Power Modes in the MAX, Balanced Power

ISOLATED vs. BALANCED POWER

Power Modes in the MAX® 5510

Single-phase grounded-neutral power

The standard method of residential power delivery in the U.S. The neutral, or "grounded" conductor, is bonded to the earth, or "grounding" conductor. The N-G panel bond creates a severe imbalance with respect to common-mode currents, which can lead to "hum" in A/V equipment. There are three problems with this configuration that are specifically targeted by our "Isolated" and "Balanced" power modes:

1.Line and neutral current imbalance. Unbalanced currents in the L-N can radiate magnetic fields, which can couple inductively from connected power cords to nearby A/V cables.

2.Ground skew. Voltage drops due to common-mode current flowing into the earth ground can cause a skew between signal ground references in interconnected A/V equipment.

3.Line and neutral voltage imbalance. Unbalanced voltages from line and neutral to ground can cause connected power cords to radiate electrical fields, which can couple capacitively to nearby A/V cables.

Balanced Power

With "Balanced Power", the asymmetric, zero-volt N-G reference at the panel is replaced by a symmetric ground reference between line and neutral. Hum-producing common-mode cur- rents (2) and radiated electrostatic fields in the connected power cords (3) are both eliminated by voltage phase cancellation. Radiated magnetic fields can still be evident (but to a much less- er degree than with grounded-neutral power), unless the imped- ances from L-G and N-G in the connected equipment are equal.

Isolated Power

With "Isolated Power" the N-G panel bond is broken by floating the line and neutral, and the ground reference voltage is driven to neutralize the hum-producing ground leakage currents (2). Consequently, L-N currents are equalized, effectively eliminating magnetic field radiation from connected power cords through cur- rent phase cancellation (1). Radiated electrical fields can still be evident (but to a much lesser degree than with grounded-neutral power), unless the impedances from L-G and N-G in the connect- ed equipment are equal.

Conclusion

"Balanced" and "Isolated" Power are both exceedingly efficient at overcoming the inherent problems of the unbalanced earth ground reference in domestic single-phase power systems, with small but definable distinctions. They are both effective in reduc- ing common mode currents and radiated magnetic and electro- static fields from connected power cords. The primary difference is simple: "Isolated Power" is better at reducing the magnetic (inductive) component, and "Balanced Power" is better at reduc- ing the electrical (capacitive) component. Because all A/V cables have some amount of inductance and capacitance (defined col- lectively as "impedance"), they are susceptible to both types of interference, and the trade-offs will vary with the system config- urations.

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