ERICO Practical Guide to Electrical Grounding - Manual (Page 124)

117 Chapter 7: Application Of Surge Protection Devices
Location Category And Exposure Levels As Defined By IEEE STD C62.41-1991
For Line-Line & Line-Neutral
Table 7-1
Location System <<Peak Values (3)>> 1.2/50 µs Volts
Zone (1)Exposure Volts - kV peak Current - kA peak, and 8/20 µs Amps
(2) 1.2/50 µs 0.5 µs-100kHz Ring Wave -kA pk (4)
A1 Low 2 70
A2 Medium 4 130
A3 High 6 200
B1 Low 2 170 1
B2 Medium 4 330 2
B3 High 6 500 3
C1 Low 6 3
C2 Medium 10 5
C3 High 20 10
Location Category And Exposure Levels As Defined By IEEE STD C62.41-1991
For Neutral-Ground
Table 7-2
Neutral Distance System 0.5 µs/100 kHz 1.2/50 x 8/20 µs
Grounding From Exposure (3) Ring Wave Peak Peak Volt.
Practice (1) Surge (2) Voltage - kVp kVp
Neutral earthed Close All None None
at service Nearby All 1 None
entrance Far away All 3 None
Ungrounded All Low 2 2
neutral at service All Medium 4 4
entrance All High 6 6
Note 1. See figure 7-1.
Note 2. See Section 7.3.3 of above standard.
Note 3. Waveshapes are defined in above standard.
Note 4. Combination Wave defined in above standard.
Note 1. Bonding the Neutral to Ground at the service entrance prevents further propagation of Neutral to Ground voltage
and current from sources beyond the service entrance (or any separately derived source). When the Neutral is not bonded to
the earth or the building ground, then Neutral to Ground voltages may be similar to Line to Neutral voltages and Table 7-1
should be consulted.
Note 2. This has not been defined and is a matter of experience and judgment.
Note 3. See section 7.3.3 of above standard.
RECOMMENDATIONS
1. Specify SPDs for the voltage and energy levels as
defined in ANSI/IEEE Std C62.41.
2. Specify SPDs which are UL Listed.
3. SPDs can fail. They usually fail in the short circuit
mode. If this feature is important, decide what to do about
it. For example, fusing the SPD prevents its shorting from
taking out other equipment, but the SPD no longer pro-
vides protection.
4. Is the overall grounding system, to which the SPDs are
connected, the lowest practical impedance?
5. Are connecting leads short, clean and tight?
6. Is the SPD enclosure, if any, suitable for the operating
environment?
Grounding Book 4/14/99 10/5/99 6:02 PM Page 117 (Black plate)