Insulating EMT from PV Racks, etc?

VicVic Solar Expert Posts: 2,998 ✭✭✭✭
For a new off-grid roof-mounted PV installation, am looking for a code complinat method of electrically insulating EMT Conduit being secured to UniRac SolarMount (standard rail). The conduit will be attached to the rail, substantially below the solar panels. Have seen the common red fiberglass channel, and L-brackets used inside electrical distribution equipment, but bet that it is not rated for exposure. Some form of L or U would be nice.

I could make something from UV-resistant ABS, BUT this would not be rated for the exact application.

The insualtion is needed as an attempt to reduce RFI emissions. The racks will be grounded in the traditional way with WEEBs and the Uni grounding clips.

ONE other question: I believe that it is still permitted in the latest NEC, to have NO disconnect on the roof, and place the combiner box (93-ish Vmp) either in an attic space, or in the power room, which is below the arrray. The EMT conduit run will terminate at the Charge Controller breaker box (ie be in metal pipe for the entire run to the CC).

Would normally place the Combiner(s) on the roof, but with fixed mounts, close to the roof, there are some shadows cast by an upright combiner, and do not like to lay the combiner flat against the 30-degree slope of the roof.

Thanks for the thoughts, Vic
Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.

Comments

  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?
    Vic wrote: »

    ONE other question: I believe that it is still permitted in the latest NEC, to have NO disconnect on the roof, and place the combiner box (93-ish Vmp) either in an attic space, or in the power room, which is below the arrray. The EMT conduit run will terminate at the Charge Controller breaker box (ie be in metal pipe for the entire run to the CC).

    Check with your AHJ. Here in Austin, any rooftop PV installation whose wiring penetrates the building must have a disconnect on the roof.
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Hi ggunn,

    Thanks for the reply. Am trying to design and implement to the latest NEC, guess that is 2011. Have 2008 NEC book here, and from that felt that in metal all the way inside the power room structure, to the Combiner was OK. So either am misintreptreting that book, or it has changed in the 2011 code.

    The AJH for the Center of Nowhere is quite absent, for better or worse.

    So there are two arrays, mirror-imaged on the roof total of 8 strings of three panels, and was going to have a combiner for each array, penetrate the roof for each, where the conduit is merged into one, and on to the two main PV breakers and then into two CCs. Shadowing is a bit of a concern, can move the combiners a bit lower on the roof to reduce the shadow etc.

    BUT think that two combiners, each with four string breakers may not constitute "a (one) Disconnect", and 8 breakers may be too many to constitute a Disconnect, and so on. May need to do the merge on the roof, and place a disconnect on the opposite side of a single combiner, if I am reading and inferring correctly.

    Anyway, thanks, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?
    Vic wrote: »
    Hi ggunn,

    Thanks for the reply. Am trying to design and implement to the latest NEC, guess that is 2011. Have 2008 NEC book here, and from that felt that in metal all the way inside the power room structure, to the Combiner was OK. So either am misintreptreting that book, or it has changed in the 2011 code.

    The AJH for the Center of Nowhere is quite absent, for better or worse.

    So there are two arrays, mirror-imaged on the roof total of 8 strings of three panels, and was going to have a combiner for each array, penetrate the roof for each, where the conduit is merged into one, and on to the two main PV breakers and then into two CCs. Shadowing is a bit of a concern, can move the combiners a bit lower on the roof to reduce the shadow etc.

    BUT think that two combiners, each with four string breakers may not constitute "a (one) Disconnect", and 8 breakers may be too many to constitute a Disconnect, and so on. May need to do the merge on the roof, and place a disconnect on the opposite side of a single combiner, if I am reading and inferring correctly.

    Anyway, thanks, Vic

    Combiner and disconnect, um, combined:
    http://www.solarbos.com/products.php?cat=54&prod=14
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Thanks ggunn,

    Boy, the target system is Off-Grid. This code requirement seems to me to be directed toward grid-tied systems, as is this linked disconncet. Being 600 VDC capable, it does seem like overkill.

    But, I did ask, and you did tell, and seems that i do not like the answer. I thought that I had a shadow problem before ... OK Thanks. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Insulating EMT from PV Racks, etc?

    There is no NEC requirement for a disconnect on the roof. Such requirements, where they exist, are local.
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Hi jaggedben,

    Well, in studying the latest NEC that I have, 2008, think that it is not required, but thought that this requirement had crept into NEC 2011. and wanted to try to meet the latest code, But, I am too cheap just now to buy a new NEC. Our jusrisdiction is still using NEC 2008, for most things, at least.

