Specifications

73
© 2012 Emerson Climate Technologies, Inc.
Printed in the U.S.A.
AE8-1368 R2
• Wire size shown in this table is suggested when contactor coil is powered by the 24 volt CoreSense
Diagnostics v2.11 module.
NOTE: For reliability, Emerson recommends that the temperature class of the transformer be a minimum of
CLASS B (130 degrees C) (Ambient + Internal Temperature) In addition, it is recommended that Inrush VA
at 40% power factor use the 95% Secondary voltage. This accounts for a 10% variance in the supply
voltage. If at all possible, the primary transformer should be wired for 208/230 volts or higher to reduce
voltage droop on the secondary due to higher currents and resulting voltage drops. Adequate ventilation is
required to ensure that ambient and internal temperatures do not exceed the temperature class of the
transformer, and that suffi cient mounting hardware be used to support the weight.
Pilot Duty Relays:
Relays are available in many sizes and confi gurations having high mechanical and electrical reliability along
with manageable cost. Like transformers, relays are sized according to their Steady State/Continuous and
Inrush VA’s published by the manufacturer.
Some of the benefi ts of using a pilot duty relay would be lower transformer cost due to lower VA and system
wire size. Care should be given to NEMA style contactors with 24V coils because total VA can be exceeded
in class 2 circuits quickly because of the high inrush VA and sealed VA associated with them. Pilot duty
relays can be advantageous in these situations by transferring system voltage and current to these higher
power devices. It is recommended that a pilot duty relay be used with any NEMA contactor.
Relays such as Stancor 91-901 DPDT or 184-912 SPNO have been used with success in applications
where transformer loading exceeded 100VA and a pilot duty relay was required.
Example Of Determining Wire Length:
Contactor
25 FT
Transformer
TOTAL LENGTH OF WIRE = 4 STRANDS X 25 FT
TOTAL LENGTH OF WIRE = 100 FT
Table C-6
Wire Sizing
Recommended Secondary (24V) Minimum American Wire Size (AWG)
These Sizes Will Keep Voltage Drops To Less Than One Volt With XFMR Producing Rated Current
Continuous
VA XFMR
Nameplate
25 Linear Ft.
Wire Size
AWG
50 Linear Ft.
Wire Size
AWG
75 Linear Ft.
Wire Size
AWG
100 Linear Ft.
Wire Size
AWG
40 18 18 18 14
50 18 18 16 14
60 18 18 16 14
75 18 16 16 12
100 18 16 14 12