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Before signing a colocation lease, require evidence that the proposed space can deliver your actual electrical load, keep your equipment within its environmental limits, and remain supportable during failures and maintenance. A Tier label, an “N+1” claim, or a headline uptime percentage is not enough on its own. Trace the power and cooling paths, test realistic outage scenarios with the operator, and convert every material promise into the lease, technical schedule, and service-level agreement (SLA).
Start with your own requirements
A facility cannot be judged in the abstract. Your required load, rack density, equipment types, jurisdiction, recovery objectives, and tolerance for planned or unplanned interruption determine what “suitable” means.
Document the electrical load
- List the expected IT load now and at each planned growth stage, in kilowatts (kW) and, where relevant, apparent power (kVA).
- Identify the maximum draw of servers, storage, network equipment, accelerators, and in-rack devices rather than relying only on nameplate averages.
- State whether your requirement is a fixed reserved capacity, metered consumption, or a combination of both.
- Specify single-cord and dual-cord equipment, input voltages, plug types, phase requirements, and any transfer switches or rack power distribution units you will provide.
- Define acceptable operating limits and the consequence of exceeding an allocation, including throttling, additional charges, or a required expansion.
Describe the heat and airflow profile
For air-cooled equipment, record the expected rack inlet temperature and humidity range, airflow direction, and watts per rack. A room-wide average can hide a hot spot at the front of a high-density rack. For liquid-cooled systems, document the coolant type, supply-temperature range, flow, pressure, connection standard, heat-rejection capacity, leak detection, and what happens when the liquid loop is unavailable.
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Decide which events may be tolerated, for how long, and with what operational response. A tenant running a stateless web tier may accept an orderly shutdown that a latency-sensitive database, regulated workload, or industrial control system cannot. This decision drives the required UPS ride-through, generator-backed cooling, maintenance design, notification times, and contractual remedies.
Request evidence for the exact space and lease
Ask for documents that describe the building, phase, room, and distribution serving your proposed footprint—not a generic corporate specification. Useful evidence includes:
- A current single-line electrical diagram showing utility services, switchgear, transformers, automatic transfer equipment, UPS modules, batteries, generators, downstream panels, and the final circuits offered to your racks.
- A mechanical or cooling schematic identifying computer-room air handlers, chillers, pumps, cooling towers or dry coolers, controls, valves, and the distribution path to your room or suite.
- Capacity and density calculations for the exact room, including the amount reserved for your contract and the assumptions behind that number.
- Maintenance procedures, test records, commissioning or integrated-systems-test summaries, and incident records that the operator is willing to disclose.
- Certification documents with the certified site, building, phase, scope, issue date, and current status clearly identified.
- The proposed order form, technical schedule, and SLA, including definitions of availability, exclusions, planned maintenance, measurement, credits, and termination rights.
Have the operator walk through the diagrams with you. If a diagram is redacted, ask which components are shared, which are dedicated, and whether an unshown common bus, control system, or distribution panel can affect your service.
Trace the complete power path
Utility service and distribution
Confirm the number and independence of utility services, the utility voltage and service capacity, and where the facility’s responsibility ends and yours begins. Two labels such as “A” and “B” do not prove independence if both paths share a service entrance, switchgear lineup, transformer, bus, or trench. Ask which path feeds each of your circuits and what remains energized during maintenance on any shared element.
UPS function and ride-through
A UPS conditions incoming power and supplies stored energy during a disturbance. Its purpose is to bridge the interval until generator power is available or an orderly shutdown can be completed. Verify the UPS topology, module arrangement, battery technology, autonomy at your contracted load, recharge behavior, bypass mode, maintenance procedure, and alarms delivered to the operations team.
Do not treat a stated battery duration as a universal guarantee. Runtime changes with load, battery age, temperature, discharge limits, and the operating mode. Ask the operator to state the committed minimum duration and the conditions under which it is measured.
Generators and transfer equipment
Determine which generators support your circuits, whether they are dedicated or shared, the starting and transfer sequence, fuel type and on-site storage, replenishment responsibility, and the testing and maintenance schedule. Ask what happens if a generator fails to start, a transfer switch malfunctions, or a fuel delivery is delayed. Generator presence does not equal uninterrupted service: the UPS must carry the load during detection, start, synchronization, and transfer.
Final circuits and rack delivery
Confirm the number and rating of circuits, breaker coordination, receptacle type, phase balancing, metering point, and whether dual-corded equipment reaches genuinely separate power paths. Ask whether a tenant-installed rack PDU, remote-hands change, or load transfer requires approval. Establish who owns and maintains each component from the facility bus to the receptacle.
