×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Fuse sizing
3

Fuse sizing

Fuse sizing

(OP)
Do fuses have 75% or 80% ratings?  For E-rated fuses,a rule of thumb for fuse sizing can be 1.25% to 1.33% of rated primary full load amps of the transformer or can be as high as 600% based on secondary protection of the transformer. So if 100E fuses are used and it sees a spike of 75A off and on.  Does this weaken the fuse element and fuse may open on the next spike?
I have read the Bussman fuse reference but it does not address my question of weaken fuse elements if current were to reach 75% of fuse rating. Bussman does go into melting minium points and maxium clearing time curves.

Is there any other fuse reference material?

RE: Fuse sizing

3
Switch operations definitely deteorate fuse element by changing it's resistance caused by mechanical stress endured during on/off cycles. As an example, typical 100A rated fuse is capable to handle no more than 500 motor starts. Other factors such as fuse ambient temperature, start duration etc should also be considered if more accurate estimate is required. Ask fuse manufacturer for characteristic showing number of expected cycles to fuse failure as a function of % of nominal melt current.

RE: Fuse sizing

mykh,
I've sometimes suspected this to be the case, but never seen any published data. Can you point me to a specific source where this type of information is availble?

It seems like there would be a minimum current (as percentage of fuse rating), below which the damage does not occur.

RE: Fuse sizing

Not sure if your application is limited to low voltage, but you might check with Cutler-Hammer.  They make both current-limiting and expulsion type medium-voltage fuses and I have found them to be more forthcoming than other fuse suppliers on these types of questions.

My (limited) understanding is that fuse damage is more an issue with current-limiting fuses than with expulsion fuses.  But all low-voltage fuses will be current-limiting, probably.  

RE: Fuse sizing

alehman,

I used the plot below to estimate number of cycles before fuse operation. It is coming from paper named The Effects Of Cycling Loading On Motor Circuit Fuses issued long time ago by Gould Shawmut company.

The fuse sizes are typically selected so as not to exceed 60 to 65% of the fuse melt current based on the motor starting time. These sizes will give over 100,000 operations.


RE: Fuse sizing

Thanks, mykh. Very intersesting. I will ask Gould for a complete copy of the report.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources