Swapping out failed inverter without DC shutoff to panels

[barneyfoot]

I'm going to swap out a failed Xantrex 4KW inverter with a new Sunny Boy 3.8KW. There is no DC shutoff to the panels.

Can I safely do the swap using existing DC connectors since I won't be working with exposed wire? The array is rather large so there's no easy way to cover it from sun.

Of course there is AC shutoff that I will be using.

Attached photo of the existing DC connectors (both to old and new). My other Xantrex was previously replaced by a solar professional so I plan to use his install for reference.

Thanks in advance.

Note - couldn't upload attachments so photo links are here:

old

https://drive.google.com/file/d/1pbKQ1PvlrfD0mze8GGSDgJy3_y_udg90/view

new

https://drive.google.com/file/d/1pg1Xxw6hK3wbjgC7AryeXgdMnYoOOcLd/view

[peakbagger]

If I doubt, do it at night with a headlamp.

[solarix]

1) Turn off the AC.
2) Go on roof and disconnect one panel from each string.
3) Measure voltage on DC conductors at inverter to make sure you got step 2 correct.
4) Swap inverters.
5) Reconnect the array.
6) Measure voltage on DC conductors at inverter to make sure you got step 5 correct.
7) Turn on AC and check inverter for correct operation.

or Buy an expensive pair of electrician's gloves and get-r-done.

or Just carefully tape the DC conductor's ends as you remove them and be careful as you do the swap.

I've done all three methods over the years - and you pays your money, you takes your choice.

[Mike90250]

i'd do it at night, and while I was at it, install a DC shutdown. If the inverter ever fails in a bad way, you have no way to disconnect 3kw of DC feeding the fire

[Ampster]

Fortunately that looks like a ground mount so you have easy access to the panel connectors. They should only be disconnected when there is no load. Shutting down the AC should do that. The switch on the bottom if the Xantrex is a convenient place to do that, but remember to also shut off the breakers at the service panel so there is no power on the AC conductors inside the inverter.

[Mike90250]

Turning off the AC power should (in theory) cease most of the DC current from the solar array. But dealing with a failed unit, it's tough to say that this would be a safe way to proceed. String inverters often run 400-500VDC which, if the inverter is consuming any DC power, will arc (ruin) the connections as you make and break them.

Connecting the new unit, there is very likely some capacitance inside the inverter, which will draw a brief arc as the final connection is made. Again, damaging the conductor.

[Ampster]

That is good advice. If this is the old style Xantrex GT inverter the switch at the bottom is an AC/DC disconnect. Check the manual and the internals to verify.

[barneyfoot]

That is good advice. If this is the old style Xantrex GT inverter the switch at the bottom is an AC/DC disconnect. Check the manual and the internals to verify.

Yeah, it has a switch but I'm assuming the wires from array are live if I'm doing it during daytime right? If so then maybe I just need to work in evening or early morning and git r done.

[Ampster]

Yeah, it has a switch but I'm assuming the wires from array are live if I'm doing it during daytime right? If so then maybe I just need to work in evening or early morning and git r done.

Yes they will be live. The switch should remove load so that you can disconnect a connector at the panel and remove voltage as suggested above. Nightime would be safer if you are not comfortable with determining whether there is any current. Load is what causes current to flow. A clamp DC Amp meter would tell you if there was current flowing. If in doubt, call your electrician.

[Mike90250]

The vintage XW's had an issue with the "bottom of the unit DC switch" failing. There was even a recall on them, a new part was issued and could be swapped in. I was there !

Still does not solve the connecting to the new inverter, which will have input circuits to charge.

[barneyfoot]

1) Turn off the AC.
2) Go on roof and disconnect one panel from each string.
3) Measure voltage on DC conductors at inverter to make sure you got step 2 correct.
4) Swap inverters.
5) Reconnect the array.
6) Measure voltage on DC conductors at inverter to make sure you got step 5 correct.
7) Turn on AC and check inverter for correct operation.

or Buy an expensive pair of electrician's gloves and get-r-done.

or Just carefully tape the DC conductor's ends as you remove them and be careful as you do the swap.

I've done all three methods over the years - and you pays your money, you takes your choice.

This whole thread has been really helpful. I think what folks are saying is that as long as both inverters have DC shutoff (which they do) I should be able to swap without issue. As long as there's no load then I'm fine. I'll be sure to test with a clamp meter. Will probably pick cloudy day or low light morning evening just to be safe.

My initial post was due to concern about not having a DC shutoff switch between array and inverter.

[Mike90250]

Most clamp on meters are pretty lame below an amp. half an amp @ 400V is still 200w of HV DC arc. Or it may work out fine

[bcroe]

Put out a big work light and do it in the night. To make that and other work easy, I have regular
120VAC outdoor outlets mounted about every 70 feet along the back. Bruce Roe