Careful With That 40VA Transformer

September 5, 2018

A 40VA transformer is rated for 40 VA or volt-amps on the secondary.

For a typical 24 volt secondary, this is simply using Watt's law to calculate amperage. (For more information on Watt's or Ohm's laws, please check out this article HERE.)

40 ÷ 24 = 1.666666 ∞ (round up to 1.67 already)

So, you cannot place more than 1.67 amps of constant load on the transformer without overloading it.

Many accessories use 24-volt power, such as zoning systems, UV lights, alarms, etc.

The common UV light pictured above uses 0.65 amps. If you connected to the existing transformer, that would leave only 1.01 amps for the system controls.

It is generally a safer bet to either add in an additional accessories transformer or upsize the existing transformer to 60 or 75 VA.

When adding an additional transformer, make sure it either has an internal fuse or that you add a fuse inline to protect the transformer and connected devices.

—Bryan

#overload #transformer #uv #va

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HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this episode of the HVAC School podcast, Bryan welcomes back Jim to discuss the groundbreaking SureSwitch contactor technology from Copeland. This isn’t just another incremental improvement – it’s a complete reimagining of how contactors should work in modern HVAC systems. Jim brings his expertise and even demonstrates the technology with a special cutaway camera setup, giving listeners and viewers an inside look at this innovative solution.

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Key Topics Covered

· Contactor Evolution and Industry Innovation

o Historical perspective on contactor design changes from heavy-duty to cost-optimized

o Why the HVAC industry needed to innovate forward rather than continue cost-cutting

· Multi-Voltage Flexibility

o Single contactor handles 24V, 110V, and 240V coil applications

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o Optical sensor monitoring system for detecting electrical arcing

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o Internal power supply eliminates dependency on weak control voltage

o Magnetic latching system prevents contact bouncing during brownout conditions

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o Brownout protection with automatic voltage monitoring (184V threshold)

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o Short cycle timer protection working independently of thermostat timers

· Installation and Compatibility Considerations

o Compatible mounting holes with standard contactors

o Proper crankcase heater wiring configurations

o Training considerations for technicians adapting to new terminal layout

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o Applications in high-end residential and commercial installations

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