AUTOMATIC TRANSFER SWITCH
FOR GENERATOR CIRCUIT DIAGRAM
HOW TO MAKE AUTOMATIC TRANSFER SWITCH PANELS?
FOLLOW OR 12-STEP TUTORIAL ON HOW TO MAKE A TRANSFER SWITCH PANELS
A smart way to build an automatic changeover switch is using two contactors driven by an ATS controller Follow our automatic transfer switch for generator circuit diagram to make an automatic changeover switch using contactors: it is about two, electrically controlled, contactors.
The contactors are not allowed to close simultaneously, but only one at a time. The two contactors are joined together with a ‘mechanical interlock’ mechanism. The mechanical interlock will not allow both contactors to be in a ‘closed position’. In the automatic transfer switch control wiring diagram Pdf the automatic transfer switch for generator circuit diagram, the contactors are indicated ‘KG’ for generator and ‘KM’ for utility power.
This guide will help you to make your own generator automatic transfer switch control panels for a standby generator. Please strictly follow our automatic transfer switch diagram 3-phase. You will understand how to build an automatic changeover switch by following our STEP-BY-STEP 60kVA ATS panel manufacturing procedure.
An automatic transfer switch panel fitted with an ATS controller manages, in a fully automatic way, the connection assignment of the LOAD to utility power or GENERATOR as indicated in the following automatic transfer switch for the generator circuit diagram. The panel includes an automatic battery charger and a set of electronic circuit boards complete with power relays that interface directly with the engine. The ATS controller is conveniently tasked with driving the circuit breakers or switchgear. Despite the fact that the power configuration and general arrangement are the same for all panels, the input-output lines for the engine connection and ancillary equipment depend on the type of controller fitted to the panel. The ATS controller continuously monitors the status of the utility power. You can set low/high limits for Mains Voltage and Frequency. In other words, when the voltage and the frequency are within the limits, the ATS controller transfers the load to the utility power. If the voltage drops below the lower limit (or rises above the high limit), the ATScontroller will disable the utility power circuit. This prevents, after a programmable delay, severe damage to your load. If the failure persists for a long time (a programmable timer is available) the ATS controller will take care to start the generator. Once again the ATS controller does its business to check the quality of the generator voltage and frequency. Once detected that the parameters are within the programmed limits, the ATS controller will enable the generator circuit breaker. Now, in case of prolonged power outages, your load is safely supplied by the generator. During the power outage, the automatic transfer switch controller continuously monitors the utility power. When the utility power parameters will return within the programmed settings, the ATS controller will transfer the load to utility power. This will happen after a delay that will ensure that the utility power is in stable conditions. After connecting your load to the utility power, the engine will run for a programmable time (so-called COOLING DOWNTIME) offload After the cooling downtime, the engine will stop and the automatic transfer switch is ready for a new power outage.
AUTOMATIC TRANSFER SWITCH
CONTROLLER BLOCK DIAGRAM
The automatic transfer switch controller (4) is wired to UTILITY POWER (7) via protection fuses (2). It features high impedance on the voltage measurements inputs. The controller is wired to the GENERATOR (15) via protection fuses (12) as well. The current of the generator is measured via current transformers (10). The automatic transfer switch controller (4) drives the coils of the contactors (6) & (8). The ATS controller is connected to the engine (14) via cables and relays (21). In some cases, extra driver relays are required if the distance is over 100 meters (17) & (18). The ATS controller (4) is tasked to monitor and charge the battery (19) via a battery charger (not shown). The Power contactors (6) & (8) are included in the panel in a way to connect the Load (9) to the Generator (15) or Mains (7). A serial interface (20) allows you remote control and monitoring. The components are enclosed in a steel cabinet (3). The frontal doors feature a key lock to avoid mot authorized to access and an Emergency Switch to disable the panel and/or the Generator. The ATS controller features a user-friendly interface via push buttons and display. A more complex automatic transfer switch panel may include an extra relay for extra-alarm indication and electronic boards to interface with an external programmable logic controller (19) All modes of operation are normally chosen directly on the front panel of the ATS controller, but in some cases, some extra key switches are required to switch the mode of operation (22).
