Voltages of various inverter systems

[shet]

Think about it this way. Let's say you have kids in your house. All they need is a fork and they can connect themselves to 120 volts AC. They are not going to be able to get near that 450 volt DC line that goes from the panels to the inverter.

I agree and as SunEagle said what matter is that terminations be secure and protected. Thanks goodness for today's superior arc and ground fault protection breakers. A few months ago I accidentally shorted the hot wire/screw inside a switch to its metal case when the metal probe of my multi-meter slipped in the narrow gap. The metal probe burnt and melted slightly along with associated sparks/fireworks but the AFCI breaker tripped instantly. I think that saved me even though I was wearing rubber shoes and holding the plastic end of the probe.

[SunEagle]

Correct and incorrect. Current = Voltage / Resistance. Current kills you but voltage is the source (provided power source has enough power to provide the required amp [actually in tens of mA] which is fatal to the heart). A car battery is 12V but can supply hundreds of amps but will not kill you if you touch it because 12V divided by human body's resistance is not enough to kill you (assuming you are not all wet or you are not holding a metal wrench and then connecting across it's terminals). Voltage is not "part" of the danger. It is the "whole" danger itself.

I would say above 30 or 40V is fatal for humans.

Well actually both OSHA and the NEC classify any voltage AC or DC above 50V should be avoided by all not electrical certified personnel. When means just about anyone can play with systems with voltages in the 30 to 40v range. That still doesn't mean you can't be hurt by a 12volt battery if you come in contact with the positive terminal and ground while creating a low resistance path.

Hey. If voltage is your trigger point then that is fine with me. But before you make claims that 600VDC is not a good installation for pv you really should do the research or at least get some personal field experience.

[SunEagle]

eeh, yes and no. Electric fences are typically in thousands of volts and certainly not fatal.
Almost any electrician or handy man has been shocked by 120V AC as well, and still not fatal.
some even 240V.
12V or 24V or 48V battery banks (more amps than car batteries), can be very deadly. Biggest danger due to arc flash, but also to under sized wires, and lack of fuses.

PV is a bit funny in the voltage/current though.

Don't go and empty your bladder on one of those electric fences. You will get the shock of your life.

[ButchDeal]

never did that but did grab someone else (sisters ) and touch the fence. I was expecting it, they never were.

[jflorey2]

I agree and as SunEagle said what matter is that terminations be secure and protected. Thanks goodness for today's superior arc and ground fault protection breakers. A few months ago I accidentally shorted the hot wire/screw inside a switch to its metal case when the metal probe of my multi-meter slipped in the narrow gap. The metal probe burnt and melted slightly along with associated sparks/fireworks but the AFCI breaker tripped instantly. I think that saved me even though I was wearing rubber shoes and holding the plastic end of the probe.

Note that with that much energy involved (melting the shaft of a probe) you were more likely protected by the breaker's overcurrent function.

[shet]

Hey. If voltage is your trigger point then that is fine with me. But before you make claims that 600VDC is not a good installation for pv you really should do the research or at least get some personal field experience.

Yes, doing more research. So it is 350V DC of SolarEdge vs 240V AC of micro-inverters. 240V AC corresponds to 339V AC peak (Peak to Peak is double that). So they are both equivalent roughly. Now with voltage being equal, I found two things about AC vs DC so far as safety is concerned.

1) More DC currents required to cause fibrillation of the heart than AC. This typically takes place at 30 mA of AC or 300 – 500 mA of DC. So DC wins here

2) AC arc can self-extinguish (since AC goes through zero 50 or 60 times a second). DC arc cannot self extinguish. So AC wins here.

[ButchDeal]

Yes, doing more research. So it is 350V DC of SolarEdge vs 240V AC of micro-inverters. 240V AC corresponds to 339V AC peak (Peak to Peak is double that). So they are both equivalent roughly. Now with voltage being equal, I found two things about AC vs DC so far as safety is concerned.

1) More DC currents required to cause fibrillation of the heart than AC. This typically takes place at 30 mA of AC or 300 – 500 mA of DC. So DC wins here

this is only an issue if you are planning to work on the systems. From what you have posted so far I think you should NEVER open any of the sealed electrical systems.

2) AC arc can self-extinguish (since AC goes through zero 50 or 60 times a second). DC arc cannot self extinguish. So AC wins here.

The AC thing only matters if the distance the arc is traveling over is widening like in a switch. In other words if there is a short on the roof and you are getting arc to ground that arc will continue until something stops it.
With DC there is arc fault protection required in most codes and with SolarEdge, the inverter will use the rapid shutdown to drop the DC current.
With micros, you would be relying on breakers.
With a string inverter that has arc fault protection, it with shutdown and get the MPPT down, but you may still have large DC voltages and current at the array .

