Construction Electrician exam: Voltage drop

Key points

• Drop grows with current, conductor length and conductor resistance.
• For a two-wire circuit the current travels out and back, so use twice the one-way length.
• A bigger conductor (smaller AWG number) has lower resistance and less drop.
• