Understanding Ratings on Component Label

Rating labels of modern control motor controls, such as Manual Self Protected Motor Controllers (MSPs or UL Type E controller) contain many different types of information.  Proper understanding of the label content is essential in properly applying these products.

In the image above, note the 480Y/277V and 600Y/347V “slash” ratings shown in the orange box.  These slash ratings require that the electrical service feeding these components be from a transformer with a solidly grounded or high resistance grounded Y secondary.  Note that in US markets, most, but not all, transformers that would be connected to electrical equipment, such as panel boards, motor control centers, industrial control panels, etc., have a grounded Y secondary.  UL and NEC requirements are that an industrial control panel label must clearly state if the panel is to be connected to a grounded Y, or slash rated, transformer secondary.

If these components are connected to a transformer with an ungrounded secondary, then the maximum allowable applied voltage is the lower “slash” voltage rating.  According to the label pictured above, if this component is connected to an ungrounded transformer secondary, then the maximum allowable applied voltage is 347V.

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