Electronics Guide

Service Entrance Equipment

The utility service entrance establishes the interface between utility power and building distribution:

Main switchgear: Service entrance switchgear typically includes main disconnect switches, protective devices, and metering. Large circuit breaker operations create switching transients that propagate throughout the building distribution system. Adequate surge protection at the service entrance limits transients entering from the utility.

Service transformers: Buildings may include service transformers that step down utility voltage to building distribution voltage. Transformer saturation during voltage disturbances creates harmonic currents. Transformer magnetic fields couple to nearby equipment and cables. Proper transformer selection and location minimizes these effects.

Power factor correction: Capacitor banks for power factor correction can create resonances with distribution system inductance that amplify harmonic voltages. Capacitor switching creates significant transients. Harmonic filters or detuned capacitor banks prevent resonance problems.

Utility interaction: Power quality issues originating from the utility, including voltage fluctuations, harmonics, and transients, enter the building at the service entrance. Coordination with the utility and appropriate building-side mitigation addresses utility-sourced power quality problems.

Distribution Transformers

Transformers within buildings step voltage down for utilization circuits and provide electrical isolation:

K-rated transformers: Standard transformers are not designed for the harmonic-rich currents produced by modern electronic loads. K-rated transformers with enhanced thermal performance handle harmonic heating without derating. The K-factor rating indicates the transformer's capability to serve nonlinear loads.

Isolation transformers: Transformers provide galvanic isolation that prevents common-mode currents from propagating between their primary and secondary windings. Shielded isolation transformers with electrostatic shields between windings provide additional common-mode rejection and are often used for sensitive electronic loads.

Transformer location: Transformer magnetic fields can couple to nearby electronic equipment and data cables. Maintaining adequate clearance from transformers protects sensitive circuits. Shielding or distance addresses cases where sensitive equipment must be located near transformers.

Neutral-ground bonding: Separately derived systems from isolation transformers require proper neutral-ground bonding at the transformer secondary. This bonding point affects the return path for ground fault currents and common-mode noise currents.

Feeder and Branch Circuits

The distribution of power through feeders and branch circuits creates the conducted emissions environment:

Conductor sizing: Conductors sized only for current capacity may have excessive impedance at harmonic frequencies, causing voltage distortion at loads. The skin effect increases conductor resistance at high frequencies, further increasing impedance for harmonic currents.

Neutral conductor loading: In three-phase systems serving single-phase electronic loads, triplen harmonics (3rd, 9th, 15th, etc.) add in the neutral conductor rather than canceling. Neutral conductors may require oversizing for harmonic-rich loads to prevent overheating and voltage distortion.

Cable routing: Power cables routed near signal cables couple interference through magnetic and electric fields. Proper separation and crossing angles minimize coupling. Armored or shielded power cables reduce emissions from power distribution.

Circuit isolation: Providing dedicated circuits for sensitive electronic equipment prevents conducted coupling from other loads. Isolation transformers or filters at sensitive load panels provide additional protection.

Grounding and Bonding

The grounding and bonding system affects both safety and EMC performance:

Equipment grounding: Equipment grounding conductors carry fault currents for personnel safety and provide a reference for electronic equipment. Ground conductor impedance affects both fault clearing time and high-frequency reference quality.

Supplementary grounding: Signal reference grids and supplementary ground buses provide lower-impedance grounding for electronic equipment than provided by the safety grounding system alone. These supplementary grounds must bond to the main grounding system.

Ground loops: Multiple ground connections between equipment create ground loops that can carry interfering currents. Proper grounding topology, optical isolation, or balanced signaling addresses ground loop problems.

Building steel: Bonding building steel to the grounding system creates a massive, low-impedance ground reference that supplements conductor-based grounding. However, building steel can also carry stray currents that affect nearby sensitive circuits.

Generator Systems

Engine-generator sets provide emergency and standby power for buildings:

Generator electrical characteristics: Generators produce power with different characteristics than utility power. Generator output voltage waveforms may have higher harmonic content, and frequency may vary during load changes. Voltage regulation during load transients depends on generator size and regulator characteristics.

Harmonic effects: Nonlinear loads can cause excessive harmonic distortion on generator power because the generator has higher impedance than the utility. Generator sizing must account for harmonic loading to prevent excessive voltage distortion and heating.

