Solar Disconnect

[ts8501]

Sorry if this is already covered, but 2 questions related to installing a disconnect switch on my Victron 150/35. 1) install only on the + side? 2) what size disconnect switch should I install? 2022 25-FBT International for reference.

[Tyler2you]

NEC (not applicable to RVs) requires both poles be disconnected. RVIA I believe recommends a dual pole disconnect for RVs as well. There's plenty of folks running a single pole disconnect switch however. You'll have to decide.

As far as which one to use. If you were to go dual, something like this would work:

https://www.bluesea.com/products/703...anel_Mount_40A

And for a single pole switch:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

And if you care to dig into the why of it all, this is a good, but long explanation, so I won't try to paraphrase:

https://forum.solar-electric.com/dis...Comment_396500

[TNOutback]

Somehow, the RV industry has managed to remain self-regulated when it comes to code regulation, which just boggles the mind. NEC DOES apply to RVs - at least certain specific sections of it. Sections of NEC 551 pertains to RVs in particular, but somehow the industry has not adopted code related to PV systems which is found in a separate section of code. I think (?) it is Article 613 that pertains to solar PV system safety, and here NEC calls for simultaneous disconnect of PV conductors, so a best practice would be a double throw DC-rated circuit breaker.

[Tyler2you]

Originally Posted by TNOutback

Somehow, the RV industry has managed to remain self-regulated when it comes to code regulation, which just boggles the mind. NEC DOES apply to RVs - at least certain specific sections of it. Sections of NEC 551 pertains to RVs in particular, but somehow the industry has not adopted code related to PV systems which is found in a separate section of code. I think (?) it is Article 613 that pertains to solar PV system safety, and here NEC calls for simultaneous disconnect of PV conductors, so a best practice would be a double throw DC-rated circuit breaker.

I think a part of the problem in this area is that nobody is able to clearly explain, in layman's language, what the potential risks of only disconnecting on the positive side are. Everyone just falls back to the residential code or says it's best practice.

[OutdoorIdaho]

My understanding on the need for a disconnect is to protect the charge controller when batteries are disconnected. If that is the case, then why disconnect both poles? Am I mistaken here?

[AKNate]

Originally Posted by Tyler2you

NEC (not applicable to RVs) requires both poles be disconnected. RVIA I believe recommends a dual pole disconnect for RVs as well. There's plenty of folks running a single pole disconnect switch however. You'll have to decide.

As far as which one to use. If you were to go dual, something like this would work:

https://www.bluesea.com/products/703...anel_Mount_40A

And for a single pole switch:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

And if you care to dig into the why of it all, this is a good, but long explanation, so I won't try to paraphrase:

https://forum.solar-electric.com/dis...Comment_396500

Pay careful attention to the voltage rating of your disconnect if you use series wiring on your solar panels. A series of three sets of panels can be 60V, which far exceeds the rated DC disconnect voltage on many switches.

[Tyler2you]

Originally Posted by OutdoorIdaho

My understanding on the need for a disconnect is to protect the charge controller when batteries are disconnected. If that is the case, then why disconnect both poles? Am I mistaken here?

Yes, the reason most folks install a disconnect is to protect the charge controller when the batteries are disconnected. Another reason is to break the circuit for maintenance.

How you go about implementing the disconnect is where the question comes in. Many will recommend a dual pole disconnect since the residential portion of the NEC requires it.

And others will tell you that as long as your panels are grounded back to the batteries/frame, it's not necessary (ground referenced) and a single pole is adequate. The link I posted above does a decent job of explaining it. I suppose if your battery disconnect is on the negative side, you could have some risk from a short circuit.

[OrangeCrush]

The requirement for disconnecting both legs of the solar panels has been proliferated by Nate of Explorist life who claims it is required by NEC article 690. RVIA specifies electrical requirements for RVs and they only reference NEC 1192 (RV parks) and ANSI Low Voltage spec, neither of which specify any such requirement. I like Nate and he does some good quality DIY videos but he is dead wrong on this be a requirement for RVs.

So why is it required in NEC 690 and should we be doing it anyway? The primary reason is for worker safety (reference linked NEC conference presentation from 2016 - warning, it’s a snoozer). Large home PV installations can have quite high voltages and most modern installations have a ground fault protection device (GFPD) in the negative leg. A worker safety issue can arise if a ground fault is tripped and the negative leg floats. This is also the case with isolated systems. NEC 690.15 states “The PV system disconnecting means shall simultaneously disconnect the PV system conductors from all conductors that are not solidly grounded from all conductors of other wiring systems”. This means GFPD and isolated systems must have a disconnect of the PV- but systems that have the PV- solidly grounded do not. The most common MPPT controllers, Victron, have the PV- connected directly to the battery - so these installs are neither isolated or ground fault protected and the PV- leg is directly connected to ground. Even if NEC 690 applied to RVs you still would not need to put a disconnect in the negative lead as it is solidly grounded. Yes, I am neglecting the fact chassis ground in an Airstream is not earth ground, but unless you are putting several panels in series the voltages we are dealing with are well within safe limits.

