How to Wire a Multi-tap Transformer

August 20, 2019
Tech Tuesday

Every once in a while, in Tech Support, we get a call from one of our customers asking which wires to connect to our multi-tap transformers. This is understandable considering all the wires involved, but luckily the solution is an easy one to remember once you know it.

A large part of being able to figure this out is knowing how your 3-phase incoming power is set up. Typically, they’re in either a delta or wye configuration.

A delta configuration can look something like this:

And a wye configuration can look something like this:

An easy way to remember this is that the delta configuration looks like a delta symbol, and the wye configuration looks like the letter “Y”. The wye configuration also looks a bit like a flux capacitor from Back to the Future if that helps. Please note that not every delta or wye set up will have these voltages, these are just two examples. The main point to get from this is that your incoming power typically has three phases and one neutral. This allows each configuration to provide two to three different voltages. Usually, between neutral and a phase is a smaller voltage, and between two different phases is a larger voltage. Knowing which voltage is between which two wires is key when installing one of our multi-tap transformers.

If you don’t know which wire is which, you can always measure it using your multimeter. Once you know which two wires have the voltage for the tap you want, simply connect one power wire to the wire on our transformer with the voltage tap you want, and the other power wire to the wire on our transformer labeled “Comm”. Then separately insulate each of the unused wires. It’s that easy!

For the sake of clarity let’s do some examples. Take a look at the wiring diagram for our TR50VA015:

Let’s say you want to connect the above delta configuration to our TR50VA015. If you wanted to connect 120 Vac to the primary, you would connect your neutral (WHITE) to the transformer Comm (Blk). Then you would either connect phase A or C (BLACK or BLUE) to the 120 Vac tap on the transformer (Wht). If you wanted to use 240 Vac on the primary, you would take any two of the three phases and connect them to the orange and black wires on the transformer. It doesn’t matter which phase goes to which wire.

For the above wye configuration, you would connect your neutral (GRAY) and any phase to the black and brown wires on the transformer for a 277 Vac primary. Similarly, any two phases on the wye configuration should be connected to the gray and black wires on the transformer for a 480 Vac primary.

Hopefully this clarifies how to wire one of our transformers. As always, if you’re still confused, feel free to call us at Tech Support.

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About the Author

Tym Moore is an Electrical Engineer who hails from the best state of Colorado.
He graduated from Colorado State University in 2017 and moved to Indiana shortly afterward to marry his now wife. Outside of work, Tym spends most of his time driving back home, and complaining about how flat Indiana is.

Be sure to give Tym a call for tech support. He will always do his best to find a solution for you.