PV to THNN/ THWN connection

[bob-n]

I don't know about MC4 crimp tools, but there are some respectable Chinese crimp tools on the market now in the $20 price range.

[Mike90250]

MC4 connectors work well when installed properly. Of course, the problem is, installing them properly without expensive crimp tools

[Ddwarf]

What about using an MC4 connection - would they work better? Can they be used in a junction box?

[Mike90250]

............... I ended up wiring it myself with a simple junction box per the three line. I used wire nuts..........

Please consider replacing them with split bolts. Wire nuts will be seeing a hours long continuous load and can often overheat in a solar application,

[PVAndy]

Interesting, I just went through this exact process myself. Ground mount with Rapid shut down. I contacted a solar installer to do the final hookup and they wanted to add dc disconnects at the array(would need 3 disconnects for 3 strings). When I questioned the need, they insisted that "it's just how it's done". I ended up wiring it myself with a simple junction box per the three line. I used wire nuts.

Inspector said it was fine. With RSS the need for one DC disconnect is questionable, why would I want another set??

Remind the inspector that an MC4 connector is rated as a non load break DC Disconnect

Andy

[Ddwarf]

Interesting, I just went through this exact process myself. Ground mount with Rapid shut down. I contacted a solar installer to do the final hookup and they wanted to add dc disconnects at the array(would need 3 disconnects for 3 strings). When I questioned the need, they insisted that "it's just how it's done". I ended up wiring it myself with a simple junction box per the three line. I used wire nuts.

Inspector said it was fine. With RSS the need for one DC disconnect is questionable, why would I want another set??

[badwithusernames]

Well, after a tense few emails we had a discussion that ended favorably for me. In the end he agreed that the manual DC disconnect at the barn would serve no real purpose, and I get to have a junction box after all.
Thanks again
SD

[nwdiver]

Thank you for the input. I agree that having multiple points of shutoff is pointless. With the inverter based shutoff, and Tigo RSS, you can shut it down at the panel end, or the inverter end; having a disconnect mid way serves what purpose?
I have forwarded a bunch of info to my inspector and am waiting for a response. PITA, as he's the kind of guy that doesn't like to be told what to do, so I have to carefully choose my words. I know if I tell him the disconnect doesn't need to be there he'll want me to install three of them, just to be a dick.
SD

??? You have RSS AND he wants an additional DC disco ? Jeeze that's idiotic. Does he know about the RSS?

[badwithusernames]

Thank you for the input. I agree that having multiple points of shutoff is pointless. With the inverter based shutoff, and Tigo RSS, you can shut it down at the panel end, or the inverter end; having a disconnect mid way serves what purpose?
I have forwarded a bunch of info to my inspector and am waiting for a response. PITA, as he's the kind of guy that doesn't like to be told what to do, so I have to carefully choose my words. I know if I tell him the disconnect doesn't need to be there he'll want me to install three of them, just to be a dick.
SD

[bcroe]

With my 2 inverters inside the shed, the disconnects are on the outside. My installer broke
only the plus (hot) side of the DC run from the array. Unfortunately while disconnected and
repairing an array wire, I must have brushed something against the frame and blew the
ground fault fuse in the inverter. This caused some distress and a service call.

The moral of this story is to break BOTH DC leads from an array with the disconnect switch.
Here can be seen a second DC disconnect box added, for enough poles to break all DC
wires from the array. The smaller boxes are AC disconnects. Bruce Roe

PVdiscon.jpg

[nwdiver]

DC disconnect can be dangerous

And pointless. A DC disconnect at the inverter or charge controller is probably a good idea so you can de-energize your equipment but that's usually built into the inverter. I've seen ground mounts with DC disconnects mounted at the array. Why? It's not going to de-energize the array. If you need to stop current then open the disconnect at the inverter or CC. Adding to the pointlessness is if you have optimizers or rapid shutdown. 'LOL' there's solar arrays out there with like 4 different ways to shut it down.

[bob-n]

It's your choice what you install. nwdiver makes a good point that simpler is better.

DC disconnect can be dangerous because of stored energy in cable inductance and the arc possible when you disconnect. That switch is rated for DC disconnection and high voltage, so should be fine. It looks like it was designed for solar use. You're right that you need to find the right enclosure. If you want the switch lever accessible from outside the box, you also need the right front mounting. That may mean a large round hole or something more complex. It's tough to tell from the web page. If it is not accessible from outside the box, it may not meet the inspector's requirement.

I just thought of one alternative that you might not have considered for joining cables. There are low-cost crimps that will make a solid connection between cables. I recently bought a low-cost imported crimp tool with ratchet mechanism and machined hardened jaws and it works remarkably well, especially compared to the old-fashioned combination tools. Crimps are probably equal in performance and dependability to the Burndy device mentioned above, but cheaper.

That said, the Burndy connector is reusable, but you won't want to reuse the same wire stub. With the Burndy connector, the DC disconnect switch you found, or any screw terminal, you need to torque the bolts per specification. A Harbor Freight 1/4" torque wrench with 1/4" hex socket and screwdriver bit is fine for that.

[nwdiver]

he was not happy that the plans didn't show a dc disconnect on the barn.

*sigh* .... I don't know why people insist on adding more things that can fail into flames...

The Greatest Debacle in Solar PV: Australia’s Rooftop DC Isolator Fires

[badwithusernames]

Searching around for different types of connectors and hardware, I found this:

https://www.factorymation.com/SI25-PM64R-6

One knob to shut down all three strings, it solves my splice problem, and I think it will make the inspector happy. He was here yesterday to insect all of the conduit/ device locations prior to pulling wire, and he was not happy that the plans didn't show a dc disconnect on the barn. It's IP66 rated, so I would just have to mount it in the right weathertight box
SD

[Ampster]

Why not a transition/combiner box?

I think that is a given, as well as appropriate breakers which might serve as the connection devices. In my case it was one string so a waterproof junction box, some grommets a drain hole, and Burndy connectors is all I needed to transition from PV wire to THNN..