Specifications

72
© 2012 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
AE8-1368 R2
Example of transformer size calculation when contactor is directly powered by the class 2 transformer:
Again, use the same 3D example with one unloader, calculate the total inrush VA and steady state VA for
devices that will be powered. Refer to Table C-4 for VA values. The contactor selected for this example is a
Square D NEMA size 00. The contactor specifi cation indicates 33 VA sealed and 165 VA inrush. Direct
control eliminates the use of a pilot duty
Table C-4
Inrush VA Sealed VA
CoreSense Diagnostics Modules 3.78 VA 3.78 VA
One Unloader 37.4 VA 18 VA
Nema 00 Contactor 165 VA 33 VA
Total VA 206.18 VA 54.78 Va
Formula A
TOTAL INRUSH VA = Σ VA sealed + Σ VA inrush
TOTAL INRUSH VA = 260.96 VA (Use this inrush value for transformer selection)
From transformer regulation Table C-5, select a transformer greater that the sealed VA of 54.78 VA. This
would be a 60 VA transformer and the inrush is 250 VA, which is greater than the 206.18 calculated above.
We would therefore select a 75 VA transformer from this table to satisfy the sealed and inrush VA’s for this
example.
When contactors are powered directly by the class 2 transformer, it is essential to use the manufacturer
inrush and sealed VA values for the selected contactor because these can vary by a signifi cant amount.
This is true when using a Defi nite Purpose Contactor or a NEMA style contactor from different manufac-
tures.
Keep in mind, you cannot exceed 100VA sealed and stay within the UL guidelines for class 2 circuits.
A wire size Table C-6 is also provided as a reference, actual wire size specifi ed must conform to local and
NEC (National Electrical Code)
Transformer Regulation Table C-5
(Consult Transformer Manufacturer For The Particular Product/Brand)
24 VAC Class 2 Transformer Data
Transformer Regulation Data
Stancor/White Rodgers
Part Number
Continuous VA
Transformer Nameplate
Inrush VA @ 40% Power Factor
95% Secondary Voltage
T40-24F3 / 90-T40F3 40 160
T50-24C3 / 90-T50C3 50 205
T60-24C3 / 90-T60C3 60 250
T75-24C3 / 90-T75C3 75 325
T100-24C2 / 90-T100C2 100 450