Question on test.

[LarryFine]

I never thing of even a known still-connected neutral as safe to touch beyond the service.

Should have been "think."

 

[Eddie702]

It is a bad question and I think you answered it correctly.

 

[tortuga]

Could a manufacturer in theory make a PV system that has a grounded DC neutral and a functionally grounded conductor as part of the same circuit? I always thought of functionaly grounded as a odd way of saying ungrounded wire monotored by ground detector as there is no connection to ground.

 

[ggunn]

This is much ado about nothing. In modern PV systems none of the DC conductors are grounded, functionally or otherwise. On the AC side there is no controversy.

 

[LarryFine]

Could a manufacturer in theory make a PV system that has a grounded DC neutral and a functionally grounded conductor as part of the same circuit?

That reminds me of the HRG (high-resistance ground) of telephone wiring.

What would the difference be between your grounded and the functionally-grounded conductors?

Or should I say, what would be the connection between them?

On the other hand, one conductor could theoretically be shared by two totally different circuits.

 

[ggunn]

This is much ado about nothing. In modern PV systems none of the DC conductors are grounded, functionally or otherwise. On the AC side there is no controversy.

But I hasten to add that off grid systems might be different; I don't do off grid.

 

[tortuga]

This is much ado about nothing. In modern PV systems none of the DC conductors are grounded, functionally or otherwise.

Are you sure ? I have read conflicting things on that some say most are functionally grounded.

That reminds me of the HRG (high-resistance ground) of telephone wiring.

What would the difference be between your grounded and the functionally-grounded conductors?

Or should I say, what would be the connection between them?

On the other hand, one conductor could theoretically be shared by two totally different circuits.

I dont think it would be possible to have a solidly grounded and functionally grounded in the same system but I am no expert.

Just for simplicity sake say a DC PV source circuit is 3 wire 120/240 (shared neutral), and some electronic circuitry is constantly making sure the voltage between the -120 and the +120 and the neutral is correct, but the neutral has no direct connection to earth and no voltage reference to earth, but its kept at zero volts.
Thats what my understanding of functionally grounded is.

 

[ggunn]

Are you sure ? I have read conflicting things on that some say most are functionally grounded.

I didn't think that was true, but if it is, what does it mean? The inverter itself is not "functionally grounded"; it is solidly grounded by the EGC, so that's not an issue. The EGC passes through the inverter to the racking, so the racking isn't functionally grounded. There is no reason for any of the DC conductors to be green, gray, white, etc. (and they never are). It seems to me that the test answer is correct but it's subject to interpretation and furthermore, it's a moot point.

Nothing to see here. Move along.

 

[tortuga]

Nothing to see here. Move along.

I personally dont get why the white / gray requirement stayed in the code when other color codes got removed. and the DC requirements are even more silly.
I rarely trust color codes to be correct, there is a building I used to work on that had black / red / blue for phase 1, 2 and 3 then somewhere it became blue / red / black for phases 1,2,3

 

[solarken]

690.31(B)(2)(b) defines the identification requirements. Nonsolidly grounded negative conductors (i.e. functionally grounded) shall include imprinted negative signs or similar marking on the insulation of a color other than green, white, gray, or red. Only solidly grounded PV system dc circuits shall be marked in accordance with 200.6

So none of the answers you could choose from were correct. The correct answer is "a color other than green, white, gray, or red".

 

[don_resqcapt19]

Functional grounding is only used in 690 so we are not going to find it called out in the general Art. 200. In 200 is refers to grounded conductors.

And functionally grounded conductor is a special case of grounded conductor. The code needs work on this.

 

[ggunn]

I personally dont get why the white / gray requirement stayed in the code when other color codes got removed. and the DC requirements are even more silly.
I rarely trust color codes to be correct, there is a building I used to work on that had black / red / blue for phase 1, 2 and 3 then somewhere it became blue / red / black for phases 1,2,3

But of course you know that the BRB color code is a local thing and not in the NEC.

 

[ggunn]

And functionally grounded conductor is a special case of grounded conductor. The code needs work on this.

So, exactly what is a functionally grounded conductor and where can it be found? With transformer coupled inverters one could say that the negative DC conductor was functionally grounded, but they have gone the way of the dodo.

 

[solarken]

And functionally grounded conductor is a special case of grounded conductor. The code needs work on this.

A functionally grounded conductor is a special case of a non-solidly grounded conductor, which is a special case of a grounded conductor, but the nonsolidly grounded conductor color coding is defined clearly in 690.31(B)(2)(b), so I don't see why any further code work is needed.

 

[tortuga]

So none of the answers you could choose from were correct. The correct answer is "a color other than green, white, gray, or red".

Just a nit pick you could have a functionally grounded positive.
just like the positive grounded systems such as -48 DC.

 

[tortuga]

But of course you know that the BRB color code is a local thing and not in the NEC.

The building has two systems so they post the phase identification means, but then they change the phase relationship somewhere.

 

[solarken]

Just a nit pick you could have a functionally grounded positive.
just like the positive grounded systems such as -48 DC.

Yes, the same NEC article I referenced includes the color code requirements for nonsolidly grounded positive. So SEI did have a correct answer for that specific case, but they did not specify POS or NEG, so I think I agree with everyone this was a badly worded question.

 

[tortuga]

The insulation on a functionally grounded conductor must be:
Select one:
white or gray
green or bare copper
red or black
any color except white, gray, or green

the nonsolidly grounded conductor color coding is defined clearly in 690.31(B)(2)(b), so I don't see why any further code work is needed.

I'd say that last sentence "Only solidly grounded pv system dc circuit conductors shall be marked in accordance with 200.6" should be its own paragraph (c) as its not enforceable if the functional ground is a neutral.

 

[Tulsa Electrician]

So the question was more about definitions than color nowledge.

View attachment 2572091

Love that show. Yout, what's a yout.

 

[tortuga]

Its a trick question as Larry pointed out, and for good reason you would not want to see a 'functionally grounded' wire landed on a ground or neutral bar tied to ground. And old systems are out there, I recently repaired a trace inverter from 1999 that is UL1729 listed and pumping out 4kw.