NEC 2017 labels

[Zee]

Time to review what labels are needed per NEC 2017.

1.
This one is new to me:

NEC 705.12(B)(2)(3)(c)
WARNING
THIS EQUIPMENT FED BY MULTIPLE
SOURCES.
TOTAL RATING OF ALL OVERCURRENT
DEVICES EXCLUDING MAIN SUPPLY
OVERCURRENT DEVICE SHALL NOT EXCEED
AMPACITY OF BUSBAR.

Is it needed on all PV systems, or any?

2.
This seems to be a good idea to apply to an Enphase CB, or dedicated solar AC combining panel. Is there any code reference for it?

PHOTOVOLTAIC CIRCUITS ONLY.
NO ADDITIONAL CIRCUITS ALLOWED

3.
This seems to have gone away:
NEC 690.35 (F)

WARNING
ELECTRIC SHOCK HAZARD.
THE DC CONDUCTORS OF THIS
PHOTOVOLTAIC SYSTEM ARE
UNGROUNDED AND MAY BE ENERGIZED

4.
Looks like the 4-line DC V and A label went away and is now just 2 lines (3 lines if charge controller)
What is the max current, 15A or 18.75, on an optimizer system?
and in general: Isc or Isc x 125%?

MAXIMUM VOLTAGE 480 V
MAXIMUM CIRCUIT CURRENT 18.75 A

Apply at DC Disconnects - NEC 690.53

5.
And, for the love of god, stop putting this on the AC side.

WARNING
ELECTRIC SHOCK HAZARD
TERMINALS ON THE LINE AND
LOAD SIDES MAY BE
ENERGIZED IN THE OPEN POSITION

Apply at DC Junction boxes, DC Disconnects
NEC 690.13(B)

 

[Carultch]

Label 1 applies, if you are using the sum of the breakers <= busbar rating rule, in order for the busbar interconnection to comply. If you are not using that rule, you would ignore it. Label 2 would apply if you are dedicating a panelboard to the solar, i.e. an AC combiner, and don't want foreign loads added in the future that would make it no longer NEC compliant.

In label 4, it is 1.25*Isc that would apply for your current, if it comes directly from the panels without any current-limited power electronic device prior to this point. Of course if circuits are paralleled, you would multiply by the number in parallel as well. If it does use optimizers or other DC/DC converter, then it would be the value directly off that datasheet for the DC/DC converter's maximum current. So it would be 15A for optimizers. Multiple optimizer circuits in parallel would start at being qty*15A, but if it exceeds the maximum input that the inverter can take (for instance 45A for 3 strings exceeding 40A for the 14.4kW unit), it would be the maximum input current of the inverter.

 

[ggunn]

One thing to keep in mind about label #1 is that it applies to the busbar, not necessarily the panel as a whole. For example, if you are using a 3 phase panel to aggregate multiple single phase inverters, only the breakers that land on a busbar count toward the breaker limit for that busbar.

 

[Zee]

Whoa, slow down. re #1, I missed this rule!

-Are you saying that in a residential service panelboard, rated 200A, main breaker also 200A , and I total the (E) load breakers.....subtract that total of load breakers from the main brkr......then I can install the balance as PV?

-e.g. 200A rated service /200A main breaker with (E) 2 @ 2p60A breakers in it .....I can install: 200-(60+60) = 80A PV brkr?

- Would this label #1 apply to an existing residential service panel where I exploit the 120% rule, opposite feed, etc? (dont see why it would, but others contest this)?

To be totally clear: is it EITHER label #1, OR the "DO NOT RELOCATE....." label (120% rule)?

 

[Zee]

One thing to keep in mind about label #1 is that it applies to the busbar, not necessarily the panel as a whole. For example, if you are using a 3 phase panel to aggregate multiple single phase inverters, only the breakers that land on a busbar count toward the breaker limit for that busbar.

Would this math work in similar fashion for a single phase 240VAC busbar ....such that I may be permitted to total single pole breakers separately for each relevant busbar they attach to?

 

[jaggedben]

Whoa, slow down. re #1, I missed this rule!

-Are you saying that in a residential service panelboard, rated 200A, main breaker also 200A , and I total the (E) load breakers.....subtract that total of load breakers from the busbar.....then I can install the balance as PV?

-e.g. 200A rated service /200A main breaker with (E) 2 @ 2p60A breakers in it .....I can install: 200-(60+60) = 80A PV brkr?

You've been missing this rule for three years, it was in the last code, too.

I highlighted one small correction I made, which ggunn already alluded to. In your example, if the busbar happened to be 225 you'd have another 25A to work with, or 105A.

With that said, in three years I don't think I ever used that rule once on an existing panel. Most load breaker sums exceed the panel busbar rating.

- Would this label #1 apply to an existing residential service panel where I exploit the 120% rule, opposite feed, etc? (dont see why it would, but others contest this)?

To be totally clear: is it EITHER label #1, OR the "DO NOT RELOCATE....." label (120% rule)?

No, and yes.

 

[Carultch]

Would this math work in similar fashion for a single phase 240VAC busbar ....such that I may be permitted to total single pole breakers separately for each relevant busbar they attach to?

For single phase 120/240V systems, or anything else with busbars at an equal and opposite voltage from neutral:
Put all the L1 to neutral circuits in column 1.
Put all the L2 to neutral circuits in column 2.
Put the 2-pole circuits connected to both L1 to L2 in both columns.
Add up both columns separately. Whichever is greater, is the one that governs.

