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

[Chris Anderson]

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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