Questions and Answers

Voltage Reduction

Q: What is a voltage reduction?

A voltage reduction lowers the system voltage by five percent. The voltage reduction almost immediately reduces power demand system-wide by nearly two percent.

Q: Why do utilities do this?

A voltage reduction essentially reduces customer demand and allows a utility to stretch out its supply during times of excess demand. This is one of a series of steps that allows utilities to maintain uninterrupted service to customers.

Q: Why is there potential for more voltage reductions during the summer?

Hot weather, combined with limited availability of generating capacity, could mean utilities need to take this measure to meet demand for power and to continue to provide uninterrupted service to customers.

Q: Would there be any advanced notification of voltage reductions?

When possible, utilities alert customers through broadcast media when a potential for voltage reductions exists. In extreme circumstances, however, there may not be time for notice.

Q: What effect would this have on my service?

Generally, a voltage reduction would have no appreciable effect on your service. Standard household appliances and electrical equipment are manufactured to tolerate a ten per cent plus/minus change in voltage. And utilities regularly perform five percent voltage reduction tests with little notice to customers.

Customers with concerns about their electric service or about sensitive electronic equipment should check equipment manuals or with their equipment suppliers about precautionary measures to protect equipment or data. Computer users should save files and data frequently.

Q: What if I depend on electricity for life-support systems or other health-related equipment?

People who use electrically powered life support systems should always have a backup.

Q: How long would a voltage reduction last?

The reduction would last until ISO New England can achieve a balance between capacity and demand. If voltage reductions are necessary, they will typically be between the hours of 12:00 p.m. and 8 p.m.

Public Appeal

Q: Why do you ask customers to avoid using power?

The appeal is made to reduce customer demand, to balance generating capacity and demand in New England and to help maintain uninterrupted power for customers.

Heavy electricity use, hot weather and limited available generating capacity can prompt ISO New England, in conjunction with New England’s utilities, to issue this appeal.

Q: How much difference can turning out lights and appliances really make?

It makes a big difference -- about 400 to 450 megawatts region-wide -- which in times of peak use is a very important part of the utilities efforts to safeguard the electric system. (A megawatt is one million watts and serves roughly 300 single homes.)

Q: How long would this situation last?

It would last until ISO New England determines that capacity and demand have been balanced. New England’s utilities would keep customers informed of the situation through broadcast media. Appeals are most likely to be issued between the hours of 12:00 p.m. to 8:00 p.m.

Q: How many times would you have to do this?

Public appeals are one of several steps utilities can take in times of excess demand to safeguard the electric system. During periods of hot weather and when available generating capacity is limited, appeals may be issued whenever heavy electricity use reduces power reserves to unacceptably low levels.

Q: What would happen if not enough people pay attention to the appeal to reduce consumption?

If an extreme situation was to persist and public appeals were unsuccessful, it could be necessary to disconnect some customers. If load is extraordinarily high or generating units are off line, the system would automatically disconnect customers to avoid system instability, widespread blackouts and system damage. Depending on where problems occur, different areas would be disconnected.

During such an emergency, utilities might not be able to keep power on at essential facilities such as hospitals, sewage treatment plants, airports and specific sections of large cities with networked circuits. The utilities would restore power to these essential facilities as quickly as possible, if necessary by disconnecting other areas as part of controlled rolling blackouts.

Load Shedding

Q: What is load shedding?

Load shedding -- an almost instantaneous cutting of power to customers -- would be used only in extraordinary situations, such as losing a major generating station or a large power line. This is done to preserve the electric system and so utilities can continue to provide service to the large majority of its customers. It would likely come without warning. The next step utilities could use in this emergency response process is the rolling blackout. These would be managed interruptions that would last for specified time intervals, usually no more than a few hours. When possible, advance warning of either load shedding or rolling blackouts would be given, but in most cases action may be necessary without time for notice.

Q: How do you decide which customers should have their electricity cut?

Groups of circuits in each utility's service area are picked so a certain amount of demand can be eliminated and the electric system can be balanced. The circuits are from a wide area, so small numbers of customers in varied parts of the state would be affected. Utilities attempt to ensure that facilities such as hospitals, airports, sewage treatment plants and specific sections of large cities served by networked circuits are exempt from these blackouts.

Q: Could this happen to customers more than once?

Yes, but it is unlikely. When load shedding occurs, the electric companies would disconnect as many customers as necessary and then restore them when rolling blackouts begin. Rolling blackouts disconnect blocks of customers in rotating sequences and would continue until the utilities are able to bring supply and demand back in balance.

Q: What should customers do with appliances and electronic equipment?

If power to your home or business is interrupted, the best thing to do is leave only a light or two on -- so you know when power is restored. Turn any air-conditioning appliances off, if possible. Keep any refrigerators or freezers closed as much as possible until power returns.

Customers are asked to turn off electrical equipment during a blackout so that when power is restored, the system can return to normal as quickly as possible. If large equipment is not switched off, the surge of power trying to restart all of this equipment will trip a circuit breaker again. This could delay by hours the orderly restoration of power to an area.