Re: [RE-wrenches] down-sizing main breaker
Allan: I whipped up three drawings that indicate three overload scenarios possible with incorrectly sized distribution equipment. They are on our web site at: http://millersolar.com/case_studies/case_studies.html Click on Point of connection. Click on any drawing to see a larger version. I hope this helps with understanding the concept. William Miller At 06:19 PM 8/1/2009, you wrote: William, I have been following this back-and-forth thread and need you to please explain one thing: Your 140A point makes perfect sense (from the point of 690.64 in requiring that the busbar to which both utility and PV feeds are connected. No question there. But you write: It is my understanding that if one is going to install a load side tape, the back feed calculations need to work for every link of the distribution system upstream to the meter. It seems to me that there's still no way to exceed main disconnect current rating. * 100A utility (using 100A subpanel main) + 40A PV tied into subpanel busbar = 140A, which is OK if the subpanel busbar is rated at least 125A (residential) or 150A (commercial). * 100A + 40A tapped into subpanel ahead of 100A main breaker: * maximum current passing through 100A main breaker = 100A. Adding 40A of PV only reduces amount through conductors from main AC panel to 60A. * no AC load in daytime = 40A of current back to main AC load center * some subpanel loads in daytime reduces 2.b. above * At the main panel, maximum current flow through breaker feeding subpanel is 100A, as any PV reduces load at breaker. However, main panel must itself meet 690.64, as it's still possible to feed 40A of PV (daytime with no subpanel load) into main panel. So same busbar requirements apply in the main panel as in the subpanel. But that's all. The subpanel feeders don't need to be upsized. What am I missing here, please? Allan Sindelar mailto:al...@positiveenergysolar.comal...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 http://www.positiveenergysolar.comwww.positiveenergysolar.com -- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Saturday, August 01, 2009 6:11 PM To: RE-wrenches Subject: Re: [RE-wrenches] down-sizing main breaker Dick: Your logic is correct but incomplete. Consider it like this: The buss bars in the service panel can handle 100 amps (they are rated for that amount). The main breaker feeds 100 amps into that buss, maximizing it's capabilities. If you feed an additional 40 amps into that buss bar, you have the potential of exceeding the ampacity of that buss assembly. If no other loads are fed from that buss bar, there is no over current scenarios. Say, however, someone puts more breakers on that buss bar and draws 140 amps from them. 100 amps comes in from the utility, 40 amps comes in from the PV and the buss is overloaded. This is the scenario for which 690.64(B) was written. This will occur only if the overload amperage is not drawn from a space on the buss bar between the utility feeder and the PV feeder. If, however, the PV feeder breaker and the utility feeder are both on one end of the buss and the load is on the other end, then the loads are additive on the buss assembly. Some want the code passage re-written to say that if the feeder is on one end of the bus assembly and the PV is on the other, there is no possibility of an overdraw on the buss bar and the installation is legal. This has not happened yet. William ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] Surge protector update?
To piggy-back on the question, and also continue my grounding on a glacier question is anyone familiar with point dissipators and have used them. Todd mentioned Nott LTD http://www.nottltd.com/lightning.html in my last string and I have come acrooss Lightning Masters http://www.lightningmaster.com/index.html Both I believe use some form of point dissipation. They are suppose to take ambient static buildup and dissipate it slower at high voltage levels keeping the current and damage to equipment at a minimum. Have anyone of you used these systems, or know much about using them on an array, glacier, spaceship, marmot, midget, motorhome, or the like? Jay Jay Pozner Nunatak Alternative Energy Solutions Crested Butte, CO 970 349-3432 On Sat, Aug 1, 2009 at 10:09 AM, Exeltech exelt...@yahoo.com wrote: Jay, Installing a part in a factory doesn't make a product ok. Would be nice, but it doesn't work that way... I use UL here .. but it can be any Nationally Recognized Testing Lab (ETL, CSA, UL, etc) Any UL Listed product, or any UL Recognized part or sub-assembly must either use components that in of themselves are also Listed and/or Recognized to specific UL Standards, or prove during UL testing of the final product that any uncertified component(s) used within the product being tested fully meet the applicable Standard(s) for such parts. Failing that, the unit in question won't qualify for Listing/Recognition, and no UL (or equivalent lab) certification will be issued for that product by any Nationally Recognized Testing Lab. UL. ETL. CSA. etc... Just as all grounding components in a system must meet code, which requires the use of agency certified parts .. use of a non-certified part as a protective element is likely to get the system red-tagged, as Holt pointed out earlier in this thread. For notes .. not everyone is aware that agency certification refers to UL, ETL, CSA, and a number of other OSHA-certified Nationally Recognized Testing Labs. Product approvals from any of these labs are equivalent, though they're not always treated as such by AHJs or others who aren't well informed on this issue. Thankfully, the It must be UL attitude by AHJs and others is steadily fading as an issue. Not gone - but fading... Dan --- On Sat, 8/1/09, jay peltz j...@asis.com wrote: Sure, if you install something electrical that is not UL, they can fail it. Even though that same part installed in a factory is OK. jay ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] down-sizing main breaker
