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AC Line Conditioning
- Air-gap and semiconductor disconnect
- HF noise filtering
- "Surge protection"
Despite whole-house "surge protection" at the outside meter installed and guaranteed by the electric utility company, we have suffered damage to electronic components in our house during storms.
The AC electrical wiring in our house fully meets the US National Electrical Code (NEC), but that code is written to protect lives, not to protect the semiconductors in the electronic devices that have proliferated in modern homes.
Part of the solution was to improve the earth ground. Among other problems, 1) the single existing ground rod had been installed near the foundation where the (presumably) back-filled earth material was poorly consolidated and 2) the connection to the rod itself was problematic.
In addition, the electrical conditioning circuit in a 12”x 12” pull-box (picture below) was revamped to allow the home automation system to disconnect the two separate 20-amp electrical circuits used for the audio-visual equipment and home automation.
Two Crydom D2425-B normally-closed zero-crossing DC-controlled 25-amp solid state relays (SSR’s) are attached to the sides of the box (top and bottom in picture). They are controlled by a low-voltage DC signal from the home automation system and provide part of the electrical disconnection. The relays are normally closed, so failure of the HA system to generate a signal will effectively cause the disconnect system to be inoperative, instead of causing an unwanted disconnect as would occur if the SSR's were of the more common normally open design.
When the SSR’s are opened
by a positive dc signal,
power to the two transformers (center left) is interrupted which in turn
de-energizes the normally-open mechanical double-pole relays (left top and left
bottom) that provide
air-gap isolation
of the hot and neutral wires of each
circuit.
The 12vdc output of the transformer + rectifier circuits can be used to confirm disconnect status and to control/power other devices.
Two UL-listed 20-amp
Corcom filters
provide filtering (-44 db @ 500 khz ; -4db @ 120 khz ) on hot and neutral of both circuits (right
center).
Corcom 20VR1
schematic
There is also a large UL-listed surge protector (left bottom outside) that connects each AC phase to neutral. The metal enclosure is connected to earth ground by a ground conductor as required by the US National Electrical Code (NEC).
Fish paper insulators (not
shown) are use to provide additional isolation of low-voltage and AC components.
