HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
REGISTER   |   LOGIN   |   HELP
Blogs
Guest Blogs

Circuit Protection by the Numbers

NO RATINGS
Page 1 / 2 Next >
View Comments: Threaded|Newest First|Oldest First
tekochip
User Rank
Platinum
Good Article
tekochip   9/18/2012 9:14:12 AM
NO RATINGS
Thanks for the article.  Engineers often overlook circuit protection and because it's not as straightforward as it appears.  To make matters even more complicated, as you pointed out, there are many products available with similar ratings but very different performance.  Fuse selection is also dependent on tests that may be performed for agency approval.  I once had to increase the size of a fuse a very small appliance because the MOV in the power supply was pulling a great deal of current during Fast Transient Burst testing.  The appliance only needed fractional current, but in order to pass FTB I had to increase the fuse size to an Amp or more.


SparkyWatt
User Rank
Platinum
Re: Good Article
SparkyWatt   10/17/2012 1:44:59 PM
NO RATINGS
If you want to get parametric about it (an approach that makes more sense to me than these arbitrary fast/slow ratings), your typical fuse has two parameters of importance: The current that will raise it to its melting temperature (Imax) and the energy required to melt it (usually expressed in current and time, I²t).  Using the second requires evaluating an integral, but it can be approximated pretty easily.

One of the most common errors I see in circuit protection is when wires are sized according to the load, instead of the protection.  You see it all the time, you get a lamp fed by these little tiny wires.  If you ask about it, the answer always is "the lamp will never draw that much."  True, but if you short the lamp, the wire explodes.  Wires should be sized according to the available current, not the expected current.  If you want to use smaller wires, the available current should be limited first.

OLD_CURMUDGEON
User Rank
Platinum
Circuit Protection By the Numbers...
OLD_CURMUDGEON   9/19/2012 2:02:26 PM
NO RATINGS
TJ:

Would it be OK to use a BUSSMANN fuse instead of the Littelfuse in your applications?

On the serious side ...... A GREAT short article to explain the importance of selecting the proper circuit protection device rating.  It SHOULD be required archiving for EVERY engineer/designer who has any involvement with circuit protection.

On that note, here's an interesting story from my annals.....

We had built an extensive temperature-control system for a large home appliance manufacturer.  They had recently converted a critical component of an appliance from a metal unit to an injection-molded piece.  The plant supply was basically 480/ 3-phase Delta service.  The heaters are rated at 240.  Our equipment was designed for the typical 240 service, BUT we also had available an accessory kit for those installations where the mains were 440-480.

When the unit arrived, it was connected by the plant electricians, and set to go.  However, it was NOT energized initially because other equipment was not yet installed.  When the day finally arrived to power up, the primary side fuses blew immediately (with MUCH gusto, I was told!)  When the plant electrician did some preliminary investigation, he discovered that SOMEONE (in our plant) had supplied a set of SUPER FAST-BLOW, CLASS H style fuses in the main disconnect, instead of the RK5 fuses.  Obviously, THIS error was the problem.  The electrician called our company to inquire, and we apologized for the error, and sent a couple of sets of correct fuses as a token of our appreciation.  Once that error was corrected, the temperature controller worked as advertised for years WITHOUT further problems.

 

Partner Zone
More Blogs from Guest Blogs
Practicing engineers have not heeded Yoda's words.
Connected sensor-enabled applications will improve the consumer experience -- and generate new revenue streams.
As an industry, we now need to up our game and provide contractors with easier ways to properly identify and report counterfeit products and build collaboration between manufacturers, design engineers, industry organizations, and government.
It’s your job to find the right people, ask the right questions, to dig deeper, and properly prepare your users so they can provide you the most useful and productive answers possible.
The shift to aluminum is gaining momentum and the demand from automakers for aluminum is soaring, "expecting to reach one billion pounds this year, up from 200 million in 2012, and to grow by more than 30% annually through 2020."
Design News Webinar Series
3/27/2014 11:00 a.m. California / 2:00 p.m. New York / 7:00 p.m. London
2/27/2014 11:00 a.m. California / 2:00 p.m. New York / 7:00 p.m. London
12/18/2013 Available On Demand
11/20/2013 Available On Demand
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Apr 21 - 25, Creating & Testing Your First RTOS Application Using MQX
SEMESTERS: 1  |  2  |  3  |  4  |  5


Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.
Next Class: April 29 - Day 1
Sponsored by maxon precision motors
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Datasheets.com Parts Search

185 million searchable parts
(please enter a part number or hit search to begin)
Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service