What is the difference between wye and delta connections?

Are you talking about 3 phase motors?? If so, here's the difference....

Let's first look at Y (wye)(star) connection. We are going to pay attention to just one pair of supply wires. You have a supply voltage coming to a pair of motor windings connected in series. So right here, you can tell, you have voltage divided between the two windings. Also, the current will be lower because of series resistence/reactance. Because of it, you'll consume less power but get less torque.

Now, look at delta connection. You have a supply voltage coming into a single motor winding. Right away, you can tell, the whole supply voltage is applied across this single winding. You get more current flowing through it as well. As such, you consume more power, but also you get more torque.

It is common that in 3 phase and heavy loaded motor hookup, a switch star-delta is connected, so you'll first turn to delta and get it moving, then switch to star to keep running and consume less power.

If this is not about motor, consider the voltage across any two wires and current.

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