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What is the method for testing and rating SQ D Transformers for dB sound levels ?

Issue:
What is the method for testing and rating SQ D Transformers for dB sound levels ?

Product Line:
EX transformers

Environment:
Application

Cause:
Installation location

Resolution:
SQ D /SE determines sound levels following rigorous NEMA ST-20 methods and per that Standard:

Sound levels are measured in a laboratory setting where the ambient is 10 dB below rated and no acoustically reflecting surfaces are within 10 feet of the transformer.
Measurements are made all around the unit (including the top) at a distance of 1 foot and averaged.
The adjusted room ambient sound level is factored into the final sound level value.