Automatic Transfer Switches: The Component Your Generator Depends On When the power goes out, most facility managers think about the generator. Did it start? Is it running? Is the fuel level good? Those are the right questions — but they skip the component that actually determines whether your building gets power: the automatic transfer switch. […]
When the power goes out, most facility managers think about the generator. Did it start? Is it running? Is the fuel level good?
Those are the right questions — but they skip the component that actually determines whether your building gets power: the automatic transfer switch.
The ATS is the critical link between your generator and your facility’s electrical system. When it works correctly, the handoff from utility power to generator power happens in seconds, automatically, without anyone lifting a finger. When it doesn’t work, your generator can run perfectly and your critical loads still go dark.
This post covers what automatic transfer switches do, how they fail, and what a proper ATS inspection looks like — so you can make sure the full system is ready when it actually matters.
An automatic transfer switch monitors your incoming utility power continuously. The moment it detects a loss of voltage — an outage, a significant voltage drop, or a frequency deviation — it executes a sequence that most facility managers never think about until something goes wrong:
| Step 1 | The ATS detects utility power loss and starts the timer on its built-in time delay. |
| Step 2 | After the delay (typically 5–15 seconds, to avoid nuisance transfers during momentary blinks), it sends the start signal to the generator. |
| Step 3 | The generator starts and builds to rated voltage and frequency — usually within 10–30 seconds depending on the unit. |
| Step 4 | The ATS confirms that generator power is stable and within acceptable parameters. |
| Step 5 | The ATS opens the utility connection and closes the generator connection. Power transfers to your facility. |
| Step 6 | When utility power is restored and stable, the ATS transfers back and signals the generator to cool down and shut off. |
The entire sequence — from outage detection to full transfer — typically takes 15–45 seconds. In a hospital, data center, or water treatment plant, those seconds are engineered and tested. In facilities where the ATS hasn’t been properly maintained, they’re a gamble.
Some facilities, particularly smaller commercial buildings and older industrial sites, still rely on manual transfer switches. A manual switch requires someone to physically be present, recognize the outage, go to the transfer switch location, and operate the switch to connect generator power.
The practical problems with that approach:
Automatic transfer switches eliminate the human response requirement. The system detects, decides, and transfers on its own — which is exactly the reliability that critical facilities need.
Not all automatic transfer switches are built the same way. The two primary configurations handle the actual moment of transfer differently, and that difference matters significantly for sensitive loads.
The most common type. During transfer, the ATS opens the utility connection completely before closing the generator connection. This creates a brief interruption — typically 100–200 milliseconds — during which neither source is connected.
For most commercial and industrial loads, this interruption is acceptable. Lighting may flicker. Some equipment may restart. UPS systems and battery backup handle the gap for truly sensitive loads.
In a closed-transition transfer, both sources are briefly connected simultaneously during the switch — ensuring absolutely no interruption. This requires tight synchronization between the utility source and the generator (voltage, frequency, and phase must be matched before transfer occurs).
Closed-transition ATS is the appropriate choice for:
How Wolverine Power Systems Can Help
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Automatic transfer switches fail quietly. Unlike a generator that won’t start — an obvious, immediate problem — ATS failures often develop slowly and only reveal themselves at the worst possible moment: during an actual power outage, when the transfer doesn’t happen as expected.
Here are the six failure modes our service technicians see most frequently across Michigan facilities:
| Failure Mode | What Goes Wrong | Consequence | Detectable By |
| Contact Wear | Transfer contacts degrade over thousands of switching cycles | Failed load transfer — generator runs, facility stays dark | Visual inspection + contact resistance test |
| Voltage Sensing Loss | Sensing circuit fails to detect utility outage accurately | ATS doesn’t initiate transfer; generator never starts | Voltage relay test + signal trace |
| Timing Relay Drift | Time delays shift out of spec due to component aging | Transfer too early (equipment damage) or too late (false alarm recovery) | Timing verification under simulated outage |
| Control Board Failure | Logic board fault from heat, moisture, or voltage spike | Random failures, nuisance transfers, or no response | Board diagnostics + fault code review |
| Mechanical Binding | Internal mechanism corrodes or seizes from infrequent use | ATS physically cannot switch despite electrical command | Manual exercise test + lubrication check |
| Neutral Position Fault | Open-transition ATS loses neutral momentarily during transfer | Brief power interruption causes equipment restart or damage | Transfer timing analysis under load |
The transfer contacts inside an ATS are the physical mechanism that makes and breaks the electrical connections between the utility source, generator source, and facility load. Over thousands of switching cycles — routine monthly exercises, nuisance transfers during brief outages, and actual emergency transfers — these contacts wear.
Worn contacts can arc excessively, creating heat that damages surrounding components. In advanced cases, contacts can weld together (preventing transfer) or fail to maintain adequate contact pressure (causing high-resistance connections and heat buildup under load).
Contact wear is detectable through contact resistance testing and visual inspection — but only if someone opens the ATS and looks. It’s not visible from the outside and not detectable during a no-load exercise test.
