What does N+1 mean? 

By on

As a professional electrical engineer, people sometimes remind me that what I take for granted is a new concept for other people.  Following a recent admonishment, I should make more effort at covering introductory level topics.

The term 'N+1' relates to redundancy and simply means that if you required 'N' items of equipment for something to work, you would have one additional spare item.  If any one item of equipment breaks down, every thing can still work as intended.  For example if you need two UPS for a small data centre, you would install three to have N+1; if you have a water pump in your building your would install a second one for N+1; if you require three transformers to power your facility you would install four for N+1.

People sometimes use the term 'N-1' to mean the same thing (i.e. if you lose one item you can still work).  This is a less common.

This type of terminology is often expanded.  '2N'  (sometimes referred to as 1+1) means you have twice as many items as you need - in the data centre example you would install four UPS.  The pumping example is already 2N (in addition to being N+1).  Less common, but possible are things like 'N+2", '2N+1", etc.

A final word on topic levels.  I do try to mix my posts at varying levels so that anyone visiting the site will find something of value.  If while browsing the site you have an idea for a short post on a particular topic or  want some thing explained in simpler terms or in greater detail;  just let me know.  You can leave comments on related posts or use the Contact Us page to send in a request.  While there is no guarantees, I will try to address as many requests as I can.



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



Michael Faraday (the father of electrical engineering)

Famed English chemist and physicist Michael Faraday was born on September 22, 1791, in Newington Butts, a suburb of Surrey just south of the London Bridge...

A mechanical engineering paper, some history and memories

I was digging in my bookshelf and came across the 80th Anniversary Association of Mine Resident Engineers, Papers and Discussions Commemorative Edition...

Lighting Design - An Introduction

From the earliest times, humans have found ways to create light. Pre-historic peoples used natural materials (moss, grass, etc.) soaked in animal fat and...

Maximum Demand for Buildings

Estimating maximum demand is a topic frequently discussed. Working out how much power to allow for a building can be very subjective . Allowing too much...

Autonomous Vehicle Challenge

Two driverless and solar power vans have departed from Italy on their way to China via the silk road. During the 13,000 kM trip the vans will drive themselves...

IEC 61439 - The Switchgear Standard

The new standard IEC 61439 replaces the old 60439. Compared to the old standard, the new 61439 is a more clearly defined and takes into account the assembly...

Lead Acid Batteries

Lead acid batteries are cost effect and reliable, making them suitable for many applications.This note examines topics of interest associated with the...

Network Theory – Introduction and Review

In electrical engineering, Network Theory is the study of how to solve circuit problems. By analyzing circuits, the engineer looks to determine the various...

LED Replacement Light Bulb

The inventor of the first visible light-emitting diode makes history again this year as it begins to show customers a 40-watt replacement GE Energy Smart...

Fault Calculations - Typical Equipment Parameters

A frequent problem in fault calculations is the obtaining of equipment parameters.  While it is always preferable to use the actual parameters of the equipment...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note