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Understand redundancy terms instead of accepting labels
| Term | What it commonly indicates | What it does not establish | Evidence to request |
|---|---|---|---|
| N | The minimum number of components or capacity needed to carry the design load. | Any spare capacity or ability to perform maintenance without interruption. | Load calculation, component ratings, and the single failure that would remove service. |
| N+1 | One additional component beyond the minimum, such as an extra UPS module, chiller, or pump. | Independent paths, concurrent maintainability, or protection from a shared failure. | A topology diagram and a maintenance scenario showing the spare component carrying the required load. |
| 2N | Two complete capacity sets, often described as two systems each capable of carrying the design load. | Physical or utility independence, correct dual-cord connections, or reliable transfer between sets. | Separate-source diagrams, common-point analysis, and proof that each set supports your actual circuits. |
| Concurrently maintainable | Maintenance or replacement of a defined component without shutting down the critical load. | Immunity to every fault, operator error, or simultaneous failure. | Defined boundary, maintenance procedures, isolation points, and test evidence for the exact space. |
ASHRAE states: “The term N+1 is often used in the industry to describe a level of redundancy. However, this term alone does not provide sufficient detail to fully understand the level of redundancy provided, or to ensure that the resulting facility is actually concurrently maintainable.” Use that principle in every technical meeting: ask what is redundant, where the common points are, and what the maintenance state looks like.
Evaluate cooling against your equipment
Air-cooled environments
Obtain the permitted equipment-inlet temperature and humidity range, not merely the room set point. Compare those limits with each manufacturer’s allowable operating conditions and warranty requirements. Ask how the operator measures inlet conditions, how often sensors are calibrated, where sensors are located, and how alarms are escalated.
Confirm the airflow model: supply and return arrangement, containment or open aisles, raised-floor or overhead distribution, rated airflow, and the maximum rack density supported in your reserved area. A stated room capacity may depend on a particular blanking-panel layout, containment system, or equipment mix. Require the assumptions in writing.
High-density and liquid-cooled equipment
If your racks exceed the facility’s standard density, obtain a written approval before leasing. Identify the supported cooling interface, connection hardware, supply conditions, flow and pressure limits, heat-rejection capacity, controls, leak detection, and isolation procedure. Clarify whether the provider supplies the secondary loop, manifolds, pumps, and maintenance, or whether those are your responsibility.
Ask what happens during planned maintenance or a cooling-system fault. A temporary rise in temperature can be acceptable only if it remains within your equipment’s allowable excursion and the operator’s documented response time. ASHRAE’s Thermal Guidelines for Data Processing Environments, referenced in its handbook as the 2021 fifth edition, provides background ranges; it does not replace a comparison with your equipment manuals and the candidate site’s actual limits.
Cooling redundancy and environmental excursions
Identify spare air handlers, chillers, pumps, cooling towers or dry coolers, controls, and distribution paths. Ask whether one unit can be isolated while your load remains supported, and whether capacity depends on outdoor temperature, economizer mode, water availability, or equipment that is not yet installed. ASHRAE notes that redundancy configurations vary and that failure modes require careful evaluation. Request the operator’s response plan for a failed fan, pump, chiller, control panel, valve, or shared pipe.
Walk through failure and maintenance scenarios
Schedule a technical review in which the operator explains the sequence of events, remaining capacity, alarms, notifications, and recovery actions for each case below. Record the answers and attach them to your lease review.
- Planned UPS maintenance: Which modules and bypasses are used? Does the maintenance state leave a single remaining path, and is your load within its rating?
- Loss of a utility feed: Which switchgear and transfer equipment operate, how are dual paths affected, and what does the UPS carry during transfer?
- Generator start failure: What alarm is generated, who responds, how much stored energy remains, and what load-shedding or shutdown procedure is authorized?
- Transfer-equipment failure: Can the affected circuits be supplied by another path, or does a shared switch or control system become a single point of failure?
- Chiller, pump, or air-handler outage: What spare capacity starts, how is the failed unit isolated, and what inlet-temperature trend triggers escalation?
- Loss of a shared distribution element: Which tenants and your circuits are affected, and is there a documented workaround?
- Control, monitoring, or communications failure: How does the facility operate manually, and how will you receive an incident notice if telemetry is unavailable?
For every scenario, ask for the detection method, automatic actions, human response, notification target, expected restoration sequence, and the exact SLA treatment. A verbal assurance that “the system is redundant” is not an operating procedure.
Use Tier certification as context, not a guarantee
Uptime Institute Tier classes address capabilities relating to maintenance, power, cooling, and fault tolerance. Certification can help structure questions, but verify the certificate’s scope: site, building, phase, systems covered, issue date, and current status. A rating may not cover a later expansion, a separately leased room, or your tenant-side distribution.
The limitations are visible even in the description of Tier I: it includes a UPS, dedicated cooling, and a generator, while preventive maintenance can still require a full shutdown. Component presence therefore does not prove continuous operation. Ask what the rating assumes, which components are outside its boundary, and how the operator’s actual procedures and SLA protect your service.
Turn technical claims into lease and SLA terms
Technical brochures become useful only when the contract defines what is delivered and what happens when it is not. Review the following items with counsel and your facilities or engineering team:
- Service boundary: State whether the commitment covers utility service, UPS output, generators, switchgear, distribution to the rack, cooling, environmental conditions, and monitoring.
- Capacity commitment: Specify reserved kW or kVA, voltage, circuit count, density, metering point, expansion rights, and the process and charges for exceeding the allocation.
