DC LABEL

[Zee]

I have multiple questions about the correct amperages to print on the "DC LABEL".
This is the label required on any DC system that lists:

Rated Maximum Power-point Current:
Rated Maximum Power-point Voltage:
Maximum System Voltage:
Rated Short-Circuit Current:


Take this example: module Imp is 8 A, and module Isc is 9 A.

a. If only one string in system, then what are the amounts to print in the two lines?

b. If two strings and I combine in a CB, then what are the amounts to print in the two lines?

c. If two strings but I do NOT combine in CB, but run in separate conductors to single inverter (where they are combined in effect), then what are the amounts to print in the two lines?

 

[Carultch]

I have multiple questions about the correct amperages to print on the "DC LABEL".
This is the label required on any DC system that lists:

Rated Maximum Power-point Current:
Rated Maximum Power-point Voltage:
Maximum System Voltage:
Rated Short-Circuit Current:


Take this example: module Imp is 8 A, and module Isc is 9 A.

a. If only one string in system, then what are the amounts to print in the two lines?

b. If two strings and I combine in a CB, then what are the amounts to print in the two lines?

c. If two strings but I do NOT combine in CB, but run in separate conductors to single inverter (where they are combined in effect), then what are the amounts to print in the two lines?

A: The first line is based on the OPERATING current. Maximum power-point current or Imp on a module datasheet.
The final line is based on the short circuit current, also including the 1.25 enhancement factor, as a worst case scenario current. Start with Isc on a module datasheet, then multiply by 1.25.

B: When I make this label for combiners, I make a version that describes the input with a title that says "Single source circuit input", and then a version that describes the output with a title that says "Combined DC Output". Or at an inverter, the title might be "Total inverter DC input".

C: If the circuits within the enclosure are not combined, then I recommend only the one version describing the individual circuits on their own. Also, this label is not required at a transition enclosure. It is required at inverters, combiners, and any enclosure with an OCPD or disconnect.

 

[GoldDigger]

It is required at inverters, combiners, and any enclosure with an OCPD or disconnect.

And, IMHO, at each inverter it should only describe the DC input to that inverter if there is more than one inverter.

If there are two inputs to one inverter, each with separate disconnects, I think Carultch is saying that technically the required label for the inverter will be different from the labels of the two disconnects.

 

[Carultch]

And, IMHO, at each inverter it should only describe the DC input to that inverter if there is more than one inverter.

If there are two inputs to one inverter, each with separate disconnects, I think Carultch is saying that technically the required label for the inverter will be different from the labels of the two disconnects.

Agreed. No point in describing the DC input to other unrelated inverters.

As for an inverter with multiple inputs, that makes it much more interesting. If you are thinking of an inverter like a typical central inverter, that has several DC breakers combined in a subcombiner, and then a master OFF switch, I'd put one of these labels on each of the subcombiner breakers identifying the details of that particular zone, and then provide a combined label for the master switch.

If you are talking about an inverter with multiple MPPT zones, then I'd make a label for each, which say "Input A: DC Specifications" and "Input B: DC Specifications".

 

[jaggedben]

If you are talking about an inverter with multiple MPPT zones, then I'd make a label for each, which say "Input A: DC Specifications" and "Input B: DC Specifications".

This is what most residential inverters will involve these days if there's more than one string. I agree with the approach.

 

[SolarAlternativesDesign]

In small residential systems I have been assuming that if two or more source circuits come into an inverter it would be sufficient to list the current and voltage of the one with highest current. It would give a worst case notice to workers without the clutter of more labels. Is that the purpose of these labels?

 

[jaggedben]

If you look at the 2014 code, 690.53 (4) was amended to say that for multiple outputs the maximum current should be specified for each output. (Output here is from the PV source, so the same as an inverter input.) Oddly, this applies only to maximum current, so if you don't do a whole new label for voltage or operating current you're still code compliant.

I honestly don't know what the exact purpose of the label is supposed to be, but I think the general idea is that someone servicing the system is supposed to be able to figure out the level of hazard they face, as well as quickly determine if there is something wrong. In that sense, the clearer the info the better.

 

[SolarAlternativesDesign]

I hadn't noticed the 2014 change. Strange that it requires multiple labeling of current but not voltage. In the cases I've seen, the differing inverter input circuits are single strings of different lengths coming into different MPPT groups so the voltage varies between circuits but the current is the same.

A residential inverter with integrated DC disconnect is usually pretty cluttered with labels. Would it be good to just put both currents in the space, like "9.2A/9.2A" rather than placing multiple labels?

I see the Hellermann Tyton DC disconnect labels are still the same as in the past and pvlabels.com has the same information boxes but changed colors from red and white to black and white with a black on yellow caution symbol.

 

[jaggedben]

I agree it's weird the code doesn't explicitly require labeling the different voltages. After all, if you have one string on each MPPT and they are different lengths, then you have different voltages but the same current per MPPT (presuming all the modules are the same, of course.) Occasionally you'll have two strings connected to one MPPT and one to the other, in which case both are likely different.

The simplest solution to me is just to put two Hellerman labels, one per MPPT. Clutter notwithstanding.

 

[Anode]

I have multiple questions about the correct amperages to print on the "DC LABEL".
This is the label required on any DC system that lists:

Rated Maximum Power-point Current:
Rated Maximum Power-point Voltage:
Maximum System Voltage:
Rated Short-Circuit Current:


Take this example: module Imp is 8 A, and module Isc is 9 A.

a. If only one string in system, then what are the amounts to print in the two lines?

b. If two strings and I combine in a CB, then what are the amounts to print in the two lines?

c. If two strings but I do NOT combine in CB, but run in separate conductors to single inverter (where they are combined in effect), then what are the amounts to print in the two lines?

