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======Auto Mains Fail Transfer Switch :: Relay Logic ====
This Auto Mains Fail or Automatic Transfer Switch uses [[https://en.wikipedia.org/wiki/Relay_logic|"Relay Logic"]] to control two motor contactors (rated 100A or above) to transfer power to a load circuit between utility power and a standby generator.  

{{ :zref:ats:rs-pro_136-5381.png?direct&150|}}
One or more [[meters|multi-meters(s)]] can be included but is included in the wiring diagram. 

====Motor Contactor Selection==
The appropriate size of motor contactors should be selected based on the load served and the genset size. The 400A frame is a good general purpose selection, but smaller or larger can substituted. Recommended source: [[https://www.factorymation.com/Contactors_Overloads_qs/Metasol-Contactors-Overloads-9-to-800A?Coil_Voltage=240V-AC-Class&Nominal_Amps=150,225,400,800|FactoryMation.com]] //(225A frame and larger have 100-240VAC/DC coils)// 

  * //See the discussion at [[:zref:ats:start#contactor-based-atspro-con|ATS Pro & Con]] for reasons why this may or may not be an appropriate choice for your application.// 

=====One-Line Diagram===
{{ :zref:ats:e116.1_r6_auto_transfer_switch.png?direct&600 |}}

===Auto Mains Fail Transfer Switch -- Selector Switch==
<WRAP col2>
  * {{ :zref:ats:e116.1-3_r6_auto_transfer_switch_selector.pdf |E116.1-3 r6 Transfer Switch (PDF)}}
  * {{ :zref:ats:e116.1-3_r6_auto_transfer_switch_selector.dsn |E116.1-3 r6 Transfer Switch (DSN)}}
</WRAP>
//(.dsn) files can be edited with [[https://www.metatek.org/TinyCAD|]].//

====Description of Operation===
Contactors K-U [13] and K-G [14] are mechanically and electrically interlocked to ensure that only one can be closed at a time. 

===Definitions==
  * **Utility Connected:** Two Green indicators (L-U, L-KU)
  * **Generator Connected:** Two Blue Indicators (L-G, L-KG)
  * **Load Connected:** White Indicator(s) (one per phase, if desired)
  * **K-G [13], K-U [14]**: Utility & Generator Power Contactors, 400 Amp 3-pole
  * **K-PHM-U [2], K-PHM-G [10]** : Phase Monitor -- Loss of phase, phase rotation, and low voltage relay
  * **K-VM-UA [3], K-VM-GA [9]** : Over voltage relay
  * **K-US [4], K-GS [8]** : Time Delay (Voltage stabilization)
  * **K-U ENABLE [5]** : Time delay to ensure utility/grid power stability & minimum generator run-time
  * **K-G STOP [6]** : Generator cool-down delay
  * **K-G START [7]** : Generator start delay after utility power failure

===Utility Power Failure==
  - Starting with Utility Power being supplied to the load: Contactor K-U [13] is closed, and all timers have expired.((Time delays listed are defaults, and can be adjusted as desired.)) Timer K-G STOP [6] has expired and its contacts are closed. 
  - Power is removed from the coil for K-U [13] if: 
    - Utility power fails
    - A phase is lost or the voltage drops below the limit set by K-PHM-U [2]
    - Voltage goes above the limit set by K-VM-UA [3]
  - When K-U [13] opens: 
    - Load is disconnected (Preventing damage to equipment caused by low voltage.) 
    - Removes power from timer K-G START [7], which starts its timer. 
    - If Utility/Grid returns before K-GS [8] time delay closes K-G [14]:
      - K-U [13] will close after K-US [4] delay
      - K-G STOP [6] will time out, potentially running the genset for up to K-G STOP [6] time delay. 
  - When timer K-G START [7] expires (30 seconds), its contacts close, which causes the selected genset to begin its autostart sequence. 
  - Once the generator is supplying power: 
    - K-PHM-G [10] qualifies all phases live, phase rotation, and minimum voltage
    - K-VM-GA [9] qualifies maximum voltage
    - Illuminates L-G (Blue) indicating generator power is OK.
    - K-GS [8] begins its countdown (30 seconds). 
  - K-G [14] then closes: 
    - Supplies generator power to the load
    - Opens the neutral connection for the coil on K-U [13], preventing K-U [13] from closing by accident. 
    - Illuminates L-KG (Blue) indicating that generator is supplying the load. 

===Utility Power Return==
  - When Utility Power returns, it must meet the constraints: 
    - K-PHM-U [2] for phase (all phases live, correct phase rotation) and minimum voltage
    - K-VM-UA [3] maximum voltage 
    - Indicator L-U (Green) illuminates to confirm utility grid voltage is acceptable
  - K-US [4] begins voltage stabilization delay (10 seconds). 
  - K-U ENABLE [5] begins time delay (15 minutes), which ensures:
    - The utility grid has time to stabilize
    - Delays adding loads to the grid after an outage
    - Eliminates short-cycling if the grid drops again shortly after returning
    - Provides a minimum run-time for the generator to ensure it gets up to temperature
  - When K-U ENABLE [5] turns on, it opens the coil for K-G [14]: 
    - Disconnects load from Generator
    - Connects neutral of K-U [13] coil
  - K-U [13] closes immediately
    - Connects load to Utility Grid
    - Disables K-G [14] by disconnecting neutral of coil
    - Illuminates L-KU (Green), indicating Utility/Grid is supplying load
    - Provides power to K-G STOP [6]
  - K-G STOP [6] begins time delay (2 minutes) for Generator cool-down (running with no load)
  - K-G START [7] turns on, disconnecting the generator auto-start signal 
    - Genset stops

====Bill of Materials==
===116 ATS -- Automatic Transfer Switch-Contactor===

  * [[https://docs.google.com/spreadsheets/d/1_wC8IrVGSBzF0N8M5elPFTP66rg2xVx9F6NlgHCPepY/edit?usp=sharing |BOM-116 (G Sheets)]]
  * [[https://docs.google.com/spreadsheets/d/1_wC8IrVGSBzF0N8M5elPFTP66rg2xVx9F6NlgHCPepY/pub?gid=0&single=true&output=pdf |BOM-116 (PDF)]]
  * [[https://docs.google.com/a/metatek.org/spreadsheets/d/1_wC8IrVGSBzF0N8M5elPFTP66rg2xVx9F6NlgHCPepY/export?format=xlsx&id=1_wC8IrVGSBzF0N8M5elPFTP66rg2xVx9F6NlgHCPepY |BOM-116 (XLSX)]]
  * [[https://www.factorymation.com/ShopAll-Pushbuttons-Indicators?Category_=22mm-Pilot-Devices&Item_Type=Contact-Blocks,Knob-Selector-Switch,Lever-Selector-Switch|Alternate selector switch choice]]

<html><iframe width="950px" height="600px" src="https://docs.google.com/spreadsheets/d/1_wC8IrVGSBzF0N8M5elPFTP66rg2xVx9F6NlgHCPepY/pubhtml?gid=0&amp;single=true&amp;widget=true&amp;headers=false"></iframe></html>
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