Combiner boxes

[Eros]

I typically use a Soladek when combining strings on a roof with shingles, but is there a combiner designed for a metal roof - seamed or not ? Thx

 

[69gp]

I typically use a Soladek when combining strings on a roof with shingles, but is there a combiner designed for a metal roof - seamed or not ? Thx

Any kind of combiner box can be used if it is properly mounted and approved for the position in which it is mounted.

 

[jaggedben]

(Why combine on the roof?)
(If residential, generally speaking, why combine at all?)

 

[Eros]

I am combining due to multiple strings of different voltages. I have also found that the
AHJ prefers a "string disconnecting" means within site of the array for possible servicing. Not my call

 

[ggunn]

I am combining due to multiple strings of different voltages. I have also found that the
AHJ prefers a "string disconnecting" means within site of the array for possible servicing. Not my call

Different voltages? Combining in parallel strings of different voltages will result in less than optimum performance.

 

[jaggedben]

what ggunn said.
Rooftop disconnects are a PITA, but...

Try out one (or two) of these multi pole disconnects on your AHJ.
http://www.industrialcontroldirect.com/dc-disconnects-316/enclosed-dc-disconnects-317/

If it's a grounded system, Square D's line of 600V switches are rated for DC and would also be good for disconnecting up to three strings.

I still probably wouldn't combine unless I couldn't meet the requirements with two disconnects. Two disconnects = roughly the same cost as one combiner and one disconnect.

 

[Carultch]

If it's a grounded system, Square D's line of 600V switches are rated for DC and would also be good for disconnecting up to three strings.

For Square D's standard line of 600V switches, that is only true when you connect them with two poles in series. If you have an ungrounded system, you have to do that anyhow.

Other manufacturers often require 3 poles in series.

Also be aware of the NEMA ratings. NEMA3R means it must be mounted upright if outdoors, unless otherwise specified by the manufacturer. Not always easy to mount upright on a sloped roof.

 

[Carultch]

I am combining due to multiple strings of different voltages. I have also found that the
AHJ prefers a "string disconnecting" means within site of the array for possible servicing. Not my call

Never combine multiple strings of different nominal voltages.

It's OK if you are within individual volts, probably due to mixing sequential models within a product family (such as 255W and 260W). Manufacturing tolerances will do this anyhow.

But if you exceed 20 Volts difference, don't do it.

Because think about it. What does a combiner have to do with mixed voltages on its inputs? Well, the output voltage must be the same. And thus the voltage at the combining busbar must be the same for all strings.

The difference in voltages will come from the current adjusting in each string, such that the voltage drop in the circuit will equalize all voltages once combined.

 

[Carultch]

I have also found that the
AHJ prefers a "string disconnecting" means within site of the array for possible servicing. Not my call

Introduce the AHJ to the SolarEdge solution. Disconnect it at the inverter, and the string voltage defaults to 1 volt per optimizer in series, a "safe DC" voltage. And there is little if any, electrical advantage to having a disconnect closer to the array than the inverter. Module-level voltage stops at the input to the module-level optimizer.

No one wants an ugly disconnect on their sleek array. No one cares about flat commercial roofs that aren't visible anyway, but for sloped roofs, it is an eyesore to see any equipment on the roof that isn't concealed by modules.

Maybe there is a better place your AHJ can agree to put it, where it may not necessarily be within sight, but it is within the accessibility path of servicing the array.

 

[jaggedben]

For Square D's standard line of 600V switches, that is only true when you connect them with two poles in series. If you have an ungrounded system, you have to do that anyhow. ...

That's an interesting idea that the two poles of an ungrounded system are connected in series and thus meeting such a requirement. Never really thought about it that way before. I was about to say that the switch label doesn't say anything about this, but I had one handy to look at and there's a very fine print asterisk that denotes to use the outer poles. It's not more specific than that. Seems like I could use the two outer poles for two different circuits and still meet the letter of the label.

 

[Carultch]

That's an interesting idea that the two poles of an ungrounded system are connected in series and thus meeting such a requirement. Never really thought about it that way before. I was about to say that the switch label doesn't say anything about this, but I had one handy to look at and there's a very fine print asterisk that denotes to use the outer poles. It's not more specific than that. Seems like I could use the two outer poles for two different circuits and still meet the letter of the label.

They have a data bulletin which describes this in more detail:
http://www.bfciaei.org/download/pvapplicationsafetyswitches3110DB0401.pdf

 

[jaggedben]

They have a data bulletin which describes this in more detail:
http://www.bfciaei.org/download/pvapplicationsafetyswitches3110DB0401.pdf

Thanks for the resource. I wonder what some AHJs will think of a self-certified non-UL listed application.

 

[BillK-AZ]

Consider the Siemens Photovoltaic Switches

The Power of Three: Solar Photovoltaic Switches

With its truly innovating design, a single Siemens Safety Switch can perform the work of 3 switches by disconnecting up to 3 separate 600V DC circuits with the help of 3 powerful magnets. One of our switches can replace 3 standard switches resulting in lower material and labor costs. Great results, more savings.

Powerful magnets are incorporated into the line base of the switch and are strategically aligned to dissipate the very hot arc generated when a DC circuit is opened under load. This design innovation allows this new disconnects to perform at a level far beyond that of any conventional safety switch on 600V DC circuits.

Siemens enclosed solar photovoltaic switches are available in 30-200A ratings, in Type 1 and 3R enclosures and in both fusible and non-fusible versions. Both negative ground and positive ground switches are available. They are specifically designed for use in photovoltaic applications, which must comply with article 690 of the NEC.

http://w3.usa.siemens.com/powerdistribution/us/en/product-portfolio/switches/solar/Pages/solar.aspx

 

[Carultch]

Consider the Siemens Photovoltaic Switches

The Power of Three: Solar Photovoltaic Switches

With its truly innovating design, a single Siemens Safety Switch can perform the work of 3 switches by disconnecting up to 3 separate 600V DC circuits with the help of 3 powerful magnets. One of our switches can replace 3 standard switches resulting in lower material and labor costs. Great results, more savings.

Powerful magnets are incorporated into the line base of the switch and are strategically aligned to dissipate the very hot arc generated when a DC circuit is opened under load. This design innovation allows this new disconnects to perform at a level far beyond that of any conventional safety switch on 600V DC circuits.

Siemens enclosed solar photovoltaic switches are available in 30-200A ratings, in Type 1 and 3R enclosures and in both fusible and non-fusible versions. Both negative ground and positive ground switches are available. They are specifically designed for use in photovoltaic applications, which must comply with article 690 of the NEC.

http://w3.usa.siemens.com/powerdistribution/us/en/product-portfolio/switches/solar/Pages/solar.aspx

Those switches are polarity sensitive. Use with caution.