When an emergency strikes, your backup power system either performs or it doesn’t. There is no middle ground. Whether you’re operating a petrochemical plant, a hospital with life-safety systems, or an offshore installation subject to SOLAS requirements, the accuracy of your emergency power load sizing study determines whether every critical load stays energized when grid power fails.
Getting the numbers wrong has real consequences. Generators trip on overload. Transfer switches fail to close. NFPA 110 ↗ compliance reviews uncover undersized systems months before a facility opens. Our engineering team provides rigorous, code-compliant emergency power load sizing studies that eliminate those risks before they become operational failures.
What Is Emergency Power Load Sizing?
Emergency power load sizing is the engineering process of systematically identifying, classifying, and calculating the total connected and demand loads that must be supplied by a backup or standby power system during a loss of normal utility power. A correctly executed study produces a generator capacity recommendation aligned to NFPA 110, NEC Articles 700/701/702, and IEEE 446, factoring in starting transients, demand diversity, and future load growth.
The process is not simply adding up nameplate ratings. Load classification under NEC Article 700 (Emergency), Article 701 (Legally Required Standby), and Article 702 (Optional Standby) changes everything about system design, circuit segregation, and the required transfer time. Misclassifying a load at this stage propagates errors through every downstream design decision.
Our Emergency Power Load Sizing Service: Scope & Deliverables
Our service delivers a complete, audit-ready engineering package. We handle every step from initial load inventory to final generator sizing recommendation, giving your team a document set that satisfies both internal design reviews and third-party compliance audits.
Recognized for excellence.
PROJECTS DELIVERED ACROSS THE GLOBE
Load Inventory & Classification
We begin by compiling a full electrical load schedule from your one-line diagrams, equipment datasheets, and facility layout drawings. Every load is individually assessed and classified as Emergency, Legally Required Standby, or Optional Standby per the applicable NEC article. This classification directly governs which loads the backup system must serve within defined transfer time windows.
Key activities at this stage:
- Review of existing electrical single-line diagrams and MCC schedules
- Identification of life-safety loads (fire pumps, egress lighting, medical equipment)
- Separation of process-critical loads from optional loads
- Documentation of motor starting requirements and inrush current data
Demand Factor & Diversity Analysis
Raw connected load is never the right number to design a generator for. We apply electrical load demand factors drawn from NEC Tables, IEEE 446 guidance, and facility-specific operating profiles to calculate realistic peak demand. For facilities with staggered load pickup sequences (hospital wings, data hall phases), diversity analysis can meaningfully reduce the required generator kW rating without compromising reliability.
Where motor loads are significant, we calculate starting kVA impact on generator terminal voltage. A 250 kW generator can collapse under the starting inrush of a 75 hp fire pump if that scenario isn’t modeled explicitly.
Generator Sizing Recommendation Report
The final deliverable is a formal emergency generator sizing report that includes:
| Report Element | Detail Provided |
| Load Schedule Summary | Classified loads, connected kW, demand kW per circuit |
| Demand Factor Basis | Applied factors with code/standard reference |
| Starting Transient Analysis | Voltage dip and recovery modeling for largest motor starts |
| Recommended Generator Rating | kW, kVA, power factor, with oversizing margin |
| Load Growth Allowance | Capacity reserve for future expansion |
| Compliance Matrix | NFPA 110, NEC 700/701/702, project-specific codes |
Compliance Standards We Work To
Emergency power systems are among the most heavily regulated electrical systems in any facility. Our load sizing methodology is built on the following standards, and every report we issue references the specific clause that governs each engineering decision.
| Standard | Scope | Key Requirement |
| NFPA 110 | Emergency and Standby Power Systems | Generator performance, load transfer time, fuel supply duration |
| NEC Article 700 | Emergency Systems | Load classification, circuit wiring methods, transfer equipment |
| NEC Article 701/702 | Legally Required / Optional Standby | Scope boundaries, permissible sources |
| IEEE 446 | Emergency Power for Industrial Facilities | Load analysis methodology, design guidance |
| SOLAS Chapter II-1 | Marine / Offshore Emergency Power | Emergency generator capacity, positioning, starting requirements |
| IEC 60092-301 | Electrical Installations in Ships | Marine emergency source sizing |
For projects subject to regulatory body review (AHJ, DNV, Lloyd’s Register, or a state health department), we can structure the load sizing report to align directly with the reviewer’s submission format.
Industries We Serve
Healthcare & Hospitals
Hospitals operate under some of the most prescriptive emergency power requirements in existence. NFPA 99 and NFPA 110 together mandate specific branch segregation (life safety, critical, equipment) and maximum transfer times of 10 seconds for life-safety systems. A single miscalculated load on the life-safety branch can trigger a citation during a Joint Commission survey.
Our team understands the difference between an OR lighting circuit and a nurse call system in terms of NEC branch classification. We have sized backup power systems for acute care hospitals, surgical centers, and outpatient facilities where regulators scrutinize every line of the load schedule.
Oil, Gas & Offshore Platforms
Offshore platforms present a unique challenge: the emergency generator must supply enough power to safely shut down the facility, support escape and evacuation systems, and maintain fire and gas detection without access to utility grid support. SOLAS regulations and classification society rules (DNV-ST-0373, ABS) define minimum load categories and maximum permissible generator failure rates.
We perform backup power load analysis for FPSOs, fixed platforms, and onshore LNG facilities where the emergency source is the last line of defense against a catastrophic loss of control scenario.
