17.2 Protective devices for power transformers
[Basic requirements]
Power transformers that have a rated output of 15 VA or higher shall incorporate protective devices, in order to prevent smoke emission, ignition, fire and electric shock hazards.
[Design standards]
1) Such transformers shall contain a thermal fuse or be provided with an overheating protection device.
2) A protective device may not be required if the winding temperature, upon short circuit of the secondary winding, does not exceed the values given in the table below.