If you work in the HVAC industry, then you might already know that they use Class 2 control transformers to lower the voltage to 30 volts or less. This is with a power rating of 100VA or less. The essence of doing that is to allow HVAC professionals run low voltage wiring outside of an enclosure without electrical conduit.
By now you should be aware that the transformer power is rated by VA capability. The VA should be large enough to handle the total control power requirements. So, a high enough VA should be selected. However, not everyone understands what it takes to properly size a transformer.
While you might have easy access to a transformer calculator, it doesn’t mean you will get done with everything hassle-free. To ensure you have a smooth ride, you should first select the primary voltage. If the primary voltage is 208v, care should be taken to wire only to the 208V primary tap.
If at all the primary voltage is 240V, care must be taken to wire only to the 240V primary tap. 208V wired to the 240V tap results in low secondary voltage. This will cause contractor, relay chatter or failures. That’s a situation you never want to put yourself in at any given time. No wonder you should this when installing 208/240 volt package equipment.
You might not know this, but transformers are designed to fail if a short in the control or secondary side occurs. If your transformer fails, there is a good chance you have a short or overload somewhere in the control circuit. The good news is you can find and repair it before replacing the transformer.
Either way, you should take it upon yourself to better understand how a transformer calculator works. There is no way you can get the sizing right if you struggle with such simple calculations. Luckily, this information is readily available online from the comfort of your home. You can even choose to enlist help from electrical experts to avoid the hustle and bustle that accompanies starting your search from scratch.