Floating an array

[jaggedben]

That is how all systems are built - or should be - agreed. I mount panels at very end in a couple hours.
But mounting panels has to be concurrent with making series connections. No way around it.

On large systems, where mounting dozens or hundreds of panels is basically a whole project in itself, then its easier to schedule in such a way as to essentially complete everything else and then install panels. On large ground mounts, mounting arrays and plugging in series strings can happen on different days, or different weeks. Labor and equipment costs do not have to be affected to a high percentage.

On residential size systems, where three or four guys are given one to three days to install a system, it slows down the job to leave the panels on the truck while the whole crew works on a 3/4" condiut run that one guy could do almost as fast. If the crew has to come back an extra day that has a much more significant effect on labor cost. This is why I think you won't ever find a company that makes this a policy, at least not in residential installation.

 

[jaggedben]

Finding a ground fault is extremely rare. Very rare.

Agreed. In the last two full years plus of installing I can think of maybe 3 that I encountered.

ALternatively, with large systems and multiple strings and hence BIG AMPS, I do as follows:
[snip]

This is fine, although I'm not sure where in the process you are checking each string. Again, if you are not checking each string independently, then if you do discover a ground fault, you won't be able to isolate it without undoing all of the grounded conductor connections. And you won't catch strings with open circuits. When one of things does happen, which is rare, I like the amount of time that is saved by knowing the what and the where right away.

BUT i gotta say.....:roll: if you or your installers are regularly crushing those poor, defenseless 600 VDC PV wires so that you have multiple shorts in a single system, then hire my younger brother! Even he can do better work.:lol:

Well, in our defense, nobody I worked with ever stuck a screwdriver into the end of a connector.

The multiple shorts worry really applies only to very large systems.

 

[Zee]

This is why I think you won't ever find a company that makes this a policy, at least not in residential installation.

I bet many don't make this a policy. With 3-4 people on a resi job you are right, they'll be done on roof and waiting before the elec guy finishes conduit and equipm..,


There are only two guys on our crew. It is easier to plan.
We always split right away into DC and AC teams = Roof and ground = Racking and AC equipment (inverter discos etc).
Then when all ready, panels go on.

 

[Zee]

Sounds like you got a good system for yourself. Having disconnect possibilities is always a great thing!

I check strings at end.

It is a good compromise - for me.
All my systems have 1, 2 MAYBE 3 or 4 strings.

Open circuits show up on ammeter in dc disco. Or simply in inv. watts. (again, only on very small resi systems)

It is clear you do excellent work. I hope it is clear i was making an attempt at humor, and no slight! (ONly slighting my own brother haha.)

Why do you say regarding Ground Faults that, "you won't be able to isolate it without undoing all of the grounded conductor connections" ? I am curious. I believe i can test each gr. conductor to gr. and find the culprit. And exactly which panel in the series has the fault too.

 

[jaggedben]

I hope it is clear i was making an attempt at humor, and no slight! (ONly slighting my own brother haha.)

It was clear, I thought it was funny.

Why do you say regarding Ground Faults that, "you won't be able to isolate it without undoing all of the grounded conductor connections" ? I am curious.

The short answer is that it has been my experience.

The long answer is probably best illustrated with a diagram, but I don't have one right now. I'll try with words...

I believe i can test each gr. conductor to gr. and find the culprit.

Typically (for example, in an SMA integrated disconnect), all the grounded conductors are landed on terminals that connect to the same bus. So it is impossible that you could get a different voltage readings by testing at different points along the same bus. That's what I mean when I say you have to disconnect all (but one) of the grounded conductors in order to read individual strings. Of course the GFDI fuse must also be removed (or blown) to get meaningful voltage readings.

Perhaps you made a typo and meant ungrounded conductors. In this case you can remove fuses and indeed the grounded conductors won't be connected to the same bus. But the odd thing is that with two strings, you will still get the same reading on both ungrounded conductors if the grounded conductors are still connected to the common bus.

Suppose you have a ground fault between the 3rdth and 4th panel of String A on an 8 panel string, on a system with two 8 panel strings. If you test between String A's ungrounded and ground, you will only read 3 panels worth of voltage. So far so good. But if you test String B's voltage (ungrounded to ground) you get the same reading. Here's why: The path you are testing goes like this : String B ungrounded conductor -> through string B, 8 panels of voltage -> to the grounded bus -> through String A in the opposite direction, subtracting 5 panels of voltage -> to the ground fault > to ground and the other probe of your meter. You end up with the same voltage as before, 3 panels worth.