Industrial Plants & Process Facilities
A refinery or chemical plant shutdown is not like a power outage in an office building. Critical load calculation for process facilities requires engineers who understand which loads are safety-instrumented system (SIS) related, which are required for orderly shutdown, and which are truly optional. Undersizing the emergency bus here doesn’t just trip a breaker it can compromise a Safety Instrumented System that prevents a process excursion.
We work from HAZOP outputs, SIS cause-and-effect matrices, and P&IDs to ensure the emergency power load sizing study reflects actual process safety requirements.
Data Centers & Mission-Critical Infrastructure
For data centers, the conversation shifts from life safety to business continuity, but the engineering rigor doesn’t diminish. PUE targets, modular UPS deployments, and phased IT load growth all affect how emergency generator capacity is allocated and how the automatic transfer sequence is structured. We support Tier II through Tier IV data center load studies per the Uptime Institute topology standard.
Our Engineering Methodology
Our emergency power load sizing process follows a structured six-step methodology that produces a defensible, code-referenced engineering report not a spreadsheet with a number at the bottom.
Here’s how we work through a study:
- Scope Definition. Confirm applicable codes and standards, facility type, regulatory jurisdiction, and load classification framework.
- Data Collection. Gather one-line diagrams, equipment lists, motor schedules, vendor datasheets, and existing load schedules.
- Load Classification. Sort every load into Emergency, Legally Required Standby, or Optional Standby categories per NEC 700/701/702.
- Demand Calculation. Apply demand factors, coincidence factors, and diversity analysis to calculate realistic peak kW and kVA demand.
- Starting Transient Modeling. Analyze motor starting sequence, voltage recovery, and generator voltage dip for worst-case starting scenarios.
- Report & Recommendation. Issue a formal backup power load analysis report with a generator kW/kVA recommendation, load growth margin, and compliance matrix.
Each phase is internally reviewed before the report is issued. We don’t issue preliminary numbers; we issue final engineering recommendations.
Why Undersized or Oversized Emergency Power Systems Fail
Both extremes carry real risk, and both show up in completed facilities more often than the industry admits.
Undersized systems are the obvious problem. A 500 kW emergency generator installed because the original load study missed the HVAC load on the life-safety branch trips on overload within seconds of transfer. The facility loses power during the precise event the emergency system was built to handle. We’ve reviewed load studies from facilities that didn’t account for the motor starting inrush of their fire pump package. That single oversight can account for 30-40 kW of effective generator derating during the critical seconds after transfer.
Oversized systems carry a different cost. A generator running at less than 30% of rated load for extended periods develops wet stacking (unburned fuel deposit in the exhaust system), reduced engine efficiency, and shortened maintenance intervals. Procurement cost for a 1,000 kW generator versus a correctly sized 650 kW unit can represent a $200,000+ capital expenditure difference on a single project.
The right emergency power load sizing study eliminates both failure modes before procurement. It is an engineering deliverable, not a procurement shortcut.
Start Your Emergency Power Load Sizing Study
If you’re in the early design phase, preparing for a regulatory audit, or reviewing an existing facility’s backup power capacity, our team is ready to support you with a formal emergency power load sizing study.
We work with engineering contractors, owner-operators, and EPC firms across oil and gas, healthcare, industrial, and critical infrastructure sectors.
Contact our power systems team to discuss your project scope and timeline.
Frequently Asked Questions
An emergency power load sizing study includes a classified electrical load schedule, applied demand and diversity factors, motor starting transient analysis, a formal generator kW/kVA sizing recommendation, load growth allowance, and a compliance matrix referencing applicable standards such as NFPA 110 and NEC Article 700.
Emergency systems under NEC Article 700 serve life-safety loads egress lighting, fire alarms, and similar systems. Legally Required Standby (Article 701) covers loads required by law but not life-safety. Optional Standby (Article 702) covers all other backup loads. Classification determines wiring methods, transfer time requirements, and source requirements.
NFPA 110 establishes performance requirements for emergency and standby power systems, including generator capacity to carry connected load, maximum transfer time (typically 10 seconds for Level 1 systems), fuel supply duration, and testing protocols. Any generator powering life-safety loads in a commercial or healthcare facility must meet NFPA 110 Level 1 or Level 2 requirements.
Demand factors vary by load type and facility. NEC Table 220.44 provides diversity factors for certain load groups, while IEEE 446 offers additional guidance for industrial applications. For most emergency power load sizing studies, the demand factor ranges from 0.8 to 1.0 for life-safety loads, as these must be available at full capacity without diversity assumptions.
Yes. Offshore and marine emergency power systems are sized to SOLAS Chapter II-1, classification society rules (DNV, ABS, Lloyd’s Register), and flag state requirements. The load scope typically covers navigation, fire and gas detection, ESD systems, escape and evacuation lighting, and communication systems. Our team has direct experience with FPSO, fixed platform, and onshore LNG terminal emergency power studies.
Study duration depends on facility complexity and data availability. For a straightforward industrial facility with complete electrical documentation, a study typically takes two to four weeks. Hospitals or offshore platforms with complex load classifications and regulatory submission requirements may require six to eight weeks. We issue a project schedule at kickoff based on actual data readiness.
If load demand exceeds generator capacity, the system risks overload, voltage collapse, and generator trip during a real emergency event. Resolution options include load shedding schemes (automatic non-critical load dropping), increasing generator capacity, or splitting loads between multiple sources. Our load sizing study identifies this condition before procurement so solutions are engineered, not patched in during commissioning.