# Control Transformer Selection Guide

### Selection Procedure

The following steps will ensure that the secondary voltage delivered by your transformer will be either 85%, 90% or 95% of the nameplate secondary voltage under maximum inrush conditions, at the rated input voltage.

#### Step 1:

Calculate the total sealed (steady state) VA load of your control circuit. This is done by adding the continuous VA requirements of the maximum number of components that will be energized at any given time, including non-inductive as well as inductive components. For sealed VA data, see the Component VA Chart below.

#### Step 2:

Calculate the peak inrush VA for your control circuit.

1. Analyze the sequence of operation of all components.
2. Add together the inrush VA ratings of the components that will be energized simultaneously.
3. Determine the peak - or maximum simultaneous - inrush VA load that the transformer will "see." The VA requirements for indicating lights, timers, and other non-inductive components which do not have an inrush VA also should be included since they will present a load to the transformer at the time of maximum inrush.

#### Step 3:

Calculate the transformer selection inrush VA. Use the following formula:

Selection Inrush VA =  √((VA Sealed)2 + (VA Inrush)2)

NOTE: Transformer selection inrush VA also can be determined by adding the inrush VA and sealed VA arithmetically, but this usually results in an oversized transformer.

#### Step 4:

Determine the correct transformer nameplate VA Rating. Refer to the Inrush/Regulation Data Chart :

• If the line supply to the transformer is fairly stable (does not vary more than 5%), use the 90% secondary voltage column - the 90% column is most commonly used.
• If the line supply voltage varies up to 10%, use the 95% voltage regulation column.

To determine the correct VA transformer rating, go down the column until you arrive at the inrush VA rating closest to, but not less than, the transformer selection inrush VA calculated in Step 3. The left-hand column of the table will give the corresponding transformer nameplate VA rating.

NOTE: When evaluating supply-line stability remember that supply-line voltage drop frequently is associated with motor-starting inrush current. When motors and motor controls are connected to a common feeder, the controls will experience a momentary voltage dip when the motor starts. This reduces the control transformer voltage supplied to the motor starting contactor and may cause the contractor to chatter or drop out.

## Component VA Chart for Starters, Contactors, Relays, and Timers

### Sealed Devices

Device Sealed
VAR Watts VA
FREEDOM SERIES STARTERS AND CONTACTORS: AE16, AN16, AE56, CE15, CN35, CE55, CN55, MCE15
IEC Sizes A‑C 7.1 2.4 7.5
IEC Sizes D‑F 9.2 3.1 10.0
IEC Sizes G‑K 27.0 7.8 28.0
IEC Sizes L‑N 48.0 13.0 49.8
IEC Sizes P‑S 96.0 27.2 100.0
NEMA Size 00 7.1 2.4 7.5
NEMA Size 0 9.2 3.1 10.0
NEMA Sizes 1‑2 27.0 7.8 28.0
NEMA Size 3 48.0 13.0 49.8
NEMA Sizes 4‑5 96.0 27.2 100.0
NEMA Size 6 11.0 21.0 25.0
CITATION CONTACTORS AND STARTERS:
A10, A50, B10, B50, C10, C50
Size 00: Series C1 7.1 2.4 7.5
Sizes 0‑1 18.7 7.0 20.0
Size 2 22.0 9.3 24.0
Size 3 48.0 13.0 49.8
Sizes 4‑5 96.0 27.2 100.0
Size 6: Series C1 11.0 21.0 25.0
Size 7: Series B1
Interposing Relay
5.1 6.8 8.5
Size 7: Series B1
Main Contactor
170.0 60.0 180.0
Size 8: Series B1
Main Coil
56.0 50.0 75.0
RELAYS
Type AA (1‑2 Pole) 8.0 6.6 11.0
Type D15 7.1 2.4 7.5
Type M (2‑12 Pole) 20.0 9.0 22.0
Type M Latch Coil 13.0 11.0 17.0
Type MRD -- 13.2 13.2
Type MRD Ltc. Coil -- 21.6 --
Type R -- 6.0 6.0
Type RM‑Set -- 3.5 3.5
Type RM‑Release -- 3.1 3.1
Type TF 3.0 3.0 4.0
Type TH 4.0 4.0 5.0
TIMERS
Type D80 18.0 6.0 19.0
Type D80 with
Installed Contacts
20.0 7.0 21.0

### Inrush Devices

Device Inrush
VAR Watts VA
FREEDOM SERIES STARTERS AND CONTACTORS:
AE16, AN16, AE56, CE15, CN35, CE55, CN55, MCE15
IEC Sizes A‑C 64 49 80
IEC Sizes D‑F 78 65 100
IEC Sizes G‑K 210 95 230
IEC Sizes L‑N 374 112 390
IEC Sizes P‑S 1132 240 1158
NEMA Size 00 64 49 80
NEMA Size 0 78 65 100
NEMA Sizes 1‑2 210 95 230
NEMA Size 3 374 112 390
NEMA Sizes 4‑5 1132 240 1158
NEMA Size 6 868 1345 1600
CITATION CONTACTORS AND STARTERS:
A10, A50, B10, B50, C10, C50
Size 00: Series C1 64 49 80
Sizes 0‑1 81.5 63 103
Size 2 115 80 140
Size 3 374 112 390
Sizes 4‑5 1132 240 1158
Size 6: Series C1 868 1345 1600
Size 7: Series B1
Interposing Relay
29 68 74
Size 7: Series B1
Main Contactor
6275 2989 6950
Size 8: Series B1
Main Coil
1262 2100 2450
RELAYS
Type AA (1‑2 Pole) 18.0 8.5 20.0
Type D15 64.0 49.0 80.0
Type M (2‑12 Pole) 122.0 95.0 155.0
Type M Latch Coil 36.5 18.5 41.0
Type MRD -- 168.0 --
Type MRD Ltc. Coil -- 21.6 --
Type R -- 6.0 6.0
Type RM‑Set -- -- --
Type RM‑Release -- -- --
Type TF 3.0 3.0 4.0
Type TH 4.0 4.0 5.0
TIMERS
Type D80 60.0 67.0 90.0
Type D80 with
Installed Contacts
89.0 95.0 130.0

## Inrush/Regulation Data

### Inrush/Regulation Data: 95% and 90% Secondary Voltage

Transformer VA Rating at 55℃ Inrush VA‑40% Power Factor
At 95% Secondary Voltage At 90% Secondary Voltage
60 137 185
95 242 329
105 294 407
180 592 842
225 929 1312
275 1271 1801
320 1581 2224
380 2124 3048
550 3196 4604
850 5500 7914
1100 8382 12067
1500 11100 16066
2000 21820 24356
3000 29123 32770
5000 74595 111000
7500 104000 162000
10000 111000 166000

### Inrush/Regulations Data: 85% Secondary Voltage

Transformer VA Rating at 55℃ Inrush VA‑40% Power Factor
At 85% Secondary Voltage
60 227
95 409
105 512
180 1071
225 1663
275 2288
320 2816
380 3895
550 5896
850 10141
1100 15477
1500 21032
2000 41100
3000 59997
5000 145000
7500 219000
10000 237000

### Available Transformers

#### All Transformers

Warning: When using this information to perform electrical work, call a licensed electrician and consult the NEC® for safety. All licensed electricians have passed examinations covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages.