Grounding the Protected Junction Box
Page 7
G
ROUNDING
THE
P
ROTECTED
J
UNCTION
B
OX
Grounding the Protected Junction Box at terminals JP1 and JP2 provides both
surge protection and filtering of radio frequency interference (RFI).
Surge Protection
The Protected Junction Box includes a microgap surge absorber on each sensor
input wire that shunts current pulses to ground. The surge absorbers operate
when the voltage exceeds 200 Volts (the weather station is designed to with-
stand short pulses at 200 Volts) and can handle current pulses of up to 500
Amps. They provide excellent protection against electrostatic discharge (ESD)
and most secondary surges caused by lightning. Surge absorbers will not, how-
ever, withstand a direct or near lightning strike.
Note:
You may see blue flashes inside a surge absorber when they are operating. This is a normal indi-
cation that surges are being absorbed.
If the current load is too great, surge absorbers will “blow” (when “blown,”
they will appear black inside). It is possible, in extreme cases, for an absorber to
shatter, so it is important that you keep the clear plastic cover on the Protected
Junction Box at all times. Unless it has been otherwise damaged, the Protected
Junction Box will continue to function normally when surge absorbers “blow,”
however the surge protection will no longer be present.
In order for surge protection to be effective, you must connect the Protected
Junction Box to an earth ground from terminal JP1. This connection should use
as heavy and as short a wire as possible. The 16.5-foot (5 m) 12AWG wire pro-
vided works well. Connect one end of the ground wire to terminal JP1 and con-
nect the other end to a suitable earth ground. The best earth ground is a copper
rod driven into the earth. Alternatively, you may connect to a grounded metal
cold water pipe.
