[RE-wrenches] Equipment Rating vs. Terminal/Lug Rating

Thu Jan 24 14:10:52 PST 2013

Chris/August:

1)      The terminal temperatures in a piece of equipment should have been evaluated as part of the Listing process.  The manufacturer should specify the temperature rating of the terminals and the wire temperature and type, e.g.  (Al/Cu).  The NRTL will do temperature measurements on the minimum specified wire and terminals at max power and max specified ambient.  If all the temperatures are ok then the product would be approved for 90C wire even if the temperature rating of that terminal was lower.  This is because a Listed terminal is approved for general use and no temperature tests will be run in the field.

This issue also ties into the minimum and maximum wire sizes allowed and the wire bending space inside the product.  For Example: A product might be designed for copper wire only due to wire bending.  The wire bending space required for the larger Al wire might be greater than available space in the product (this is typically a significant cost driver). The use of Al wire would be precluded even if the Al wire would fit in the terminal and the terminal were rated from Al/Cu.  In our case we specify 90C copper wire only and test for that at the minimum wire size allowed by NEC to carry the design current and at max power / max ambient we specify.  Min and max torques must also be specified.  All of this should be on the unit rating label or in the manual.

What happens on the other end of the wire is a separate issue and you need to make sure the terminal at the other end also meets NEC requirement at the conditions specified by the manufacturer of that equipment.

Best Regards,

John Berdner
General Manager, North America

[cid:image001.jpg at 01CDFA3C.9E6DCC30]

SolarEdge Technologies, Inc.
3347 Gateway Boulevard, Fremont CA 94538 USA  (*Please note of our new address.)
T: 510.498.3200, X 747
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From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of August Goers
Sent: Thursday, January 24, 2013 11:59 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] Equipment Rating vs. Terminal/Lug Rating

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-bounces at lists.re-wrenches.org<mailto:re-wrenches-bounces at lists.re-wrenches.org> [mailto:re-wrenches-bounces at lists.re-wrenches.org<mailto:re-wrenches-bounces at 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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