Technical FAQs

Ask a Question

How do I select the appropriate rated over current protection for a 9070 Type T or TF control transformer? Example: 9070TF100D1

Over current protection (OCP) is dictated by NEC table 450-3(b).  In the European community where they choose to not use the NEC and rather use CE, then it is currently dictated by IEC standard EN 60-742.  It is the responsiblity of the installer to select the appropriate OCP for the device.  Square D does have recommended fuse sizes for the primary and secondary to meet the NEC and/or CE.  This is found on pages 10 and 11 of the Industrial Control Transformers (Type T and TF)  Catalog, document number 9070CT9901 which is available through Literature Fulfillment and on-line at SquareD.com.

Example:  With the 9070TF100D1 being a 100VA, 240 x 480 primary to 120V secondary, using both primary and secondary OCPs, and using page 10 of the aforementioned catalog, the proper primary OCP for 240V applied is 1 amp and for 480V applied is 1/2 amp, and the proper secondary OCP is 1-1/4 amp.
Also from that page, it is shown that the primary fuses are midget type (1-1/2`` x 13/32``) class CC time delay type, and the secondary fuse is a midget type and does not need to be a class CC.


CTA-ID : 16051
Was this helpful?
What can we do to improve the information ?