Exactly! Working around live grounded 120/240 VAC always bothers me, I’m far more comfortable with floating 400-500 VDC. In most situations all that would happen if you got a tool across both DC legs is an arc and burned tool tip, you would have to be doing some stupid stuff and not using your head at all to get shockedIt would be much more dangerous to hit a 120 volt line on a grounded system than a 600 volt line on an ungrounded system.
You guys are forgetting how all this works. It would be much more dangerous to hit a 120 volt line on a grounded system than a 600 volt line on an ungrounded system. Using concrete is an unnecessary expense unless the conduit is too shallow to meet code requirements. And then you need a minimum of 2" of concrete cover.
Exactly! Working around live grounded 120/240 VAC always bothers me, I’m far more comfortable with floating 400-500 VDC. In most situations all that would happen if you got a tool across both DC legs is an arc and burned tool tip, you would have to be doing some stupid stuff and not using your head at all to get shocked
I'm sorry but this is just complete and absolute rubbish.would be much more dangerous to hit a 120 volt line on a grounded system than a 600 volt line on an ungrounded system.
How so?I'm sorry but this is just complete and absolute rubbish.
Talk about rubbish...Are you doing a permitted install, a half decent install or DIY lash up?
For a DIY lash up you could use direct burial 10 AWG and call it a day
I have checked for AC on mine repeatedly over the past 7/8 months after reading the threads on the subject and have never seen any sign of any.Or, transformerless inverter (either off-grid or on-grid) is is probably referenced to AC voltage. In some cases it also has AC voltage riding on it.
Stick your digging device through any pair of cables carrying a decent amount of power and let me know how it goes for you.How so?
Talk about rubbish...
And why is using cable that is specifically designed for burial and will carry the current that the OP wants rubbish?How so?
Talk about rubbish...
Because I understand how electric circuits work, I know that the amount of power being carried by a cable has no effect on what happens if you cut into it. You have to get in the circuit to be shocked by it. A single point of contact with a shovel on an ungrounded system won't hurt you. Even if you hit both conductors, the current will flow through the shovel head between the wires. Even if the system negative is ground referenced, it is likely to be through a charge controller with a GFP system that will open that ground connection and leave the PV side ungrounded.Stick your digging device through any pair of cables carrying a decent amount of power and let me know how it goes for you.
I have checked for AC on mine repeatedly over the past 7/8 months after reading the threads on the subject and have never seen any sign of any.
Would you be willing to explain or provide a reference explaining “probably referenced to AC”?
Only if current exceeds 1A (GFCI fuse in my old Sunny Boys) or 0.5A (breaker used for GFCI of Midnight Classic), or whatever detection threshold yours has.Even if the system negative is ground referenced, it is likely to be through a charge controller with a GFP system that will open that ground connection and leave the PV side ungrounded.
Growatt MIN-11400-TL-XH-US (Version 2)What model?
Lets see if I can redirect the conversation back to my needs. (all you worried about how I burry this -- I'll do it right when the times comes!)Voltage drop doesn't matter for arrays.
10 awg will lose less of your power on the wires, but 12 or 14 awg is also acceptable.
You need to calculate the Vmax and Vmin that your array will output, you can do that either using online tables or calculations. Vmax and Vmin are dependent on the max and min temperatures you expect to see in your area, you can use your own experience, or if you need to submit documentation for a permit you can get those numbers from the ASHRAE handbook. Once you know the Vmin you can select the wire size based on %voltage drop you want. That's typically 2-3% but you can get it as low as you want by spending more money on bigger wire. The Vmax will determine the insulation rating on the wire. There is no requirement to derate the wire since you are burying it so there are no high temperatures involved, but you need to use the NEC table to choose an adequate wire size based on current. Since this is treated as a feeder you will use NEC table 310.12(A) to find the required wire size. You can't use anything smaller that called out in the table, but if it's not adequate for voltage drop you can of course go larger. You need to use the wire required at 75C in the table because the equipment on the end (breakers, enclosures, etc) is rated for 75C, and code requires you use the lowest rated device to size the wire.I need to understand getting HV DC from a solar array back to a different location for the inverter. Trying to understand what is involved, what ratings and rules must be followed.
Just an FYI Yes you might have to derate because it is a continuous load therefore can only be loaded to 80%You need to calculate the Vmax and Vmin that your array will output, you can do that either using online tables or calculations. Vmax and Vmin are dependent on the max and min temperatures you expect to see in your area, you can use your own experience, or if you need to submit documentation for a permit you can get those numbers from the ASHRAE handbook. Once you know the Vmin you can select the wire size based on %voltage drop you want. That's typically 2-3% but you can get it as low as you want by spending more money on bigger wire. The Vmax will determine the insulation rating on the wire. There is no requirement to derate the wire since you are burying it so there are no high temperatures involved, but you need to use the NEC table to choose an adequate wire size based on current. Since this is treated as a feeder you will use NEC table 310.12(A) to find the required wire size. You can't use anything smaller that called out in the table, but if it's not adequate for voltage drop you can of course go larger. You need to use the wire required at 75C in the table because the equipment on the end (breakers, enclosures, etc) is rated for 75C, and code requires you use the lowest rated device to size the wire.
You asked earlier about what kind of wire. I prefer XHHW aluminum for this application. It will be about half the cost and weight of copper, and even though the XHHW insulation is tougher than THWN, it is more flexible so it's easier to work with at the ends. It's also resistant to chemicals if that matters in your application. It is slightly more expensive than THWN, maybe 15% or so.
It's a bit confusing because there is an 83% rule that allows a feeder to be 83% of the required ampacity. So if you need 100A you can select a feeder size that carries 83A. You're correct that for continuous service (>3 hours) you need to upsize the wire by 120%. But those two things cancel out, so if you just use the table you get the right wire choice for continous service.Just an FYI Yes you might have to derate because it is a continuous load therefore can only be loaded to 80%
He's talking about the 125% rating for continuous loads. The breaker and wire has to be rated at 125% of the load current. Consequently, a breaker can only be loaded to 80% of the rating.It's a bit confusing because there is an 83% rule that allows a feeder to be 83% of the required ampacity. So if you need 100A you can select a feeder size that carries 83A. You're correct that for continuous service (>3 hours) you need to upsize the wire by 120%. But those two things cancel out, so if you just use the table you get the right wire choice for continous service.