RCDD · Question #127
An isolated ground is used to:
The correct answer is C. Reduce EMI/RFI. An isolated ground outlet provides a dedicated, insulated ground return path that prevents common-mode noise coupling, specifically reducing EMI and RFI on sensitive electronic equipment.
Question
An isolated ground is used to:
Options
- AReduce transients
- BPrevent interruptions
- CReduce EMI/RFI
- DReduce swells and sags
How the community answered
(30 responses)- A7% (2)
- B17% (5)
- C70% (21)
- D7% (2)
Why each option
An isolated ground outlet provides a dedicated, insulated ground return path that prevents common-mode noise coupling, specifically reducing EMI and RFI on sensitive electronic equipment.
Transient suppression requires surge protection devices (SPDs) or UPS units with filtering; isolated grounds only provide a low-noise reference path and do not clamp voltage spikes.
Preventing power interruptions requires redundant supply paths or uninterruptible power supplies, which isolated grounds cannot provide.
An isolated ground (IG) outlet, governed by NEC Article 250.146(D), runs an insulated ground conductor back to the panel without connecting to intermediate metallic enclosures, eliminating ground loops that would otherwise allow EMI and RFI to couple into equipment. This clean ground reference is critical for sensitive electronics such as computers and audio/video gear that are susceptible to noise on the ground plane. Isolated grounds do not regulate voltage magnitude, supply redundant power, or suppress transient spikes independently.
Swells and sags are RMS voltage magnitude variations corrected by voltage regulators or online UPS devices, not by grounding topology changes.
Concept tested: Isolated ground outlet function - EMI/RFI noise reduction
Source: https://www.nfpa.org/codes-and-standards/nfpa-70-national-electric-code-nec/70
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