A Guide To Various Types Of Transfer Switches

By Author: Blades Power Generation Ltd
Total Articles: 22
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Today power outages are a common issue. To combat it, we often supply the required electricity from any external source. But while supplying it, we need to prevent it from going back into the grid. This is done using a device called a transfer switch which safely connects the house wiring to an external generator or the utility lines. Used with fixed standby generator systems, they come in two forms- Manual transfer switch and Automatic transfer switch.


Typical transfer sequence


In a typical transfer sequence, the following steps occur systematically:-

Power outage occurs with normal power failing.

Once the power from the generator or another external source becomes stable with requisite voltage and frequency, the electrical load is shifted to the emergency power switch via a transfer switch, which can be either automatic or manual.

On the restoration of utility power, the transfer switch again ...
... returns the power source back to the normal one using either automatic or manual mode.

Types of Transfer Switches


According to the National Electrical Code (NEC), it is mandatory for all transfer switches to have a three-position “LINE-OFF-GENERATOR” or “ON-OFF-ON” switch to prevent the power from accidently back-feeding. This three position switch makes the switch mandatorily go through the off position when it travels from the generator position to the line position and again fully disconnects the generator every single instance the main utility switch is turned on.


We already know that there are two types of transfer switches: - manual and automatic. Let us understand each type individually with their benefits and utility-


Manual Switches


Here the switch needs to be turned in manually during use. One of the biggest advantages of manual changeover switch is that they are significantly cheaper to design, fabricate and install compared to automatic switches. Being smaller in size, they are not only easier to install but also quicker to fabricate than the automatic ones. These need to be hardwired to the control panel and are ideal to be used with portable power supplies and optional standby generators.


The biggest disadvantage of this switch is its much longer downtime as it takes time for you to connect the temporary electrical power supply in comparison to automatic types.


Automatic Transfer Switches


This is ideal for entities like hospitals, data centres etc. which cannot afford to have their power supply interrupted even for a minute. Here the secondary source of power in the scenario of a power outage is connected automatically as its special circuitry is controlled by the computer. This seamless connect and disconnect is its biggest advantage.


Its second advantage is it’s built in sensors which detect even the slightest fluctuation in the voltage and frequency of the main power supply. They have an optimum set mark as soon as power mark goes below it; they automatically turn the generator on and switch the power to it. They also turn off the generator as soon as they detect the restoration of the line power. In case an establishment faces any power trip in any of its part, the generators are immediately connected to handle the power shortage.


Another advantage is that these switches have a time delay mechanism which protects both the generator device and the electrical circuits from power fluctuations. During the beginning of power transfer from the mains to the generator, the time delay strikes at between 0-5 seconds. Again, the end of the transfer session witnesses a time delay of 1-30 minutes during which the generator normalizes based on the main power supply before fully transferring the circuits to the main.


It also has some disadvantages. Its biggest disadvantage is a higher margin of error for some establishments. Discrepancies can creep in when selecting the appropriate power of switch to support the given number of generators which can lead to the failure of the entire mechanism. They are also more expensive and require more technical and elaborate maintenance routine than manual ones.


Blades power generation is a leading UK company which specializes in power generation supplies to homes, offices and even in areas considered inaccessible. Get in touch with them as your one-stop destination for manual and the automatic changeover switch, manual transfer switch, generator switchgear, ATS, new generator, used generator or any such requirements.