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Q I have two questions about Sec. 384-16(e).
1. What is a "delta breaker?" The quotation marks suggest this is a slang term, but I find no definition of it in the NEC, nor can I find an item listed as such in my catalogs of circuit breakers. Several electricians whom I queried don't know, and each wondered what the difference was between a delta and a wye CB. They contend the voltage and AIC ratings are appropriate.
2. Isn't the intent of Art. 3 84 to prohibit the use of a three-pole circuit breaker in a single-phase (two-pole) panelboard? If so, why doesn't it simply say so? The wording seems to obscure the intent.-E.G.L.
AA delta breaker is a 3-pole breaker with one of its poles isolated. The isolated pole does not connect to a bus in a panelboard. This type of breaker is used with "High-leg" delta systems (Fig. 1), which the NEC refers to as "four-wire" delta systems with the midpoint of one phase connected to ground.
If an installation was one with a 240/ 120V single-phase service, sometimes called an "Edison System" (Fig. 2), and later required a limited amount of 3-phase power, two smaller transformers would be added to provide a "High-leg" delta system, thus supplying 240V, 3-phase power. To avoid installing a 3-phase panelboard, a delta breaker would be put into the existing 240/120V, single-phase panelboard, and the B phase [high leg per Sec. 384-3(f)] would be run to the isolated pole using an orange wire per Sec. 230-56 and Sec.384-3(e).-R.N.B.
A A little history is behind the "delta breaker." It applied to 120/240V, 3-phase, 4-wire delta services. The "delta breaker" was used in a situation where most of the electrical load on a service was single phase, but 3-phase power was required for one load such as a motor. Examples of this situation are a small building with one air-conditioning unit that is...