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Positioning of EMI/RFI Filters, Line Reactors, Surge Suppressors and Fuses
Copyright © 2004 Francis J. Martino

I have a drive with a line reactor. I want to install a surge suppressor.
Where would I install it. On which side of the reactor?


Dear Bob,

You may find differences in philosophy among manufacturers, so
I present here the rational for my own philosophy.

Closest to the input terminals of the drive should be the EMI/RFI
filter. The purpose of the filter is to provide a return path for the EMI
that is passing out of the drive and entering the ground plane via
the parasitic capacitances of the motor and motor bearings.

The EMI must be returned to the input of the drive over the shortest
possible path. See AC Drives and EMI/RFI Mitigation

Next along the path from the drive to the power source will be the reactor.
The reactor will reduce the harmonic currents that are being both generated
by the drive and fed to the facility distribution system. The reduction in
current at this point will reduce the current flowing through the fuses, lowering
the possibility of nusiance blowing that may be caused by the increased
heating of the fuses by the harmonic currents.

The EMI/RFI filter will not be affected by the harmonic currents for
the reason that the filter is current rated. For a six-pulse PWM drive
that is fully loaded, select a filter that is rated for six per cent
above the maximum input requirement of the drive when the drive is
running at full load.

Between the reactor and the suppressor will be the line fuses.

Connected directly to the power source will be the surge suppressor.
It will be positioned to deal with surges coming from the power
source and will give protection to keep the surges from blowing
the fuses.

If the drive has a disconnect then the disconnect will be between the
suppressor and the power source, thus allowing all equipment within the
drive to have power removed when the disconnect is opened.

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