It started two weeks ago when one of the four underwater cables providing electricity to the Vineyard failed somewhere between Falmouth and West Chop.

Then, last Saturday, a second cable failed.

NSTAR Electric and Gas Corporation work crews have stepped up emergency measures to provide continuous electricity to the Vineyard's 17,000 customers. While for the moment it may not appear to be a crisis, the electrical utility is taking no chances. On Monday, the company brought in backup generators in case one of the two remaining cables malfunctions.

Meanwhile, it could take from six to eight weeks before the damaged cables are repaired.

John B. Murdock, lead engineer for NSTAR, said his company is taking every step possible to insure that the flow of electricity is uninterrupted.

On Monday, four portable electricity generators were brought in from locations across New England. A transformer to serve the generators arrived from Philadelphia. Installed in Tisbury, they were ready for operation Wednesday, capable of delivering a total of five megawatts of electricity.

These temporary additions augment five other generators installed permanently on the Island - three at the NSTAR service headquarters on the Edgartown-Vineyard Haven Road and two at the Martha's Vineyard Airport. Each of these is capable of producing two-and-a-half megawatts.

The two lines which failed each carried 15 megawatts of power.

The first cable failure occurred on Thursday, Oct. 16 at approximately 5:15 p.m. The cable, which runs from Falmouth to West Chop, is known as Line 91 and was installed in 1986. The failure caused power outages that lasted about an hour and 15 minutes.

The second cable, Line 99, failed last Saturday at 8:20 a.m. It runs from Falmouth to Oak Bluffs, near the Martha's Vineyard Hospital. This cable provides fiber optic service to the Vineyard. Mr. Murdock said part of the cable is still operating.

Using high technology equipment on land, the utility was able to pinpoint the place where each of the cables failed. Mr. Murdock said divers went down Monday to examine Line 99 and found the problem. Line 99 was installed in 1996 and is still under warranty with the manufacturer, Okonite Cable Company of Ramsey, N.J., maker of all four cables.

The two breaks are miles apart and their failures are not related. Mr. Murdock said the utility is working with Woods Hole Oceanographic Institution and the U.S. Coast Guard to find the causes. It could be weather: Strong currents from a storm have been known to move cables. "Previous to the breaks, there were some pretty good ocean storms," Mr. Murdock said. NSTAR is trying to rule out the possibility that a sea scallop dredge might have caused the problem.

It has ruled out high solar activity as a cause, though the storms on the surface of the sun are known to be stressing transformers in the electrical system and causing problems in higher latitudes.

If there is a preferable time to have a power outage, it is autumn. During the height of the summer, peak demand for electricity rises to 42 megawatts, and winter peak demand reaches 34 megawatts.

But in this season, Mr. Murdock said, the remaining cables carrying electricity to the Vineyard can meet most customer needs.

The two remaining working lines are as follows: Line 97, installed in 1990, provides 15 megawatts and has never had a failure; Line 75, installed in 1995, failed shortly after it was installed and was then reenergized in 2002; it delivers 5 megawatts.

Taken together, that delivery of 20 megawatts of power to the Island meets the day-to-day needs at this time of year.

Mr. Murdock said the Island's peak need during the day is around the dinner hour.

Mr. Murdock said neither cable is being stressed by usage.

He said when cables are delivering more than they are designed to carry, they heat up.

With the site of the damaged submarine cables pinpointed, efforts now shift towards hiring a contractor to make the repairs. Mr. Murdock said the company is in touch with the manufacturer of the cable.

Weather plays a big part in how the work progresses.

As in the past with cable failures, a marine contractor will bring a large barge with a crane aboard. The barge will likely be kept at Woods Hole and brought by tugboat to the two repair sites.

Mr. Murdock said the cable will then be raised from the bottom and spliced on deck. The specialists will cut the cable back far enough to find a dry section of the line. A new cable will be spliced to the old. The end result, when completed, will be two splices on that one cable.

While Martha's Vineyard is the only Island to which NSTAR provides electricity, it is not the only customer serviced by submarine cable. Mr. Murdock said there are also submarine cables serving the New Bedford and Chelsea areas.

Mr. Murdock said the company has the expertise to resolve submarine cable issues. "We found where the fault was within 24 hours by testing from the land," he said. "New technology has helped us find and isolate problems. But it hasn't helped when it comes to fixing the problem underwater."

Last Saturday morning, Mr. Murdock was fixing a door at his home in Duxbury when he got the phone call that the second cable had failed. The loss of electricity impacted 7,000 customers on the Vineyard. Electricity was out in Oak Bluffs, Edgartown and parts of Tisbury. About 2,400 customers had their electricity restored in 30 minutes. The remainder had electricity in slightly more than an hour.

Island service is a good deal more sophisticated than it was years ago, when there was another significant submarine cable failure. Mr. Murdock said that in the last year crews have been installing automated switching devices that can be controlled by radio in Plymouth.

Still, in the latest incident, crews were also dispatched to do some hand switching on the Island.

The power outages of recent days have been a concern to those who depend on electricity for business.

Steve Bernier, owner of Cronig's, with locations in West Tisbury and Vineyard Haven, has concerns beyond keeping produce refrigerated. "We are in the 21st Century," he said. "With the advent of electronic equipment, the ability of NSTAR to deliver consistent electricity is important. Twenty years ago, my concern was refrigeration. Now there are other areas," mening computers and the storage of data.

Cash registers no longer run on 110 volts, for example. They are tied into a data system to allow people to pay by credit and debit cards. "They can get disrupted," Mr. Bernier said. "Computer equipment doesn't usually fail right then. There are UPS [Uninterrupted Power Supply] and surge protectors. But I might have a hard drive seize up on me weeks from now. It is a problem."

Mr. Bernier does have generator power and it has been tested in the last two weeks.

Pat Gregory, owner of EduComp in Vineyard Haven, runs a service business for computers. "When you get widely fluctuating electricity you can get damage to circuits over time," he said. "UPS and surge protecting devices are designed to clip those wildly fluctuating spikes and they do protect computers. {but] a surge protector won't protect your data during a power outage."

To owners of computers and other sensitive electronic devices, he suggests buying one of these devices. "They are less than $100. I'd like to see every computer have one. Yesterday and today, we had 15-second power outages. A UPS device would have helped," Mr. Gregory said.

In the last two weeks he has heard from customers complaining of data corruption due to these power outages. "The biggest problem is data corruption when a computer turns off without going through the normal shutdown procedure," he said.

The Martha's Vineyard Hospital does have its own generator. Spokesperson Rachel Vanderhoop said the generator is ready to turn on if there is a failure and it has been working. Backup power is provided for all the critical areas of the hospital - the emergency room, imaging department, operating room and other essential equipment. There is power for the heating and ventilation system. "It is pretty darn important and it works," she said.

Martha's Vineyard has a seasonal hunger for electricity.

Growth is most noticeable in the summer, less in the winter. In 1990 the summer peak was 34 megawatts. It rose to 37 in 1994 and 42 megawatts in 2002. Winter usage has been flatter because customers have shifted away from electrical heat to other alternatives.

Submarine cables shouldn't fail, said Mr. Murdock.

The first cable serving the Island was put in in 1940 and it ran uninterrupted for 46 years.