Electrical start-up following an extended shutdown period

Switching high-power electrical devices (such as machinery, air conditioners, and refrigerators) creates sudden, brief demands for power that can upset the steady voltage in the electrical systems. These are known as ‘switching surges’, and can be severe enough to damage components. Some equipment may fail to start after being idle for a long period but a surge could cause significant damage to electrical installations.

Undervoltages, overvoltages, and overcurrents caused by switching surges can also damage insulation or cause insulation flashover (an unintended electric discharge over or around the surface of an insulator). Damage and flashovers can often lead to power system outages, eroded components, and increased risk of fire.


Undervoltage occurs when the voltage in an electrical circuit drops below the lower design limit and is often referred to as a ‘brown out’. A common cause of undervoltage is the starting up of large loads. Electro-mechanical components, such as single and three-phase motors, are designed to operate at very specific voltages. Devices allowed to operate at a reduced voltage will result in them drawing a higher current and inducing an overcurrent event.


Overvoltage occurs when the voltage in an electrical circuit is raised above its upper design limit. Overvoltage events can be transient (i.e. a temporary spike in the voltage) or permanent, leading to a power surge. Typical causes of overvoltage are insulation failure and poor regulation of power sources.


Overcurrent occurs when a larger-than-intended electrical current is drawn through an electrical circuit, leading to an excessive build-up of heat. The rise in temperature of the winding coils can cause damage to the critical insulation that protects them. The prolonged operation can lead to life cycle reduction, and premature and/or catastrophic failure.

If areas of commercial property have been electrically isolated, there is a sequence to follow to help avoid surges:

− Ventilate the building and turn the central heating on, if available, to reduce condensation within accessories and appliances.

−Work backward through the distribution system before reinstating the power:

1. Switch off and unplug equipment.
2. Isolate the fixed final circuits (e.g. lights, machinery, equipment, etc).
3. Safely isolate as many circuits as possible at each distribution board by switching off the individual circuit breakers (MCBs).

To avoid power surges:

1. Switch on the power at the main switch.
2. Turn on the distribution board switches.
3. Turn on individual switches.
4. Energize or plug in required equipment.

− Allow sufficient time for battery back-up systems to charge (e.g. emergency lighting)

Refer to operation and maintenance manuals for buildings relating to the correct isolation and start-up procedures, and to individual manufacturers’ literature for single items of equipment.

Our guidance for commercial property owners/building managers should not replace the defined maintenance start-up processes and prescribed procedures of equipment/ installation operation manuals or any applicable codes and local regulations. An inspection should be carried out and documented before start-up commences, and only qualified and authorized persons should be engaged in starting up machinery or electrical installations.

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© 2020 The Hartford Steam Boiler Inspection and Insurance Company. All rights reserved. This article is for informational purposes only and is not intended to convey or constitute legal advice. HSB makes no warranties or representations as to the accuracy or completeness of the content herein. Under no circumstances shall HSB or any party involved in creating or delivering this article be liable to you for any loss or damage that results from the use of the information contained herein. Except as otherwise expressly permitted by HSB in writing, no portion of this article may be reproduced, copied, or distributed in any way. This article does not modify or invalidate any of the provisions, exclusions, terms or conditions of the applicable policy and endorsements. For specific terms and conditions, please refer to the applicable endorsement form.

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