ABOUT BE242 ATS CONTROLLER
THE 12 STEPS TO REACH YOUR GOAL
You can observe on the schematics the connections of the current transformers wired on the load side. This allows the Be242 to display the current when a contactor is closed. So, you can read the current into the load even when connected to the utility power. You can set up alarms (warning or shutdown) in case of an over-current. The Be242 will trigger the alarm only when connected to the generator. It is obvious that you can set up all other important protections about Over/Under frequency, voltage, and so on. The Be242 does include relays to interface with all kinds of engines: gas-gasoline-diesel. The Be242 is designed to drive two contactors. A best practice, in addition to the electrical interlock, is to use a good mechanical interlock. This will avoid back-feeding in case of damage to the Be242 controller. You can connect digital sensors directly to the Be242 inputs. The outputs of the Be242 are suitable for automotive relays 12V or 24V (according to the battery of the engine).
The first step in building an automatic changeover switch is collecting suitable components. In this example, we build a 60kVA panel using the Be242 controller. According to the automatic transfer switch 3-phase wiring diagram, you need the following components.
- BE242 controller and BE242RB interface board with interconnection cable (supplied with the KIT).
- Emergency, normally closed push button. Steel panel box IP62 800(700)x500x250.
- 2 X 4 POLES 10Amp circuit breakers (or as an option a set of suitable fuses).
- 2 power contactors, 4 poles rated at 110 Amps class AC1.
- Mechanical interlock with normally closed auxiliary contacts for each contactor.
- Din rail 1 meter, plastic conduits.
- 12 pcs terminal block sizes 35 mmq. Terminal block holder and cover.
- Battery charger 12V2A and 3-phase current transformer (or 3 separated CTs).
- Labels with a basic indication for MAINS, GENERATOR, and LOAD.
In choosing the components it may help the following table. It includes information about the size of the contactors and the size of the wires.
The expected life of the coil of the contactor is about 20 to 30 years. But you have to maintain the operating temperature as lower as possible. The ambient temperature inside the panel over 50 degrees Celsius may reduce the life of the coil.
For this reason, we recommend that you store inside the panel a spare coil. In case of failure, you can replace the coil in a few minutes. We always recommend 230V coils instead of 400V coils. To guarantee a long life of the panel, take into account the number of the operation of the contactors. In normal conditions, a standby generator will work 2-3 times a week. You can dimension the size of the contactors based on class AC1. But in case you supply high inductive loads or a higher number of weekly operations, we recommend dimensioning the contactors based on the AC3 class.
The second step is to make a template on the transparent sheet (normal white paper as an option). You can also directly draw on the backplane the position of all components.
First of all, It is really important that you have a clear picture of the final backplane.
This will make it easy to make the connections to all parts. After checking the wiring diagram, dimensions of the components, and the sizes of the cables, you will start drawing, on the backplane, the positions of all parts.
This is the most crucial initial part of the job. It is better that you make all necessary holes before installing the components. Avoid any mechanical work while you are assembling the panel. Various dirty remains coming from iron drilling or filings may severely affect the quality and reliability of the panel. Just as a reference you see, in the following pictures, the final setup for a 25kVA and 60kVA panel by using the cost-effective BE242 controller. This controller drastically reduces the total components of your panel.
TYPICAL 15KVA UP TO 30KVA ATS AMF PANEL
In the above picture, you can observe
 TERMINAL BLOCKS  POWER CONTACTORS  CURRENT TRANSFORMERS
 PLASTIC CONDUITS  BATTERY CHARGER  BE242 RELAY BOARD  UNCOMMITTED RAIL
TYPICAL 40KVA UP TO 80KVA ATS AMF PANEL
 TERMINAL BLOCKS  POWER CONTACTORS  CURRENT TRANSFORMERS
 PLASTIC CONDUITS  BATTERY CHARGER  BE242 RELAY BOARD
 &  CIRCUIT BREAKERS TO PROTECT THE AUXILIARY CIRCUITS
After fixing the template over the backplane, you have to mark the centers of all holes. This will help the manual drilling. You can use a steel pin and a light hammer.
