AUTOMATIC TRANSFER SWITCH

FOR GENERATOR CIRCUIT DIAGRAM

HOW TO MAKE AN AUTOMATIC

TRANSFER SWITCH PANEL

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.

 

AUTOMATIC TRANSFER SWITCH CONTROL WIRING DIAGRAM PDF
 
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 to 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 by your own generator automatic transfer switch control panels for standby generator. Please strictly follow our automatic transfer switch diagram 3-phase.

 

  You will understand how to build automatic changeover switch by following our STEP-BY-STEP 60kVA ATS panel manufacturing procedure.

 

WHAT IS AUTOMATIC TRANSFER

SWITCH CONTROLLER

An automatic transfer switch controller is the ideal choice in cases where you have to control a standby generator. In other words a system that supplies the load when utility power is normal and supply the load from the generator when there is a failure of the utility power.
  An automatic transfer switch panel fitted with an automatic transfer switch 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 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 automatic transfer switch controller is conveniently tasked with driving the circuit breakers or switch-gear. Despite the fact that the power configuration and general arrangement is the same for all panels, the input output lines for the engine connection and ancillary equipment depends on the type of controller fitted to the panel.
 
  The automatic transfer switch 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 automatic transfer switch controller transfers the load to the utility power.
  If the voltage drops below the lower limit (or rises above the high limit), the automatic transfer switch controller will disable the utility power circuit.
  This prevent, after a programmable delay, a severe damage to your load. If the failure persists for a long time (a programmable timer is available) the automatic transfer switch controller will take care to start the generator.
  Once again the automatic transfer switch 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 automatic transfer switch 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 automatic transfer switch controller will transfer the load to utility power. This will happen after a delay that will ensure that the utility poweris in stable conditions.
  After connecting your load to the utility power, the engine will run for a programmable time (so called COOLING DOWN TIME) off load.
After the cooling down time 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. Current of the generator is measured via current transformers (10).
  The automatic transfer switch controller (4) drives the coils of the circuit breakers (6) & (8). The 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 controller (4) is tasked to monitor and charge the battery (19) via a battery charger (not shown).

 

  The Power Circuit Breakers (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 a remote control and monitoring. The components are enclosed in a steel cabinet (3).
  The frontal doors features a key lock to avoid mot authorized access and an Emergency Switch to disable the panel and/or the Generator.

 

The automatic changeover switch controller features a user friendly interface via push buttons and display. A more complex automatic transfer switch panel may include extra relay for extra-alarm indication and electronic boards to interface with external programmable logic controller (19).

 

All modes of operation are normally chosen directly on the front panel of the automatic changeover switch controller, but in some cases, some extra key-switches are required to switch the mode of operation (22).

 

200 AMP AUTOMATIC TRANSFER SWITCH
WIRING DIAGRAM
Automatic transfer switch for generator circuit diagram

ABOUT BE242 ATS CONTROLLER

AUTOMATIC TRANSFER SWITCH FOR

GENERATOR CIRCUIT DIAGRAM

You can observe the connections of the current transformers wired on the load side. This allows the Be242 to display the current when a circuit breaker 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 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 kind 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 of 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).
Automatic transfer switch for generator circuit diagram

STEP BY STEP INSTRUCTIONS FOR

MAKING A 60KVA ATS PANEL

HOW TO BUILD AUTOMATIC CHANGEOVER SWITCH

STEP ONE

 

The first stepin building an automatic changeover switch  is collecting suitable components. In this example we build a 60kVA panel using the Be242 controller. According to 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 beakers (or as option a set of suitable fuses).

 

- 2 power contactors, 4 poles rated at 110 Amps class AC1.

 

- Mechanical interlock with a 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 basic indication for MAINS, GENERATOR and LOAD.

 

DOWNLOAD THE
AUTOMATIC TRANSFER SWITCH
CONTROL WIRING DIAGRAM PDF

 

In choosing the components it may help the following table. It includes information about size of the contactors and 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. 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 long life of the panel, take into account the number of the operation of the contactors. In normal condition 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.

 

applications up to 40 degree Celsius temperature.