Transfer transients: Transfer switches switching between utility and generator power create transients and momentary power interruptions. The characteristics of these transients depend on transfer switch type (open, closed, or delayed transition) and load characteristics.

Engine and controls: Generator engines produce vibration and acoustic noise with low-frequency electromagnetic components. Electronic engine controls and voltage regulators can be susceptible to EMI and are sources of radiated emissions. Proper shielding and grounding of control systems ensures reliable operation.

Automatic Transfer Switches

Automatic transfer switches manage transitions between power sources:

Transfer types: Open-transition transfers briefly interrupt power during source switching. Closed-transition (make-before-break) transfers momentarily parallel sources, requiring source synchronization. Delayed-transition switches allow generator stabilization before transfer.

Switching transients: Contact operation creates transients related to arc interruption and contact bounce. The magnitude depends on load characteristics and switch design. Electronic transfer switches using solid-state switching have different transient characteristics than mechanical switches.

Control circuit EMC: Transfer switch control circuits must sense voltage on both sources and control transfer operations. These circuits can be susceptible to transients and must operate reliably during the disturbed conditions that often accompany power failures.

Generator loading: The transfer switch presents the full building load to the generator simultaneously in some configurations. Staggered loading sequences reduce generator transients but may leave some loads unpowered longer during outages.

Emergency Lighting

Emergency lighting systems illuminate egress paths during power failures:

Central systems: Central battery systems power emergency lighting from a common source. The inverter converting battery DC to AC for lighting loads generates harmonic currents and switching noise. Inverter output filtering reduces conducted emissions on emergency lighting circuits.

Unit equipment: Self-contained emergency lighting units with integral batteries are distributed throughout the building. These units contain charging circuits and inverters that generate emissions during both charging and discharge operation.

LED emergency lighting: LED emergency fixtures use drivers that convert battery voltage to LED operating voltage. These drivers have EMC characteristics similar to standard LED drivers, including conducted emissions and potential flicker.

Testing requirements: Regular testing of emergency lighting activates charging circuits and inverters, creating emissions that may affect nearby equipment. Test scheduling should consider potential EMC effects.

UPS Topologies

Different UPS architectures have different EMC characteristics:

Double-conversion (online) UPS: Online UPS systems continuously convert utility AC to DC to charge batteries, then convert DC back to AC for the load. The output is synthesized, providing isolation from most utility disturbances. Input rectifiers draw harmonic currents; output inverters may produce output harmonics depending on design quality.

Line-interactive UPS: Line-interactive systems pass utility power through to the load during normal operation while conditioning voltage and maintaining battery charge. These systems have lower losses than online systems but provide less isolation from utility disturbances. Inverter operation during outages has EMC characteristics similar to online systems.

Standby (offline) UPS: Standby UPS systems power loads directly from utility until detecting an outage, then transfer to inverter operation. The transfer time leaves a brief gap in power. Input surge protection and output filtering vary by product quality.

Rotary UPS: Motor-generator UPS systems use rotating mass for energy storage and provide natural filtering of input power disturbances. The rotating elements produce mechanical vibration but provide excellent output power quality without the switching noise of static UPS systems.

UPS EMC Characteristics

UPS systems both generate and attenuate electromagnetic interference:

Input harmonics: UPS rectifiers draw nonsinusoidal input currents with significant harmonic content. Active power factor correction in modern UPS systems reduces input harmonics to meet regulatory requirements, but the high-frequency switching of PFC circuits creates other emissions.

Output waveform: UPS inverter output waveforms range from stepped approximations to pure sine waves depending on design quality. Sensitive electronic loads may require true sine wave output. The output waveform affects conducted emissions on load circuits.

Common-mode behavior: UPS systems can create common-mode voltage between output neutral and ground, depending on internal topology and grounding configuration. This common-mode voltage can affect connected equipment, particularly ground-referenced analog circuits.

Bypass operation: UPS systems with bypass capability can transfer loads to utility power if the inverter fails or is overloaded. Bypass operation removes the UPS filtering from the power path, potentially exposing sensitive loads to utility disturbances.

UPS Installation EMC

Proper UPS installation optimizes EMC performance:

Input and output separation: UPS input and output cables should be separated to prevent coupling of input noise to the output. Routing input and output through separate conduits or cable trays maintains separation.