Wear safety glasses to protect your eyes from any metal particles during work. Drill the holes according to the size of the screws. You can use a 4,5 mm bit (M4 screws) and a 3,2 mm bit for self-tapping 3,4 mm screws.
Cut the rails according to the template drawing. Start fixing the rails to the backplane using self-tapping screws.
Clean the backplane. Remove various dirty remains. Metal particles can damage the contactors.
After cleaning the backplane you can install the mechanical interlock following the manufacturer's instructions, Install the auxiliary contacts following the manufacturer's instructions.
Assemble the contactors and fix them by using eight M4 screws. Check the movement of the contact assemblies.
You must be able to mechanically operate only one contactor at a time.
This is how it will look like the backplane before commencing the connections
CIRCUIT BREAKERS INPUT CONNECTIONS
The controller has to sense the voltage of the utility power (mains) and a generator. You have to provide power to the contactor's coils as well. It is quite dangerous to connect these loads to the high power source.
Utility power can be able to supply hundreds of amperes. For this reason, it is mandatory to put a circuit breaker that limits the current. This will prevent major damage in the case of a short circuit. We consider that 10 Amps are more than enough for this application.
Follow the indication of the picture. By turning OFF the circuit breakers, you can easily carry out maintenance to the parts without risk.
Connect Phases L1-L2-L3-N from the ‘generator’ terminal block to the entrance of the circuit breaker on the left side.
Do the same connections for the circuit breaker on the right side by connecting the R-S-T-N terminal blocks.
We recommend using 1,5 square mm flexible stranded copper cable. See the above picture.
VOLTAGE MEASUREMENTS CONNECTIONS
With this task, you will connect the voltage measurements circuits. You can see in RED color the three cables for the generator voltage measurements (5-6-7).
The three YELLOW cables provide utility power (mains) voltage measurements (1-2-3). We recommend using 1,5 square mm flexible stranded copper cable. See the picture below
BATTERY CHARGER & CURRENT TRANSFORMER
With this task, you will connect the current measurement transformers to the BE242RB current inputs.
The end side of the common cable must be grounded.
In this step, you are also required to connect the phase ‘2’ and neutral ‘4’ to supply the battery charger.
We recommend using a 1,5 square mm flexible stranded copper cable. See the above picture.
WIRING THE KG CONTACTOR AUXILIARY CIRCUITS
You are required to wire the coil of the KG (terminals A1 & A2 on the left side) and the electrical interlock contacts of the KM (utility power contactor). Follow the wiring diagram and the below picture.
According to the wiring diagram, the KG will only energize if the KM is in the OFF position. As a matter of fact, the OFF position of the KM will hold closed the interlock auxiliary contact in a way to let the KG coil energize.
If the KM, for any reason, is in the ON position, the auxiliary contact, being in the open state, will not allow KG to energize. In blue color the connection to the neutral terminal of the generator via the circuit breaker.
WIRING THE KM CONTACTOR AUXILIARY CIRCUITS
You are required to wire the coil of the KM (terminals A1 & A2 on the right side) and the electrical interlock contacts of the KG (GENERATOR power contactor on the left side).
Follow the wiring diagram and the below picture. According to the wiring diagram, the KM will only energize if the KG is in the OFF position.
As a matter of fact, the OFF position of the KG will hold closed the interlock auxiliary contact in a way to let the KM coil energize. If the KG, for any reason, is in ON position, the auxiliary contact, being in open condition, will not allow KM to energize.
In blue color the connection to MAINS neutral terminal via the circuit breaker.
WIRING THE CONTACTORS INPUTS
This is the most critical part of the job. Particular skills are required to connect wires of big size. You have to follow the recommendations and instructions of the contactor manufacturer.
This will avoid overheating of the connection points. You have to use the recommended force to guarantee good contact especially when high currents are involved (in this case the nominal current is about 110Amps).
Connect phases ‘L1’-’L2’-’L3’-‘N’, connect phases ‘R’-‘S’-‘T’-‘N’.
In choosing the size of the cables considers the table on page 7. According to the table, a 60kVA panel requires a 25 sqmm size.