We will always use multiple labels if MPPT's are different, but here is my own approach and reasoning to both this and the amperage question:

If you have two strings in one channel and two in the other, provide two labels.

Label one, provide the combined amperages; label two, just the single string. Reasoning is, one, it is nice for the homeowner or inspector to be able to add up those values and ensure that there is no issue with the ratings of the dc box. Two, it just makes sense to label the max value you might see if you tested at a point where the strings are combined with testing equipment, or what you might come in contact with if you weren't a careful electrician.

To put that in perspective, would you want to see ratings of one string on an 8 string combiner? I would want to see what the total amperage is there, for convenience and safety.

 

[Zee]

I appreciate the input from all y'all. :thumbsup:

1. Would everyone agree that Imp doesn't get the 125% factor applied.... while Max Amps = Isc multiplied by 125%?

2. Here are some samples of how i deal (I print the labels on desktop) (all numbers are just made up here)
a. 2 strings of different length:

Rated Maximum Power-point Current: 8A
Rated Maximum Power-point Voltage
string 1 and 2: 320V, 400V
Maximum System Voltage
string 1 and 2: 480V, 600V
Rated Short-Circuit Current: 9A (<------i guess i should be adding 25% here)

b. Combiner Box. I split it into 2 labels:
PV SOURCE CIRCUITS:
Rated Maximum Power-point Current 8A
Rated Short-Circuit Current 9A (<------i guess i should be adding 25% here)
Rated Maximum Power-point Voltage 400V
Maximum System Voltage 600V

COMBINED OUTPUT:
Rated Maximum Power-point Current 16A
Rated Short-Circuit Current 18A (<------i guess i should be adding 25% here)Rated Maximum Power-point Voltage 400V
Maximum System Voltage 600V

 

[Zee]

To put that in perspective, would you want to see ratings of one string on an 8 string combiner? I would want to see what the total amperage is there, for convenience and safety.

I would want to see both.

 

[jaggedben]

I appreciate the input from all y'all. :thumbsup:

1. Would everyone agree that Imp doesn't get the 125% factor applied.... while Max Amps = Isc multiplied by 125%?

Yes. To be honest, I haven't been doing it either (we do very few straight string systems), but looking at 690.8 and 690.53 language, yes we should be.

 

[Zee]

Yes. To be honest, I haven't been doing it either (we do very few straight string systems), but looking at 690.8 and 690.53 language, yes we should be.

Well i'll gotta change then. Darn! By a whole 25%.

 

[jaggedben]

Just one thing to add, for what it's worth...

On SolarEdge systems we put max circuit current as 15A based on the optimizer's limit, and we DON'T add 25% in that case, and I'm not going to change doing that. Code needs to catch up on optimizers but I the extra 25% for source circuits is based on possible higher current from better-than-STC conditions. Doesn't apply to optimizer outputs.

 

[ggunn]

Just one thing to add, for what it's worth...

On SolarEdge systems we put max circuit current as 15A based on the optimizer's limit, and we DON'T add 25% in that case, and I'm not going to change doing that. Code needs to catch up on optimizers but I the extra 25% for source circuits is based on possible higher current from better-than-STC conditions. Doesn't apply to optimizer outputs.

And that is true for calculating conductor sizing and OCPD as well for SolarEdge systems.

Once I had an inspector fail a SE system of mine for overvoltage because he saw my strings of 17 and multiplied Voc by 17. He knows better now.

 

[Zee]

And that is true for calculating conductor sizing and OCPD as well for SolarEdge systems.

Once I had an inspector fail a SE system of mine for overvoltage because he saw my strings of 17 and multiplied Voc by 17. He knows better now.

Aahhh live and learn.
Yes, good point on SolarEdge systems. Technically, it is a string of optimizers...not a string of modules. There is no Code for that.
(After all, the modules plug individually into their own optimizers, the modules never daisy-chaining together. So optimizer specs are relevant.)

My labels always look something lie this:
15A (30A if two strings, 45A etc)
350V
500V

 

[Carultch]

Aahhh live and learn.
Yes, good point on SolarEdge systems. Technically, it is a string of optimizers...not a string of modules. There is no Code for that.
(After all, the modules plug individually into their own optimizers, the modules never daisy-chaining together. So optimizer specs are relevant.)

My labels always look something lie this:
15A (30A if two strings, 45A etc)
350V
500V

Another issue that old-school skeptics have with Solaredge systems is that they may see that the maximum optimizer voltage is 60 Volts. And a skeptic might take a Murphy's law approach, assuming that all optimizers in series produce full voltage simultaneously. Far exceeding the 500V limit controlled by the inverter, and the 350V normal operating target voltage of the inverters among the optimizers.

No optimizer string produces the full 60V per optimizer all at once. That is simply a margin, in the event that some optimizers are not producing much at all, and the others have to "pull up the slack". The inverter limits the maximum voltage, and has another voltage that it targets.

 

[SolarAlternativesDesign]

SolarEdge provides a technical document documenting 690.53 labeling values for their systems.

http://www.solaredge.com/sites/default/files/pv_power_source_labeling.pdf

They point out that the rated maximum power point current is either the array rated power/350V (for 240V systems), or the inverter max input current rating, whichever is less.

For max power point voltage they use 350V (for 240V systems).

For max system voltage they use 500V (for their single phase inverters) which is the inverter max input voltage, noting that if the inverter is not operating the array voltage is reduced to 1V/module by the optimizers.

For max circuit current, they use 15A/string X no. strings.