William, Wow - you're a master at whipping up drawings! OK, I get the concept, and it's just as I described. The scenarios in drawings one and two are OK as long as both busbars are rated 150A (commercial) or 125A (residential. You then show that the reason for the upsized feeders is to handle a short. But wait! Even if the short could produce 140A, as you have indicated, the conductors will still not carry more than the 100A that they're rated to carry. One would carry 100A from one panel and 40A from the other, Nowhere would that conductor carry 140A, and the mate to it would carry at most 60A. Increasing conductor size wouldn't change anything in that (or any) scenario. So why would you have to increase conductor size? Thanks, Allan _ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Saturday, August 01, 2009 11:13 PM To: RE-wrenches Subject: Re: [RE-wrenches] down-sizing main breaker Allan: I whipped up three drawings that indicate three overload scenarios possible with incorrectly sized distribution equipment. They are on our web site at: http://millersolar.com/case_studies/case_studies.html Click on Point of connection. Click on any drawing to see a larger version. I hope this helps with understanding the concept. William Miller At 06:19 PM 8/1/2009, you wrote: William, I have been following this back-and-forth thread and need you to please explain one thing: Your 140A point makes perfect sense (from the point of 690.64 in requiring that the busbar to which both utility and PV feeds are connected. No question there. But you write: It is my understanding that if one is going to install a load side tap, the back feed calculations need to work for every link of the distribution system upstream to the meter. It seems to me that there's still no way to exceed main disconnect current rating. 1. 100A utility (using 100A subpanel main) + 40A PV tied into subpanel busbar = 140A, which is OK if the subpanel busbar is rated at least 125A (residential) or 150A (commercial). 2. 100A + 40A tapped into subpanel ahead of 100A main breaker: 1. maximum current passing through 100A main breaker = 100A. Adding 40A of PV only reduces amount through conductors from main AC panel to 60A. 2. no AC load in daytime = 40A of current back to main AC load center 3. some subpanel loads in daytime reduces 2.b. above 3. At the main panel, maximum current flow through breaker feeding subpanel is 100A, as any PV reduces load at breaker. However, main panel must itself meet 690.64, as it's still possible to feed 40A of PV (daytime with no subpanel load) into main panel. So same busbar requirements apply in the main panel as in the subpanel. But that's all. The subpanel feeders don't need to be upsized. What am I missing here, please? Allan Sindelar al...@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com _ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Saturday, August 01, 2009 6:11 PM To: RE-wrenches Subject: Re: [RE-wrenches] down-sizing main breaker Dick: Your logic is correct but incomplete. Consider it like this: The buss bars in the service panel can handle 100 amps (they are rated for that amount). The main breaker feeds 100 amps into that buss, maximizing it's capabilities. If you feed an additional 40 amps into that buss bar, you have the potential of exceeding the ampacity of that buss assembly. If no other loads are fed from that buss bar, there is no over current scenarios. Say, however, someone puts more breakers on that buss bar and draws 140 amps from them. 100 amps comes in from the utility, 40 amps comes in from the PV and the buss is overloaded. This is the scenario for which 690.64(B) was written. This will occur only if the overload amperage is not drawn from a space on the buss bar between the utility feeder and the PV feeder. If, however, the PV feeder breaker and the utility feeder are both on one end of the buss and the load is on the other end, then the loads are additive on the buss assembly. Some want the code passage re-written to say that if the feeder is on one end of the bus assembly and the PV is on the other, there is no possibility of an overdraw on the buss bar and the installation is legal. This has not happened yet. William ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette:
Re: [RE-wrenches] down-sizing main breaker
Allan: At the point of the short circuit, the amperage will exceed the rating of a 100 amp feeder. If the main panel had no extra breaker spaces, it could still be subject to a short circuit if, for example, a wrench is dropped into it. I should add that I am not an electrical engineer nor am I trying to justify the codes that apply. I am just trying to explain how I see the codes are applied. It is necessary to understand this to avoid incorrect system design and fruitless discussions with building officials. William At 07:22 AM 8/2/2009, you wrote: William, Wow youre a master at whipping up drawings! OK, I get the concept, and its just as I described. The scenarios in drawings one and two are OK as long as both busbars are rated 150A (commercial) or 125A (residential. You then show that the reason for the upsized feeders is to handle a short. But wait! Even if the short could produce 140A, as you have indicated, the conductors will still not carry more than the 100A that theyre rated to carry. One would carry 100A from one panel and 40A from the other, Nowhere would that conductor carry 140A, and the mate to it would carry at most 60A. Increasing conductor size wouldnt change anything in that (or any) scenario. So why would you have to increase conductor size? Thanks, Allan -- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Saturday, August 01, 2009 11:13 PM To: RE-wrenches Subject: Re: [RE-wrenches] down-sizing main breaker Allan: I whipped up three drawings that indicate three overload scenarios possible with incorrectly sized distribution equipment. They are on our web site at: http://millersolar.com/case_studies/case_studies.html Click on Point of connection. Click on any drawing to see a larger version. I hope this helps with understanding the concept. William Miller ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] down-sizing main breaker
