In older homes the original wiring did not have a ground wire connected to the outlets. These ungrounded outlets are easily distinguished by their two hole / slot configuration verses the newer grounded type of outlet that has three holes / slots. Ungrounded outlets that have two holes / slots used in a home that was originally wired in this manner and has not been rewired are considered acceptable.
The problems for the owners of older homes start when
grounded type outlets are substituted for the ungrounded type without the
necessary rewiring that adds a ground wire to the new three prong grounded type
outlet. Grounded type (three hole / slot) outlets may not be substituted for
ungrounded outlets unless a ground wire is connected.
An exception to this rule is allowed by the National
Electric Code, when the outlet is protected by a ground fault interrupter (GFI
or GFCI).
There is a correction available for those home owners who do
not want to rewire the entire house. Replace the outlets with Ground Fault
Interrupters. There are two types of GFI available, one takes the place of the
regular circuit breaker in the load center. The second type that is available
takes the place of the standard outlet and replaces it with a special GFI
protected outlet. These are commonly used in the kitchens and bathrooms of
newer homes. Most people know them for their black and red reset buttons.
A surge protector plugged into an ungrounded outlet will not
operate as the manufacturer intended. When a large surge or spike hits, the
surge protector uses the ground wire to take the "hit" away from the
protected equipment and send it safely to ground. If the surge or spike is not
sent to ground by the surge protector it will destroy the delicate electronics
you were trying to protect. The warranty offered by the surge protectors
manufacturer offer, is only valid if the surge protector is used in a properly
grounded outlet.