Annapolis banks on its Colonial charm, which each year draws millions in tourists' dollars. But lurking inside many historic Georgian and Victorian buildings is outdated electrical wiring, some of which could date from the late 19th century, when electricity was first introduced to the city.

Archaic wiring, combined with narrow streets and a lack of sprinkler systems, makes the downtown district, a National Historic Landmark, a looming fire hazard, city officials say.

"Old buildings, lack of access -- we're doing what we can to mitigate these hazards," said Capt. Joseph F. Martin, a fire department spokesman.

Officials still do not know what caused the five-alarm blaze that ripped through three late 19th century buildings Friday. None of the buildings had sprinkler systems, a problem throughout the historic district. Only 16 of 79 buildings on Main Street have sprinklers, according to a 2003 survey, the city's most recent. That same survey showed that six of 29 buildings along the city dock and on Prince George Street have sprinkler systems.

The city requires fire suppression systems for new construction or renovations but not for existing structures.

Investigators say the fire started in the floor space between the first and second stories of Zachary's Jewelers, at 122 Main St. The building has been condemned and is scheduled for demolition. Two adjacent buildings also suffered extensive damage but are salvageable, officials said.

Electrical wiring was suspected as a cause for the blaze, but the charred and unstable structures have made close examination difficult. Foul play has been ruled out, Martin said.

The Annapolis Electric Light Co. introduced electricity to the city in 1889, historian Jane McWilliams said.

Clinton Pratt, the city's electrical inspector, said that many buildings still retain the original "knob-and-tube wiring" that was used widely from the late 1880s to the 1940s.

The system, in which copper wires run through porcelain knobs across interior walls or between floor and ceiling spaces, is considered safe when kept in good condition. But it can become dangerous when modern wiring is spliced into it, causing overloads.

The city barred such splicing in 1997, although it is still an accepted practice nationally.

"Anytime you have a historic city, you're going to have this kind of wiring," Pratt said.

The old wiring, designed to run through open air, also becomes dangerous when insulation or air-conditioning ducts are placed on top of it, causing damage from excess heat, Pratt said.

Although electrical codes bar such practice, many insulation installers and carpenters performing renovations do not know about the restrictions or the dangers, Pratt said.

Increasingly, insurance companies are requiring property owners to replace knob-and-tube wiring. Officials also say it is difficult to dig into the interiors of old buildings to inspect old wiring.

Fire officials determined the cause of the last major fire in downtown Annapolis -- a Dec. 9, 1997, blaze that destroyed two century-old buildings -- to be electrical wiring, a claim that insurers later disputed, Martin said.

After that fire, a safety commission made 21 recommendations for reducing fire dangers downtown. A number of those have been implemented, including enhancing fire codes and starting a low-interest loan fund to help business owners install sprinklers.

But the guts of the proposals, which would have mandated sprinklers for downtown businesses, were never passed by the City Council after property owners objected to the costs.

The city funded a loan program in last year's budget, but property owners have been slow to apply. Only three had submitted applications before Friday's fire.

"I suspect that after this weekend we will see much more interest," City Administrator Robert D. Agee said.

Hillard Donner, owner of Mills Wine & Spirit Mart, has sprinkler systems in the liquor store his family has run downtown since 1946 as well as in a four-story office building he owns next door. He said he hopes last week's fire makes other business owners on the street reconsider installing fire suppression systems.

"I think they'll come around," he said. "Sprinklers would have saved that building, but now it's gone."

Zachary's Jewelers, the center building, has been condemned and will be torn down, although buildings on either side can be salvaged. One downtown shopkeeper said that "sprinklers would have saved that building, but now it's gone."