- How to determine and calculate the maximum generator load
- Connecting the generator to the mains
- Connecting a generator as the sole source of electricity
- Calculation of the cross-section of the connecting cable
- Connecting a generator as a backup power source
- Automatic generator commissioning systems (ATS)
This article will give answers to questions on how to correctly and safely connect an electric generator in your own home, outdoors or on a construction site, what are the hidden features of connecting a gasoline or diesel generator to the mains, how to avoid mistakes when connecting an electric generator.
How to determine and calculate the maximum generator load
In order to connect the generator to the mains, it is necessary to calculate the permissible load on the generator. In this case, it is important to take into account not only the rated power, but also the inrush current, as well as the possible increase in energy consumption during the operation of the connected device. Therefore, the real load on the generator may be greater than the rated power indicated on the electrical appliance..
In a simplified way, the required generator power can be calculated by multiplying the rated power of the connected electrical appliance by the factor below:
- For incandescent lamps and heaters, you can take a coefficient equal to one.
- For household appliances (TV, refrigerator, fluorescent lamps), the coefficient will be in the range from 1.2 to 1.5.
- Hand-held power tools (drill, angle grinder, jigsaw, milling cutter) – the coefficient will be in the range from 1.5 to 2.
- Powerful equipment (pumps, welding transformers, machine tools, powerful electric motors without a soft start system) – 3.
Let’s say we have purchased a generator with a nominal power of 3 kW and a maximum power of 3.45 kW. You need to connect to it at the same time:
- Incandescent lamps 3 pcs. 100 W.
- Washing machine, with an electric motor power of 300 W and a heating element – 1700 W.
- TV, power 100 W.
- Refrigerator – 150 W.
- Drill – 450 W.
We make a verification calculation of the required generator power, taking into account the type of load:
- P = (3 x 100 + 300 x 2 + 1700 + 100 x 1.2 + 150 x 1.5 + 450 x 1.5) / 1000
- P = 3.62 kW
The resulting value is higher than the maximum allowable power for the purchased generator. Therefore, for safe operation, it is necessary to abandon some kind of electrical appliance so that the total load power of the generator does not exceed the rated power of 3 kW, for example, from a drill.
The power of the drill is: 450 x 1.5 = 675 W.
The maximum load power without using a drill will be 2945 W, which is comparable to the rated power of the generator.
It is important to remember that the generator cannot operate for a long time with a load below 30% of the nominal. Also, short-term but frequent overloads (when consumption reaches the maximum allowable value) negatively affect its performance.
Connecting the generator to the mains
When connecting an electric generator, it is important to remember the main rule: “You cannot connect more than one source of electricity to the power grid at the same time” Failure to comply with this rule guarantees damage to the generator..
Connecting a generator as the sole source of electricity
In nature or a summer cottage, where there are no other sources of electricity besides the generator, the connection is made through the sockets built into the generator case. The maximum current of single-phase sockets is within the range of 16-20 A, three-phase – 40-50 A. To connect the load, you must use both special and conventional extension cords, depending on the type of generator output socket.
To connect to the generator, it is necessary to use an electric cable (extension cord) capable of withstanding the load generated by the consumers connected to its sockets. Since the generator can be transported from site to site, it is better to use double insulated copper flexible cable for installation..
Important! Almost all generators need additional protection against water or snow ingress, so they should be installed under a shed or indoors.
Calculation of the cross-section of the connecting cable
The required cable section can be calculated based on the maximum power of the generator. In the previous example, we took the maximum generator power equal to 3.45 kW. Determine the required copper cable cross-section for its connection:
- Without taking into account the peculiarities of the load, according to Ohm’s law, we calculate the maximum output current of the generator: I = P / U = 3450/220 = 15.7 A.
- For exposed copper electrical wiring, the optimal current density is 5-10 A per 1 mm section2 copper conductor.
- The optimal wire cross-section is obtained by dividing the maximum flowing current by the permissible current density: S = 15.7 / 5 = 3.14 mm2 and S = 15.7 / 10 = 1.57 mm2.
- To connect, select a standard electrical cable, the cross-section of which must be more than 1.57 mm2, but not much exceed 3.14 mm2.
- A copper cable with a cross-section of 3 mm is ideal for connection2.
Core cross section 4 mm2 will have an increased margin and is justified only if it is necessary to transmit the eclectic energy generated by the generator over a distance of more than 25 m (an increase in the wire cross-section is used to minimize losses in the communication line).
