From 2001 UL White Book:
GROUND-FAULT CIRCUIT INTERRUPTERS (KCXS)
This category covers ground-fault circuit interrupters for use in accordance
with the National Electrical Code, NFPA 70.
A ground-fault circuit interrupter is a device whose function is to interrupt
the electric circuit to the load when a fault current to ground exceeds some predetermined value that is less than that required to operate the overcurrent protective device of the circuit.
A ground-fault circuit interrupter is intended to be used only in a circuit
where one of the conductors is solidly grounded.
A Class A ground-fault circuit interrupter trips when the current to ground has a value in the range of 4 through 6 milliamperes.
A Class A ground-fault circuit interrupter is suitable for use in branch and feeder
circuits, including swimming pool circuits.
However, swimming pool circuits installed before local adoption of the 1965 National Electrical Code may include sufficient leakage current to cause a Class A ground-fault circuit interrupter to trip.
A Class B ground-fault circuit interrupter trips when the current to ground exceeds 20 mA. This product is suitable for use with underwater swimming pool lighting fixtures installed before the adoption of the 1965
National Electrical Code.
A ground-fault circuit interrupter of the enclosed type that has not been found suitable for use where it will be exposed to rain, is so marked.
The ‘‘TEST’’ and ‘‘RESET’’ buttons on the GFCIs are only intended to check for the proper functioning of the GFCI. They are not intended to be used as ‘‘ON/OFF’’ controls of motors or other loads unless the buttons
are specifically marked ‘‘ON’’ and ‘‘OFF.’’
Products with ‘‘ON’’ and ‘‘OFF’’markings have been additionally Listed as ‘‘Miscellaneous Motor Controllers’’
and may be found under the (NMFT) category.
Some ground-fault circuit interrupters include receptacles, and are intended to be installed in an enclosure like a receptacle.
Such receptacle types found to meet appropriate requirements are marked hospital grade and/or ‘‘CO/ALR.’’ See ‘‘Receptacles for Attachment Plugs and Plugs’’ for
This category also includes rebuilt or refurbished portable ground-fault
These are factory rebuilt to the extent necessary to replace components such as cords, plugs or cord connectors.
Rebuilt ground-fault circuit interrupters are subject to the same requirements and
Follow-Up Service as new ground-fault circuit interrupters.
For additional information, see Electrical Equipment for Use in Ordinary
The basic standard used to investigate products in this category is UL 943, ‘‘Ground-fault Circuit Interrupters.’’
The Listing Mark of Underwriters Laboratories Inc. on the product is the
only method provided by UL to identify products manufactured under its
Listing and Follow-Up Service. The Listing Mark for these products includes the UL symbol (as illustrated in the Introduction of this Direc-tory)together with the word ‘‘LISTED,’’ a control number, and the product name ‘‘Ground-fault Circuit Interrupter,’’ or the product name preceded
by either the word ‘‘Rebuilt’’ or ‘‘Refurbished.’’
[This message has been edited by Joe Tedesco (edited 09-12-2002).]
Joe Tedesco, NEC Consultant