NOMINAL

POWER

Contactors size

(AC1 current)

Minimum

Dimensions

Cables

Gauge

Expected Weight

(kg)

15 kVA 32A 500x400x210 6 sq.mm 14
25 kVA 40A 500x400x210 10 sq.mm 16
40 kVA 63A 700x500x250 16 sq.mm 22
60 kVA 100A 700x500x250 25 sq.mm 28
80 kVA 135A 800x600x300 35 sq.mm 34
100 kVA 150A 800x600x300 50 sq.mm 44
130 kVA 200A 800x600x300 50 sq.mm 54
160 kVA 250A 1000x700x400 70 sq.mm 64

 

STEP TWO
The second step is to make a template on transparent sheet (normal white paper as 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 making the connections to all parts. After checking the wiring diagram, dimensions of the components, 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 reference you see, on the following pictures, the final set up for a 25kVA and 60kVA panel by using the cost-effectibe 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
[1] TERMINAL BLOCKS     [2] POWER CONTACTORS     [3] CURRENT TRANSFORMERS
[4] PLASTIC CONDUITS   [5] BATTERY CHARGER   [6] BE242 RELAY BOARD   [7] UNCOMMITTED RAIL
TYPICAL 40KVA UP TO 80KVA ATS AMF PANEL

 

[1] TERMINAL BLOCKS     [2] POWER CONTACTORS     [3] CURRENT TRANSFORMERS
[4] PLASTIC CONDUITS   [5] BATTERY CHARGER   [6] BE242 RELAY BOARD
[7] & [8] CIRCUIT BREAKERS TO PROTECT THE AUXILIARY CIRCUITS
STEP THREE
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 particle during the work. Drill the holes according to the size of the screws. You can use a 4,5 mm bit (M4 screws) and 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.

 

STEP FOUR
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 instruction, Install the auxiliary contacts following the manufacturer instruction,

 

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 the time.

 

This is how it will look like the backplane before commencing the connections

 

 

 STEP FIVE
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 contactors 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 case of 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 to use 1,5 square mm flexible stranded copper cable. See the above picture.

 

STEP SIX
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 to use 1,5 square mm flexible stranded copper cable. See the picture below

 

 

 

STEP SEVEN
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 1,5 square mm flexible stranded copper cable. See the above picture.

 

 

 STEP EIGHT
WIRING THE KG CONTACTOR AUXILIARY CIRCUITS
You are required to wire the coil of the KG (terminals A1 & A2 on teh 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 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 to energize.

 

If the KM, for any reason, is in ON position, the auxiliary contact, being in open state, will not allow KG to energize. In blue color the connection to the neutral terminal of the generator via the circuit breaker.

 

 

 

STEP NINE
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 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 to 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.

 

 

STEP TEN
WIRING THE CONTACTORS INPUTS
This is the most critical part of the job. Particular skills are required to connect the wires of big size. You have to follow the recommendations and instructions of the contactor manufacturer.

 

This will avoid over heating of the connection points. You have to use the recommended force to guarantee good contacts 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 consider the table on page 7. According to the table, a 60kVA panel require a 25 sqmm size.
This size will allow a continous current of about 100Amps. For terminal blocks the better choice is to use 35 sqmm size.

 

STEP ELEVEN
WIRING THE CONTACTORS OUTPUT
This is the most critical part of the job. Particular skills are required in connecting the wires of big size. You have to follow the recommendations and instructions of the contactor manufacturer.

 

This will avoid connections over heating. 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.

 

 

STEP TWELVE
DRILLING THE DOOR OF THE PANEL

 

The main advantage in using the BE242 controller is time saving. As a matter of fact the BE242 is the only AMF ATS controller of 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 1:1 ratio. Choose the correct position for the template [1] over the panel [5]. Use a paper tape to fix and hold the template. Make a round hole in between 56mm up to 64mm.

 

This will be the main hole for the BE242 controller. Make four holes [3] 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 [4] if you need to install an emergency stop button. See the picture.

 

DOWLOAD THE TEMPLATE

 

After drilling you may complete the work using a curved-cut file and some paint to prevent rust on the long term. You can finally fix the BE242 controller by using four metric 4mm nuts.

 

READ MORE ABOUT BE242

 

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 check list

 

Very well done. You supposed to finish your panel. Your work is not over yet. We recommend that you print the following check list. Check carefully, step by step, each item. T
his 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. Surface of the panel is clean.
2) Make sure the nuts for grounding of 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 to 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, auxiliary contacts are properly tight.
5) Verify that there is 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 the time.
11) Hold the panel in 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 is no extra items (screws, loose terminals, tools, piece 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 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 matches 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 final packaging