pv dc disconnect

[chrisw5]

Quick question here: I'm getting my solar ready to install and was wondering about dc disconnects. I will have two different arrays installed on the roof. 1 string of 8 in series of 305W panels (Voc of 40V) and another string of 6 in series 305W panels (also each at Voc of 40V). I have a Sol-Ark 5k inverter with 2 solar panel inputs (MPPT1 and MPPT2). Solar Panel String 1 will feed MPPT1. String 2 will feed MPPT 2.

The closest direct path to my inverter in the garage will be through the roof. I will be using a Soladeck enclosure to feed the dc wire through the roof into a flexible metal conduit that will terminate into a metal wireway to feed into the Sol-Ark.

From what I have gathered, since I'm not paralleling any panels, no combiner box is needed, nor fusing. The Sol-Ark has a pv dc disconnect integrated into the unit. Do I need a pv dc disconnect between the inverter and the panels? If so, is there harm in putting a dc disconnect inside in the garage? I have seen some examples mainly in Australia where they require DC isolators where these types of disconnects have failed or caught fire due to shorts due to water penetration of the enclosure.

My locality does not require rapid shutdown, and I'm not planning on installing any automatic rapid shutdown device.

I already have an IMO dc disconnect, so I'm not sure if there would be benefit to installing it or not. With the amount of voltage in my system, I'm a little leery of any additional contact point that could pose a potential failure point. Thoughts?

 

[OffGridInTheCity]

If you have a way to disconnect the incoming PV at the SolArk - then that's all you need. The main points of 'disconnects' are
1) Code / quick disconnect outside - doesn't apply to you per your comments
2) Multiple combined strings case - its nice to be able to turn on/off each string for diagnosis at the combiner - you can do this at the SolArk? - e.g. you have a breaker for each string?
3) A local breaker at the main power panel (inside typically) to disconnect PV power for safetly when working on things.

If you can disconnect each string at the SolArk - then it sounds like you have it covered

 

[chrisw5]

Thanks! It appears the Sol-Ark’s pv dc disconnect only isolates the inverter from the pv inputs, so if I needed to move, isolate, or reconfigure mppt inputs this could not be done safely without an additional dc disconnect between panels and inverter, yes?

 

[OffGridInTheCity]

Thanks! It appears the Sol-Ark’s pv dc disconnect only isolates the inverter from the pv inputs, so if I needed to move, isolate, or reconfigure mppt inputs this could not be done safely without an additional dc disconnect between panels and inverter, yes?

Sounds correct and to help with communication, let me provide a visual. I could be misunderstanding and this is up to you in any case

In my system I have 3 set's of 15 panels. Each set is combined outside to a pare of wires carrying 100v@45a routed inside to it's respective charge controller. But just before they they go into the charge controller (SolArk in your case) I have a circuit breaker on each set so I can shut off the incoming power - either an individual array or all of them. Here's a pic of the 3 circuit breakers (1 for each array) and the 3 Midnite Classic 150 Charge Controllers.

I'm suggesting that you should have 2 circuit breakers - 1 for each string - before they enter the SolArk.

 

[Bryan WV]

Sounds correct and to help with communication, let me provide a visual. I could be misunderstanding and this is up to you in any case

In my system I have 3 set's of 15 panels. Each set is combined outside to a pare of wires carrying 100v@45a routed inside to it's respective charge controller. But just before they they go into the charge controller (SolArk in your case) I have a circuit breaker on each set so I can shut off the incoming power - either an individual array or all of them. Here's a pic of the 3 circuit breakers (1 for each array) and the 3 Midnite Classic 150 Charge Controllers.
View attachment 66118
I'm suggesting that you should have 2 circuit breakers - 1 for each string - before they enter the SolArk.

I've yet to build out a system but have acquired most of the components. @chrisw5 had almost the same question but I don't think my Sungoldpower SP6548 has the same features as the SolArk system. Please see the attached "diagram" (I may have tried to stuff too much into it) and let me know any recommendations for a PV DC Disconnect or if one is even needed. I'm planning to use 10g wire for all of the PV wiring. Any criticism or guidance is appreciate from you, or anyone else that might chime in. Thanks in advance.

 

[rmaddy]

let me know any recommendations for a PV DC Disconnect or if one is even needed.

You should have a PV disconnect per array. Since you have two MPPT inputs each with their own array, use 2 disconnects.

For your 5S2P array run the final two wires (one neg, one pos) into one PV disconnect.
For your 3S array run the two wires into the other PV disconnect.

