Relay / Fuse / Breaker failure

Posted by Glenn Bullion on
Relay / Fuse / Breaker failure

1. Introduction:

Relay/fuse/breaker is used as a safety device in every electrical installation. This prevents fire hazard when an electrical short circuit is triggered. These switchgears work below certain peak amplitude of current rating. If it crosses that limit then dielectric insulationgets broken and it opens up the closed contact points to provide the electrical isolation from incoming supply.

2. Common causes of relay/fuse/breaker failure:

  • a. High peak amplitude of the phase current that the device is carrying
  • b. Presence of high current harmonics( Measure with MachineSense PA ) which indirectly increases peak amplitude of the phase current.

Effect of high current peak


Let us assume that a conductor is carrying 5Amp (rms) pure sinusoidal current. Relay/fuse/breaker has a rating of 7A (Fig.2)


Let us assume a conductor is carrying a non-sinusoidal current of 5Amp (RMS). Relay/fuse/breaker having the same rating of 7A.
Considering above two cases, relay/fuse/breaker will trip in second case as peak current is exceeding 7A rating of the safety device. It is quite obvious that current shape is also an important factor for safety device like elay/fuse/breaker. Current shape gets highly distorted when it carries lots of harmonics in it.
Use MachineSense Power Analyzer (PA) to measure the current peak and current harmonics. MachineSense PAwill monitor the abnormalities 24x7 and SMS/email whenever any alarming condition is detected.
You can contact ( MachineSense PAteam to get rid of nuisance tripping of the protecting device and keep your system running without any interruption.

Relay / Fuse / Breaker failure

Fig. 2: Sinusoidal current with 5A RMS

Relay / Fuse / Breaker failure" class="img-responsive" />
<h4 align="center"><em><strong>Fig. 3: Non sinusoidal current with 5A RMS</strong></em></h4>
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<h2 align="center">Solution</h2>
<p align="justify">You need proper LC filter to reduce your system harmonics and make current waveform as clean as possible. Use MachineSense Power Analyzer (PA)to get free guidance to select proper LC filter</p>