advanced search

Telephone Reaches Out And Shocks Someone

Sep 1, 2001 12:00 PM, By Alexander Kusko, Sc.D., P.E.

An electrician's poor judgment and lack of NEC knowledge leads to a disabling shock of an unsuspecting telephone user.

Every now and then you expect to get shocking news while on the telephone. Receiving a high-voltage electric shock while on the phone, on the other hand, is something few of us expect and even fewer experience. But that's just what happened to an unlucky man in an Eastern city after he dropped his 35 cents in an electrically charged public telephone.

After witnesses found the victim unconscious near the phone, local utility representatives arrived on the scene and discovered the potential for the powerful shock between the telephone stand and a nearby sidewalk grille. Subsequent to sustaining brain injuries that prevented him from continuing his career as a teacher, the victim filed suit against the utility and hired my forensic engineering firm to investigate the accident.

Our initial investigation uncovered the electric utility's report that a sump pump in a network transformer vault beneath the sidewalk grille had failed prior to the accident. At the time of the accident, the 1,000kVA underground utility network transformer was fed by a 13.2kV primary cable, which supplied 3-phase 120/208V power to the utility's low-voltage street network.

When we investigated the vault, we found a sump pump in one corner of the 200-sq-ft room. The sump collected water that accumulated in the vault and pumped it out of the area.

Typically, a utility installs a circuit breaker panel in the vault to provide single-phase 120V power for the sump pump. Then it runs a branch-circuit from the circuit breaker to the sump pump. The installation in question was not set up this way, and it violated applicable electrical codes.

We found the electrician in charge of the initial wiring had scraped the insulation off one of the 750-kcmil, 120V secondary cables and taped the bare end of a No. 16 insulated wire on the bare spot of the cable's conductor. Two No. 16 wires ran between the sump and the neutral bus in the vault and served as the 120V return and grounding wires. The sump's cast-iron discharge pipe ran through the wall of the vault to the street. The sloppy wiring created the potential for contact between the taped wire/conductor connection and ground.

In addition, we reconstructed the accident and concluded it took place after the sump pump motor winding burned out and brought the motor windings in contact with the metal parts of the motor. As a result, the pump had to apply 120V across the motor terminals to activate the pump's float switch, and the fault current from the motor winding to the motor burned through the grounding wire, which left the sump pump ungrounded. Now energized by the winding-to-frame contact, the sump pump had a voltage potential of 120V. This energized the metal discharge pipe that passed under the telephone to the same potential as the sump pump. As a result, the pipe energized the telephone stand. Although a portion of the sump pump's charge dissipated before reaching ground level, the telephone stand was still tested at 80V at the time of the accident.

The re-creation proved our client received the shock when he touched the telephone stand while his feet were in direct contact with the grounded metal sidewalk grille.

Our subsequent review of the electric utility's standards drawings for below-grade network transformer vaults correctly showed a panel with a circuit breaker and an outlet for installation of a sump pump, leading us to believe the installing electrician had not followed the plans properly. Our investigation and affidavit describing the improper installation led to the court granting the victim his motion on liability. As a result, he proceeded to a jury trial on damages and won an equitable award.

Kusko is vice president of Exponent Failure Analysis Associates, Natick, Mass.

Want to use this article? Click here for options!

© 2012 Penton Business Media, Inc.

---

Acceptable Use Policy blog comments powered by Disqus

Browse Back Issues Select an Issue May 2011 April 2011 March 2011 February 2011 January 2011 December 2010 November 2010 October 2010 September 2010 August 2010 July 2010 June 2010 May 2010 April 2010 March 2010 February 2010 January 2010 December 2009 November 2009 October 2009 September 2009 August 2009 July 2009 June 2009 May 2009 April 2009 March 2009 February 2009 January 1, 2009 December 2008 November 2008 October 1, 2008 September 2008 August 2008 July 2008 June 1, 2008 May 2008 April 2008 March 2008 February 2008 January 2008 December 2007 November 2007 October 2007 September 2007 August 2007 July 2007 June 2007 May 2007 April 2007 March 2007 February 2007 January 2007 December 2006 November 2006 October 2006 September 2006 August 2006 July 2006 June 1, 2006 May 1, 2006 April 2006 March 1, 2006 February 2006 January 2006 December 2005 November 2005 October 2005 September 2005 August 2005 July 2005 June 2005 May 2005 April 2005 March 2005 February 2005 January 2005 December 2004 November 2004 October 2004 September 2004 August 2004 July 2004 June 2004 May 2004 April 2004 March 2004 February 1, 2004 January 1, 2004 December 1, 2003 November 1, 2003 October 1, 2003 September 1, 2003 August 1, 2003 July 1, 2003 June 1, 2003 May 1, 2003 April 1, 2003 March 1, 2003 February 1, 2003 January 1, 2003 December 1, 2002 November 1, 2002 October 1, 2002 September 1, 2002 August 1, 2002 July 1, 2002 June 1, 2002 May 1, 2002 April 1, 2002 March 1, 2002 February 1, 2002 January 1, 2002 December 1, 2001 November 1, 2001 October 1, 2001 September 1, 2001 August 1, 2001 July 1, 2001 June 1, 2001 May 1, 2001 April 1, 2001 March 1, 2001 February 1, 2001 January 1, 2001 December 1, 2000 November 1, 2000 October 1, 2000 September 1, 2000 August 1, 2000 July 1, 2000 June 1, 2000 May 1, 2000 April 1, 2000 March 1, 2000 February 1, 2000 January 1, 2000 December 1, 1999 November 1, 1999 October 1, 1999 September 1, 1999 August 1, 1999 July 1, 1999 June 1, 1999 May 1, 1999 April 1, 1999 March 1, 1999 February 1, 1999 January 1, 1999 December 1, 1998 November 1, 1998 October 1, 1998 September 1, 1998 August 1, 1998 July 1, 1998 June 1, 1998 May 1, 1998 April 1, 1998 March 1, 1998 February 1, 1998 January 1, 1998 December 1, 1997 November 1, 1997 December 1, 1996 November 1, 1996 October 1, 1996 September 1, 1996 August 1, 1996 July 1, 1996 June 1, 1996 May 1, 1996 April 1, 1996 March 1, 1996 February 1, 1996 January 1, 1996 December 1, 1995 November 30, 1995 November 1, 1995 October 1, 1995 September 1, 1995 August 1, 1995 July 1, 1995 June 1, 1995 May 1, 1995 April 1, 1995 March 1, 1995 February 1, 1995

browse e-newsletters