Grounding: UPS grounding must be coordinated with the building grounding system. The relationship between UPS input, output, and battery ground affects common-mode behavior and safety grounding.

Battery connections: DC connections between batteries and UPS are low-voltage but high-current paths. Proper cable routing and termination prevents these connections from becoming EMI antennas or picking up interference.

Room design: UPS rooms housing large systems should consider EMC in layout, cable routing, and equipment spacing. Ventilation requirements for UPS cooling may require penetrations that affect room EMC if shielding is desired.

Transformer EMC Considerations

Power transformers affect the electromagnetic environment in several ways:

Magnetic field emissions: Power frequency magnetic fields from transformers extend into surrounding spaces. The field intensity decreases rapidly with distance from the transformer. Sensitive electronic equipment and medical devices should maintain specified clearances from transformers.

Inrush current: Energizing a transformer creates inrush current that can be many times rated current. This transient can cause voltage sags that affect other equipment and may trip protective devices. Point-on-wave switching or pre-insertion resistors reduce inrush effects.

Saturation effects: DC components in transformer current, or asymmetrical faults, can saturate transformer cores, creating harmonic distortion and additional heating. Geomagnetically induced currents (GIC) during solar storms can cause transformer saturation in extreme cases.

Acoustic noise: Transformer magnetostriction causes vibration at twice the power frequency. This acoustic noise can be objectionable in occupied spaces and can couple vibration to building structure. Low-noise transformer designs and vibration isolation address these issues.

Switchgear Operations

Switching operations in electrical distribution create transients:

Circuit breaker switching: Opening and closing circuit breakers creates transients from arc interruption and current chopping. Vacuum and SF6 circuit breakers have different transient characteristics than air magnetic breakers. Surge protection limits transient propagation from switchgear.

Contactor operations: Motor contactors and lighting contactors switch regularly during building operation. Each operation creates switching transients. Arc suppression and snubber circuits reduce transient generation.

Protective device operations: Fault clearing by circuit breakers and fuses creates transients throughout connected circuits. The transient magnitude depends on fault current magnitude and protective device characteristics.

Switching frequency: Frequent switching operations, as with motor starters on frequently cycling equipment, create repeated transients that may affect nearby sensitive equipment. The cumulative effect of repeated transients can exceed the impact of single events.

Panelboards and Distribution Boards

Distribution panelboards serve as concentration points for branch circuit wiring:

Wiring practices: How conductors are organized within panelboards affects both safety and EMC. Phase conductors for three-phase loads should be grouped to minimize magnetic field emissions. Proper neutral and ground connections prevent common-mode noise issues.

Panel grounding: Metal panelboard enclosures should be properly grounded and bonded. The enclosure provides some shielding and establishes a local ground reference for connected equipment.

Surge protection location: Surge protective devices at distribution panels protect branch circuit loads from transients originating in the building distribution system. SPD installation should follow manufacturer requirements for lead length and conductor routing.

Sensitive load panels: Panels serving sensitive electronic loads may include isolation transformers, filters, or enhanced surge protection. These panels should be dedicated to sensitive loads, with other loads fed from separate panels.

Fluorescent Lighting EMC

Fluorescent lighting remains common in many building applications:

Magnetic ballasts: Traditional magnetic ballasts operate at power frequency with relatively simple electromagnetic characteristics. These ballasts create modest harmonic currents and can produce audible hum from magnetostriction.

Electronic ballasts: High-frequency electronic ballasts operate at frequencies from 20 kHz to over 100 kHz. These ballasts eliminate visible flicker and audible hum but generate conducted and radiated emissions at the ballast switching frequency and its harmonics.

Dimming ballasts: Dimming electronic ballasts add complexity to maintain lamp operation across the dimming range. Some dimming methods create additional EMC issues, including lamp acoustic resonance that can affect nearby ultrasonic sensors.

Aggregate effects: Large buildings with many fluorescent fixtures exhibit aggregate conducted emissions that can exceed the sum of individual fixture contributions due to constructive interference at certain frequencies. System-level EMC assessment may be needed for large installations.

LED Lighting EMC

LED lighting is increasingly dominant in new construction and retrofits:

LED driver emissions: Switch-mode LED drivers generate conducted emissions similar to other switching power supplies. Driver quality varies significantly; budget products may have minimal EMC filtering. Specifying compliance with appropriate EMC standards ensures baseline performance.

