Installation practices
When applying a modern Surge Protective Device
(SPD) to an existing power system, you cannot simply hook it up and turn it
on. It is important that you recognize problems associated with the high
frequency characteristics which are typically encountered during lightning and
surge activity. You must consider lead length, proximity and layout as key
factors which ultimately affect clamp voltages and determine the level of
protection to electrically connected loads.
Normally, the electrician is concerned with how
the customer's equipment operates when connected to system voltage at a
frequency of 60 Hz. Typically, the customer's surge environment is one that
(except during surge activity) runs at 60 Hz. During surges and transients a
wide spectrum of frequencies are generated; the higher the frequency, the
greater the problem. It is imperative that certain installation guidelines are
followed by the electrician performing the installation.
Length: shorter is better
Lead length is the most important factor when
installing a hard wired SPD; the longer the leads, the higher the surge
voltage connected equipment sees. The formula which follows, though somewhat
simplified, demonstrates the affect lead length has on an installation:
Lead length factor ................. V=L di/dt
+ R I
M-Ti performed tests in our lab comparing lead
lengths and its affect on the clamp voltage. (See Test Results)