This will allow a continuous current of about 100Amps. For terminal blocks, the better choice is to use a 35 sqmm sizes.
WIRING THE CONTACTORS OUTPUT
This is the most critical part of the job. Particular skills are required in connecting wires of big size. You have to follow the recommendations and instructions of the contactor manufacturer.
This will avoid connections overheating. Currents over 100Amps may circulate in these wires. Use the recommended force to guarantee good contacts.
Connect phases ‘L1’-’L2’-’L3’-‘N’ together with the phases ‘R’-‘S’-‘T’-‘N’ Each output phase must enter the proper current transformer before connecting the terminal blocks. The neutral wire must be directly connected to the terminal block.
DRILLING THE DOOR OF THE PANEL
The main advantage of using the BE242 controller is time-saving. As a matter of fact, the BE242 is the only AMF ATS controller of the square size that requires a round hole. This means that you can make the hole using a circular saw. You are required to download the template.
Double-check the dimension reported on the drawing. This is particularly important if you are not sure that your printer is able to exact print in a 1:1 ratio. Choose the correct position for the template  over the panel . Use paper tape to fix and hold the template. Make a round hole between 56mm to 64mm.
This will be the main hole for the BE242 controller. Make four holes  of about 4,5mm.
These holes will allow you to fix the controller on the panel by using 4 nuts 4MA. You can additionally make a 22mm hole  if you need to install an emergency stop button. See the picture.
After drilling, you may complete the work using a curved-cut file and some paint to prevent rust in the long term. You can finally fix the BE242 controller by using four metric 4mm nuts.
You can finally wire the emergency button and connect the 25-poles cable on both sides. Make sure the fixing screws of the connectors are tight.
HOW A 60KVA ATS PANEL LOOKS LIKE
The quality of your panel & final checklist
Very well done. You are supposed to finish your panel. Your work is not over yet. We recommend that you print the following checklist. Check carefully, step by step, each item. This is a general guide. You can integrate it based on your experience.
1) The controller is very well fixed on the front door. Make sure the nuts are tight. The surface of the panel is clean.
2) Make sure the nuts for grounding the front door and panel structure are tight.
3) The backplane that supports the hardware is normally held in place by 4 bolts M6.
Make sure you have a spacer between it and the frame of the panel. Being the bolts soldered, if you apply too much force, without a washer spacer, you can de-solder the bolts.
4) Verify that all screws of the terminal blocks, fuse holders, CTs, circuit breakers, and auxiliary contacts are properly tight.
5) Verify that there are no strands exposed on each cable termination. You could get arcing or overheating.
6) Check if the bolts, or screws, on the contactors are tight according to the contactor specifications.
7) When using multipolar connectors check the holding screws: must be tight.
8) The emergency switch on the front door must be carefully verified. If necessary use thread locker adhesive to avoid rotation of the switch.
9) Verify the size of the fuses. Put a proper label indicating the value. Add spare fuses for the user.
10) Check the free mechanical movement of the contactors. Check the mechanical interlock. You must not be able to activate both contactors. The mechanical interlock will allow only one contactor at a time.
11) Hold the panel in a vertical position. Hit gently the panel with a rubber mallet. Check for vibration and collect various dirty remains (iron filings, copper remains, and so on) on the bottom of the panel. Use a powerful vacuum cleaner. Make sure there are no extra items (screws, loose terminals, tools, pieces of wire, and so on)
12) Verify the presence of the labels indicating Mains, Generator, Load, Phases, Electric Danger, and so on.
13) Put inside the door an adhesive sheet that illustrates the schematics and the nominal data of the panel. This may help an electrician in case of service.
14) Mechanically check the closure of the door. If your panel is over IP42, check the gasket.
15) Proceed with the electric test. The contactors, when activated, should not emit noise. The presence of noise could be caused by iron filing pollution on the body of the contactors.
16) Make sure the settings of the AMF controller match the size of the current transformers.
17) Remove all connections after testing. Tight the bolt again without forgetting the washers (this in case connections are directly made on the contactors)
18) Do not forget to put on a small box, or envelope, the spare Panel Fasteners. It will be important for the user.
19) Close the door of the panel. You can proceed with the final packaging
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