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

[August Goers]

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] *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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