A proposed location for a 112-kVa 480Y/277 dry transformer suspended above the working space for a switchboard raises several questions.
If the headroom below the transformer and above the required working space in front of the switchboard is 6 feet, 6 inches or more, then the transformer location is acceptable. The transformer does not intrude upon the dedicated space directly above the switchboard, as required by Sec. 110-26(f). The seismic bracing of the transformer, which is suspended on threaded rods, is governed by the building code.
But can the transformer be located without proper working space in front of it? There may be times when voltage readings must be taken at the terminals, or there may be voltage taps that need to be changed. The voltage readings can usually be taken at locations other than at the transformer itself, and tap changes should never be made while power flows through the transformer.
Sec. 450-13(a) says that dry transformers 600 volts or less and located in the open need not be readily accessible though there has to be room at the terminal box to allow safe observation and tests. This should be a horizontal distance of not less than 30 inches, taken from 110-26(a)(1), Exception No. 1. This requires a working space of 30 inches for working on de-energized parts at the rear of switchboards, and appears to be reasonably applicable to dry transformers 600 volts or less.
Do you believe that some rules are made to be broken? Then consider this: National Electrical Code Section 110-26 requires working space around all electrical equipment, and imposes the distances in Table 110-26(a) on the working space about equipment "likely to require examination, adjustment, servicing, or maintenance while energized."
Take a receptacle in the wall above a kitchen counter and below hanging cabinets. This is likely to require examination, servicing, or maintenance while energized, but the required working space is not there because the counter is below and the cabinets above. Panel 1 rejected a proposal to have the equipment to which Sec. 110-26(a) applies to include: "switchboards, panelboards, motor control centers, circuit breakers, fused switches, heating and air conditioning controls, service equipment, and other equipment."
In the 1998 Report on Comments, Panel 1 stated: "Code-Making Panel 1 intends that the rule apply in its entirety to all live parts of equipment and not just to a restricted list."
Another common example is a three-way toggle controlling the light(s) for a stairway. Sec. 210-70(a)(2) requires a wall switch at each level of interior stairways of six or more steps. In many stairways, there is no wall in which to place the switch other than above a stair tread. The tread may be as small as 11 inches in width, very different from the 30 inches required by Sec. 110-26(a)(2) for the width of the working space. Such a switch will certainly require operation, examination, servicing, and maintenance while energized.
If kitchen counter receptacles and stairway switches are to be included, then this Code section is violated thousands of times every day in every new dwelling. A requirement so often violated should not remain in the Code without
Obviously, the application rests with the authority that has jurisdiction. Nevertheless, the inspector should not have to fall back on Sec. 90-4 when the application of the requirements of Sec. 110-26 could so easily be made. On the other hand, some inspector with little field experience may attempt to enforce Sec. 110-26 as written.
This brings us back to our transformer up in the air. It may be considered by some to require working space at the terminal box, but a dry transformer is so seldom touched after installation that many inspectors consider Table 110-26(a) working space unnecessary. They realize the transformer will rarely be examined, serviced, adjusted, or maintained while energized.
SCHWAN is an electrical code consultant in Hayward, Calif. He can be reached at firstname.lastname@example.org.