When it comes to color coding wires. Are white (or gray) wires / conductors grounded and neutral, or negative? This confuses me as I tend to relate white to negative, however in the text white appears to be neutral and grounded. If that is the case (white wires being neutral and grounded), what would be the color code for negative?
I am totally new to electrical design... sorry if the question sounds redundant? Thanks!
That is a very good question. It is always confusing to people, since many dc wires that are not covered by the NEC use red for positive and black for negative. If you get that wrong on your car, it would not be good and the digital multimeter that we use to measure voltage with is also using the red/black system. We can use the red/black color codes for "ungrounded' inverters/systems. Most grid tied inverters are ungrounded these days, so it is recommended, but not required to use red for positive and black for negative.
Here are other names for ungrounded inverters:
Here are names for grounded conductor
2-Neutral (usually used for ac and not PV source circuits)
A grounded inverter has a grounded conductor and the grounded conductor has to be white or gray. Everyone makes it white or marked white for PV circuits that are exposed to sunlight with PV wire or USE-2 wire.
Like I said, grounded inverters are more rare now, but you will see a lot of them that are already installed. One way to tell it is a grounded inverter is that it has a Ground Fault Detection and Interruption (GFDI) fuse in it.
Grounded inverters can be negatively grounded or positively grounded. Most of the time when they are positively grounded, they are used with old Sunpower PV. Sunpower used to have to be positively grounded to work right.
With normal negatively grounded systems, the negative is white and the positive can be any color that is not already reserved (can't be white, gray, green). Usually on negatively grounded systems the positive is black, since black is more common and stands up better to UV rays when it has special carbon black in it.
This is ironic, since when we are measuring voltage on a negatively grounded PV system with a digital multimeter, we take the black probe and put it on the wire that is not black (negative).
Usually when you have wires 6AWG and smaller, the wire has to be colored and not just marked, however 200.6 in the NEC allows us to mark a black wire white (like with white electrical tape) to indicate that it is a grounded conductor when it is outside USE-2 or PV wire.
I have been informed that in the 2017 NEC, which will be adopted for most installations in the country in 2020 has a big change with respect to the white grounded conductor on dc PV circuits. The white wire will not only not be required, it will not be allowed on systems that are grounded through a fuse. This is very technical and something we cover in detail in our advanced course. Since the grounding is through a fuse, the 2017 NEC committees have decided that it is not "solidly grounded" and should not be white.
Here is another definition that might either clear things up or create more confusion (understanding grounding is something that takes years, decades or a lifetime).
System Grounding: is connecting a current carrying conductor to a ground reference. System grounding is how we ground our grounded conductors. System grounding is not done to ungrounded systems. System grounding is done only in one place per system. If a big building has transformers, then system grounding is done at each transformer. We call this a separately derived system. If we did system grounding at 2 separate places per system, then currents would want to run through the grounded equipment to go from one place to another. We do not want currents to travel on equipment.
Equipment Grounding: is connecting equipment and metal together. We do equipment grounding on grounded and ungrounded systems. Equipment grounding is also known as bonding.
If all of this grounding talk is confusing, take in a little bit and you will see it again throughout this course and the advanced course if enrolled. Grounding is something that people on the Code panels argue the most about when they are writing the Code, because it is a very difficult subject. Don't expect to suddenly understand grounding today. Give yourself a break.
Just remember this for now:
Grounded systems have a grounded current carrying conductor that must be marked white. The negative is usually the grounded conductor in grounded systems, but it can be the positive. Most inverters installed now do not have a dc grounded conductor.