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#67177 - 06/28/06 04:55 PM Odd Circuit Breaker Behavior  
wendel  Offline
Member
Joined: Aug 2004
Posts: 55
I have a subpanel whose feed protected by two 30 amp old stlye (glass) fuses on each of the 120 volt lines.

In the subpanel is a 20 amp breaker for a pool pump.

The capacitor for the pool pump died and one of the 30 amp glass fuses blew.

My question is why didn't the 20 amp breaker trip before the 30 amp fuse blew?


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#67178 - 06/28/06 07:27 PM Re: Odd Circuit Breaker Behavior  
Rewired  Offline
Member
Joined: Jan 2006
Posts: 558
Hamilton, Ontario, Canada
Fuses in general especially if they are NOT time delay will open a circuit FASTER than a breaker will under a short circuit or severe overload condition, which I assume happened here..

A.D

[This message has been edited by Rewired (edited 06-28-2006).]

[This message has been edited by Rewired (edited 06-28-2006).]


#67179 - 06/28/06 10:10 PM Re: Odd Circuit Breaker Behavior  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
Sometimes a 100A CB (or > ) will pop before say a 20A CB, depending on the trip curve of the CB, or just the general condition of the CB.... [Linked Image]


Mark Heller
"Well - I oughta....." -Jackie Gleason

#67180 - 06/28/06 11:26 PM Re: Odd Circuit Breaker Behavior  
jay8  Offline
Member
Joined: Jul 2005
Posts: 183
Vancouver, BC
Yes, it happens all the time where a branch circuit doesnt trip but the main does - whether a fuse or breaker. This is one of the reasons why its bad practice try to short out a circuit to identify it at the panel.


#67181 - 06/29/06 02:13 AM Re: Odd Circuit Breaker Behavior  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
Or NONE will trip at all....


Mark Heller
"Well - I oughta....." -Jackie Gleason

#67182 - 06/29/06 04:03 AM Re: Odd Circuit Breaker Behavior  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Quote
Or NONE will trip at all....


Been working with Federal Pacific recently? [Linked Image]


#67183 - 06/29/06 07:07 AM Re: Odd Circuit Breaker Behavior  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,402
Vienna, Austria
Oh, 1960s Schrack breakers (Austrian) were good at that too... few months ago I swapped out an entire panel at a friend's place because he complained dead shorts usually blew the 25A main fuse instead of the 10A breaker... the breaker was H characteristic, supposed to be much faster than a fuse.


#67184 - 06/29/06 08:16 PM Re: Odd Circuit Breaker Behavior  
WFO  Offline
Member
Joined: Sep 2005
Posts: 202
Cat Spring, TX
Fuses tend to fatigue over time as well. They get weaker (particularly if they've been subjected to numerous faults) with age and will blow faster than their original published curves.


#67185 - 06/30/06 12:52 AM Re: Odd Circuit Breaker Behavior  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
Quote

My question is why didn't the 20 amp breaker trip before the 30 amp fuse blew?


Could be one, or more, of the following:

<OL TYPE=A>

[*] Fuse was Non-Time Delay type (Fast Acting),


[*] Terminations at the Fuse were generating heat, which assisted in a more rapid melting of the Fuse's element,


[*] Circuit Breaker's contacts are welded closed, from continuous reclosing on a faulted circuit,


[*] Circuit Breaker is of the infamous "FPE Trip-Free", or "No-Blow Zinsco" designs,


[*] Motor Circuit is maybe not fed "Entirely" through the 20 Amp Breaker,


[*] Non-Selective coordination between the Feeder's OCPD and the Panelboard's OCPD.
</OL>

Sounds more likely that the Fuse was just a Fast Acting type.

At least the E base Fuse did not have a
"Capacity Extending Device"
or
"Trip Eliminator"
(AKA "Coin behind the Fuse")
[Linked Image]

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#67186 - 06/30/06 05:43 PM Re: Odd Circuit Breaker Behavior  
Rewired  Offline
Member
Joined: Jan 2006
Posts: 558
Hamilton, Ontario, Canada
HEY NOW!
Easy on the FPE my place is full of it [Linked Image]

( and believe it or not they DO work!!)

A.D



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