Product Brochure

52
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Accurate Assessment of Electrical Systems
Precise identification of the electrical system is critical in the proper selection and application of the most effective surge protective
device. Since SPD performance is directly related to nominal line-voltage parameters, line voltage measurements should always be
taken by a qualified electrician before the SPDs are specified and installed. Measurements should be taken even when the electrical
system configuration is known.
The figure below shows some common electrical systems used throughout the USA and Canada. Specific systems present in a given
facility should be identified by measuring with a voltage meter across each line to neutral, and line to line. The readings should be
written down and referred to when ordering the required SPDs.
Surge Current Capacity
The surge current capacity of an SPD is the maximum surge current the SPD device is capable of surviving on a single impulse basis
without suffering degradation of performance of more than 10 percent. It is required to be listed by mode (in kA), since the number and
type of components in any SPD may vary by mode. It can also be stated by phase.
Modes of Protection – Per Mode and Per Phase
A “mode” is a potential path for a surge to be diverted to (e.g. L-N, L-G, N-G). The number of modes depends on the configuration of the
electrical system (single phase, 3-phase WYE, 3-phase Delta, etc.). The per-phase rating is the total surge current capacity connected
to a given phase conductor.
Calculating “surge current per phase”
The per-phase rating is the total surge current capacity connected to a given phase conductor. For example in a WYE system, L1-N and
L1-G modes are added together because surge current can flow on either parallel path. If the device has only one mode (e.g., L1-G),
then the per-phase rating is equal to the per-mode rating because there is no protection on the L1-N mode. The industry standard is to
publish surge current “per phase” by summing modes L-N + L-G in a WYE system and L-L + L-G in Delta systems.
Accurate Assessment of Electrical Systems
L
N or L
V(L-N) or V(L-L)
Single Phase 2-Wire
L
L
L
L
L
L
L
N
L
V(L-N)
V(L-N)
V(L-N)
Single Phase 3-Wire
Three Phase 4-Wire WYE
Three Phase 3-Wire Delta
V(L-L)
V(L-L)
V(L-L)
V(L-L)
V(L-L)
N
L
L
V(L-N) 1
V(L-N) 2
V(L-N) 3
L
N
Three Phase 4-Wire Delta (Split Phase)
COMMON VOLTAGES (VAC)
V(L-N) 120,220,277,346
V(L-N) 208,240,380,480,600
V(L-N) 120 240
V(L-L) 240 480
V(L-N) 120 277 346
V(L-L) 208 480 600
V(L-L) 240 480 600
V(L-N)1 120
V(L-N)2 208
V(L-N)3 120
Voltage Measurements Can Be
EXTREMELY DANGEROUS! PLEASE BE VERY CAREFUL!