Generators
During a power cut, or when we have to turn the power off to work on the power lines, generators can be used to run lights and appliances until power is restored. In general they are very safe, but you should follow a few rules when you use a generator.
There are two main types of generators:
Using portable generators safely
Portable generators are designed to be move from site-to-site. They are not intended to be connected directly to your electrical system. Normally they are single-phase units and you should only use them to supply appliances through flexible cords.
You should never...
- attempt to connect your generator to a wall outlet supply or by altering your house wiring. This would feed electricity back into our lines and risk the lives of line workers who may be working some distance from your home
- connect loads that exceed the generator's maximum output rating. Most generators have a maximum rating in watts, for example 2000 watts (two kilowatts)
- use a generator indoors. You risk carbon monoxide poisoning from the fumes and also risk fire
- add fuel while the generator is running
- use damaged leads or appliances. You should also use a safety switch designed especially for generators
- connect all appliances at the same time; start with the largest and progressively add successive ones up to the generator's maximum output
- 'piggy back' cords - always use a multiple-outlet box with built in load limiters.
Using caravan generators safely
If you want to run your caravan from a generator, get your electrician to make a special lead that couples to the 16 amp inlet socket. To avoid overloading the generator, make sure that the generator has a cut-out switch that is limited to the maximum output of the generator.
Most appliances are rated in watts, but some are rated in amperes. To find the wattage of an appliance, multiply the amperes by 230 volts (watts = amps x volts). For example, an appliance rated at 7.5 amps has a power rating of 1725 watts. In this case, the generator needs a rating greater than this value.
Electric motors
The label on the name plate of a motor lists the output power in watts. To correctly match the generator's output, an allowance must be made for losses within the motor. As a rule, add about 20% to the motor rating to allow for losses.
Electric motors require about 2.5 to 6 time's normal running current to start. Therefore, a 1000 watt motor, with assumed input of 1200 watts, will take 5.22 amperes normal running. To start the motor, the generator may need to provide anything from 13 to 32 amps. If the starting current is too high for the generator, it will stall. In this example, a generator of about 7.5 kW would be required just to start the motor.
Once running, the generator output drops back and additional loads can be added.
Using stand-by generators safely
A standby generator is designed to provide large amounts of power and can be connected to the installation wiring. Standby generators are installed either as fixed units or through a special inlet plug (usually for mobile generators).
- installations have either an automatic or manual change-over switch that disconnects the incoming mains and couples the generator to the installation wiring
- connected loads must not exceed the maximum rating of the generator. To limit the load to the maximum load rating of the generator, the installation wiring is split into essential and non-essential sections so that only the essential loads are supplied by the generator
- if you want to connect a generator to the house wiring you must comply with the Australian/New Zealand Standard AS/NZS 3000 : 2000 Wiring Rules (section 4.8 - alternative supply systems) available from Standards New Zealand
- a licensed electrician must install the generator and alter the wiring as necessary. If you plan to install a generator, first talk to your electrician
- one point to note is that the generator connection must be on the installation side of the energy meter - otherwise you will be billed for using your own power
- generators designed to start automatically and connect to the installation should be test-run on load at periodic intervals - usually once a week
- some units have special test switches for this testing, but the best way to ensure that the generator will start and change over when the mains fails is to turn off the building main switch
- we recommend that you ensure the generator is regularly serviced by a company that specialises in that type of work.
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