A procedure has been adopted by the IEC for identifying three phase winding connections. Letters and numbers are used as follows. The high voltage (HV) terminals have upper-case letters e.g. A-B-C, R-Y-B, U-V-W, L1-L2-L3 and the low voltage (LV) terminals have lower-case letters e.g. a-b-c, r-y-b, u-v-w, l1-l2-l3. Each winding has a start numbered 1 and a finish numbered 2.
The choice of letters and numbers tends to be a national preference, see the table below for a rule of thumb guide:
The choice of letters and numbers tends to be a national preference, see the table below for a rule of thumb guide:
| Geographical Area | Letters and Numbers Used |
|---|---|
| USA | L1 L2 L3 or 1 2 3 |
| Europe | U V W or R S T |
| United Kingdom | R Y B or A B C |