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9-95 Log #1160 NEC-P09 Final Action: Accept in Principle
(404.2(C) (New) )
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Submitter: Vince Baclawski, National Electrical Manufacturers Association
(NEMA)
Recommendation: Add a new subparagraph 404.2(C) and exception to read as
follows:
404.2 Switch Connections.
(C) Switches Controlling Lighting Loads. Where switches control lighting
loads supplied by a grounded general purpose branch circuit, a grounded circuit
conductor shall be provided at the switch location.
Exception: Grounded conductors shall not be required where conductors for
switches controlling lighting loads enter the device box through a raceway.
Substantiation: There are electronic lighting control devices that require a
standby current to maintain the ready state and detection capability of the
device. This allows immediate switching of the load to the ?on? condition.
These devices require standby current when they are in the ?off? state, i.e.,
when no current is flowing to the the load. The typical design of these devices
may utilize the grounding conductor for the standby current flow.
In many, if not most commercial installations, a grounded conductor is not
provided in the switch box for switches controlling lighting loads. This forces
the design of these control devices to utilize the grounding conductor to
conduct the standby current. Occupancy sensors are permitted by UL 773A to
have a current of up to 0.5 mA on the grounding conductor. In fact, a number
of UL Standards permit up to a 0.5 mA ground leakage current as
acknowledgment of an operational necessity.
This is allowed because the function of an occupancy sensor requires a low
level standby current. The standard permits this current on the grounding
conductor because in a typical installation there may be no grounded circuit
conductor in the switch box which can be used as the return conductor for the
standby current. The leakage current is additive and multiple devices on the
same circuit could possibly create a risk. The lack of a grounded conductor in
the switch box forces the use of the grounded conductor for the operation of
the device. Product designers have no reasonable option but to accommodate
the lack of a grounded conductor by relying on the grounding conductor. This
not only promotes the risk outlined above, but limits the functionality of the
device due to low current level allowed. Products can and are designed to
utilize a grounded conductor. However, installers will continue to use the
grounding conductor in lieu of the grounded conductor when there is no
grounded conductor available in the lighting control switch box, again,
promoting the same possible risk.
Sensor manufacturers could distribute the necessary supervisory current
through the load for some devices, but this solution has several drawbacks.
Current cannot pass through ballasts and transformers, so this method limits
control to incandescent lamps, which are seldom used in commercial buildings
due to requirements of the same energy codes that dictate sensor use. Leaking
to load also requires sizing the device to the load, and specifying minimum
loads to prevent glowing filaments. Finally, having current flowing at the load
when the device is presumed to be off could create a similar risk.
Many lighting control devices are installed as a means of realizing significant
energy savings associated with the control of lighting circuits. Due to
escalating energy costs and the increased recognition and adoption of energy
saving codes, it is expected that there will be a substantial increase in the
installation of these products. It is becoming less of a design decision or
personal preference and more of a legislative requirement. In order to ensure
the safe use of these products, the NEC should recognize an installation
practice that requires the appropriate circuit conductor to be available for the
standby-operation of the control device. An occupancy sensor can be installed
in any switch location. It is impractical to expect the customer or installer to
anticipate all instances where an occupancy sensor will be installed.
Since revisions to the NEC often results in advances in technology with
respect to electrical installations, mandating a neutral in switch boxes will
encourage device manufacturers to develop products that need a power supply
in order to deliver advances in the control of electricity and reduce improper
wiring methods where a grounding conductor is improperly used.
Although the current design of many lighting control devices relies on the
grounding conductor for conducting current, adopting this proposed
requirement will ensure that future designs will take advantage of the presence
of the grounded conductor in the switch box and no longer compel the design
of the product or installation practice to use the grounding conductor to
conduct the standby current. The availability of a grounded conductor will also
promote the design of many new and improved lighting control products.
The proposal allows an exception for installations utilizing some form of
raceway instead of cable. The raceway would accommodate the installation of
a grounded conductor at a latter time if needed
