UFC 3 -520-01
June 10, 2002
D-2.6
Modes of Protection.
D-2.6.1 UL 1449, Table 34.2, provides the various test configurations to provide
different modes of protection. The total possible modes of protection depend on the
system design and voltage level, as shown below in Table D -4.
Table D -4. UL 1449 Modes of Protection
Single phase
Single phase
Three phase
(2-wire + ground)
(3-wire + ground)
(4-wire + ground)
L1 N
L1 N
L1 N
L1 G
L2 N
L2 N
N G
L1 G
L3 N
L2 G
L1 G
L1 L2
L2 G
N G
L3 G
L1 L2
L1 L3
L2 L3
N G
D-2.6.2
Wye Connections.
D-2.6.2.1 For single phase and three phase wye connected systems, the following
modes of protection are recommended:
Each phase to neutral (L N).
Neutral to ground (N G).
D-2.6.2.2 Phase to ground (L G) protection will be important if the grounding system
is of poor quality or in other countries where neutral and ground are not connected. By
protecting both the neutral and ground paths, any differences in potential between the
two points will still be protected against surge events.
D-2.6.2.3 Phase to phase (L L) protection is not needed for wye -connected systems
provided that the other modes of protection are provided.
D-2.6.3
Delta Connections. Provide the following modes of protection:
Phase to phase (L L).
Phase to ground (L G).
D-2.7
Internal Fusing. UL 1449 listing provides assurance that the surge protector
can be applied safely. Some older surge protector designs could overheat and catch
D-6
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