Transformer Technical FAQ

Transformers Technical FAQ

See the answers to some common questions about transformers you may have.

How do I size a transformer for mixed single and three phase loads?

Answer: Example : 480v 3 phase supply wanting to run 100 amps @ 208v 3 phase as well as 2p c, 20 amp circuits per line @ 120v single phase.

Step 1: *Calculate out the single phase load KVA needs.

120v x 40a (2 - 20 amps circuits) /1000 = 4.8 KVA per line x 3 (3 lines of this) = 14.4 kva total for single phase loads

Step 2: Calculate 3 phase kva load.
208v x 100 x 1.732 /1000 = 36.03 kva

Step 3: Add the total KVA together.
36.03 + 14.4= 50.43 KVA of load

Step 4: Select appropriate size of transformer.

Make sure to take into account local codes and typical sizing recommendations to leave 20-30% of overhead above needed KVA select size of transformer.

50.43 x 1.3 = 65.56 kva suggested size (standard sizing that meeds this requirement is a 75 kva transformer)

(Other standard sizes - 3, 6, 9, 15, 30, 45, 75, 112.5, 150, 225, 300, 500, 750, in for larger sizes)

*Ideally, all single phase loads are balanced across all three lines. If they are not balanced, use the highest amps per line for calculation.

How do I connect my wires to the wire in a Buck Boost transformer?

Answer: When connecting a larger wire to a smaller wire there are several options:

• Use ring terminals and bolt them together.
• Use a Mechanical Lug and tighten them together.*
• Crimp them together with a Parallel connector.*
• Solder them together.

*These methods work best if you wrap the stripped section of the smaller wire around the stripped section of larger wire to help ensure a solid connection.

Can I use a TEMCo Euro transformer for alternate voltages?

Answer: Yes, The Euro Plus/Standard Series of transformers are very versatile. Not only do they have multiple input (504, 480, 456, 240, 208) and output (380, 400, 415) voltages for standard voltages, you can also use these variations to get to less standard configurations by using the output voltages as extra taps.

Calculation: (On site voltage / Primary tap voltage) x Secondary Tap Voltage = Output Voltage

Example 1: You need to power a machine at 400V, but your building's 480V is coming in high at 530V. Use the 504V input top and set the output up for 380V. When you over feed the primary with your 530V, the secondary will be 400V.

(530 / 504) x 380 = 399.6v

Example 2: Your building's 240V input is coming in low at 220V and your machine needs 380V. Use the 240V tap on the primary and set the secondary up for 415. When you underfeed the primary, your output will be 380V.

(220 / 240) x 415 = 380.4v