National Electrical Installation Standards

Standards as High as Your Own

Thursday, August 10, 2017


When adding low voltage transformers in the space, we have always been told the secondary had to be 100VA or less or the secondary had to be in conduit. Is this true and where would we find it in the book?

Roy Benson



Hey Roy thanks for your question. I don't know what you mean about "in the space" but in general single conductors must be installed as part of a wiring method in Chapter 3 as stated in 30.3(A). Various cable assemblies are allowed in addition to conduit and other raceways. If it is a Class 2 or Class 3 circuit then the wiring methods in 725.130 are acceptable. The power source must be one of the types in 725.121. Depending on the voltage the 100 VA limitation is included in Tables 11(A) and 11(B) which is often covered in the power supply listing.

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