Be Safe With Standby Generators
Most of us take it for granted, but electrical service can be interrupted. While Hill County Electric (HCE) crews work hard to keep these interruptions short, natural disasters and Montana’s unpredictable weather may cause extended interruptions when people need power the most. In these cases, HCE encourages members to have standby generators, especially for heating. Standby generators assure electricity during power failures. However, improperly connecting a portable generator to electric wiring can produce “back feed” - a dangerous current that can electrocute or critically injure you or others. Back feed into power lines from a generator could create “hot” power lines during an outage. Linemen who expect the line to be de-energized could be injured.
One good way to avoid back feeding is to install a double-pole, double throw transfer-switch. The term double-throw means that the operator can place or “throw” the switch into two different positions. Such a switch will prevent electricity, generated by the standby unit, to flow simultaneously to both the meter and back into the utility’s system. Installing a double-throw or transfer switch can keep you and HCE linemen safe.
The double throw transfer switch is installed under or in place of the customer’s meter base, before the entrance cable enters the building to the breaker panel. This switch will allow the operation of any circuit in the breaker panel—up to the limitation of the generator’s capacity. Double throw transfer switch installations for 120/240 V, single-phase service, must be bonded according to National Electrical Code requirements and local regulations:
• The double throw or transfer switch must have a capacity (100AMP or 200AMP) equal to or greater than the capacity of the breaker panel (i.e., if you have a 200AMP breaker panel you must use a 200AMP transfer switch). See figure 1.
• Only install the double throw switch on the exterior of the building or on the meter pole. It is normally installed at the meter location. HCE members are responsible for assuring that the point of attachment is substantial enough for the switch to be secured to the building or meter pole.
• The double throw switch allows you to safely energize any circuit in the house with the generator while assuring that it cannot back-feed into HCE power lines. The number of circuits that can be energized at one time is determined by the output capacity of the generator.
• Although a double throw and transfer switch/meter base combination is more costly, it is highly recommended. It has a better appearance and eliminates shifting the meter base on the house to allow room for just a double throw switch. The switch/meter base combination usually covers siding, holes or marks left from old equipment, but there may be some exceptions. HCE is not responsible for repairs.
For single-phase, 120/240 volt power, the transfer safety switch should be a double-pole, double-throw type. Double pole means that there are two pairs of wire lugs available for connection of hot conductors. The third wire (neutral wire) is continuous through the transfer enclosure, and is typically not switched (NEC Article 230-83). The ground wire also passes through the switch enclosure to provide a safe and continuous ground connection.
A three-phase generator would require a three-pole, double-throw switch. Some electric services use current transformer (CT) metering. This may require the use of a pole-top transfer safety switch. The operation of these switches is essentially the same, except that an extended manual switch lever is needed to allow the user to operate the switch from ground level.
HCE recommends having a certified electrician install your standby generator. Contact Joe Troiano, HCE’s Master Electrician, at 1-877-394-7804 when planning to buy a standby generator and he can provide you with an estimate to have your system installed.
Standby Generator Tips:
- Purchase the right size generator for what you need to power.
- Install generator in a proper location, outside for ventilation and away from areas susceptible to flooding (basements, etc),
- Follow all manufacturer’s recommendations.
- Inspect the unit at least annually.
- Hire a qualified technician when repairs are necessary.
- Don't remove or tamper with safety devices; they are there to protect you and your property.
- Don’t touch the unit while it’s operating, as serious burns can occur.
- Learn how to properly disconnect from your utility service before turning on your standby generator.