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5 Advantages of the 5101 Engine Start Monitoring System

Facilities rely on automatic transfer switches (ATSs) to start emergency engine-generators when utility outages occur. But that cannot happen if an engine start circuit is damaged by work activity inside a facility or a backhoe excavating soil between a transfer switch and an outdoor generator. This Application Note explains how the ASCO 5101 Engine Start Monitoring System helps facilities avoid this outcome and comply with code requirements.


A National Electrical Code® (NEC®) compliant engine-generator starts automatically when it receives a start signal from an automatic transfer switch. If signaling wires are damaged, an engine will not receive the start signal needed to begin supplying mission-critical power. Without a means to monitor the integrity of the start signal circuit, facility personnel will never know when wiring is compromised, placing the facility at risk for an outage.

To mitigate this risk, requirements to monitor the integrity of the engine start circuit were first promulgated in the 2017 Edition of the NEC. Article 700.10(D)(4) of the 2020 Edition states:

The integrity of the generator remote start circuit shall be monitored for broken,
disconnected, or shorted wires. Loss of integrity shall start the generator(s).


The ASCO Power Technologies Engine Start Module System brings new and existing backup power systems into compliance with NEC requirements. It consists of two UL-listed electronic modules, which are shown in Figure 1. At left, a transfer switch module mounts inside each automatic transfer switch. At right, a generator module mounts on inside of a generator set. One generator module can communicate with up to eight transfer switch modules.

By transmitting a proprietary signal along the start circuit signal wires, the Engine Start Modules monitor circuit integrity continuously. The modules detect electrical faults that could cause a start circuit to fail. When that happens, the modules will:

1. start the generator to ensure power availability, as required by code
2. annunciate the conditions via visual indicators on the modules and connected annunciators
3. send real-time notices and alarms to other customer devices via dedicated contacts

Figure 2 shows a conceptual application.


Article 700.10(D)(4) was added to the National Electrical Code to ensure that damage to or faults occurring between transfer switches and engine-generators would not go undetected and subsequently lead to a power outage when backup power is required. By locating the Engine Start Modules inside the protective enclosure of each device, the solution provides the monitoring required between both monitors. It also avoids potential problems that could be associated with some 3-wire systems that rely on Normally Open and Normally Closed contacts to be in opposing states under normal conditions (Figure 3), where an open that develops along the start signal circuit could go undetected by the normally closed contact. Read the ASCO Power Technologies White Paper entitled Monitoring the Integrity of Engine Start Signal Circuits for more information.


The advantages of the 5101 Engine Start Monitoring System include:

1. Compatibility with conventional 2-wire engine start signal circuits avoids a need to install 3rd wire, a feature especially useful when retrofitting existing equipment
2. Continuous monitoring of engine start signal circuit performance for verification of integrity at all times
3. Individual LEDs for each start circuit quickly identify faulty conductor to reduce troubleshooting time
4. Meets or exceeds the NEC requirement
5. UL Listing evidences safety testing and compliance

Additional Information

• Product Webpage: ASCO 5101 Engine Start Monitoring System
• Digital Binder: ASCO 5101 Data Sheet
• Technical Brief: Engine Start Monitoring Overview
• White Paper: Monitoring the Integrity of Engine Start Signal Circuits
• Video: ASCO 5101 Engine Start Monitoring System

To learn more, contact a local ASCO representative or ASCO Customer Care at 800-800-2726 or customercare@ascopower.com.