Think Twice About Surge Protection & Power Conditioning
Taking the correct steps dealers can solve issues such as ground loops without having to resort to shortcuts that include adapters that lift proper grounding.
July 27, 2015 There are disadvantages to all power isolation transformers and they include:
- Faraday shields (a.k.a. “electrostatic shields”) prevent coupling of high frequency noise from primary to secondary. But, if the shield is tied to the local safety ground, it simply injects more noise, which explains why users often report that the problem got worse.
- Impressive attenuation numbers are based on ground-plane measurements in a lab. They don’t apply to a real world plug-and-cord connection.
- Because all transformer windings have resistance, the output voltage will always have poorer regulation (voltage drop under load) than the power line they’re connected to. This is a serious consideration for power amplifiers.
Unfortunately, isolation transformers that violate regulations are readily available. Beware of bogus “approvals” like “Meets NAFTA Requirements” or “Compliant with the Federal Trade Agreements Act (TAA) for GSA Schedule purchases.” Legitimate, and applicable, agency approval is necessary to be legal.
Isolation transformers, as well as their “balanced power” variant, are often claimed to eliminate “common mode” (between neutral and safety ground in the world of AC power) transients and/or noise. While that is technically true, the importance of common-mode voltage is vastly over blown (see APC white papers #9 and #21).
A Few Words About “Spike” and “Transient” Protection
Devices that “clamp” peak powerline voltage are designed to conduct no current until the voltage across them reaches a predetermined value. At voltages even slightly higher, they conduct very high current and effectively absorb (convert to heat) the excess energy.
Various semiconductor devices (MOV, “avalanche diode”, TSS diode, etc.) can perform this “shunt” suppressor function. The most popular, and least expensive, is the MOV (metal oxide varistor). However, an MOV degrades with use, eventually causing constant conduction, overheating and sometimes fires. This basic scheme is called “shunt-mode” suppression and the transient current is usually dumped into safety ground. The high current can causes huge voltage differences to briefly appear between pieces of system equipment often damaging signal interfaces—-a concern for this scheme.
An alternative scheme is called “series mode” suppression. It puts an inductor in series between the line and the protected load. Since brief transients contain mostly high-frequency energy, the inductor has a high impedance allowing very little current to flow. However, at 60Hz, it effectively looks like a piece of wire. The benefit is that potentially damaging high voltages aren’t created in the ground system.
In this video, Dave Hill of Jensen Transformers explains some of the products the company offers that dealers can use to safely deal with issues such as ground loops:
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