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Welcome to electriciansjournal.com. My name is Jim Bernth, founder of Electrician’s Journal. I’ve been an Electrical Engineer for 36 years, and really enjoy writing condensed technical articles about topics that can benefit others in the Electrical industry. My goal is to summarize and condense potentially complex topics that are most important to Electricians as well as Electrical Engineers into a “take-away” format, and also share application-specific insight and experience. Every topic posted will likely be important to most people in the electrical industry at every level. Each post should take the average reader no more than 15 to 30 minutes to read. The number of topics posted are growing every day. If you have any questions or have interest in a particular topic and would like to see it posted, send all inquiries to: jimbernth@gmail.com.

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Jim Bernth, EE

NOTE: The author, James Bernth, assumes NO liability for the misapplication or inaccuracy of any information found herein. All published information on this site is for the sole purpose of personal and professional enrichment and is never intended to be the sole resource. All critical information should be thoroughly researched by multiple resources to confirm its validity before being applied.

Safety Disconnects

Safety Disconnects

James Bernth
Electrical Power Systems

Introduction

The purpose of a safety disconnect is to provide a safe means of disconnecting a machine or appliance from the circuit in the event of an emergency or maintenance. Safety disconnects are available in fusible and non-fusible types for both single-phase and three-phase electrical systems. However, it is generally not the only current limiting device between the source and load. It is for added safety to personnel, equipment, and also for convenience. Safety disconnects used as a “disconnecting means” will also save wear and tear on circuit breakers; especially large circuit breakers.

“Disconnecting Means” Defined

The National Electrical Code (NFPA 70) defines a “disconnecting means” as “A device or group of devices, or other means by which the conductors of a circuit can be disconnected from their source of supply.” (Article 100)

Disconnect Specifications

The following is a heavy duty, non-fusible, three-pole safety disconnect rated at 30A, 600VAC, 250VDC, 30HP Max @ 600VAC/3-Phase. The enclosure is a NEMA Type 1, so it is designed for indoor use only. All device ratings are shown in detail inside the enclosure on a door sticker. Shown below.

3P Disconnect_Door Closed.jpg
3P Disc_Front Door Open.jpg
3P Disc Device Ratings Chart.jpg

Disconnects are rated in terms of current [Amps] AND in terms of horsepower [HP] when the device is used in a motor application. See below.

3P Disc HP Chart.jpg

It should be noted that NEC 230.71(B) still allows two (2) to a maximum of six (6) disconnects on a single service entrance. However, there are some extremely important recent changes to this code making it more stringent for safety reasons. Exceptions apply. NOTE: See National Electrical Code (NEC), NFPA70, 2020 for latest details. See below:

NEC_Safety Disc_230.71(B).jpg

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