having it fused, a dead short anywhere between the PV string and the inverter will cut off the circuit and limit damage.

 

[Henderson]

Required or not, I recommend a fused disconnect on each string between the PV and the inverters. When you want to do some work on the system during sunlight hours, you can easily (and safely) shut down the incoming DC from the PV stings by opening the disconnect. By having it fused, a dead short anywhere between the PV string and the inverter will cut off the circuit and limit damage.

Yes, totally agreed. Thank you. The breakers I was looking at (Tomzn from aliexpress) was more for that purpose, isolation more so than for OCP. I tend to tinker alot so would definitely want an easy way to disconnect the panels.

 

[OffGridForGood]

I am not a fan of breakers for this application between the PV and the inverter, I use fuses, in a fused disconnect. If you pick the equipment carefully ie a disconnect that is rated to handle 30A even if you start out needing a smaller fuse say 15A to start, this leaves the option open later you can change the fuse (up to the limit of the disconnect) to increase the amperage, say if you were playing with the PV stings/added a couple panels and needed to increase the amperage rating. Fuses are both fast acting, and inexpensive. A breaker can allow considerable over current before it opens, and this can be a problem in this application in my opinion.

 

[OffGridInTheCity]

In the beginning I bought some cheap breakers similar to this - https://www.amazon.com/ZOOKOTO-Circuit-Breaker-Trolling-Inverter/dp/B076FVV287/ref=sr_1_9 I used one as power on/off to my iCharger X8 but after ~20 on/offs, it partially failed and wouldn't shut off. Yikes!

In my home solar system I use Midnite Solar DC ETL rated breakers like this - https://www.amazon.com/MidNite-Solar-MNEPV15-Midnite-Solar-MNEPV15/dp/B007IAAGPE/ref=sr_1_4 Midnite Solar makes a range of breakers that are pretty reasonably priced. After 4 years of operation, they all continue to work.

So one risk is that cheap breakers may not hold up if you use them on/off very often and may either fail or partially fail. While I understand that you shouldn't use breakers as 'regular' on/off switches, 20 on/offs over a couple of years is possible if you're working/expanding your solar system. So in general, I'd recommend UL/ETL breakers for serious situations.

 

[Zwy]

In the beginning I bought some cheap breakers similar to this - https://www.amazon.com/ZOOKOTO-Circuit-Breaker-Trolling-Inverter/dp/B076FVV287/ref=sr_1_9 I used one as power on/off to my iCharger X8 but after ~20 on/offs, it partially failed and wouldn't shut off. Yikes!

In my home solar system I use Midnite Solar DC ETL rated breakers like this - https://www.amazon.com/MidNite-Solar-MNEPV15-Midnite-Solar-MNEPV15/dp/B007IAAGPE/ref=sr_1_4 Midnite Solar makes a range of breakers that are pretty reasonably priced. After 4 years of operation, they all continue to work.

The Midnite Solar breakers are only rated to 150VDC. EG4 inverters can have panels in series to 450VDC working limit. The advantages of the high VOC rating of the EG4 would be limited by the use of a Midnite Solar breaker.

So one risk is that cheap breakers may not hold up if you use them on/off very often and may either fail or partially fail. While I understand that you shouldn't use breakers as 'regular' on/off switches, 20 on/offs over a couple of years is possible if you're working/expanding your solar system. So in general, I'd recommend UL/ETL breakers for serious situations.

I have found the IMO disconnect is rated to 32A and 600VDC. IP66 rated, this is the way to go for a PV disconnect at a ground mounted array. Then either a breaker or fuse after the disconnect.