It doesn't matter much if there are more strings, it still generally works the same with any other faultless string on the system.

Finally, a disclaimer: with some equipment (e.g. Power One inverters with dual MPPT inputs), the grounded conductors are not connected to a common bus so none of this is a problem. (Another example would be ungrounded systems where all conductors have removable fuses.) But with most equipment, including combiners for grounded systems, it is.

And exactly which panel in the series has the fault too.

Yes, I agree. Once you isolate the affected string it is just a matter of dividing by panel voltage to find the fault.

 

[sparkease]

Sparkease

Sparkease

[aQUOTE=Zee;1371209]

Floating an Array​

I just got the biggest shock of my PV career last Summer. As my installation partner and I were laying down panels on a rack, he was shocked. ANY SHOCK CAN KILL YOU. EVEN THE "LOW" AMPS IN PV PANELS ARE 1000'S MORE AMPS THEN NEEDED TO STOP AND SEIZE YOUR HEART MUSCLES.

We analyzed the situation until we could figure out why he was shocked.
I checked online.
I checked with other experts. (Wiles included)

I found that ?floating an array? is key to installer safety.I was surprised to find I never heard the term "floating" before. Nor was I ever taught the practice. (I won't detail my experience, but it's lengthy)
I WANT TO SHARE WHAT I LEARNED AS PART OF MY NEW YEAR'S SAFETY RESOLUTION.


Basically: BEFORE installing PV panels, remove the GFDI fuse or otherwise disconnect the grounded conductor (usually negative) from ground (usually in the inverter). This simple action could be a lifesaver.
The Handbook states: " (GFDI) Devices meeting 690.5 are intended to prevent fires in DC PV circuits due to ground faults." That means that the fuse will not protect life.

Background: NEC 690.5 requires that most PV systems be GFI protected. If you land all wires in DC disconnects and inverters before installing panels, then the GFDI fuse links PV negative (usually, sometimes positive) to ground. (And, landing wires BEFORE energizing them (adding PV PANELS) is a best practice.) That means all metal racking on the roof, all conduit and grounding wire every where is effectively charged (usually negative) - and exposed to the touch. Like one big, exposed and charged bus bar. All I need to do in order to get hurt is to accidentally contact PV positive. I am all but guaranteed to be simultaneously in contact with racking, grounding wire or a module frame by holding, leaning, or sitting on a grounded component, like a rail, i.e. negative. Maximum potential would then exist between the positive wire I accidentally touch and the exposed - negatively charged - metal of anything. Between the two.... my body would be the connection!
Is this unlikely? I used to think so.
Yet....this just happened to my partner on a rooftop. ( I also had a buddy shocked through the seat of his pants while sitting on a rail and wiring an array.) While tightening the set-screw in the bonding lay-in-lug on the underside of the module frame with his screw-driver, and laying the #10 bare copper grounding conductor into it, his screwdriver must have slipped into the MC Connector of the positive lead of the module! He was shocked and yelled.

However, if you remove the GFDI fuse then both polarities should be separately derived from ground - and thus the racking. Potential - in my understanding - should really exist only between the two polarities. If you manage to connect these two with your body, then ....well..... you are talented.

Anyways, just my two cents.

tip #2 Wear gloves. Gorilla brand neoprene fit like a secondskin for me. So I actually wear them!
tip #3 Use insulated screwdrivers. Even when grounding! (as we were)
tip #4 Remove pointy drill bits and pointy tools from toolbelts while installing panels. (MC Connectors are ?touch safe?, only to adegree - but not when handling pointy drill bits and screwdrivers. When handling 100's of modules it is just a matter of time before something slips inside the MC Connector or you crush or nick a wire)[/QUOTE]

 

[sparkease]

Sparkease

Sparkease

if possible cover array with tarp before making final connections and still treat as live,this is recommended by inverter manufacturers, the racking should be bonded together and grounded using listed devices.

 

[Zee]

Jaggedben -
Ok, that was one of the first eye opening things i have learned in a long time.:ashamed1:
I drew up a diagram.
I see exactly your point.
I never realized that some of the panels from a gr. faulted string "A" would subtract Voltage from the intact string, "B", consequently making their V's equal.!

Very good description.
Thanks for the patient and well-written explanation.
(BTW - Yes, it was a typo. Sorry, I meant isolating individual ungrounded conductors)

Interesting implications for troubleshooting a gr. faulted (DC side) commercial system...... Given the multiple strings in CB's all landed on common buses. No?

 

[highvolts582]

Is this safe

Is this safe

I always complete my grounding first after racking. Then I set the panels. I wire all my home runs in. Once that is done I connect all of my MC connectors I try to arrange home runs to be where I can connect after system is installed I then check all of my pv volts from each string then put in fuses then go down and turn on.

Does anyone think it is safer to keep grounding disconnected until system is in? I make it a point to ground it incase of a short I want it to short. Won't the panels open power when they are
Shorted without damage to string? This is why I ground each panel individually instead of weeb
Clips. So if you are removing a shorted panel you have ground intact while you have panel off
The rack.

 

[jaggedben]

...I try to arrange home runs to be where I can connect after system is installed ..

This is the advantage of the whips method. All strings can be connected in one place, at the junction box, which you put under a top-corner panel. Especially helpful on steep roofs.

I then check all of my pv volts from each string then put in fuses then go down and turn on.

Sounds like you are using combiners on the roof (otherwise you'd 'go down' before putting in fuses.) If the combiner has touchsafe fuse holders (some don't), then yes, it works pretty good to do things in the order you describe. The only drawback, as I've explained in this thread, is that you have easier ground-fault diagnosis if the grounded conductors are not connected to a common bus.

Does anyone think it is safer to keep grounding disconnected until system is in?

Well, I guess Zee does (by removing the GFDI fuse). In my opinion, a better method is to keep all strings disconnected at whips outside the junction box. Plugging in the whips and putting down the last panel is then the last thing you do before turning the system on. Either method provides safety against the situation he described at the beginning of this thread.

I make it a point to ground it incase of a short I want it to short.

Do you want it to short through you? (Answer: no. )

Grounding a solar system does nothing to protect installers, period. If the grounded end of the string is already connected to ground (via the GDFI fuse), then contact with racking and the ungrounded end of the string exposes installers to hundreds of volts of shock hazard. Since contact with the racking is basically guaranteed when installing, it is imperative either to avoid contact with the ungrounded conductor (hard to guarantee), or to keep both conductors disconnected from ground until the last possible moment (better percentage play). If there is a ground-fault and the GFDI fuse has opened, then either the grounded or ungrounded conductor for that string can be a shock hazard when touching the racking.

Won't the panels open power when they are Shorted without damage to string?

I'm not sure what you mean by 'open power'. Strings of PV panels will not damage themselves if short circuited, this is true (except maybe if left that way for years).

This is why I ground each panel individually instead of weeb Clips. So if you are removing a shorted panel you have ground intact while you have panel off the rack.

This comment does not make much sense. In the weeb system the racking is the ground so it also stays intact when you remove a panel.

 

[Zee]

Hello HIGHVOLTS,
You cannot count on metal frames and racking to be disconnected from ground. Paths to ground are potentially numerous and unintentional. Wet hardware, or conduit itself may create a path to ground. The important thing is to FLOAT your array during installation or repair.
Floating refers to temporarily removing any link between positive and negative to ground.
It DOES NOT unground exposed metal frames, conduit or racking.
This can be accompished by removing the GFDI fuse or the "Whips" method per JaggedBen.

 

[highvolts582]

Clarifying

Clarifying

I'm sorry I meant I ground the racking before I install any panels. I agree by not grounding the
Racking ground will find away to the racking through dirt on roof and shingles to the gutters "a
Trickle ground"(I made that term up just now) I would not hook positive or negative to any thing
Until panels are in installed I do not install inverters until modules are in. The negative is grounded at the inverter (usually). So I guess by taking out the gfi thing at the inverter if it has one I
Only noticed a removable one on a small sunny boy I did not see anything I could remove on the larger grey ones small one was red I've done so many I can't remember the sizes sorry. So I install racking then I do my grounding and I just temporary run a ground down until I'm finished
With rest of wiring after I install modules. I do not think I got any voltage from just positive or
Just negative to the ground doing it this way.

I guess making all home runs come to a central easy location is not a bad idea add cost of extra MC connectors. But it is an additional place that that something could go bad down the road.

Anyone have any links to get stuff to shade panels .

I wonder what it would be like wearing a moon suit and harness in hot sun.

There is the same deathly problems on large systems as small if you add your small systems
Together you get the same ratio of bad modules to large systems so don't take the dangers for
Granted the strings all have around the same deathly voltages involved.