Federal Pacific electrical panels lost their UL rating about 25 years ago due to a high failure rate in the effectiveness of its panel breakers.  The following article, written by a home inspector for the Washington Post, provides more detail. 

If you have any questions about whether your panel might be a Federal Pacific, please don't hesitate to call us.  We'll be pleased to check the electrical panel in your property.

Federal Pacific “Stab Lok” Electrical Panels

by Alan Gould, Washington Post

January 13, 2007, page F1.

These electrical panels, widely used by builders in the 1960s and 1970s, are considered unsafe.  The problem is usually described as a latent hazard – that is, the panels and circuit breakers themselves do not cause unsafe conditions such as a short in a wire, but the breakers often will not trip when they should.  That can lead to overheating and fires.  In extensive testing by the Consumer Product Safety Commission (CPSC), the circuit breakers had a failure rate of approximately 25 percent.  I see many Federal Pacific-brand electrical panels in homes I inspect, sometimes several in a week.  They are easy to identify by the Federal Pacific and Stab-Lok branding on the panel cover.  If a household electrical circuit is overloaded, the circuit breaker in the panel is supposed to trip (cut off) so that heat cannot build up and cause scorched wires, melting and fires.  I rarely see evidence of this, but the many cases of failure have led to an industry view that because these panels are obsolete and possibly dangerous, replacement should be considered.  That usually costs between $1,000 and $1,600.  To date, there is no recall or class-action lawsuit for this panel, but the CPSC has issued safety warnings.  The product is no longer manufactured. 

Here are links to other articles supporting this information:

Federal_Pacific_Electric_Breaker_Panels

Burnt_FPE_circuit_breaker

http://www.inspectapedia.com/fpe/FPE-Hazards-Revised-070525.pdf

http://www.mikeholt.com/mojonewsarchive/Safety-HTML/HTML/Federal-Pacific-Electric-FPE-Electrical-Hazards-Website~20050530.php