[shet]

With DC there is arc fault protection required in most codes and with SolarEdge, the inverter will use the rapid shutdown to drop the DC current.
With micros, you would be relying on breakers.
With a string inverter that has arc fault protection, it with shutdown and get the MPPT down, but you may still have large DC voltages and current at the array .

SolarEdge seems to be the winner then.

[SunEagle]

Yes, doing more research. So it is 350V DC of SolarEdge vs 240V AC of micro-inverters. 240V AC corresponds to 339V AC peak (Peak to Peak is double that). So they are both equivalent roughly. Now with voltage being equal, I found two things about AC vs DC so far as safety is concerned.

1) More DC currents required to cause fibrillation of the heart than AC. This typically takes place at 30 mA of AC or 300 – 500 mA of DC. So DC wins here

2) AC arc can self-extinguish (since AC goes through zero 50 or 60 times a second). DC arc cannot self extinguish. So AC wins here.

AC does not self extinguish. It is the overcurrent protection or component that melts and opens the circuit to stop the arc blast.

I will tell you that based on certain circumstances that if an overcurrent protection device is very slow to open a short circuit at a 240 volt panel could generate enough heat, energy and blast equal to the surface of the sun and burn you up. That is because of the amount of current going through the short circuit and not because of the voltage of the circuit.

[Mike90250]

That is not good. 600V DC on the roof. 240V AC is bad enough. 600V DC is even worse.

And what technical basis is this opinion derived from ? There are many many string inverters working just fine at the rated voltages. If you use substandard practices, it will be a nightmare. If done properly, by trained personnel, it's just fine.

[bcroe]

That is not good. 600V DC on the roof. 240V AC is bad enough. 600V DC is even worse.

Avoid the stuff on the roof with a ground mount PV system. The nearest piece of my PV system is 250' from the
house. With that kind of distances, you start to appreciate the higher voltage. Bruce Roe

[shet]

And what technical basis is this opinion derived from ? There are many many string inverters working just fine at the rated voltages. If you use substandard practices, it will be a nightmare. If done properly, by trained personnel, it's just fine.

Lets say I am clearing snow off the roof using an extended metal snow-rake and it happens to contact an exposed bare metal wire (exposed because say a squirrel has chewed through the insulation few days ago). In that case, I feel lower the voltage safer it is.

I have another question actually. In terms of ground fault or arc fault, which system has better protection? The SolarEdge inverter or the Enphase/PowerOne micro-inverters setup ? In this post somebody mentioned that microinverter only have a 240V breaker. If so, what protection would that breaker provide? Only overload? How about small ground faults or how about arc faults?

[SunEagle]

Lets say I am clearing snow off the roof using an extended metal snow-rake and it happens to contact an exposed bare metal wire (exposed because say a squirrel has chewed through the insulation few days ago). In that case, I feel lower the voltage safer it is.

I have another question actually. In terms of ground fault or arc fault, which system has better protection? The SolarEdge inverter or the Enphase/PowerOne micro-inverters setup ? In this post somebody mentioned that microinverter only have a 240V breaker. If so, what protection would that breaker provide? Only overload? How about small ground faults or how about arc faults?

A solar pv system protection against (arc, short or ground fault) would be designed by the engineer based on the installation configuration and would meet all local codes. If a system is designed properly then it will isolate any electrical issue before it becomes a problem or danger.

Worrying about touching an exposed wire caused by a squirrel's chewing while clearing snow off the panels is pretty far fetched and very unlikely to happen. Although to help increase your chances of not being electrocuted you could use a plastic handle on the snow rake or electrical insulating gloves like the Electricians use when handling live work.

[jflorey2]

Lets say I am clearing snow off the roof using an extended metal snow-rake and it happens to contact an exposed bare metal wire (exposed because say a squirrel has chewed through the insulation few days ago).

Panel interconnects are below the panels; you would be using the rake above the panels.

But let's say you decided to take a metal pole and poke around under the panels for some reason (perhaps you wanted a good lawsuit or something.) You might be disappointed when you found a live conductor and the GFI protection on the inverter opened.

Now, if you are worried more about squirrels and other vermin causing wiring problems, that would argue for string inverters - because string inverters need 3-4x fewer connections and cables beneath the panels.

[bcroe]

PV array hardware is designed to entirely insulate PV potentials in an outdoor environment. But I'm not too interested in betting my life on
their 20 year integrity. There are 5 signs DANGER HIGH VOLTAGE on my array. Snow removal here is done with care using insulated
poles. Don't count on the inverter GFI doing anything to protect you. Like batteries, panels don't have on/off switches. My GFI is a 1A
fuse, and by the time that blows, its too late. Be careful about anything that could go through a panel, and that includes your arm after
you slip on the ice. Bruce Roe