Core cross section 2.5 mm2 can be used if the generator is slightly removed from the connection point (no more than 10-15 m). During prolonged operation of the generator at maximum power, it is advisable to monitor the cable temperature.
Important! It is necessary to use plugs, sockets, switches designed to operate at least with the maximum output current of the generator (in our example, 16 A) to connect to the generator.
The extension cord “plug” used to connect to the generator may differ in the shape of the contacts from the standard used in your region. To connect the load to this outlet, you must use an adapter or a specialized plug (usually supplied with the generator).
In a single-phase network, three wires are output from the generator – L (phase), N (neutral) and Pe (ground), which can also be indicated by the ground icon. The sequence of connecting L and N is not important, since this does not affect the operation of the equipment. It is important to connect the ground wire correctly. If you are not sure which ground wire is, check it with a special device – a multimeter. This requires:
- Turn off the generator.
- Turn on the multimeter in ohmmeter mode.
- Press one probe against the metal part of the generator body (select an area not covered with paint).
- With the second probe, successively touch each individual terminal of the generator outlet.
- The terminal in which the multimeter will show the resistance of the circuit close to zero Ohm, and will be ground, the remaining two are L and N.
When carrying out installation work, it must be remembered that generators equipped with a synchronous motor are sensitive to a short circuit in the load..
Remember! When connecting, touching bare live wires is dangerous to health and life..
Connecting a generator as a backup power source
In the event that the generator is used as a backup source of electricity, and it is connected to an existing electrical network, many people use a plug-to-plug adapter: one plug is plugged into a home outlet, the other plug into a generator outlet, which is strictly prohibited. What is it fraught with? When electricity appears in the main network, there is a high probability of failure of the electronics or the generator itself.
Often, in a hurry, connection errors are made, leading to irreversible damage to the generator, for example: connecting an external power supply directly to a running power source or through a connected adapter to a disconnected generator.
In order to avoid these problems, the connection of the generator to the home power grid should be made through a special toggle switch or a packet switch with a zero state. Connection to them is carried out by means of a bolted connection.
For home wiring, packet switches with a suitable operating diagram are suitable.
They are connected to them by means of a screw or push-in terminal connection. The burst switch power must correspond to the maximum load current with a margin of 50%.
Attention! Manufacturers do not recommend switching under load.
An approximate connection diagram may be as follows:
QS – rocker switch or packet switch; QS1 – input circuit breaker or fuse assembly on the branch from the mains; QS2 – input circuit breaker installed after the electric meter; QS3 and QS4 – automatic load break switches; L1 and L2 – indicator lamps rated for 220 V
Indicators for DIN-rail and panel mounting
As well as when connecting the generator through an extension cord, the correct connection of L and N to the internal network of the housing is not critical. When plugged into a generator outlet, a standard plug can be connected both conditionally “straight” or in an inverted state, while at the point of connection the type of supplied voltage changes from phase to zero or vice versa. Based on this, it makes no sense to connect the generator to the RCD unit, since with a 50% probability it will not work.
Particular attention must be paid to grounding (if it is used in internal wiring, since the old standard did not provide for its use). Improper ground connection can cause a short circuit in the generator circuit with unpredictable consequences..
Note: if the internal wiring is two-wire and does not provide for grounding, this does not mean that the generator itself does not need to be grounded.!
During operation without grounding, a rather high potential can be “induced” on the generator case, which is dangerous for human life and the generator electronics.
The sequence for turning on the generator using the burst switch will be as follows:
- Disconnect the incoming circuit breaker.
- Switch burst switch from mains to generator mains.
- Disconnect the circuit breakers.
- Connect the cable from the switch to the generator outlet.
- Start generator.
- Let it warm up.
- Apply power to the switch.
- Switch on the circuit breakers.
When the mains power supply appears, disconnect the generator from the mains in the reverse order..
Automatic generator commissioning systems (ATS)
The purchase of ready-made ATS systems that connect the generator to the electrical network, or their independent manufacture for most household generator models is an inexpedient waste of money, since the inclusion of generators, even with a built-in electric starter, is carried out under human control. This is due to the need for manual control of the throttle valve (air supply to the internal combustion engine) when starting a cold engine and then heating it. Fully automatic power supply redundancy systems can only be obtained when working with powerful generators equipped with microprocessor control systems.