    Due to shadowing issues caused by the combiner and layout, would prefer putting the Combiner/disconnect breaker inside the power room (a first for me).

    Could place a combiner/disco at the peak of the roof, but the power room is at the low end of the roof, and this makes the combiner output almost 30 feet longer and so on.

    Am still mulling these issues. Am an off-gridder in the middle of nowhere, and inspections run far behind the installations.

    Thanks for the help. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?
    Vic wrote: »

    Am still mulling these issues. Am an off-gridder in the middle of nowhere, and inspections run far behind the installations.

    Who does the inspections? Around here the power company that serves your area does them, but if you don't interconnect with the grid, they are out of the picture. I don't think if you are off-grid in Texas that you get inspected at all.

    Likewise for permitting. I once did an installation at a lake house that wasn't in an incorporated area, and I tried for days to get what I thought would be the necessary permits only to find that it was not necessary (or even possible) to get them.

    Are you sure that you will get permitted/inspected?
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Hi ggunn,

    This is very rural, and any inspections would be done by the County. This is an NO GRID for miles, so none of the normal issues with interconnect stuff.

    I will not be asking for an inspection. Some day something may happen, and the County will go on the warpath (perhaps). The neighbors DO NOT want inspectors around. THe only thing that I've ever seen inspected was one well and septic system (all at the same location). Other than that nothing.

    But, if an inspector shows up one day, want things to generally be OK, OK especially considering the location. And, generally the code benefits the property owner and neighbors etc, customarily try to do things cleanly, and as much to code as I can stand.

    At times think that the NEC goes overboard, seems like the insurance Cos want no losses at all, and of course the FireFighter reps want no loss of life (who would). Some tragic event could trigger a county wanting to "clean things up", but doubt there would be a huge revenue opporunity for them in doing so.

    Who knows, Thanks for helping with the code decode. Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    What are the problem frequencies? Have you taken a look at something like SHIELD-FLEX™ to reduce the EMI emissions?
    shieldeffectivenesschart.JPG
    http://www.electriflex.com/products/emirfi.asp

    A shield wrap can also be effective on wiring not in a conduit.
    I use the stuff at home on problems.
    http://farm6.static.flickr.com/5199/5889307539_07684c2074_b.jpg

    http://www.intermark-usa.com/products/EMC/index.shtml#EMI_CSM
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?
    Vic wrote: »
    Hi ggunn,

    This is very rural, and any inspections would be done by the County. This is an NO GRID for miles, so none of the normal issues with interconnect stuff.

    I will not be asking for an inspection. Some day something may happen, and the County will go on the warpath (perhaps). The neighbors DO NOT want inspectors around. THe only thing that I've ever seen inspected was one well and septic system (all at the same location). Other than that nothing.

    But, if an inspector shows up one day, want things to generally be OK, OK especially considering the location. And, generally the code benefits the property owner and neighbors etc, customarily try to do things cleanly, and as much to code as I can stand.

    At times think that the NEC goes overboard, seems like the insurance Cos want no losses at all, and of course the FireFighter reps want no loss of life (who would). Some tragic event could trigger a county wanting to "clean things up", but doubt there would be a huge revenue opporunity for them in doing so.

    Who knows, Thanks for helping with the code decode. Vic

    I doubt you'll ever see an inspector, considering your circumstances. A septic system is a different matter because it is a public health issue. Most utilities don't care if you burn your own house down as long as you don't light up their lines with your inverter when the grid goes down.

    Kudos to you for wanting to build to code, though. Did you look at those Soladeck flush mounted combiner boxes? It seems to me that they are just what you need.
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    nsaspook,

    Thanks for the info on the shielded flex -- The most problematic frequencies are those in the low HF range for inverters (1.8 to about 7.5 Mhz), and extending a bit higher for the MPPT CCs.

    Here, run all power wiring in metal pipe (usually EMT with the cast zinc water resistant fittings + Noalox, or if undergrounded, about 24 or more inches deep in PVC, with rigid exits from the trench (bet this combo is NOT code).

    Naturally, the PV array is still unshielded, and there is nothing that I am willing to do to shield it.

    For residential wiring, use Coleman CorraClad MC type cable -- it has a continuous aluminum extruded/corrogated outside sheath, which I use only as a shield. Because it is continuous (not spiral-wrapped), it is a very good shield:

    https://www.ccixpress.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10101&storeId=10051&langId=-1&top=Y&bu=&categoryId=10650&channel=%24&customer=

    This, plus aggressive Common-Mode chokes on the output of each inverter seperately, as well as a CM choke on the Split-Phase output of the paired inverters, and CMs on the output of each CC. Plus separation of antennas from the PV array (as much as possible) greatly reduces the emissions from the hardware.

    This emission reduction effort has been done unscientifically. THat is, knew that there would be issues with emissions, so did these things during initial construction, so do not have A vs B comparison data to show what did the most, and by what amount. But, these efforts have yielded perfectly acceptable results ... good ENUF for me.

    I do have some fairly large tinned-cpooer braid for power cords etc, but have never needed it. Things are not perfect here, but the LCD Computer monitor creates the largest Birdie, it is unstable and drifts out of the pass-band of HF receivers fairly quickly, and is quite small.

    And, ggunn, thanks again for the advice. Generally agree about the inspection, but never know when some new person will head Planning, and see all the "revenue" opportunities in 'them thar hills', and come in to try to clean things up.

    RE the SolaDeck, have looked at it. First, I just do not like the LOOK of it. Looks like it belongs on an RV. 18 GA Drawn housing, just seems something designed for 12 V or .... And, looks like it will not accommodate the MidNite/CBI breakers -- not deep enough. The included DIN-Rail is not really long enough for my application. Know that this is commonly used my Pro installers, so it must be fine, guess that I am not enough of a Pro. And you are correct, that it will solve any shadow concern, plus, the built-in flashing is great. Just like the 3R boxes that are about 12 GA steel.

    OK Thanks agiain for the advice and tips. Happy Fourth, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Maybe you need to put all that PV equipment in a Faraday cage. :D Sounds like you're got just about everything covered.
    Back in the old days when I operated at a few USN receiver sites we were always having problems with some fancy new digital equipment trashing spots on the HF band. It's one of the reasons that mechanical teletypes were kept so long instead upgrading to digital/crt displays, teletypes were very quiet on the RF spectrum. (ex Navy Radioman RM-2318 and ET-0000)

    http://www.hollandshielding.com/index.php?p=Nieuws&id=109&Lang=2

    MuCopper.jpg
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Hi nsaaspook,

    Thanks for the advice and link. The power rooms are seagoing Cargo Containers. not beautiful copper, but they are all welded steel. The only weakness in the shield is the doors. Had planned to connect each door to the main skin with several tinned-copper brains, but this possible discontinuity has caused no (known) problems. All on the I/O to/from the power rooms is in metal pipe, and the conductors inside the conduit are fairly well filtered. Works well enough -- this is a hobby radio facility.

    Am addicted to Cargo Containers, in general. They are inexpensive, tight, rodent proof and fairly secure. The official Radio Shack is also on one.

    Interesting on being an EX Radioman, and the extended use of the venerable TTY machines. I kinna liked the old Model 28s, and 32 (I think they were 32s). The 33s were inexpensive JUNK, tho. Loved the aroma of the paper tape -- the oil, I think.

    OK thanks again ggunn, and nsaspook. I am going to hack something together for the conduit insulation, prob from some PVC conduit, or non-metallic Flex, and PVC straps designed for PVC conduit. Have a nice Holiday, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • nsaspooknsaspook Solar Expert Posts: 396 ✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    Vic, I was doing some background on a project at work and remembered the chapter from this book (Great Book for basic EM field theory).

    http://www.amazon.com/Electromagnetics-Explained-High-Speed-Electronics-Engineers/dp/0750674032/ref=sr_1_1?s=books&ie=UTF8&qid=1309909117&sr=1-1#reader_0750674032

    12 EMC, page 251 on the Amazon online reader.
    It might provide some leads for your EMI problems.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    "Had planned to connect each door to the main skin with several tinned-copper brains, ......"

    vic,
    i love that typo.8):D:p
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Re: Insulating EMT from PV Racks, etc?

    nsaspook, Thanks for the pointer on the EMI Book ... was not able to look at the page referenced, but seems to be a fine book to own, and not that expensive.

    But, honestly, I have no EMI RFI problems, here. Almost unmeasurable on a transceiver, at least. These measures have worked, and am just now designing a second installation. This one is not using adjustable racks, so the approach that was used on the existing install will not work. And the latest code evidences additional concerns about about temp rise of conduit and wiring contained in it, so am trying to keep almost all of the conduit hidden under panels, hanging it on the UniRac racking seems to be a good approach.

    Will try to snag that book, Thanks!

    AND, niel, Yes, I do not read, spell, compose or see well, so thanks for catching that typo ... OH, it was really just placed there to see if anyone was paying attention.

    73, Thnaks Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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