# Transformer Question



## travis13 (Oct 12, 2012)

Hey guys, ran into a few of these transformers mounted on some 480V pole lights today. I was going to ask my teacher tomorrow if I was reading the diagram correctly, but figured I would just ask you guys. 

On the primary side with 480V, you wire nut H2-H3 together and connect one hot to H1 and one hot to H4?

On the primary side with 240V, you wire nut H1-H3 together with one hot and wire nut H2-H4 together with one hot?

The secondary side is what confuses me more. If you wire nut X2-X3 are you getting 120V on X1 and 120V on X4 and together is where you get 240V?

If you connect X1-X3 and X2-X4, is X1-X3 your 120V and X2-X4 your neutral and should that neutral be bonded to ground there? 

What does it mean under "Secondary Connection" Volts: 120/240 Leads on X1-X4?


----------



## Big John (May 23, 2010)

You described it just fine.

If you want a 240V output connection that can also produce 120V you connect to X1 and X4. In order to get 120V, you would connect between either end and X2/X3, and once you ground that midpoint that becomes your neutral connection.

Remember when looking at multi-tap transformer connections, the voltage is determined by the number of winding-turns you put in series and the amperage is determined by how many windings you put in parallel.


----------



## travis13 (Oct 12, 2012)

Ok so X1 and X4 would be 120V each and X2-X3 (which are connected) would be your neutral? If so, should X2-X4 have a bonding jumper to ground?


----------



## Big John (May 23, 2010)

X1 to X2 is 120V. X3 to X4 is 120V. When you connect them you get 240V from end to end because you're putting those windings in series. They add up just like voltage adds up when putting AA batteries in series.

In that configuration, X2 and X3 are your neutral, yes they should be grounded.


----------



## travis13 (Oct 12, 2012)

Thanks so much. So basically 90% of the time that would be the way they are wired I'm assuming? What would be the purpose of the way that is just for 120V? X1-X3 and X2-X4


----------



## Big John (May 23, 2010)

See where says that's a 750 volt-amp transformer in the upper left of the nameplate? That number is the same on both sides of the windings. You put 750 volt-amps in the high-side and you're gonna be drawing 750 volt-amps out the low side. This is true of all transformers (minus small efficiency losses).

You get volt-amps on a single-phase transformer exactly like it sounds: Multiply volts times amps.

So if changing the winding configuration on the low side changes the voltage, what do you think is happening to the amperage?


----------

