Does your facility use a bolted pressure switch?

If so, you need to be aware of the critical maintenance procedures and frequent service intervals required for these switches.

Ignoring these requirements or service frequencies could result in major electrical equipment damage, fire and extended business interruptions.

To help bring this issue to light and offer ways to mitigate the risk, we’ve written an important article that is featured as the cover-story for the fall issue of NETAWorld Journal.

NETA is the International Electrical Testing Association. NETA accredited companies are electrical professionals who specialize in the service and repair of major electrical apparatus such as bolted pressure switches. The full article is available on our website, here.

How can you identify a bolted pressure switch in your facility?

Most bolted pressure switches have long metal handles used for compressing the internal spring mechanisms. The handles need to be long due to the powerful springs used to close and open the switches.

Another way to identify this type of switch is to look for the word “bolt” used in some fashion in the product name on the switch nameplate. Various manufacturers make bolted pressure switches.

They are commonly used as the main service switch in a facility. They can also be used for other large feeder loads usually near the main switchgear.

If you need help identifying these switches, ask your local licensed electrician to inform you of any bolted pressure switches on the premises.

Examples of typical bolted pressure switches

bolted pressure switch
A typical bolted pressure switch used in the main switchgear room. Note the long operating handle on the switch for compressing the internal operating mechanism springs.
main switch failure
This is another bolted pressure switch showing the long operating handle. Look for the word “bolt” used on the switch nameplate to help identify the switch type. This is what can happen when the manufacturer’s maintenance is not performed at the required (usually annual) frequencies.

These switches are called “bolted pressure” switches because an actual threaded shaft or “bolt” is rotated after the switch blades close. Rotating the bolt causes the switch blades to clamp under screw pressure to form a tight electrical connection.

This clamping action occurs on the switch hinge-joints and at the movable-to-stationary switch contact points. A three-phase switch will have six screw clamped joints.

Maintenance is required

These switches are typically in your main electrical rooms that are not often visited. Because they do not have frequently moving parts, many assume these switches are maintenance-free.

The fact that the switch remains in the same closed position for most of its existence, actually allows the factory applied lubrication to become more “glue-like” over extended periods of time.

When the proper cleaning and lubrication is not performed as required, the switch blades can fail to transition properly when the switch is opened or closed.

Incomplete stroking of the switch blades and clamping mechanism typically causes the switch blade contacts to overheat and potentially fail catastrophically in a major arcing fault meltdown.

If you know of any switches, over one year old, that have never received any maintenance, then you should contact a NETA accredited service provider to establish a proper maintenance program for your bolted pressure switches.

Want more information like this delivered straight to your inbox? Click the “Follow” button on the bottom right, and enter your email address!


© 2016 The Hartford Steam Boiler Inspection and Insurance Company. All rights reserved. This article is for informational purposes only and 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 coverage form.

John A. Weber

John Weber is principal electrical engineer for HSB. He has over 25 years’ experience in solving facilities and electrical engineering challenges.


    • If you have identified a bolted-pressure switch in your facility, then the best information for maintaining your particular switch is available directly from your switch manufacturer. Most of the major switch manufacturers have their Owner’s Manual available on their websites. The manual typically has a section called Maintenance. This section usually defines the tasks and the frequencies for proper maintenance. The maintenance frequencies can vary based on the operating and environmental conditions present in your unique environment. You can do an online search for your brand and model number switch and the words, “Owner’s Manual.” Another option is to contact the manufacturer and request that they send a PDF version of this document to you.

  • I would like to know if they have a guide to know the maintenance of the electrical equipment

    • HSB has a great article to help you get started with an electrical preventive maintenance program:

      HSB EPM

      For more general recommendations regarding electrical equipment of all types, you can reference NFPA 70B, Recommended Practice for Electrical Equipment Maintenance. This document can be accessed for free at After you perform a free login, you can scroll to NFPA 70B to read this document in its entirety. If you are setting up a formal PM program, it may be helpful to order a hardcopy of this document for frequent use.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.