Surge Amps, Clamping Volts and Equipment Protection
Copyright © 2003 Francis J. Martino
Repetitive voltage spikes will degrade both motor insulation and electronic components, thus shortening equipment life. A suppressor will limit the peak values of both common facility generated voltage spikes and incoming power system voltage spikes caused by lightning, utility capacitor switching and other power disturbances.
The degree of protection provided by a suppresssor is defined by its clamping, or limiting, voltage. However, the voltage which a suppressor will offer a limit will depend upon both the suppressor type and the amount of amps that the suppressor is passing to ground.
Model LA603 manufactured by Delta will be used for this presentation. It is a silicon oxide varistor that will pass current to ground when it has a voltage applied to it of 850 volts or higher. With less than 850 volts applied, the suppressor will not pass current to ground.
Characteristics of the Delta Model LA603 Lightning Arrestor/Surge Suppressor:
Line to Neutral
||Motors without inverter duty insulation will withstand occasional spikes of a nominal 1000 volts.
The inverse voltage capability of 480 volt system diodes and SCRs is a nominal 1400 volts. Diode failure can be expected above that level. Thus, diodes and SCRs will have protection for surge amps up to a nominal 35,000.
||Motors with inverter duty insulation are rated for 2000 volt spike protection. Occasional spikes of 2300 volts will not seriously degrade the motor insulation.
||Facility wiring, which is normaly rated at 600 VAC, can withstand spikes well in excess of 2000 volts. It is for that reason that common 600 VAC wiring is used with variable frequency drives.
||Equipment will be protected by limiting the fragmentation of failed components.
With current surges of 80,000 to 100,000 amps, the amps will be passed as appropriate. However, the heat dissipation of the unit will allow a one time operation only and the suppressor will need to be replaced. Signs of a failed suppressor are a cracked or burned housing or rupture of the suppressor case. Install the suppressor in an enclosure to prevent injury to personnel in the event that the case ruptures.
Compare the clamping volt ratings at the 40,000 and 60,000 Surge Amp levels with the ratings of units of other manufacturers.
The Model LA603 is for three phase wye connected systems only.
The Model LA603 and other models are available for purchase:
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