For 3-phase WYE systems,as long as you don't have 2-pole circuits, the same strategy applies. 1-pole circuits go in only one column of columns A, B, or C. 3-pole circuits go in all 3 columns. Then add each of them up, to get totals Ia, Ib, and Ic. Note lowercase a, b, and c for these subtotals, as I'll use capital letters later. If there are no 2-pole circuits, we pick the largest of these three currents, and we're done.

If there are 2-pole circuits, we need another 3 columns. AB, BC, and CA. Put each 2-pole circuit in its corresponding phase-to-phase column. Add them up to get totals, Iab, Ibc, and Ica.

Then we'll use the square root formula, to combine each phase-to-phase current that contributes to each of the three phases.
IA = Ia + sqrt(Iab^2 + Ica^2 + Iab*Ica)
IB = Ib + sqrt(Iab^2 + Ibc^2 + Iab*Ibc)
IC = Ic + sqrt(Ica^2 + Ibc^2 + Ica*Ibc)

Lowercase letters after I, are the total currents on each phase, before we thought about 2-pole circuits. Capital letters IA, IB, and IC, indicate that we've now included contributions from phase-to-phase circuits. The largest among IA, IB, and IC, is what governs.

 

[Carultch]

Whoa, slow down. re #1, I missed this rule!

-Are you saying that in a residential service panelboard, rated 200A, main breaker also 200A , and I total the (E) load breakers.....subtract that total of load breakers from the main brkr......then I can install the balance as PV?

-e.g. 200A rated service /200A main breaker with (E) 2 @ 2p60A breakers in it .....I can install: 200-(60+60) = 80A PV brkr?

Define the following shorthand terms:
MCB = main breaker trip setting.
BUS = busbar ampacity
PVB = PV interconnecting breaker trip setting
Ipv = total of inverter currents

In 2011, the rule was:
MCB + PVB ≤ 1.2*BUS, as long as it is at the opposite end of the bus from the main supply
or:
MCB + PVB ≤ 1*BUS, and it could be anywhere on the busbar

Obviously, you'd like to use the opposite end of the busbar if you could, because it means you can take advantage of the fact that currents in opposite directions cancel one another out, and don't accumulate.

In 2014, the NEC replaced PVB, with the calculation that sizes it (1.25*Ipv). This avoids round-up errors being a show stopper, that inevitably happen when selecting a standard size breaker. It gives you marginally greater capacity you can interconnect on the load side.

Opposite end:
MCB +1.25*Ipv ≤ 1.2*BUS

Anywhere on the bus:
MCB + 1.25*Ipv ≤ 1*BUS

Here's an example where the difference between NEC 2011 and NEC 2014 matters:
MCB = 600A
BUS = 600A
1.2*BUS = 720A
720A - 600A = 120A

A 120A breaker isn't a standard rating. 110A is the next size down, 125A is next size up. In 2011, you'd be limited to 110A of breaker, which would mean 88A of inverters. In 2014, you'd be allowed to have up to 96A of inverters,which would need a 125A breaker.

 

[Carultch]

To be totally clear: is it EITHER label #1, OR the "DO NOT RELOCATE....." label (120% rule)?

If you use the 120% rule, it is the "do not relocate" label.
If you use the "sum of the breakers rule", it is Label #1 in the original post.

In the rare event that you use the 100% anywhere-on-the-bus rule that comes before the 120% rule in the NEC, neither of these labels would apply. There still would be labels identifying the point of interconnection, but NEC compliance would be less sensitive to the presence of other loads, or the location of the breaker. What future electricians do with the panel is more flexible.

 

[ggunn]

For single phase 120/240V systems, or anything else with busbars at an equal and opposite voltage from neutral:
Put all the L1 to neutral circuits in column 1.
Put all the L2 to neutral circuits in column 2.
Put the 2-pole circuits connected to both L1 to L2 in both columns.
Add up both columns separately. Whichever is greater, is the one that governs.

For 3-phase WYE systems,as long as you don't have 2-pole circuits, the same strategy applies. 1-pole circuits go in only one column of columns A, B, or C. 3-pole circuits go in all 3 columns. Then add each of them up, to get totals Ia, Ib, and Ic. Note lowercase a, b, and c for these subtotals, as I'll use capital letters later. If there are no 2-pole circuits, we pick the largest of these three currents, and we're done.

If there are 2-pole circuits, we need another 3 columns. AB, BC, and CA. Put each 2-pole circuit in its corresponding phase-to-phase column. Add them up to get totals, Iab, Ibc, and Ica.

Then we'll use the square root formula, to combine each phase-to-phase current that contributes to each of the three phases.
IA = Ia + sqrt(Iab^2 + Ica^2 + Iab*Ica)
IB = Ib + sqrt(Iab^2 + Ibc^2 + Iab*Ibc)
IC = Ic + sqrt(Ica^2 + Ibc^2 + Ica*Ibc)

Lowercase letters after I, are the total currents on each phase, before we thought about 2-pole circuits. Capital letters IA, IB, and IC, indicate that we've now included contributions from phase-to-phase circuits. The largest among IA, IB, and IC, is what governs.

While that is true for calculating line currents, that's not what the code says in that section of 705.12(B) or (D), depending on which code cycle you are on from 2014 and later. In subsection (2)(3)(c) it says that a bus can be qualified by having all the ratings of breakers connected to it, both supply and load, excluding the breaker protecting it, total less than the bus rating. Phase/line currents do not figure into the calculation.

 

[Zee]

You've been missing this rule for three years, it was in the last code, too.

Yeah, been having too much fun!

Excellent summary, guys, thank you!