Help me make wise decisions - First timer

Cariboocoot wrote: »

And now we talk about the difference between ESG (Electrical Safety Ground) and lightning protection.

First of all, the system doesn't need any kind of ground to function. Ground is for safety reasons. It is not for lightning protection either; that is a whole 'nother kettle of fish.

The idea of the ESG is two fold: it makes half of the wiring zero Voltage potential in respect to ground (very important on higher Voltages which are generally deemed as >60) and it provides a high current sink should anything short out to an external conductor (such as a metal casing). The former is so that anyone touching something can't become a "lower resistance path" for the Voltage and get a shock; the latter is so that if the 'hot' comes in contact with something that shouldn't be energized the circuit over-current protection will trip and shut down power.

In most cases DC doesn't have to follow these rules because it is low Voltage and doesn't provide much of a hazard to begin with. The biggest trouble with DC is its ability to sustain an arc if over 15 Volts (this is why most vehicle systems are limited to 12 Volts; more efficient than 6 without presenting the arc problems of 24). But when you put DC in a house it now has to follow the same rules as AC (even though in some cases that makes things worse). So we ground the negative (or not) and make it safer than if we didn't.

For AC tying one side (or technically the middle for split-phase 240) to Earth ground provides a couple of benefits, the main one being the zero Voltage potential for an alternate path (such as a person) to ground for one side. Then if something shorts you need only trip a single pole breaker to shut off power. When 240 is used you'll notice the breaker is double pole and tied so both side shut down at the same time (that way one wire isn't still 'live' in respect to ground).

Now about that lightning. Nothing in this world is capable of providing protection against a direct hit. Millions of Volts; it can turn any metal into slag, vaporize trees, and blow rocks into gravel. But there is something that happens in a lightning strike area that can be protected against: the air around the bolt becomes saturated with high Voltage, high frequency power. Any kind of conductor can pick this up and carry it to equipment that is not going to like being introduces to several thousand times the Voltage it was meant to operate at.

Ground the panel frames and most of that stray Voltage is led away instead of led in (which is why we like the ground wire for this outside the house). Put a surge arrestor on the PV leads and the high Voltage spikes jump across that to ground, nullifying them (up to a limit) before they can hit the charge controller or GTI. Same with the AC wiring, which can present a fairly large 'antenna' for picking it up.

Even then nothing is perfect. Lightning strikes are unpredictable, and will sometimes hit things you'd never expect them to be attracted to. You can't protect against every eventuality (although some people are obsessed with the idea that you can and keep insisting the "government do something") but you can determine what is most likely to happen and take reasonable measures to reduce the risk/damage.

BTW the ground lug on the inverter is probably not connected to negative; only to the case.

Cariboocoot wrote: »

Permanent install: ground it.
Non-permanent install: don't ground it.
Sounds strange, but as a non-permanent install it counts as a mobile application like an RV.
The only caveat I'd make there is to ground the inverter & its AC output (probably connected together). Do not tie it to the main house wiring otherwise.



Yes; that's the lug for 6 AWG to go to the grounding rod. With inverters that have outlets the neutral should be connected to the chassis internally. But it may not be. It should say in the manual. But it may not. Helpful, eh?

vtmaps wrote: »

Correct. They can't handle it safely.



I've totally lost track of this thread and your system. Can you summarize where were at?

Generally, as you raise system voltage you can get more power through a given size wire... therefore you may not need to upgrade the wiring. You may need to reconfigure your solar array to provide a higher Vmp.

--vtMaps