There are lots of people watching Nate’s video and clicking on his Amazon links for parts which gives him some kick back. My hat’s off to him as he deserves it for his good quality tutorials. That said, he is dead wrong on this being a requirement and In my opinion it is not necessary, bulky, and possibly less safe for our application. I suggest sticking with AM solar recommendation of a single pole Blue Sea switch of adequate voltage rating on the PV+ leg as close to where it enters the Airstream as possible. Here is a size comparison of the two.

http://www.fltwood.com/perm/nfpa-201...sions/W17.html

[TNOutback]

For what it’s worth, Airstream not only does not provide disconnects for the solar panels, at least in my unit they mounted the Victron solar charge controller horizontally, which is a no-no per Victron. Victron says the controller needs to be mounted vertically to ensure proper ventilation of the unit. Mounting horizontally will result in poor air circulation and potential overheating of the unit. Victron states that if mounting horizontally, a cooling fan should be installed (which Airstream did not do).

[pcskier]

Originally Posted by TNOutback

For what it’s worth, Airstream not only does not provide disconnects for the solar panels, at least in my unit they mounted the Victron solar charge controller horizontally, which is a no-no per Victron. Victron says the controller needs to be mounted vertically to ensure proper ventilation of the unit. Mounting horizontally will result in poor air circulation and potential overheating of the unit. Victron states that if mounting horizontally, a cooling fan should be installed (which Airstream did not do).

It appears airstream is as attentive of manufacturer installation specs for solar controllers, as they were for years with absorption refrigerators on models without a chimney—leaving thousands of owners to deal with poorly functioning fridges and all the macguyvering of fans and baffles to try to rectify it. 🤦*♂️

[TrvlngTinTin]

On my 2023 GB 30QG,
Airstream gaped an additional 3/4 inch under the unit for heat dissipation.
Not per the book but they did take it into account.
Cheers
Tintin

[Air2Dream]

This site offers excellent advise on installing a solar disconnect.

https://www.explorist.life/how-to-wi...trical-system/

[pcskier]

Originally Posted by Air2Dream

This site offers excellent advise on installing a solar disconnect.



https://www.explorist.life/how-to-wi...trical-system/

The info in that video was discussed at length in post #8 on this thread. Explorist is wrong on this case.

[dznf0g]

Originally Posted by pcskier

The info in that video was discussed at length in post #8 on this thread. Explorist is wrong on this case.

I agree. I saw several things (although appropriate for home or high voltage/amperage series systems) that just don't apply to the vaaaast majority of RV applications. Now, if one were to install a 100ish volt series system in an RV, then some of his "requirements" would apply.

[TNOutback]

It doesn’t matter if it is 100 volts or 10,000 volts; it is the current that kills you. A solar PV system putting out 20,30,40 volts is enough to kill a person because it’s the amps that hurt you, not the voltage. As little as 0.1 - 0.2 amps is enough to kill a person, and enough of a reason to install a solar disconnect device. Any time the panels are exposed to sunlight, they are producing lethal amounts of electricity. We should stop right there and wonder why the RV industry has not adopted regulations around solar PV installations?

We can debate whether it is necessary or not to provide a negative disconnect, but it should make you wonder if a dual disconnect device is code for land-based systems, why not an RV system? If you trust Airstream’s wiring proficiency and are confident they have property grounded the system, then maybe a positive disconnect is enough, right? Well, I’ve seen enough of Airstream’s wiring to know not to trust it. The first opportunity I get I will install a dual disconnect device. It may not be necessary, but it’s certainly an extra layer of protection that won’t cost you any more than a Blue Sea disconnect switch.

[fran&frank]

DC breakers are inexpensive and readily available on Amazon and work well as a dual disconnect-- Frank

[Tyler2you]

Or a panel mount since that's usually easier to deal with in a typical RV installation.

https://www.amazon.com/Blue-Sea-7038.../dp/B08C22QHQV

[AKNate]

Originally Posted by TNOutback

It doesn’t matter if it is 100 volts or 10,000 volts; it is the current that kills you. A solar PV system putting out 20,30,40 volts is enough to kill a person because it’s the amps that hurt you, not the voltage. As little as 0.1 - 0.2 amps is enough to kill a person, and enough of a reason to install a solar disconnect device. Any time the panels are exposed to sunlight, they are producing lethal amounts of electricity. We should stop right there and wonder why the RV industry has not adopted regulations around solar PV installations?

