Home Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

I furnished that info already in an earlier post.


But that is for transformers that fall under the jurisdiction of NEC. Not necessarily for cord and plug connected power supplies for audio and or video equipment. I think for overcuurent protection in this case it would be more under UL, NEMA, or some other safety equipment standards.

Where you see the 2 amps or less being 300% somewhere deeper in the code, that 300% figure is meant more for the overcurrent protection of control transformers not a small transformer used for power.

Control transformers are used in appliances and equipment to operate control devices that switch on and off larger power devices. Example a gas fired furnace found in a home. It will use a step down 120V to 24V control transformer to supply the power for the various control circuits. One being to start and stop the blower fan. (Note: Normally small VA rated transformers, say 25VA or so, will have built in fuse protection)

In commercial buildings and industrial facilities control transformers are found in all kinds of equipment. Example, motor control centers, Automated lighting switching equipment. Simple thing as an automatic door opener when you walk into a store.

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