Circuit Isolation

Isolate computer loads from large motor loads in the building. These loads cause the power both on their circuits and nearby ones to sag and surge each time they start and stop. A separate circuit for sensitive loads lessens this impact.

A dedicated circuit will protect the most sensitive equipment from local noise and surge conditions. However, these circuits should be protected from voltage surges that might enter the system from the outside world.

In a number of situations, isolating the electric loads power conductors is enough to resolve power problems, in particular, those problems associated with internally generated transients and voltage sags. Even if circuit isolation does not fix the problems, it does provide a much healthier overall environment for sensitive electronic loads.

The key concept in circuit isolation is recognizing that the wiring system is a natural low pass filter. It takes energy for a transient to travel down conductors, so the longer the circuit length, the more energy is required, and the less energy is available to disrupt or damage loads.

Conversely, at power frequencies, the amount of wire impedance affects load-induced voltage sags. The larger the wire size, the less impedance, and the smaller the magnitude for a sag.

In practice, this means the installation of dedicated circuits. A dedicated circuit is one where all needed power conductors, and a ground conductor, are run from the source and connected to only the sensitive load or loads. For single phase application, this includes a separate hot, neutral, and ground per load or system. Isolated grounds would be a good addition to a dedicated circuit.

What this also implies is that sharing neutrals between branch circuits is out, and daisy-chaining receptacles is tightly controlled.

If voltage instability is a concern, use a larger wire size for the dedicated circuit. One size larger reduces the chance of load induced sags, and is perfectly legal. A larger size wire will not alter the overall attenuation the wire system provides for high frequency transients.

If the concern is a high neutral current due to harmonic distortion, then two things can be done. First, provide dedicated branch circuits which eliminates shared neutrals. Second, increase the size of the neutral conductor feeding the panel. This ensures the conductor will not overheat, and minimizes the neutral-to-ground voltage that builds up due to neutral current interacting with neutral impedance.

If larger wires are installed, whether for the hot, neutral, or ground, make sure that all terminations can support the larger wire size. Do not ever trim a wire just to make it fit into a lug.