Industry — Critical Infrastructure
Resilient distribution for facilities where an electrical outage becomes a public incident
Airports, communications hubs, transit systems, emergency operations centers and similar facilities are expected to keep operating through utility disturbances, equipment failures and maintenance. Apex engineers redundant low- and medium-voltage distribution, integrates the transfer and paralleling controls that make redundancy usable, and adds monitoring so operators know the state of every source and breaker.
Operating realities
What makes critical infrastructure distribution its own discipline
Redundancy that actually works when called on
Dual utility feeds, main-tie-main buses and standby generation only deliver resilience if the transfer logic, interlocks and protection have been engineered and tested as one system. Common-mode failures such as shared control power, a single PLC or one communications path can quietly defeat a redundant one-line. Failure-mode reviews and functional testing are part of the design, not an afterthought.
Maintenance without an outage window
Critical facilities rarely get a full shutdown, so maintenance has to be performed on one section while the rest carries load. Drawout breakers, bus sectionalizing, bypass-isolation transfer switches and clear isolation points are what make that possible. Where work near energized equipment cannot be avoided, remote racking, remote operation and arc-resistant construction reduce exposure, and the facility's electrical safety program governs the work.
Visibility across many sources and buildings
A campus or terminal may have several services, generators, transfer switches and hundreds of breakers spread across buildings. Operators need one consistent view of source status, breaker states and alarms, with communication loss shown explicitly rather than as a stale green indicator. Event records with synchronized time stamps are essential for reconstructing what happened after a disturbance.
Protection under changing source conditions
Fault current and coordination change depending on whether the facility is on utility, on generators or paralleled. Relay setting groups, ground-fault schemes and selective coordination have to be validated for each operating mode. A scheme that coordinates on utility but not on generator power fails at the moment it matters most.
How Apex fits
LV, MV, automation and monitoring for critical infrastructure
Low-voltage equipment
Switchgear designed for sectional maintenance
Apex engineers UL 1558 low-voltage power switchgear with drawout LVPCBs and tie breakers where sectional maintenance is required, and UL 891 switchboards for distribution where fixed-mount devices are appropriate. Bypass-isolation transfer switches and clearly labeled isolation points are part of the layout.
Learn moreMedium-voltage equipment
Dual-fed medium-voltage distribution
Metal-clad switchgear at 15 kV or 27 kV class with main-tie-main arrangements takes two utility feeds or utility plus generation, with arc-resistant construction and remote racking evaluated against how the equipment will be operated and maintained. Loop or radial campus distribution is engineered to isolate a faulted segment without dropping the facility.
Learn moreAutomation & controls
Transfer, paralleling and load management
Main-tie-main auto-transfer with interlocking, generator paralleling with sync-check and load shedding are engineered with redundant control power and, where justified, redundant controllers. Setting groups switch with the operating mode, and all automatic actions remain governed by the approved protection and control scheme.
Learn moreMonitoring & analytics
One view of every source and breaker
Breaker states, source availability, relay events and power-quality data are collected across buildings into a single operations view with time-synchronized event records. Health scoring and anomaly detection help prioritize maintenance on the equipment that shows abnormal behavior; the operator makes the decisions.
Learn moreTypical equipment
What a critical infrastructure one-line usually contains
- 15 kV or 27 kV class metal-clad switchgear in main-tie-main configuration
- 480 V UL 1558 low-voltage power switchgear with drawout LVPCBs and tie breakers
- 480 V UL 891 switchboards for building distribution
- Bypass-isolation automatic transfer switches for critical loads
- Generator paralleling switchgear with load-shed and load-add control
- Redundant control power supplies and 125 V DC systems for protection and control
- Arc-resistant construction, remote racking and remote breaker operation
- Campus-wide power monitoring with synchronized sequence-of-events recording
Codes and standards that commonly apply
Specifications govern
- Where a facility is classified as a critical operations power system, NEC Article 708 requirements commonly apply alongside Articles 700 and 701 for emergency and standby systems; the classification is made by the owner and the authority having jurisdiction, and the project specifications govern.
- Switchboards are typically listed to UL 891, low-voltage power switchgear to UL 1558 and transfer switches to UL 1008; metal-clad switchgear generally follows IEEE C37.20.2 with arc-resistant designs tested per IEEE C37.20.7 where specified. The project specification governs.
- Maintenance practices commonly follow NFPA 70B for equipment maintenance programs and NFPA 70E for electrical safety; the facility's own program and procedures govern how work is performed.
Questions we hear
Frequently asked
+What usually defeats redundancy in a dual-fed facility?
Shared elements that were not on the one-line: a single control power source feeding both mains, one PLC running the transfer logic, a common communications switch, or relay settings that were never checked for generator-only operation. A failure-mode review of the control and protection system, followed by functional testing of each transfer case, finds most of these before they matter.
+How can we maintain switchgear when the facility never shuts down?
The design has to allow one section to be isolated while the rest carries load, which means drawout breakers, tie breakers, bypass-isolation transfer switches and defined isolation points. Maintenance is then scheduled by section with a written switching plan. Remote racking and remote operation reduce the exposure of the people doing the work, within the facility's electrical safety program.
+Does the monitoring system take any control actions on its own?
No. The monitoring and analytics layer collects data, flags abnormal behavior and recommends actions to operators and maintenance staff. Protective functions remain with the relays and trip units, and switching remains with the approved control scheme and the operators who run it.
Related engineering resources
Read next
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Main-Tie-Main Systems: Design and Automatic Transfer Logic
A main-tie-main lineup splits the bus so that two sources each carry part of the load and either can pick up the whole load when the other is lost. The value is in the automatic transfer logic, and this article explains how source loss is detected, how the transfer is sequenced, and which interlocks keep the scheme from doing harm.
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Racking a drawout breaker and closing a breaker into an unknown condition are the two switchgear operations most likely to start an arc, and both have traditionally been done by a person standing at the door. This article covers the equipment and procedures that move that person outside the arc-flash boundary and what has to be true of the interlocks for that to be safe.
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Switchgear Condition Monitoring: What to Measure and Why
Condition monitoring turns switchgear from equipment you inspect on a schedule into equipment that reports its own health. This article covers the measurements that matter for low- and medium-voltage assemblies, the sensors that make them, and how to turn raw readings into baselines, trends and alarms an operator can act on.
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Arc-Resistant Switchgear: Types, Testing and Limits
Arc-resistant switchgear is designed and tested to direct the pressure, gas and molten metal of an internal arcing fault away from people standing at defined locations around the equipment. This article explains the accessibility types, how the internal arc test works, what the plenum and pressure relief system requires of the room, and where the protection stops.
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Apex Power Distribution · ApexPower.ai
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