Question

6. You are an electrician working in an industrial plant. You are building a motor control cabinet that contains six motor starters and six pilot lamps. All control components operate on 120 volts AC. Two of the motor starters have coil currents of 0.1 amperes each and four have coil currents of 0.18 amperes each. The six pilot lamps are rated at 5 watts each. The supply room has control transformers with the following rating (in volt-amperes):
75, 100, 150, 250, 300, and 500.

Which of the available control transformers should you choose to supply the power for all the control components in the cabinet?

Answer 1

Answer:

It's indeed safer to suggest a 150 VA transformer. Following table however is the clarification given.

Explanation:

For 2 motors with 0.1 A, the Power will be:

P = $2\times 120\times 0.1$

  = $24 \ W$

For 4 motors with 0.18 A, the Power will be:

P = $4\times 120\times 0.18$

  = $86.4 \ W$

As we know, for 6 pilot lamps, the power is "5 W".

So,

The total power will be:

⇒ P = $24+86.4+5$

       = $115.4 \ W$

Now,

Consider the power factor to be "0.95"

VA of transformer is:

= $PF\times Power$

= $115.4\times 0.9$

= $109.63 \ VA$