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NEC Quiz: Article 425 Answers

by Mark Lamendola

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  1. There isn't one. Individual branch circuits can supply any VA or wattage of fixed resistance and electrode industrial process heating equipment [425.3].

  2. The so-called three foot rule is a myth that arises from misapplying one value from the NEC and OSHA working space tables and from ignoring the fact the appropriate value from either table is just a starting point. Another factor, such as maintenance requirements, can add to the appropriate table value. In the case of this equipment, you must comply with 110.26 and 110.34 [425.8(B)]. As the 425.(B) exception note states, there is an exception permitted. But it should be used only when there is no other choice due to conditions; it should not be used simply to gain floor space for some other business purpose.

  3. That depends upon the combustible material and the specifications of the equipment you are installing. You must follow the required (by the equipment manufacturer) spacing for that particular combination, unless the equipment is rated for direct contact with those specific combustibles [425.13].

  4. Yes, but only if it has a marked "off" position, is part of a fixed heater, and disconnects all ungrounded conductors [425.19(B)(1)(C)].

  5. Even though 425.85 says you do, the answer is no you don't. See the Article 100 definitions of grounding and bonding, and then read Article 250, Part V. What is meant here is to bond those metallic parts. As they are bonded (directly or not) to each other and to the equipment "grounding" (bonding) conductor, in the United States this method is called "grounding". But it's confusing to use that terminology because a ground connection is a connection to the dirt. The bonding connection is a low-impedance metallic path back to the source. The earth does not make a good bonding jumper. Instead of a fraction of an ohm of impedance, the earth might present thousands of ohms or more of impedance. If you draw out the many parallel circuits and apply Kirchoff's Law of Parallel circuits, you can see that a grounding connection does not remove dangerous potential but does allow current to circulate exactly where you don't want it to.