Driver input harmonics: LED drivers typically have power factor correction to meet regulatory requirements. Active PFC circuits reduce low-order harmonics but may generate high-frequency conducted emissions from the PFC switching.

Flicker considerations: Although not strictly EMC, LED flicker can affect video systems and sensitive individuals. High-quality drivers maintain acceptable flicker even at dimmed levels. Driver specifications should address flicker performance.

Retrofit installations: LED retrofit lamps installed in fixtures designed for other lamp types may have compromised EMC performance due to the constrained space for EMC filtering within the lamp. Native LED fixtures generally have better EMC characteristics than retrofit installations.

Lighting Control System EMC

Lighting control systems introduce additional EMC considerations:

Phase-cut dimming: Leading-edge (forward phase) and trailing-edge (reverse phase) dimmers create conducted emissions from the fast voltage transitions at dimmer firing points. Trailing-edge dimming generally produces fewer emissions but is incompatible with some lamp types.

PWM dimming: Pulse-width modulation dimming of LED fixtures creates emissions at the PWM frequency. Low PWM frequencies may cause visible flicker; higher frequencies reduce flicker but may create audio-frequency conducted emissions.

Control protocols: Digital lighting control protocols (DALI, DMX, etc.) require consideration of control cable routing and termination for reliable operation. Power line carrier lighting control systems must operate despite conducted noise from building loads.

Wireless lighting control: Wireless lighting control systems use radio frequencies that must coexist with other building wireless systems. Aggregate emissions from large numbers of wireless-controlled fixtures should be considered in wireless planning.

Motor and Drive EMC

Electric motors and their associated drives are major EMC considerations:

Motor starting: Direct-on-line motor starting creates voltage sags and inrush currents that can affect other equipment. Reduced-voltage starters, soft starters, and variable frequency drives reduce starting impacts but have their own EMC characteristics.

Variable frequency drives: VFDs are significant EMC sources, generating harmonic currents on their input and high-frequency emissions from the PWM output. Proper VFD installation including input filters, shielded motor cables, and appropriate grounding is essential for acceptable EMC performance.

Motor-side effects: VFD-driven motors experience voltage stresses from fast switching transients, which can cause bearing currents and premature insulation failure. These same transients radiate from motor cables and can couple to nearby circuits.

Regenerative drives: Drives on loads like elevators that regenerate energy back to the building power system must manage this energy without creating power quality problems. Regenerative common bus systems or active front-end drives address regeneration EMC.

HVAC Equipment EMC

HVAC equipment throughout buildings contributes to the electromagnetic environment:

Air handling units: Large AHU fans and their drives are significant EMC sources. VFD-driven supply and return fans generate emissions similar to other motor drive applications. The distributed location of AHUs throughout buildings spreads these emissions.

Packaged equipment: Rooftop units, split systems, and other packaged HVAC equipment contain integral drives and controls. Equipment specifications should include appropriate EMC performance requirements. Installation location affects coupling to building systems.

Pump systems: Hydronic pumps for heating and cooling systems are driven by constant-speed motors or VFDs. Large pump motors can cause voltage sags during starting. VFD-driven pumps have the same EMC characteristics as other VFD applications.

Control systems: HVAC controls including direct digital controls and building automation communicate over networks that can be affected by EMI from mechanical equipment. Proper installation practices including cable routing and termination ensure reliable control system operation.

Elevator and Conveying Systems

Vertical and horizontal transportation systems are significant building EMC factors:

Elevator drives: Modern traction elevators use VFDs with regenerative capability. The drive electronics generate harmonics on the input and switching noise that can radiate from the hoistway. Proper filtering and cable management addresses elevator EMC.

Safety systems: Elevator safety circuits must operate reliably despite the EMI environment in machine rooms and hoistways. Safety-rated components are designed for this environment but still require proper installation.

Escalators and moving walks: These systems use drives similar to other motor applications. Their location in public areas means any EMC issues affect tenant and visitor systems.

Material handling: Buildings with automated material handling systems have significant motor and drive loads concentrated in specific areas. EMC zoning can isolate these areas from sensitive building systems.

Plumbing and Fire Protection

Plumbing and fire protection systems have some EMC considerations:

Pumps: Domestic water booster pumps, sump pumps, and fire pumps use motors that can cause starting transients. VFD-driven pumps have additional conducted emission considerations.

