How to properly connect a generator to a private house

Recommendation points

• Why you shouldn’t plug in
• The minimum required to connect the generator
• How to provide automatic switching
• Installation of the ATS unit with autostart of the gas generator
• Possible problems and malfunctions

Energy independence of the home is the credo of many modern homeowners. To integrate a portable generator into a home network, it is necessary not only to have wiring skills, but also to know the basics of automating the backup input. Today we will answer most of the questions on this topic..

Why you shouldn’t plug in

In rare cases of emergency blackout, it is customary to “throw” power from the generator to the nearest outlet. After all, power outages are so rare, isn’t it, so why bother with a backup input system? But here, as in everything, there are a number of pitfalls..

First, the power line of a separate outlet group is not designed to take on the trunk load. It is good if the group is protected by a separate machine, selected according to the cable cross-section, and if not?

Connecting the generator to the house through a three-position switch: 1 – input circuit breaker; 2 – counter; 3 – RCD; 4 – generator; 5 – three-position switch; 6 – zero bus (N); 7 – grounding bus (PE); 8 – to consumers

Second, you cannot rely on your own commitment. Forgetting to turn off the introductory machine is a common thing. In the best case, you will supply all consumers on the main city line from the generator, which will undoubtedly cause overload and great bewilderment – why does the circuit breaker constantly work. At worst – and this is the most common cause of generator breakdowns – you will catch the “oncoming” lane and say goodbye to an emergency source of electricity for a long time.

And the last argument: you should never neglect the convenience of using a particular system. Just one turn of the switch or work in fully automatic mode – and you are always calm about the safety of your power grid and equipment connected to it.

The minimum required to connect the generator

However, for the technically correct connection of the generator to the home power grid, not much is needed. First of all – to provide a separate input. It is recommended to perform it with a copper cable of high cross-section (at least 4 mm²) and lay from the input distribution device to a specially equipped place for the generator installation.

You will also need a rocker switch. For household needs, many variants of similar devices have recently appeared in a modular design for mounting on a 35 mm DIN rail. A whole range of devices can be suggested offhand. From the cheapest TDM-63 products to the more robust and reliable E200 series from ABB or SFB from Hager.

The devices have the simplest switching circuit and principle of operation. As a rule, a common bus of outgoing loads is connected to the lower contacts. On the reverse side, where the contacts are paired, two separate inputs are connected. The switch key has three positions, on average all circuits are open. In almost all series, devices can be multi-pole, which will greatly facilitate work with a three-phase network and a complex grounding / neutralization system.

It is important to remember that a three-position (changeover) circuit breaker works on the principle of a load switch, it does not provide for either a thermal or electromagnetic release. Therefore, each input must be additionally protected with an automatic machine, the limiting current of which is determined by the permissible load on the supply line.

The simplest toggle device can also be made from a pair of two-pole circuit breakers from the same manufacturer. They need to be placed side by side, one should be turned upside down, and then the keys must be linked together by inserting a steel pin into the regular hole.

How to provide automatic switching

If the ASU flap is located in a hard-to-reach place, or you simply do not want to manually switch each time, you can rely on the automatic switching device. Its circuit is also extremely simple, you only need two modular contactors with the number of contact pairs equal to the number of power phases, as well as a pair of normally open and normally closed auxiliary contacts.

In the normal operating mode, the city input is always “on the catch” of the switched on contactor, in which the coil supply circuit is connected directly to the supply network until it is broken. If the electricity at the city input is lost, the contactor will drop and close the normally closed pair of auxiliary contacts, which will turn on the second contactor of the backup input, or at least close the power circuit of its coil.

1 – time relay; 2 – main input contactor; 3 – contactor control coil; 4 – contactor of reserve input

The connection of the “emergency” contactor is also carried out before the mains break from the generator, therefore, the device will remain in the off state until it is started. It is very useful here to add a modular time relay to the circuit so that the power supply to the consumers turns on a minute or two after the generator starts. This will allow the engine to warm up and wake up before taking on base load..

In this case, the power supply circuit of the second, backup contactor should be passed through the normally closed contact of the switch of the main input. Thus, when the CO line voltage reappears, the first contactor will turn on again and open the power circuit of the second input. Of course, a generator stopping device should be added here, but in extreme cases it will idle for some time with minimal fuel consumption.

Installation of the ATS unit with autostart of the gas generator

In the light of the above, a device that generally excludes human intervention in the operation of the emergency power supply system would be very useful. Such devices do exist and they work completely smoothly, but only with generators equipped with an electric starter and a standard shutdown system..

Developing such a system on your own is a troublesome business worthy of a separate discussion. If the work is not properly organized, there is a great risk of damage to the equipment. For example, if the generator has a breakdown of the motor part, its forced repeated start will cause at least a deep discharge of the battery, and in the worst case will lead to the failure of the electric starter windings..

There are two options for such devices, the first is a standard electronic control unit supplied with the generator and installed in the same room with it. Such a unit is connected according to the diagram attached to the instructions and controls only starting and stopping the engine, in some cases it takes on the task of adjusting the speed and output power. The main switching of the backup input is performed by contactors according to the scheme that we described earlier. Only in this case, a normally open contact at the main input is pulled by a low-current signal wire to the control unit, so that the current state of the city line makes it clear to the electronics when the generator should be put into operation or stopped..

1 – block for automatic generator start; 2 – main input contactor; 3 – contactor of reserve input

The second option is complete ATS devices with autorun. This is not a very wide range of devices, but they all require installation of additional equipment on the generator: an electric throttle actuator and a starter with a battery.

Connecting the generator through the ATS: 1 – introductory machine; 2 – counter; 3 – ABP shield; 4 – generator; 5 – control cable; 6 – zero bus; 7 – consumer machines; 8 – grounding bus

The advantage of such systems is that they have everything you need “out of the box” and completely replace the switchgear, including built-in overcurrent protection, and sometimes even have an overvoltage and leakage protection system. All that is needed for connection is to connect the conductors of the inputs and consumer buses to the switching devices, as well as to connect the secondary terminal block with the additional equipment of the generator using a four- or five-core wire.

Possible problems and malfunctions

When using a generator, you must have a complete understanding of the nature of the current generated by an autonomous source. Often these are not the usual phase and zero, but alternating phases with a half-wave of 110-125 V relative to ground.

Such generators require a well-made grounding system that is not connected to the protective conductor of the home network. Also, it is imperative that both the phase and the neutral wire of both inputs be switched, otherwise leakage into the city network is guaranteed.

This is the main reason that when connected through an outlet, the circuit breaker on the generator itself is triggered. As for differential protection devices, they will have to be installed in pairs – one for each input. The exception to this rule is three-phase networks, but they, in turn, require the device of separate grounding and grounding loops for stable and uninterrupted operation..