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Transformers

Contact Technical Services at (800) 377-4384 with any questions.

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197

Overcurrent Protection

Fusing and circuit breaker protection. How to overcurrent protect 600 Volt class transformers and associated wiring

per NEC 450.3 (B), NEC 240.3 and NEC 240.6 (A).

1. Primary protection only is required if the transformer is

single-phase and the secondary has only two wires.

Overcurrent protection rating and location are shown in

Diagram A.

Diagram A

2. If the branch circuit feeding the transformer has

overcurrent protection to meet the individual protection

requirements in Example 1, then individual transformer

protection is not required.

Diagram B

3. Primary and secondary protection is required if the

transformer has more than two wires on the secondary

circuit.

Diagram C

4. If the branch circuit feeding the transformer has

overcurrent protection to meet the individual primary

overcurrent protection requirements in Example 3, then

individual primary protection is not required. Secondary

OCP is required as shown below.

Diagram D

Primary Current Overcurrent Protection Rating

Less than 2 amps 300% maximum

2 to 9 amps 167% maximum

9 amps or more

125% of rated primary current (or

next highest standard rating)

Primary Current Overcurrent Protection Rating

Less than 2 amps 300% maximum

2 to 9 amps 167% maximum

9 amps or more

125% of rated primary current (or

next highest standard rating)

Primary

Current

Secondary

Current

Overcurrent

Protection Rating

250% primary current Less than 9 amps 167% maximum

Not more than 250% 9 amps or more

125% (or next higher

standard rating)

Primary Current Secondary Current

Overcurrent

Protection Rating

250% primary current Less than 9 amps 167% maximum

Not more than 250% 9 amps or more

125% (or next higher

standard rating)

1 2 3 4

Transformers 1
Figure 1 4

Inhaltsverzeichnis

Seite 1 - Transformers

5TransformersContact Technical Services at (800) 377-4384 with any questions. Visit our website at www.solahd.com. 197Overcurrent ProtectionFusing and

Seite 2

5TransformersContact Technical Services at (800) 377-4384 with any questions. Visit our website at www.solahd.com. 198Fuse = I times 125% next size hi

Seite 3

5TransformersContact Technical Services at (800) 377-4384 with any questions. Visit our website at www.solahd.com. 199Secondary Fuse RecommendationsSe

Seite 4 - Figure 1

5Ventilated Distribution TransformersContact Technical Services at (800) 377-4384 with any questions. Visit our website at www.solahd.com. 200Figure 1