diy solar

diy solar

electrocution on metal roof

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panchopancho

New Member
Joined
Aug 25, 2023
Messages
5
Location
canada
hi,
just wrapped up my install yesterday,
it's 8x455w in series,
i bolted aluminium bracket to the panels frames, which i screwed into my metal roof.
today, standing on aluminum ladder, while it was raining, i touched the roof and caught a pretty good zap.
i yanked out my volt meter, and tested between the ladder and the roof, about 500mV.
touched the roof, atill getting zapped.
what gives?
thanks for your input.
 
Hmmm... The most likely scenario is that there is some type of ground fault between the PV circuit and the roof, but it is really hard to say where the potential is coming from. Do you have any idea if there was a potential before the panels were installed?
Did you measure the voltage with both AC and DC settings?
Are the panels tied to the charge controller or are they still isolated?
 
FilterGuy said:
Hmmm... The most likely scenario is that there is some type of ground fault between the PV circuit and the roof, but it is really hard to say where the potential is coming from. Do you have any idea if there was a potential before the panels were installed?
Did you measure the voltage with both AC and DC settings?
Are the panels tied to the charge controller or are they still isolated?
Click to expand...
i dont get zapped when the panels are disconnected from the charge controller/inverter.
i doubt there was potential before the install, we're out in the woods, no grid within km's.
my multimeter is automatic, and records less voltage between the ladder and the roof/screws than between my fingers and the ladder.
i checked voltage with the screws, edge of the roof, scratched the coating off of things, i cant get a decent voltage anywhere, but everytime i inadvertently touch the wet roof i get a shock, and in my experience its more potent and painful than 110vAC. im at a loss.
 
First, The fact that a potential is building up on the roof tells me the roof is not grounded. It should *Definitely* be grounded.

There are two likely scenarios:

1) A short between one of the PV wires and the roof.
2) The SCC in the inverter is not isolated (Most of them are not). This is placing an AC ripple on the PV lines which is getting capacitivly coupled to the metal roof. Grounding the roof would solve this problem.
 
FilterGuy said:
First, The fact that a potential is building up on the roof tells me the roof is not grounded. It should *Definitely* be grounded.

There are two likely scenarios:

1) A short between one of the PV wires and the roof.
2) The SCC in the inverter is not isolated (Most of them are not). This is placing an AC ripple on the PV lines which is getting capacitivly coupled to the metal roof. Grounding the roof would solve this problem.
Click to expand...
and by grounding, do you mean connected to the ground?
 
As you described the installation, the panels are electrically bonded to the roof. It also seems nothing is grounded. You should have a ground attached to each panel and attached to your system ground.
 
panchopancho said:
and by grounding, do you mean connected to the ground?
Click to expand...
panchopancho said:
i realize that sounds silly, i mean, should i electrically connect the roof to the earth?
Click to expand...
Yes, he is, well sort of, no.
The racking and panel frames should be connected to earth, just the same as your inverter and AC outlet ground. All should connect to your main panel and have a single connection point to earth.
panchopancho said:
what about the fact that my meter isnt picking up that voltage?
Click to expand...
Where is your meter referenced? If the red lead is on the roof, where are you putting the black lead? The meter measures potential, got to have a potential between the two leads for it to show voltage.
 
There is a voltage transferred (coupling) to the panel frame by ungrounded operational solar panels. It is most likely not a short from the panel cells to the frame. What is supposed to be done is install one of several approved panel grounding systems. Ether by mounting bracket or a special grounding lug. In any case they pierce through the anodized frame. Then a ground wire is ran down. I don’t believe that a connection to the building is sufficient by code or as you found out, functionality. A common multi meter, regardless of position(AC or DC) probably won’t show the true voltage because of unusual frequency of the MPP in use with the panels. The “hot roof”(electrically) will instantly go away when the frames are properly grounded. Proof that there isn’t a short is that there will be absolutely no difference in power output from the panels. I’ve experienced this phenomenon “firsthand”?⚡️
 
Last edited:
As a side note, grounding the panel frames will GREATLY reduce radio interference that’s made by the MPP.
 
400bird said:
Yes, he is, well sort of, no.
The racking and panel frames should be connected to earth, just the same as your inverter and AC outlet ground. All should connect to your main panel and have a single connection point to earth.

Where is your meter referenced? If the red lead is on the roof, where are you putting the black lead? The meter measures potential, got to have a potential between the two leads for it to show voltage.
Click to expand...
I was told that dc and ac needed to be grounded separately… but I’ve heard all kinds of things when it comes tho Solar. I’m pretty new to all this too
 
400bird said:
DC shouldn't be grounded at all on most systems.

Calling DC negative "ground" is a bad habit we all have, but it isn't the same thing.
Click to expand...
Wait what? I pounded that dang rod in the ground for nothing?? ? I grounded my battery rack and built a wooden ground mount for 20 panels that we used an ironbridge? Iron ridge? ( can’t remember) racking system to that I planed on grounding tomorrow. ?
 
Blackntantoad said:
I was told that dc and ac needed to be grounded separately… but I’ve heard all kinds of things when it comes tho Solar. I’m pretty new to all this too
Click to expand...
Just to be clear modern solar panel outputs +positive and negative- remain connected to the PV connections on your charge controller or inverter but those solar panel outputs must NOT be connected to ground or earth. The panel frames yes, they are connected to ground. Your equipment chassis should also be grounded where it’s attachment points are identified.
 
Skypower said:
Just to be clear modern solar panel outputs +positive and negative- remain connected to the PV connections on your charge controller or inverter but those solar panel outputs must NOT be connected to ground or earth. The panel frames yes, they are connected to ground. Your equipment chassis should also be grounded where it’s attachment points are identified.
Click to expand...
Ohhh I gotcha, yes that makes sense. Thanks! Not to highjack this dudes post but even using an all metal racking system still needs all panel frames as well as the rack it’s self grounded individually to earth? And I suppose his roof would also need to be tied into that as well?
 
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