PV wire junction question

[BAstereo]

I just finished installing my rooftop PV system.
city inspector came out. Poked a round a but, but never looked in my DC junction box.

In the box my two strings transition from PV to THHN wire.
This is in my garage, not outside. Two condiuts in with PV wire, one out with 4 THHN

I used wire nuts expecting to discuss the correct method with the inspector. But instead he just signed off on the permit, I didn't question this, I want to start the PGE NEM process.

The wire nuts are rated at 600 volts (doesn't specify AC or DC)

I tried searching the forum, but couldn't find the right term. I either got super wide results that didn't help or super narrow results that also didn't help.


TL;DR
How do I splice DC wires with a max circuit voltage of 480 volts?

[Mike90250]

Generally, I like split bolts better. Wire nuts can loosen and often are NOT rated to actually 10 or 15A year after year. I've seen some with poor contacts heat up so much that the insulation melts off the spring - whoops !

[BAstereo]

I could do split bolts.

Now that I think about it I do have some extra MC4 connectors, maybe I'll just use those?

[emartin00]

Wire nuts are technically acceptable, but definitely not the best option.
Split bolts will work fine, but require a lot of extra work with taping. And there's a technique to the taping as well.
I would suggest a mechanical multiport connector such as the Burndy Unitaps: https://www.amazon.com/Burndy-BIT4-I.../dp/B00CBK6420

[NewBostonConst]

I have seen failures on all of these options so I still use wire nuts and just tape them.

[ButchDeal]

I have seen failures on all of these options so I still use wire nuts and just tape them.

how is the tape going to help with maintaining contact or wire nuts that are not actual rated for the amperage?

On of the best options is to do the junction at a SolaDeck (or similar) with terminal blocks.

https://www.youtube.com/watch?v=pqU0685Ax60

[NewBostonConst]

Wire nuts usually fail because they are not on securely. If you can tape the wires together and then install the nut and tape over it again and then still have them working after you are done they usually last. The tape holds the wire in place making a good connection for a long time while sealing out moisture. The wire nuts purpose is to hold the wires together and not to carry all the current. If the wire nuts are melting it is because of the connection not being secure to each wire causing heat.

As with anything if it is used wrong it will fail. You need to look at the UL listing for the wire nuts and see what size wire it can hold and how many.

I have seen terminal blocks corrode due to dissimilar metal problems and wires coming loose, have seen split nuts fail due to the tape being compromised and wires coming loose.....nothing is 100% and usually lies in the hand of the person using them.

Wire nuts have been used for 100 years with much success, are cheap and certified. Wire nuts are likely the most used connection in residential. With that many being used you are going to see failures there is no way around it, but I bet they have a higher success rate overall.

I do agree wire nuts are not good for thicker wire.

SolaDeck seems like a lot of work. He took an hour on the ground and he fast forward through some of it. Guessing it will take twice as long on the roof.

To each his own.

[ButchDeal]

Wire nuts usually fail because they are not on securely. If you can tape the wires together and then install the nut and tape over it again and then still have them working after you are done they usually last. The tape holds the wire in place making a good connection for a long time while sealing out moisture. The wire nuts purpose is to hold the wires together and not to carry all the current. If the wire nuts are melting it is because of the connection not being secure to each wire causing heat.

Wire nuts on DC tend to fail because they have higher resistance. Further even without a lot of resistance, on a hot roof you tend to have a lot of thermal expansion loosening things, which causes more resistance and eventually failure.
There are many terminal block solar solutions.

I have seen terminal blocks corrode due to dissimilar metal problems and wires coming loose, have seen split nuts fail due to the tape being compromised and wires coming loose.....nothing is 100% and usually lies in the hand of the person using them.

Use the proper terminal block for the wires and you shouldn't have this problem. It is why there are recommended practices, especially with high voltage DC which can more easily cause a fire

Wire nuts have been used for 100 years with much success, are cheap and certified. Wire nuts are likely the most used connection in residential. With that many being used you are going to see failures there is no way around it, but I bet they have a higher success rate overall.

primarily used for 100 years on lower amp AC.

Go to higher amp, higher voltage DC and you start to get resistance which means heat, which means failure. And with DC, on a string system, that could mean fire.

I do agree wire nuts are not good for thicker wire.

SolaDeck seems like a lot of work. He took an hour on the ground and he fast forward through some of it. Guessing it will take twice as long on the roof.

To each his own.

He is giving a lecture. in practice it doesn't take that long to install but there are other rail options, The Soladeck just gets you into the attic as well.
It works well in combination with a combiner as well. In my case I have a soladeck on the roof with combiner in the attic, back to back. The Soladeck is just there to get the wires into the attic without leaking and the wires are combined and change in the combiner.

[littleharbor]

Soladeck comes in a combiner configuration as well.https://www.altestore.com/store/encl...EaAuXAEALw_wcB

[Paul Land]

I just finished installing my rooftop PV system.
city inspector came out. Poked a round a but, but never looked in my DC junction box.

In the box my two strings transition from PV to THHN wire.
This is in my garage, not outside. Two condiuts in with PV wire, one out with 4 THHN

I used wire nuts expecting to discuss the correct method with the inspector. But instead he just signed off on the permit, I didn't question this, I want to start the PGE NEM process.

The wire nuts are rated at 600 volts (doesn't specify AC or DC)

I tried searching the forum, but couldn't find the right term. I either got super wide results that didn't help or super narrow results that also didn't help.


TL;DR
How do I splice DC wires with a max circuit voltage of 480 volts?

600v or 6000v ac/dc same its about wire size . Dont worry be Happy!!!!

[SunEagle]

600v or 6000v ac/dc same its about wire size . Dont worry be Happy!!!!

Uh. NO that is not true.

Most low voltage wiring devices are rated for 600v but not 6000v or even 1000v. You will need equipment (terminations, wire insulation, wire splicing devices) rated for 15kv to handle 6000v since the next smaller rating is 5000v. Going with wire insulation or splicing devices with a lower rating then they see will end up in failure and possibly fires.

[ButchDeal]

Soladeck comes in a combiner configuration as well.https://www.altestore.com/store/encl...EaAuXAEALw_wcB

Yep but i didnt want the fuses ontop of the roof under a pv module...

[Paul Land]

Uh. NO that is not true.

Most low voltage wiring devices are rated for 600v but not 6000v or even 1000v. You will need equipment (terminations, wire insulation, wire splicing devices) rated for 15kv to handle 6000v since the next smaller rating is 5000v. Going with wire insulation or splicing devices with a lower rating then they see will end up in failure and possibly fires.

I think thats what i mean you just said it better

[GRickard]

You can get the terminals that you find in the Soladeck box. Just google a Weidmuller WDU6. Order the number of terminals you need, you will also need a piece of din rail, an end barrier (I think it's WAP2.5), and two end anchors (WEW35-2).

...Or you could just use a Marathon 12 point terminal block with ring lugs. Either of these options will need to be mounted in an enclosure.

Greg Rickard
Electrical designer by day.

[BAstereo]

Well, this got side tracked.

I am not redoing my roof penetrations to add a soladeck.

My connections are not on or even within 2 feet of the roof surface. The junction box is in the attached garage.

I hate split nuts, mostly for the tape. But, I hate spending an extra $60 for the Burndy Unitaps. So I will likely just do split bolts. If the Burndy unitaps was the right connector the decision would be easier.

Unless, the MC4 connectors (just like on each panel) are ok inside a junction box. I already have them and they are xleaner than split bolts and tape.

I understand that insulation requirements for AC vs DC are about the same. But it seems that terminations and connections are more important with DC

Also, I have two strings. They will see a max of 10a and 7a, so not a huge current load.


Also, on a side note. I got my permission to operate in 3 days! Submitted Monday evening, received the PTO email Wednesday night.