- Availability measurement: Define the measurement point, calculation period, data source, treatment of partial degradation, and how an incident starts and ends.
- Planned maintenance: List notice periods, permitted windows, excluded minutes or events, required redundancy during work, and the conditions under which maintenance may interrupt service.
- Exclusions: Identify utility events, tenant equipment, upstream carriers, force majeure, emergency work, environmental excursions, and failures caused by tenant changes.
- Notification and restoration: Set contacts, severity levels, initial-notice deadlines, update frequency, escalation, and restoration or workaround expectations.
- Remedies: Define service credits, evidence required to claim them, dispute deadlines, chronic-failure thresholds, termination rights, and whether credits are the sole remedy.
- Configuration assumptions: Attach the approved rack layout, load, cord topology, cooling interface, and operating limits so the SLA cannot be narrowed later by an undocumented assumption.
There is no universal generator runtime, uptime target, credit schedule, or outage remedy established by general guidance. Those terms depend on the operator, location, facility, and negotiation. Treat the signed lease and technical schedules—not a sales presentation—as the controlling record.
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When several sites appear suitable, score them using identical evidence and assumptions. A lower quoted rate can be offset by weaker included capacity, higher metered-power charges, or a less favorable outage remedy.
| Comparison axis | Questions to answer |
|---|---|
| Committed IT capacity | How many kW/kVA are reserved, at what voltage, with what growth path and overage rules? |
| Power topology | How many utility, UPS, generator, transfer, and final-circuit paths serve the proposed racks? Where are the common points? |
| Maintenance behavior | Can each component be isolated while your contracted load remains supported? What evidence demonstrates this? |
| UPS and generator coverage | What load is protected, what ride-through is committed, and who tests, fuels, and repairs the equipment? |
| Cooling envelope | What inlet temperature, humidity, airflow, density, and liquid-cooling conditions are guaranteed? |
| Cooling failure response | Which spare units and paths start, how quickly, and what excursion is allowed? |
| Certification scope | Which building, phase, systems, and dates are covered, and what is outside the certification? |
| Operations evidence | Are maintenance records, integrated tests, incident history, and escalation procedures available? |
| SLA and remedies | How are availability, maintenance, exclusions, notices, credits, and termination defined? |
| Total lease cost | What are recurring space, reserved-power, metered-energy, cooling, cross-connect, installation, expansion, and overage charges? |
Mark an item “not stated” rather than assuming the more favorable interpretation. Resolve every such item before comparing totals or signing.
Common warning signs and how to respond
“N+1” with no diagram
Ask which component is extra, whether it is on the same electrical or mechanical path, and what happens during maintenance. If the provider cannot show the boundary and operating state, treat the claim as unverified.
A Tier certificate presented without scope
Request the current certificate and confirm that it covers the building, phase, room, and systems you will use. Ask which tenant-side equipment and procedures remain outside it.
Generator capacity but no fuel or transfer detail
Obtain the start sequence, transfer time, on-site fuel arrangement, replenishment responsibility, test schedule, and failed-start procedure. Put the relevant obligations and notification commitments in the SLA.
Cooling capacity stated only as a room total
Require rack-density, airflow, inlet-condition, and outdoor-condition assumptions. Obtain written approval for high-density or liquid-cooled deployments before ordering equipment.
Uptime percentage without measurement rules
Ask where availability is measured, what planned maintenance and utility events are excluded, how partial degradation is counted, and what remedy is available. A percentage without these definitions cannot be compared reliably.
Resistance to technical or contractual questions
Escalate to the facility engineer, request a site walk-through, and use an independent data-center electrical and mechanical engineering review if your team cannot interpret diagrams, load studies, or maintenance evidence. Such a review is an assessment service, not an endorsement of any particular provider.
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- Have you supplied a staged load forecast with peak and average values?
- Are voltage, phase, receptacle, cord, circuit, and metering details written down?
- Have you traced each power path from utility entrance to your equipment?
- Are UPS autonomy, generator transfer, fuel, testing, and failed-start responses documented?
- Do the proposed rack density and cooling interface match your equipment manuals?
- Are environmental limits, sensor locations, alarms, and excursion procedures defined?
- Has the operator demonstrated what remains in service during planned maintenance?
- Have you tested utility loss, UPS or generator failure, cooling failure, transfer failure, and shared-component loss as scenarios?
- Is any Tier certification current and applicable to your exact space?
- Do the order form, technical schedule, and SLA contain the same capacity and topology assumptions?
- Are availability measurement, exclusions, notification, restoration, credits, and termination rights explicit?
- Have legal, facilities, security, and business-continuity stakeholders approved the residual risk?
What a defensible leasing decision looks like
Proceed when the operator has shown a traceable power and cooling design for your exact footprint, demonstrated how it behaves in maintenance and failure states, and accepted measurable obligations in the contract. Defer or renegotiate when capacity, density, common points, operating procedures, or remedies remain undefined. The objective is not to collect the most impressive redundancy label; it is to establish, with evidence, what your equipment will receive and what the operator must do when conditions depart from normal.
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