Hi Chris,
Here are my thoughts on your questions/notes below. Please note that I'm in no way an expert in this field, I've only had to deal with it from time to time through our workings with various situations and AHJs. 1. I believe terminal and equipment ratings can vary within one piece of equipment. Even a typical breaker might have a 70°C rated terminal but is only rated at 40°C max operating temperature. I would think that this is the manufacturer's decision on what rating to apply to their overall equipment - and it might very well be driven by a UL type test but I don't know. I've called inverter manufacturers a few times to try to figure out what their terminal and or equipment temperature ratings are. Most of the time they don't know. More recently I've been told 75°C but wasn't given any documentation to prove it. I just saw a recent SunPower branded PowerOne inverter manual which stated it has 90°C terminal ratings. 2. NEC 110.14(C) addresses this a bit. My understanding is that the current standard for equipment rated over 100 A is 75°C (and 60 °C for less than 100 A) but that older equipment, say 40 years + old, was 60°C. This is what our inspectors in San Francisco have told me and seems to be consistent to what I see on the equipment labels (we take digital photos of equipment labels for each project) for existing equipment. Once again, this is only a rough rule of thumb and I'm sure that there are other temp ratings for certain types of equipment. For example, I'm looking at a Murray LC008DF residential load center which states "Size wire only to 60°C or 75°C ampacity limits. Size wire in accordance with breaker markings and wire bending space requirements." The breaker then in turn says "CU-AL 60/75°C WIRE." 3. Good question. 4. I guess that would be specified in the equipment manual or maybe be some internal manufacturer documentation. Or maybe once again a UL-driven type requirement? 5. Most modern load centers, panel boards, disconnect switches that I've seen are all 60/75 °C rated. I'm looking at the device label on a Square D DU324 disconnect and it says "Lugs suitable for 75°C CU - AL conductors." Anyway, this might provide some info for you. Do you have a particular issue in mind that you're trying to solve for? Best, August *From:* re-wrenches-boun...@lists.re-wrenches.org [mailto: re-wrenches-boun...@lists.re-wrenches.org] *On Behalf Of *Chris Anderson *Sent:* Thursday, January 24, 2013 6:52 AM *To:* RE-wrenches *Subject:* [RE-wrenches] Equipment Rating vs. Terminal/Lug Rating How to properly size conductors based on insulation and termination temperature ratings is an often discussed topic among PV designers. Those discussion have provided clarity and understanding of the issue but determining equipment rating, as opposed to termination rating, is still unclear. See below for questions and discussion. According to Square D documentation on terminations (Bulletin No. 0110DB9901R2/02, March 2002): The Underwriters Laboratories® General Information on Electrical Equipment Directory states the following about terminations: “A 75 °C or 90 °C temperature marking on a terminal (e.g., AL7, CU7AL, AL7CU or AL9, CU9AL, AL9CU) does not in itself indicate that a 75 °C or 90 °C insulated wire can be used unless the equipment in which the terminals are installed is marked for 75 °C or 90 °C.” Questions are as follows: 1. If a piece of equipment contains any individual components that are rated for 75deg is it still possible to for the overall rating to be 90deg? Presumably, relative location/distance of 75deg-rated components may allow for sufficient heat dissipation between components. 2. If a piece of equipment does not have a temperature explicitly marked on it's exterior is there an implied rating? 75deg? 60deg? 3. Are ratings determined by a specific UL test or are they manufacturer specified? 4. Is there a specific distance of separation required between two differently rated pieces of equipment and/or terminations? Certain equipment manufacturers have stated that an extended terminal protruding from a 75deg-rated component would allow for a 90deg-rated lug and 90deg conductor sizing. 5. Square D documentation indicates that *all* 600 V equipment is either 60 or 75deg-rated. Is this true? Referenced documentation is 11 years old. Perhaps this has changed? 1. Pertinent excerpt: For electrical equipment rated for 600 V and less, terminations are typically rated at 60 °C, 75 °C or 60/75 °C. No distribution or utilization equipment is listed and identified for the use of 90 °C wire at its 90 °C ampacity. Thanks for any input or advice, -- Regards, Chris Anderson + Ben Walter Borrego Solar Systems Lowell, MA 01851
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