Home Tweakers' Asylum

Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

Here's one for you.

About 20 years ago an electrician showed me some pictures of an electrical explosion that injured him and totally melted the guts in a Square D 120/240V load center.

He had went out on a service call to look at an outage of an outside sign that was mounted on a pole a ways from the building. The maintenance man should him the panel and the tripped single pole 20 amp breaker, that fed the sign. (Sign was 120V)

The first thing the electrician did was to try and reset the breaker. Good thing he stood to the side of the panel looking away from it.

When he pushed the breaker handle to the on position the breaker exploded outward burning his fingers, hand and arm. He was temporarily blinded by the white flash of the explosion. Though he couldn't see the panel immediately after the explosion he could hear the sound of loud arcing inside the panel enclosure.

After he returned from going to the ER, at a local hospital, he went back to asses the damage. He took pictures of what was left of the interior guts of the panel. At the bottom of the panel was a cold dry puddle of copper. The puddle was the remains of the 2 HOT copper bus of the panel.

Further investigation found that who ever installed the main lug only Square D panel (125 amp bus rating) fed it directly from the main 120/240V 3 phase 4 wire 1600 amp panel board. (Against NEC code by the way.)

The 1600 amp main never tripped open. The Square D load center just arced and burned until the 2 Hot legs burned themselves free.

//

Note: The electrician, as soon as he could after the electrical explosion, called the shop and told them what had just happened. The shop immediately sent another service driver to the business, to safely secure the electrical service.

Just one example of the power of electricity.




Edits: 12/08/16

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