Looking for "Seq. of Operations" mounting & wiring 6S2P panels on Roof: safety tips & best practice

We have the racking system installed mounted on the roof and electrical devices wired all the way to the battery:

We are ready to move the panels to the roof and start wiring them. I realized that there must be an ideal sequence of operations in this phase and I just don't know what is the best practice and I realize that a mistake could be dangerous working on (6) 400W panels in series. Therefore I am here asking for help:


I thought a lot about this and ended up with more questions than answers. Here are some of the questions it came to my mind, so far:

• Bring panels to roof, connect panels in series and wait for night time to connect last two panels to the system? Or use a blanket during the day to avoid current? I am concerned about connecting the last two leads to the junction box. How concerned should I be by connecting that last PV connection, which will close the system? OR is it not a problem since the DC disconnect will be open?
• Connect first one single panel to the system then check rest of the installation for voltage? Use a multimeter to measure voltage at different points? Sounds safer than connecting (6) in series at once. Would this work? Is this how installers do?
• Make sure all DC Disconnect and DC breakers are off before connecting system. But then which switch/breaker to turn on first? Does it matter the order of operation turning everything on?

Any feedback from actual installers is greatly appreciated. Small chance I am overthinking this process but I really would rather sound stupid than having a fire.

Thanks in advance!

Old_Skewler said:

OR is it not a problem since the DC disconnect will be open?

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This

Old_Skewler said:

Make sure all DC Disconnect and DC breakers are off before connecting system. But then which switch/breaker to turn on first? Does it matter the order of operation turning everything on?

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The detailed order of power up, depends on what equipment you have.
But in general it's, battery, solar, AC power.

I had many of the same concerns as you during my first roof array install, ended up making the final connection just before dark.
My ground mount was wired up mid-day. All connections were made with the disconnect open, everything was double checked and polarity was triple checked, then the disconnect was closed and the batteries started charging faster.

No RSD? That made me _so_ much more comfortable hooking up my roof panels!

timselectric said:

This

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Got it: keep the DC switch open during the install. Any other recommended sequence of operation when mounting & wiring the panels on the roof? Does it matter if I connect main leads to the panel before or after the panels are wired in series? Or none of this matters?

42OhmsPA said:

I had many of the same concerns as you during my first roof array install, ended up making the final connection just before dark.

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How would you do connect your solar array today? Any specific order of operation? Or just keep that DC switch off and connect panels as you bring them to the roof and mount them?

42OhmsPA said:

My ground mount was wired up mid-day. All connections were made with the disconnect open, everything was double checked and polarity was triple checked, then the disconnect was closed and the batteries started charging faster.

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Sounds amazing! Like they say, first time is a bit harder but then down the road things get easier and faster. Is there a correct way to check polarity? Did you check any voltages at any point in the install before turning the DC switch on?

Old_Skewler said:

How would you do connect your solar array today? Any specific order of operation? Or just keep that DC switch off and connect panels as you bring them to the roof and mount them?

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This.

Old_Skewler said:

Sounds amazing! Like they say, first time is a bit harder but then down the road things get easier and faster. Is there a correct way to check polarity? Did you check any voltages at any point in the install before turning the DC switch on?

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I checked voltage of panel before making the series connections, then I verified the VOC to be correct for the series string.
For polarity I verified red was positive and black was negative, I also intentionally flipped the meter leads to make sure it read - properly.

Old_Skewler said:

Got it: keep the DC switch open during the install. Any other recommended sequence of operation when mounting & wiring the panels on the roof? Does it matter if I connect main leads to the panel before or after the panels are wired in series? Or none of this matters?

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None of this matters. Just don't complete a circuit, and all will be fine.

timselectric said:

None of this matters. Just don't complete a circuit, and all will be fine.

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Thank you. We are almost there!

MC4 connectors? That makes it touch safe.
Just don't connect into a load or short circuit.
So long as a panel has both wires disconnected, you can plug a wire into it. Repeat with it's one remaining disconnected wire, plugging into next panel that has both wires disconnected.

When you get to the last connection, a wire going through conduit or into switch or inverter, you don't know for sure that is open circuit. I test voltage between the male and female with DMM. Might read 500V initially, should decay to zero. If it decays, Ok to plug in. If it holds voltage, not OK because a circuit is being completed (possibly a short, or two different length strings of panels about to be connected in parallel.

Before closing switch to feed inverter, double-check polarity and voltage. There is no reason to kill an inverter, but I just picked one up that had blown caps.

Hedges said:

MC4 connectors? That makes it touch safe.

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Yes, MC4s all around.

Hedges said:

Just don't connect into a load or short circuit.
So long as a panel has both wires disconnected, you can plug a wire into it.

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Got it!

Hedges said:

Repeat with it's one remaining disconnected wire, plugging into next panel that has both wires disconnected.

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Hedges said:

When you get to the last connection, a wire going through conduit or into switch or inverter, you don't know for sure that is open circuit. I test voltage between the male and female with DMM. Might read 500V initially, should decay to zero. If it decays, Ok to plug in. If it holds voltage, not OK because a circuit is being completed (possibly a short, or two different length strings of panels about to be connected in parallel.

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Which male & female? The male from the very first panel & the female of the last panel? Not clear I fully follow. But I thought, after connecting all panels in series, that if I were to measure Voltage across the the array, that I would get a reading. Same thing if I tried reading voltage across one panel during the day, I'd also get a reading.

Could you clarify which points I should measure voltage and get a zero reading?

Hedges said:

Before closing switch to feed inverter, double-check polarity and voltage. There is no reason to kill an inverter, but I just picked one up that had blown caps.

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This is connecting first to my Victron. And yes, I'll check voltage BEFORE switching everything on.

When connecting a pair of MC4 (one will be male, one will be female), if you can't see the far end (of extension cable, PV panel, PV array) is unconnected, then for all you know you are about to complete a circuit.

At that point I use DMM to probe the two connectors and measure voltage, before connecting them. Voltage typically jumps up for a moment, then drops down toward zero.

But be careful, because once you stick probe into MC4, exposed part of the probe is hot, and the other probe is also hot.

One of these days I'll get or make MC4/banana cables. (I already made MC3/banana cables.) That's shrouded safety bananas. Want the kind with plastic tip on contacts; some have exposed metal too close to end of shroud for comfort.