The ATS continuously monitors utility voltage using voltage sensing relays or circuits. When these sensing components fail, the ATS loses its ability to accurately detect an outage — and the consequences cut both ways.
A failed voltage sensor might cause the ATS to not respond to an actual outage (the generator never starts), or to respond incorrectly to normal voltage variations (nuisance transfers that cycle your generator repeatedly for no reason). Both create problems; the first one is the more dangerous.
Voltage sensing issues are testable by simulating an outage condition and verifying that the ATS responds correctly within the expected time window.
Every ATS has programmed time delays that govern when transfers occur. The transfer-to-generator delay prevents the system from reacting to momentary power interruptions (a car hitting a utility pole, a brief grid disturbance). The retransfer-to-utility delay ensures utility power is stable before transferring back.
These time delays are set by relays or digital timers that can drift out of specification over time — particularly in environments with temperature extremes or humidity. A delay that’s too short causes nuisance transfers during brief blinks. A delay that’s too long leaves your facility on generator power longer than necessary, or delays transfer back to utility when power is restored.
Timing verification requires testing actual delay intervals under simulated conditions — not just reviewing programmed settings, which may not reflect actual relay performance.
Modern ATS units are microprocessor-controlled. The control board manages voltage sensing, timing logic, transfer sequencing, communications with the generator, and any alarm or monitoring outputs. Control board failures can produce a wide range of symptoms — from random nuisance transfers to complete non-response to outages.
Heat, moisture, power quality events (lightning-induced surges, for example), and simply age all contribute to control board degradation. Because the failure modes are varied and can mimic other issues, control board diagnostics require a technician with the training and equipment to differentiate a board fault from a sensing fault, wiring fault, or mechanical issue.
The ATS mechanism — the physical assembly that moves the contacts between positions — is a mechanical device. In facilities where the ATS is exercised infrequently (or not at all), this mechanism can corrode, seize, or bind in ways that prevent operation even when the electrical system commands a transfer.
This is the failure mode that most directly illustrates why regular exercise testing matters. An ATS that never moves mechanically can appear perfectly healthy on every electrical test — right up until it physically cannot switch during an actual outage.
Mechanical inspection and lubrication are part of any thorough ATS service visit.
In open-transition ATS units, there is a neutral position between the utility and generator connections — a brief moment when neither source is connected. This neutral dwell time is intentional and controlled. When the mechanism doesn’t maintain proper neutral position, it can result in cross-connection of two out-of-phase sources, which is a serious electrical fault that can damage equipment and trip protective devices.
Neutral position integrity is verified through transfer timing analysis and mechanical inspection — not something visible during routine observation.
A Wolverine Power Systems ATS inspection is a structured evaluation of the entire transfer switch assembly — electrical, mechanical, and controls. Here’s what our technicians check during a service visit:
| ATS Service Frequency Recommendation Annual: Full ATS inspection including contact resistance testing, timing verification, and mechanical inspection for all commercial and industrial facilities.Quarterly: Functional exercise test — verify transfer initiates and completes correctly under real outage simulation. This is the minimum required by NFPA 110 for Level 1 systems.After any major outage or electrical event: Full inspection recommended — surge events can damage control boards and sensing circuits without obvious immediate symptoms.After extended periods of inactivity: If an ATS hasn’t been exercised in more than 90 days, a full inspection before the next storm season is advisable. |
For facilities subject to NFPA 110 (emergency and standby power systems), ATS testing requirements are not optional. The standard establishes specific testing intervals that apply to most commercial and industrial emergency power applications:
NFPA 99 (healthcare facilities) adds additional requirements specific to Type 1 essential electrical systems, including more rigorous documentation and testing protocols for ATS units serving life-safety loads.
Wolverine Power Systems provides service documentation that supports compliance record-keeping for NFPA 110 and NFPA 99 requirements. Our service reports include transfer timing data, contact test results, and technician certification — the kind of documentation that holds up to AHJ review and insurance audit.
One of the most important things to understand about ATS maintenance is that it can’t be evaluated in isolation. The ATS, the generator, and the facility’s electrical distribution system are interdependent — and a failure in any one component affects the performance of the others.
A few examples of how this plays out in practice:
This is why Wolverine Power Systems approaches generator service as a system — inspecting the generator, transfer switch, and electrical connection points together rather than treating each component as a standalone item. Issues that are invisible at the component level often become visible when you look at how the pieces interact under real operating conditions.
Wolverine Power Systems services automatic transfer switches across all major brands and configurations — in commercial buildings, industrial facilities, healthcare organizations, data centers, municipalities, and more — across all 83 Michigan counties from four service locations.
We service all generator and ATS makes and models. Our technicians are factory-trained and bring calibrated test equipment to every service visit. We provide documented service reports that support your compliance and insurance records.
| Schedule an ATS Inspection To schedule an ATS inspection or discuss a comprehensive generator service plan for your Michigan facility:📞 Call: 800-485-8068 (24/7 for emergencies)🌐 Online: wolverinepower.com/generator-service/We service all generator and transfer switch brands. Four Michigan locations. 24/7 emergency response. |