Fire pump power: Fire pumps require reliable power with specific starting characteristics. The power quality impacts of fire pump starting must be considered in electrical system design.

Piping systems: Metal piping systems can carry stray currents and provide unintended electromagnetic coupling paths. Isolation and bonding of piping systems should be coordinated with electrical system grounding design.

Electronic controls: Electronic controls on plumbing systems, including variable-speed pumps and automatic flush valves, can be affected by power quality issues and may generate emissions affecting other systems.

Power Quality Parameters

Key power quality parameters affecting EMC include:

Voltage magnitude: Voltage sags and swells affect equipment operation. Sensitive electronic equipment may malfunction or shut down during voltage disturbances that are within utility supply tolerances.

Harmonic distortion: Harmonic currents from nonlinear loads create voltage distortion that affects all equipment on the distribution system. Total harmonic distortion (THD) and individual harmonic magnitudes characterize this distortion.

Transients: Switching transients, lightning surges, and other fast disturbances can damage or upset electronic equipment. Transient magnitude, rise time, and energy content determine their impact.

High-frequency noise: Conducted noise at frequencies above the harmonic range can interfere with electronic equipment through power supply connections. This noise often originates from switching power supplies and VFDs.

Monitoring Approaches

Power quality monitoring provides data for problem identification and resolution:

Permanent monitoring: Installed power quality monitors provide continuous data on building power quality. Trend analysis identifies developing problems before they cause equipment failures.

Portable monitoring: Portable power quality analyzers support troubleshooting of specific problems. Short-term monitoring at problem locations identifies the source and characteristics of disturbances.

Monitoring locations: Strategic monitoring points include the service entrance, major distribution panels, and panels serving sensitive loads. The monitoring strategy should enable localization of power quality problems to specific areas or loads.

Data analysis: Power quality monitoring generates large amounts of data. Effective analysis requires appropriate software and expertise to identify significant events among routine variations.

Mitigation Measures

Various measures address power quality problems:

Harmonic filtering: Passive and active harmonic filters reduce voltage distortion from nonlinear loads. Filter design must consider system impedance and harmonic spectrum to avoid resonance problems.

Surge protection: Coordinated surge protective device application at service entrance, distribution panels, and sensitive load locations limits transient exposure. SPD selection and coordination follows standards such as IEEE C62.41 and C62.45.

Isolation transformers: Isolation transformers with electrostatic shields provide common-mode rejection and prevent ground loop currents between systems. Voltage regulation transformers (CVTs) also provide conditioning for voltage variations.

UPS systems: Online UPS systems provide the most comprehensive power conditioning, isolating loads from virtually all utility disturbances. For sensitive loads, UPS protection may be more cost-effective than attempting to improve overall building power quality.

System Design

Design decisions establish the foundation for building services EMC:

• Load analysis: Understanding the electrical characteristics of building loads enables appropriate system design. Nonlinear loads, large motors, and sensitive equipment require specific design attention.
• System separation: Segregating sensitive loads from noise-generating loads through separate transformers, panels, or feeders reduces conducted coupling.
• Equipment specification: Specifying appropriate EMC performance for electrical equipment ensures that individual components contribute to overall system EMC.
• Coordination: Coordinating electrical, mechanical, and electronic system designs identifies potential conflicts early when they can be addressed efficiently.

Installation Practices

Proper installation maintains designed EMC performance:

• Cable installation: Maintaining required separations, proper routing, and correct terminations ensures cables do not compromise EMC performance.
• Grounding and bonding: Following designed grounding topology and bonding requirements establishes the intended electromagnetic reference structure.
• Equipment installation: Installing equipment according to manufacturer requirements, including any EMC-specific requirements, ensures equipment operates as specified.
• Documentation: Documenting as-built conditions supports future troubleshooting and modifications.

Commissioning and Verification

Commissioning verifies that installed systems meet EMC requirements:

• Power quality measurements: Baseline power quality measurements verify acceptable conditions before occupancy.
• System testing: Testing building systems under realistic operating conditions identifies EMC interactions before they affect occupants.
• Problem resolution: Addressing any EMC issues discovered during commissioning before project completion is more efficient than post-occupancy troubleshooting.
• Documentation: Commissioning documentation provides baseline data for comparison during future building operation.