UL 6500 - SECOND EDITION

(Sub) CLAUSE/ANNEX NUMBER:

14.2

(Sub) CLAUSE/ANNEX HEADING:

Capacitors and RC-units

OTHER RELEVANT (Sub) CLAUSES/ANNEXES (as applicable):

Clauses 8.5 and 8.6

DESCRIPTION OF ISSUE:

What are the requirements and guidelines for suppression components (i.e., gas discharge tubes (GDT), surge arrestors, surge absorbers, and metal oxide varistors (MOV) connected between the mains supply and accessible conductive parts.

APPLICATION GUIDELINE:

The combination of an MOV in series with a GDT provides a fast reaction time and long life for high voltage and high current transient protection applications. In a primary circuitry application they divert destructive transients to ground and prevent circuitry damage. A GDT/MOV combination is suitable for use between the mains supply and accessible conductive parts if the GDT/MOV combinations are:

Suitable for the end product application (i.e., antenna coupling, across-the-line, line by pass, X1, Y1, or Y2)
Suitable insulation is provided (i.e., basic or reinforced insulation) and
The series MOV meets requirements identified in the Conditions of Acceptability of the GDT.

We have identified below the various types of GDT/MOV applications and the corresponding level of insulation that each combination provides:

Across-the-Line GDT/MOV Recognized combination provides basic insulation at 125 V and 250 V
Antenna Coupling GDT/MOV Recognized combination provides basic insulation at 125 V and 250 V
Class Y1 GDT/MOV Recognized combination provides reinforced insulation at 125 V and 250 V
Class Y2 GDT/MOV Recognized combination provides reinforced insulation at 125 V and basic insulation at 250 V
Line by Pass GDT/MOV Recognized combination provides basic insulation at 125 V and 250 V

Examples of various types of GDT/MOV end product applications are illustrated in Figures 1 through 16. Each figure identifies the required UL 1414 Recognition of the GDT/MOV combination and indicates whether or not the construction and UL Recognition is in compliance or not in compliance with the above criteria.

Note: An MOV itself is not acceptable between the mains supply and accessible conductive parts.

RATIONALE:

Transient overvoltage suppression components can cause a potential hazard (i.e., shock, fire) if not suitably investigated, therefore, they are required to meet applicable component requirements of UL 1414 5th or 6th Edition and shall be suitable for the application of use for which they are intended.

OTHER:

None

SEE RELATED PAG: