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The primary purpose of network protection is
the controlled interruption of fault currents
before damage occurs to cable insulations
and associated equipment, and the elimina-
tion of unnecessary service interruptions. The
limiter and fuses for network protection are
closely associated with the connectors and
are equaly vital to the safe, continuous oper-
ation of an underground system.
has developed protective devices
that have played a major role in reducing
underground system outages and the subse-
quent expenses incurred in the loss of service
and replacement of damaged cables. A basic
objective has been the design of limiter-con-
nector combinations that, in addition to pro-
tecting against the effects of fault currents,
economize on both space and installation
Limiters are designed to protect underground
secondary cable from damage by fault cur-
rents of two principal kinds: high energy arc-
ing faults and sustained faults. The arcing
fault, usually of shorter duration and lesser
intensity, is more common. While this type of
fault may sputter briefly and then clear, some
may be sustained long enough to “roast” the
A sustained fault occurs when two conduc-
tors come solidly into contact and permit the
flow of heavy short-circuit currents. Without
suitable protection, these fault currents are
heavy enough to damage cable insulation
and often produce combustible fumes
accompanied by fire and explosion.
Installed at each end of cable sections, lim-
iters have time-current characteristics
designed to avoid unnecessary outages.
Network protector fuses, installed in the
network protector on the load side of the
breaker, provide back-up protection against
failure of a network protector to open on a
primary fault. Coordinated characteristics of
limiters and fuses provide for fault currents to
be interrupted before they can cause dam-
age, but only under predetermined time-
current conditions, and only in those parts of
the system where interruption is necessary.
Engineered to interrupt the circuit before
cables carrying a fault current are visually
damaged, limiters act to confine damage to
the section of cable where the fault occurred.
The limiters are designed to prevent unneces-
sary clearing and will “hang on” during:
1. Faults which would clear without damag-
ing cable insulation.
2. Overloads from motor starting, load trans-
fer because of primary fault, or temporary
overload during fault conditions.
3. Overloads from loss of secondary con-
ductors caused by clearing of other lim-
4. Reverse current flow through the network
protector on primary faults.
5. Faults on other secondary cables.
Current – Amperes
Figure 4
250 Volt Limiters
Blue highlighted items are industry standard and most frequently ordered.
Canada: 1-800-387-6487
US: 1-800-346-4175