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| Figure 5-1 Polarity of a transformer. (A) Single-phase transformer. (B) Additive polarity.(C) Subtractive polarity. |

| c) the voltage across the two remaining leads (b and d) is either the sum or difference of the primary and secondary voltages, depending on the relative directions of the windings. If the voltage b to d is the sum, the transformer is said to have additive polarity; if it is the difference, the transformer is said to have subtractive polarity. |

| To indicate whether a single-phase transformer is of additive or subtractive polarity, the leads are marked as in Fig. 5-2. |

| If the windings of the high and low voltage coils are in opposite directions, the applied voltage and the induced voltage will have opposite directions and the transformer is said to have subtractive polarity. The H1 terminal and the X1 terminal will be on the left, when facing the low voltage bushings. |

| If the windings of the two coils are in the same direction, the applied voltage and the induced voltage will have the same direction and the transformer is said to have additive polarity. The X1 will be found on the right, when facing the low voltage bushings. |

| To connect the secondaries of two (or more) transformers in parallel, similarly marked terminals are connected together irrespective of the polarity, provided similarly marked primary terminals have been connected together. |

| The polarity of distribution transformers rated below 200 kVA and less than 8600 volts, has been standardized (American Standards Association) as additive; above 200 kVA or above 8600 volts in any rating as subtractive. The nameplate on the transformer usually identifies its polarity. |

| Figure 5-2 Polarity markings of a single-phase transformer. |

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