Wlliam, If there were to be a short circuit in the feeder or the main service panel ( the one with no extra breaker spaces ), the solar's maximum 50 amp contribution would be about the last thing to be concerned about. A short is going to result in perhaps 1000s of amps coming from the grid into the short. The service 100 amp breaker will trip immediately and clear the fault. The inverter will lose the grid and drop offline. End of story. Dick --- You wrote: Allan: At the point of the short circuit, the amperage will exceed the rating of a 100 amp feeder. If the main panel had no extra breaker spaces, it could still be subject to a short circuit if, for example, a wrench is dropped into it. I should add that I am not an electrical engineer nor am I trying to justify the codes that apply. I am just trying to explain how I see the codes are applied. It is necessary to understand this to avoid incorrect system design and fruitless discussions with building officials. William At 07:22 AM 8/2/2009, you wrote: William, Wow $F6 you$E2re a master at whipping up drawings! OK, I get the concept, and it$E2s just as I described. The scenarios in drawings one and two are OK as long as both busbars are rated 150A (commercial) or 125A (residential. You then show that the reason for the upsized feeders is to handle a short. But wait! Even if the short could produce 140A, as you have indicated, the conductors will still not carry more than the 100A that they$E2re rated to carry. One would carry 100A from one panel and 40A from the other, Nowhere would that conductor carry 140A, and the mate to it would carry at most 60A. Increasing conductor size wouldn$E2t change anything in that (or any) scenario. So why would you have to increase conductor size? Thanks, Allan -- From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@lists.re-wrenches.org] On Behalf Of William Miller Sent: Saturday, August 01, 2009 11:13 PM To: RE-wrenches Subject: Re: [RE-wrenches] down-sizing main breaker Allan: I whipped up three drawings that indicate three overload scenarios possible with incorrectly sized distribution equipment. They are on our web site at: http://millersolar.com/case_studies/case_studies.html Click on Point of connection. Click on any drawing to see a larger version. I hope this helps with understanding the concept. William Miller __ --- end of quote --- ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] down-sizing main breaker
William, You may well find inspectors and others who will agree with you on this. I remain firmly unconvinced. Yes, the code may be taken literally. . . . .and also, sometimes, be taken out of context. I believe you are doing that here. It is impossible to use words in such an airtight manner that they cannot be misinterpreted. The NEC is riddled with wording that often serves mostly to muddy the waters. I truly respect your desire and record of doing things safely and professionally to the highest standards, or if you deem those standards inadequate, to improve on them yourself. As regards our discussion here, I respectfully suggest you speak with the electrical inspector or AHJ, before you bid, so you don't include line items that may not be required. Then you may decide if you wish to include them in your bid anyhow. Or not. Thanks for your sincere concern that things be done well. I've got to get back to work. Dick --- You wrote: My goal is to interpret the code such that my designs are unassailable by building officials. I don't want unpleasant surprises after I have signed a contract and begun work for a fixed price. --- end of quote --- ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
Re: [RE-wrenches] down-sizing main breaker
Dick: I do not desire to find building official who insist on a strict interpretation of the code, but it is a reality in our jurisdictions. We have to be pro-active and know the code better than they do, or we lose money when we are assessed corrective actions that increase our costs. Bruce is a living example of this (I think I incorrectly called him Brian, sorry). I hope our discussion and Bruce's experience is a lesson for other wrenches. This is, after all, the purpose of this forum. Thanks for the kind words. It is a pleasure talking shop with you. Sincerely, William Miller At 02:47 PM 8/2/2009, you wrote: William, You may well find inspectors and others who will agree with you on this. I remain firmly unconvinced. Yes, the code may be taken literally. . . . .and also, sometimes, be taken out of context. I believe you are doing that here. It is impossible to use words in such an airtight manner that they cannot be misinterpreted. The NEC is riddled with wording that often serves mostly to muddy the waters. I truly respect your desire and record of doing things safely and professionally to the highest standards, or if you deem those standards inadequate, to improve on them yourself. As regards our discussion here, I respectfully suggest you speak with the electrical inspector or AHJ, before you bid, so you don't include line items that may not be required. Then you may decide if you wish to include them in your bid anyhow. Or not. Thanks for your sincere concern that things be done well. I've got to get back to work. Dick ___ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
