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05/2020
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ASCO 425 Surge Protective Device (SPD)
Electrical
Branch Circuit Overcurrent
Protection and Disconnect Means
Location of Surge Protective
Device (SPD)
HAZARD OF ELECTRIC SHOCK, EXPLOSION, OR ARC FLASH
• Use conductors rated for the Overcurrent Protection Device (OCPD) per
applicable codes.
• Use conductors rated for the application per applicable codes.
Failure to follow these instructions will result in death or serious injury.
A branch circuit Overcurrent Protection Device (OCPD) either in the form of
a circuit breaker or fuse must be provided for the ASCO 425 Type 2 device.
The branch circuit OCPD should either provide or include a disconnecting
means.
Since the current drawn by the ASCO 425 device during normal operation is
negligible, the ASCO 425 device can be connected to a dedicated, separate
branch circuit or connected to a suitable existing branch circuit.
When connected to a separate, dedicated branch circuit, the OCPD setting
must be selected to protect the conductors feeding the ASCO 425 device
per applicable state and local building codes.
UL 1449 Type 1 SPDs have been designed and approved for line side appli-
cations prior to the main service disconnect without supplemental overcur-
rent protection. Type 2 SPDs must be installed on the load side of the main
Overcurrent Protective Device (OCPD). All installations should either provide
or include a disconnecting means.
Type 1 SPDs can also be used in Type 2 applications (load side of OCPD).
When either Type 1 or Type 2 SPDs are used on the load side, they must be
installed per local codes.
Locate the SPD as close as possible to the circuit mains being surge-limited
to minimize the wire length and optimize SPD performance. Avoid long wire
runs so that the device will perform as intended. To reduce the impedance
that the wire displays to surge currents, the phase, neutral, and ground
conductors (wye and high-leg delta configurations), or phase and ground
conductors (delta configurations), must be routed within the same conduit
and tightly bundled or twisted together to optimize device performance.
Avoid sharp bends in the conductors. See Figures 2 and 3.
Figure 2:
SPD Wiring for Wye and High-Leg Delta Configurations
DANGER
To load(s)
Phases
Neutral
Ground
Ground bus
Neutral bus
SPD
Phase A
Phase B
Phase C
Neutral
Ground
Panel
Interconnect wiring
– Minimize length
– Avoid sharp bends
