Do not disconnect under load

[Bluedog225]

I just put this panel into service keeping my little 100 amp hour 12 volt battle born charged. I’m happy as a pig in mud in my little cargo trailer. Lights, tv, charging the phone, Blade Runner (the original) on the DVD, and a little wood stove.

It tops off the battery by noon.

Until I get the wiring settled, I want to disconnect it when I’m not there. With this low voltage, watts and amps, it is ok to pull the mc4 connectors apart without regard to load? And in full sun? What’s going to happen? A small dc arc? Or do I need to pull the fuses to disconnect the load first? I don’t want to find out through experiment.

Thanks

 

[chrisski]

With what I read about pulling fuses, that is a bad idea. I disconnect 300 watts of panels under load frequently, but I have Anderson plugs that disconnect both at once.

That amount of power can lead to an arc that can tarnish metal, but this happened when I tried crimping a live wire on the 300 watts of panels and shared leads together through my crimping tool.

With a single pole, I’d try to cover the panels first, even a little shade will greatly reduce power, and if that is not possible pull the MC4 apart and see what happens.

 

[AustinMTB]

You're asking about a single panel, right?

I interpret the "under load" part to mean, as part of an installation with many panels. With several panels, I'd definitely have a proper disconnect to interrupt the circuit.

IMO a single panel is probably not an issue, but MC4 connectors are not the easiest connectors to pull apart (and I don't think they are designed to be pulled apart frequently) and a switch of some kind would be a better idea.

 

[Bluedog225]

Anderson plugs on 10 gauge wire instead of mc4? Interesting.

 

[timselectric]

A disconnect switch is designed for this. A connector is not. It won't cost much to do it right. And would make it safe, reliable, and convenient.

 

[automatikdonn]

Here is your answer

https://www.amazon.com/Industrial-Control-Direct-Disconnect-Enclosed/dp/B07S499XRF

 

[Bluedog225]

What do you think of this one?

IMO SI16-PEL64R-2 Enclosed DC Disconnect Switch

IMO SI16-PEL64R-2 Enclosed DC Disconnect Switch IP66, 180x98x107mm, 16A, 800VDC, 2 Pole (Single String), Grey Body With Black Handle

www.solar-electric.com

 

[automatikdonn]

It will probably work great for you. All you have to do is stay under the voltage and amperage limits.

Here is more info on IMO switches

IMO DC Isolators / DC Disconnects

Since its launch, the SI range of TRUE DC isolators has set the benchmark safety standard for disconnection and isolation of the DC panel load in solar applications world-wide. Prior to the introduction of the SI series, AC modified isolators in multi-pole linked form were commonly used with all...

imoautomation.com

 

[OzSolar]

Here's a low cost option at HomeDepot that checks the boxes for DC and the amperage. There probably an even cheaper one that *also* carries the DC rating if you look around some more.

edit: to fix missing word

 

[Bluedog225]

Thanks. I see the AC rating but not DC. I’ll look around.

 

[OzSolar]

Thanks. I see the AC rating but not DC. I’ll look around.

250 VDC

 

[Symbioquine]

250 VDC

View attachment 122254
View attachment 122255

These are great! Very reassuringly solid connections/action. Don't skimp on safety hardware.

 

[pollenface]

I use cheap 1p circuit breakers for my pv isolators. The ones that everyone says not to use

 

[Bluedog225]

Ha! Thanks. There it is, right on the product. But not in the written home depot specs. My bad.

 

[OzSolar]

I use cheap 1p circuit breakers for my pv isolators. The ones that everyone says not to use

If they are QO's from Square D it's perfectly acceptable.

I've built a few load centers for small DC system load center of Square QO breakers and panels. Many years of trouble free service. I recently did some more digging into this and discovered you can use them for up to 125V DC.

Here's the tech note from Schneider.

Are QO load centers suitable for use on a 125V DC application? | Schneider Electric USA

 

[pollenface]

If they are QO's from Square D it's perfectly acceptable.

They're black with red bits on them. That's all i know.

 

[labeeman]

This is much more affordable Solar switch.

 

[SupraSPL]

I disconnect mc4 under load all the time, 20-25 amps, 40 to 50v. I've never seen, heard or smelled a spark or arc so maybe the warnings are for much higher voltage in practice?

 

[Symbioquine]

I disconnect mc4 under load all the time, 20-25 amps, 40 to 50v. I've never seen, heard or smelled a spark or arc so maybe the warnings are for much higher voltage in practice?

My cursory scan of some literature around the topic suggests that lower temperatures and higher humidity (counter-intuitively) reduce the potential for arcing through air. Perhaps you're in a cold damp place @SupraSPL?

 

[timselectric]

I disconnect mc4 under load all the time, 20-25 amps, 40 to 50v. I've never seen, heard or smelled a spark or arc so maybe the warnings are for much higher voltage in practice?

Correct
You need a high enough voltage to create an arc, and enough amperage to sustain an arc.