We can debate whether it is necessary or not to provide a negative disconnect, but it should make you wonder if a dual disconnect device is code for land-based systems, why not an RV system? If you trust Airstream’s wiring proficiency and are confident they have property grounded the system, then maybe a positive disconnect is enough, right? Well, I’ve seen enough of Airstream’s wiring to know not to trust it. The first opportunity I get I will install a dual disconnect device. It may not be necessary, but it’s certainly an extra layer of protection that won’t cost you any more than a Blue Sea disconnect switch.

Voltage very much does matter when it comes to safety. It makes a huge difference because the current of which you speak is determined by the voltage and your resistance. Current doesn’t just magically flow no matter what. Even a wet hand holding onto a bare wire typically has a resistance of 3kΩ or more. 40V / 3kΩ = 0.01 A, an order of magnitude lower than your number to kill a person. Simply touching a wire with dry fingers, a more likely scenario, your resistance is closer to 1 MΩ. Generally anything under 50V DC is considered touch safe by most codes (some use 60V DC).
AC is different because the published voltage numbers are RMS numbers and the peak voltage is actually over 40% higher. Also AC does much more havoc on your heart.
Just one of my lithium batteries can put out 900 amps, but I can touch the terminals with my bare hands all day long with no ill effects because it’s only 12 V, so I’ll never see that 900 A flowing through my body. The same is true of your 20V solar panel. Yes, the current it can produce is enough to kill you if it were theoretically flowing through you, but it can’t actually produce that current through the resistance of your body at the voltage it’s at.

[dznf0g]

Originally Posted by AKNate

Voltage very much does matter when it comes to safety. It makes a huge difference because the current of which you speak is determined by the voltage and your resistance. Current doesn’t just magically flow no matter what. Even a wet hand holding onto a bare wire typically has a resistance of 3kΩ or more. 40V / 3kΩ = 0.01 A, an order of magnitude lower than your number to kill a person. Simply touching a wire with dry fingers, a more likely scenario, your resistance is closer to 1 MΩ. Generally anything under 50V DC is considered touch safe by most codes (some use 60V DC).
AC is different because the published voltage numbers are RMS numbers and the peak voltage is actually over 40% higher. Also AC does much more havoc on your heart.
Just one of my lithium batteries can put out 900 amps, but I can touch the terminals with my bare hands all day long with no ill effects because it’s only 12 V, so I’ll never see that 900 A flowing through my body. The same is true of your 20V solar panel. Yes, the current it can produce is enough to kill you if it were theoretically flowing through you, but it can’t actually produce that current through the resistance of your body at the voltage it’s at.

I was going to respond to the prior post, but decided I didn't have the energy. Thanks for your response.

[TNOutback]

Originally Posted by AKNate

Voltage very much does matter when it comes to safety. It makes a huge difference because the current of which you speak is determined by the voltage and your resistance. Current doesn’t just magically flow no matter what. Even a wet hand holding onto a bare wire typically has a resistance of 3kΩ or more. 40V / 3kΩ = 0.01 A, an order of magnitude lower than your number to kill a person. Simply touching a wire with dry fingers, a more likely scenario, your resistance is closer to 1 MΩ. Generally anything under 50V DC is considered touch safe by most codes (some use 60V DC).
AC is different because the published voltage numbers are RMS numbers and the peak voltage is actually over 40% higher. Also AC does much more havoc on your heart.
Just one of my lithium batteries can put out 900 amps, but I can touch the terminals with my bare hands all day long with no ill effects because it’s only 12 V, so I’ll never see that 900 A flowing through my body. The same is true of your 20V solar panel. Yes, the current it can produce is enough to kill you if it were theoretically flowing through you, but it can’t actually produce that current through the resistance of your body at the voltage it’s at.

Thank you for that clarification; my statement was poorly worded and you are correct. 12V and even 24V is safe for dry human contact. (I’ve read in safety reports of a case of death at 42 volts.). The Merlin panels output 23.42 volts. If they are wired in series, then you are up to 70 volts and that certainly is in the lethal zone. However, I think they are wired parallel (?), and if so you are in a safe zone unless you are wet or doing something to make you conductive. There is a risk of shock if you accidentally short circuit the connectors or remove them under load. If you have an underlying heart condition, then that mild shock could hurt you. If for no other reason that short circuit protection, it makes sense to have disconnect in place.