When the power goes out in a storm Bermuda's fleet of residential generators can soon be heard starting up.

Whether they switch on automatically, require the push of a button or the pull of a cord, they all need to be properly and safely integrated into a home's electrical system to prevent injury to both residents and Belco's service repair staff, not to mention damage to electronic equipment and appliances.

Jeff Patterson, the general manager of Universal Electric Ltd.'s Power & Generation Division, says the biggest safety issue with regards to generator use is making sure they do not 'back feed' into the grid.

"Electricity is like water," he explains. "It runs both ways."

Generators that are installed to feed directly into a home's electrical panel pose the main threat. They are wired 'between' the panel and the meter and need a transfer switch, either automatic or manual, to prevent any power being sent back down the lines. Belco's workers are obviously aware of this concern and will shut the lines down before working on them, but what of the lines that come down in people's yards or across roads?

Of a lesser concern, but still containing a threat, are generators that people run extension cords from to power their fridges, water pumps and other essentials. Mr. Patterson says most people don't realise that these too can back feed in certain situations.

"Anytime you turn on a generator you either need a transfer switch or you should turn off the main switch at the meter," he warns. "Even for small generators."

Generators provide a wide range of power outputs and many residents rely on them to keep the power on when the lights go out.

They can be as small as 1,000W but generally the portable generators, which run on gas, produce more than 5,000W of power, providing either a couple of 20 amp circuits that can manage some of your essential home items or plugging up to 50 amps straight into a home's panel (this would require additional installation).

Universal Electric offers two portable machines, the first a 6,700W model that one person can wheel into place and that can, given the proper load distribution, even run your AC at night. The second is a 12,000W model that produces enough power to run most essential loads in a medium-sized home.

When operating generators such as these Mr. Patterson says ventilation is a critical consideration. They certainly should not be run inside, or even in a garage unless they are next to an open door and properly ventilated, and it is not safe to try and run an exhaust through the wall because of the emission of fumes. They shouldn't even be run outside the house if they are near an open window. Heavy duty extension cords with a proper ground are also necessary.

Portable generators need to be kept undercover from the rain because of the inherent risks associated with water and electricity and, perhaps most importantly, they should never be refilled while running, in fact they should be allowed to cool down first.

"The heat from the engine can cause combustion," Mr. Patterson says. "But there is also an alternator creating electricity, which could cause an explosion."

If you want to reduce the type of risk and hassle that comes with portable generators then a fixed generator might be an option. These will either be installed in a utility room or garage, and plumbed for exhaust and integration with the electric panel, or placed outside in a weatherproof enclosure away from the house.

Whilst more expensive, these models have a number of advantages including automatic start in conjunction with automatic transferring of utility, less expensive diesel or propane gas, quieter operation and use with multiple dwellings.

Fixed generators generally have far greater capacity, about 20KW or more, capable of powering an entire house and can manage power surge, both when they start up and when the utility kicks back in.

"Most of the damage comes from the power surge caused when the power comes back on," explains Mr. Patterson. "These generators not only wait until they have a stable current before they send electricity into the house, they also wait until the utility power is stable and then adjust to match that current before switching over."

Mr. Patterson says while there are regulations on the installation of residential generators and there is a programme through the National Training Board aimed at certifying Bermuda's electricians.

He also says that while Universal Electric does not insist on installing their generators they sell, they will come and commission a generator once it has been installed to ensure safety standards are met and that generators, like any engine, should be maintained on an annual basis to ensure proper performance.