Week 4

Question 1

What is the power leg voltage in a 120/240 3ph service?

Answer 1

208 volts

Question 2

WYE or DELTA? 120/208

3 ph service

Answer 2

WYE

Question 3

In a WYE-WYE bank, what must be done to the H2s on each transformer?

Answer 3

Tie them together and connect to neutral

Question 4

In a WYE-WYE bank, why is it important to parallel the secondary windings?

Answer 4

To get the full kVA rating from the transformer

Question 5

What is the hot-leg-to-hot-leg voltage (p-p) in a standard 120/208 3ph service?

Answer 5

208 volts

Question 6

How many “power” transformers are there in a closed-DELTA bank?

Answer 6

2

Question 7

What must be done to the secondary coils in a DELTA-WYE bank?

Answer 7

They must be paralleled; AC-BD

Question 8

In a 240 3ph-3wire service, what happens if one phase gets grounded?

Answer 8

Nothing. It becomes a corner ground, and the 3-phase service is still delivered. You can ground one time at any point in the service.

Question 9

WYE or DELTA? 240/480

3 ph service

Answer 9

DELTA

Question 10

What is the power-leg-to-hot-leg voltage in a 120/240 3ph service?

Answer 10

240 volts

Question 11

What does “Alley-Cat, Bad-Dog” mean?

Answer 11

When paralleling the windings for a WYE secondary, open the lid and connect A and C together to X1, and then B and D together to X2.

Question 12

WYE or DELTA? 277/480 3 ph service

Answer 12

WYE

Question 13

In a WYE-WYE bank, what must be done to the X2s on each transformer?

Answer 13

Tie them together and connect to neutral

Question 14

In a WYE-DELTA bank, what must be done to the H2s on each transformer?

Answer 14

They must be tied together, but not grounded or connected to neutral