The National Electrical Code (NEC) compliance rulings for symmetrical or “balanced” AC power refer to the power from a sub-panel device, and, thus, power distributed to a residential or commercial AC wall outlet. It was never meant to include isolation transformers (balanced, floating, or otherwise), in a component AC power product or A/V component product. This NEC ruling was created with the petitioning of Martin Glassband of Equitech. At that time, Equitech’s primary markets for balanced AC power isolation transformers were recording and broadcast facilities. As these buildings featured multiple production rooms, it was not considered practical to use dozens of individual AC power components for the wide-bandwidth common-mode noise reduction afforded by this balanced technology (there would have been difficulties maintaining proper single-point grounding, as well). Since a high current capacity balanced power unit for a large electrical room would take the place of a conventional AC sub-panel, and the output would be distributed to specified wall outlets, the NEC was keen to make certain labeling was clear and that it be limited to professional applications.
However, in the case of a component AC power product, there is no confusion for an electrician servicing the facility in question. As required by the Nationally Recognized Testing Laboratory (NRTL) and Canadian Standards Association (CSA), the AC outlets are properly marked, but in this application there is absolutely nothing unusual at all, when compared to about 50% of the pre-amplifiers, power amplifiers, and other source components with a linear power supply. This is because a “balanced power” transformer is simply a precisely manufactured transformer with a faraday screen (or faraday screens) and a center-tapped secondary. This transformer construction method goes back to the very beginning of electronics, and presents nothing at all unique or problematic from a perspective of safety.
However, there is one aspect of the design that concerned some engineers when this was introduced as a power conditioning technology over 20 years ago, and that was the presence of live voltage on the Neutral (60VAC relative to Ground, if Line to Neutral has a potential of 120VAC).
Because no one makes a practice of assuming that either the Line or the Neutral AC lead is something to “grab ahold of” (particularly with the quantity of reversed polarity AC outlets in far too many homes), there is no practical safety issue, and certainly no problem for electronics power supplies. The only potential concern is a (rare) catastrophic failure in a source component or power amplifier’s power supply. If this were to occur, there might be a small chance for live voltage to be present on the A/V component’s chassis prior to a fuse or circuit breaker tripping. We have included a Ground Fault Circuit Interrupter (GFCI) for all of the symmetrical (balanced) power outlets, to ensure that if more than 5.5mA current is drawn from Line to Ground, or Neutral to Ground, the Niagara’s main power breaker will immediately shut off. This is the same technology used by most laboratories for electronic circuit development, as it’s far safer than the power that is supplied from the wall’s AC service tap. With a properly designed GFCI, electrocution or shock is essentially impossible.