Controllers need in-sight disconnects, but does that mean a glass wall could be between the disconnect and the controller?
Can a glass wall, which provides a physical but not visual barrier, be located between a motor controller and its disconnecting means? One such case arose at a facility with glass exterior walls, such as a greenhouse. Another came up where a heavy glass wall had been installed to muffle sound but still allowed workers behind it to observe the process.
The issue involves Sec. 430-102(a):
(a) Controller. A disconnecting means shall be located in sight from the controller location and shall disconnect the controller. Unlike Sec. 430-102(b), there is no general exception that would allow a remote disconnect provided it can be locked in the open position. Therefore, a locking disconnect, even if used, won't address the merits of the question.
The EC&M panel's response
We think the disconnect may be on the other side of a glass barrier, provided the authority having jurisdiction (AHJ) agrees that environmental conditions won't be likely to obstruct the view. In the case of the greenhouse, this might be questionable, depending in part on climate, but the interior location probably is OK in most cases.
The rule allows someone working on the controller to observe the position of the disconnect handle while working. This will often be possible through a glass wall. The definition of "In Sight From" or "Within Sight From" is from Article 100:
Where this Code specifies that one equipment shall be "in sight from," "within sight from," or "within sight," etc., of another equipment, the specified equipment is to be visible and not more than 50 ft (15.24 m) distant from the other.
There is nothing in this language that gives an access requirement on top of the visibility and distance rules. The disconnect must be visible, and it must be no more than 50 ft distant. Frequently, there are industrial applications where a disconnect might be within sight and yet someone may need to go quite some distance to actually reach the handle, much more than 50 ft.
The point is to separate the ready access requirement from the visibility requirement. A motor is capable of sudden movement, and quick access to a disconnecting means is more important unless those servicing the motor can lock it out. That is why Sec. 430-107 requires that at least one disconnect in the motor circuit be readily accessible, which is also defined in Article 100:
(Readily Accessible.) Capable of being reached quickly for operation, renewal, or inspections, without requiring those to whom ready access is requisite to climb over or remove obstacles or to resort to portable ladders, chairs, etc. (See "Accessible.")
Note that this definition is qualified by the phrase "those to whom ready access is requisite." Ready access isn't required for those without the requisite need. As noted, that access might, in the case of a motor, be remote and out of sight.
If the only disconnect in the motor circuit is the controller disconnect, then it must be within sight and readily accessible. If it is on the other side of a glass wall, then the AHJ must make a field decision about exactly who should have access and whether it is an overly restrictive barrier. This is different than visibility.
Summary
The disconnect must usually be within sight of the controller, and not more than 50 ft away. That dimension is measured along the line of view, and there may be obstacles in the way. If that disconnect is also the only motor disconnect, however, it then must be readily accessible, and the AHJ may rule on the suitability of access. That decision should, however, turn on who has access and not the relative speed of access.
Panelist comment
Mr. Stallcup comments: The response is correct insofar as the text of the NEC is concerned; however, the readers should be aware that there may be other considerations. For example, one major OSHA jurisdiction has decided that if the glass panel sufficiently obstructs verbal communication, as perhaps where it is heavy and extensive or the outside wall of a building, then the remote disconnect is a hazard in terms of a safe workplace. Making that remote disconnect lockable may be a sufficient compromise, but be sure to review this with all AHJs involved.
EDITOR'S NOTE:
These answers are given by our panel of experts. I am chairing this panel, and the other panel members include Bill Summers, James Stallcup, and Dan Leaf. The opinion expressed is that of the panel. If a panelist disagrees with the majority opinion, his explanation is printed following the answer. Although authoritative, the answers printed here are not, and cannot be relied on as formal interpretations of the National Electrical Code. FPH
Frederic P. Hartwell, Senior Editor