For the PV disconnect you need a 2-pole DC breaker rated for the max PV input voltage of your SCC. That's 250V so use a DC breaker rated for at least 250VDC. Choose an amperage that is higher than any current that will go through the wire. The breaker is not to protect anything. It's there to act as a disconnect. It must be able to handle the voltage but you don't want it to trip at any expected amperage.

 

[Bryan WV]

You should have a PV disconnect per array. Since you have two MPPT inputs each with their own array, use 2 disconnects.

For your 5S2P array run the final two wires (one neg, one pos) into one PV disconnect.
For your 3S array run the two wires into the other PV disconnect.

For the PV disconnect you need a 2-pole DC breaker rated for the max PV input voltage of your SCC. That's 250V so use a DC breaker rated for at least 250VDC. Choose an amperage that is higher than any current that will go through the wire. The breaker is not to protect anything. It's there to act as a disconnect. It must be able to handle the voltage but you don't want it to trip at any expected amperage.

Thanks so much. I'm a certified techno-peasant and would ask if there are any "off the shelf" options which would meet my needs? Recommendations are welcome.

 

[rmaddy]

I have no personal experience with it but the following breaker seems to be a common choice:

https://www.amazon.com/dp/B095YFQWHK

 

[OffGridInTheCity]

I have no personal experience with it but the following breaker seems to be a common choice:

https://www.amazon.com/dp/B095YFQWHK

When I first started I was 'worried' about mounting, DIN rail, sizes etc - but it's really pretty easy as DIN rail is DIN rail.
The breakers @maddy suggested mount on standard DIN rail like this - https://www.amazon.com/gp/product/B015E4EIOK/ref=ppx_yo_dt_b_search_asin_title You can just screw the DIN rail to a backer board and snap on the breakers OR....

You can go further and buy a metal box (as in my pic above) that has DIN rail in it OR just add you're own DIN rail to a box. The 'box' is to enclose things instead of having exposed breakers/wires.

 

[Bryan WV]

Choose an amperage that is higher than any current that will go through the wire. The breaker is not to protect anything. It's there to act as a disconnect. It must be able to handle the voltage but you don't want it to trip at any expected amperage.

The link https://www.amazon.com/dp/B095YFQWHK takes me to a 2P 500V DC isolator with 8 different choices of amperages ranging from 10A to 63A. My SCC has a limit of 250V and my highest amperage "should be" 19.68A based on single panel Isc of 9.84A. Amazon has similar DCM's in 2P 250V with in 25A or 32A ratings. I'm not sure my math (or thinking) is right? https://www.amazon.com/dp/B07HG5TYPT is the link .. thoughts ?

 

[rmaddy]

The voltage rating of the breaker needs to be higher than the max PV input voltage of the SCC. If the SCC can handle 250V then you want a breaker that is higher than 250V. It means the breaker can safely handle that voltage. A 250V breaker on a 250V SCC is borderline. It's best to avoid pushing the breaker to its limit all of the time. So the 500V breaker will be "less stressed" since it will never be pushed beyond 250V.

If you panel array will be close to 20A then any breaker rated over 25A would work. But a higher amperage breaker would be better for this use to avoid any possible nuisance trips and to allow for a little growth incase you add more panels. The 63A breaker gives you lots of room to grow. Again, for a disconnect the idea is to pick a breaker that isn't going to trip ever. It's not there to protect the wire like all other breakers and fuses in your system. This one is just for a disconnect. It need high enough voltage so that you are not over stressing the breaker and it needs high enough amperage that it will never trip.

BTW - the link I provided takes you to the 63A version of the 500V breaker. If you choose a different amperage it will be a different ASIN.

 

[Bryan WV]

The voltage rating of the breaker needs to be higher than the max PV input voltage of the SCC. If the SCC can handle 250V then you want a breaker that is higher than 250V. It means the breaker can safely handle that voltage. A 250V breaker on a 250V SCC is borderline. It's best to avoid pushing the breaker to its limit all of the time. So the 500V breaker will be "less stressed" since it will never be pushed beyond 250V.

If you panel array will be close to 20A then any breaker rated over 25A would work. But a higher amperage breaker would be better for this use to avoid any possible nuisance trips and to allow for a little growth incase you add more panels. The 63A breaker gives you lots of room to grow. Again, for a disconnect the idea is to pick a breaker that isn't going to trip ever. It's not there to protect the wire like all other breakers and fuses in your system. This one is just for a disconnect. It need high enough voltage so that you are not over stressing the breaker and it needs high enough amperage that it will never trip.

BTW - the link I provided takes you to the 63A version of the 500V breaker. If you choose a different amperage it will be a different ASIN.

your explanation made sense to me. My primary objective was to simply have an inexpensive way to switch off the power from my array. I'm another step closer to getting this system built. Thank you so much!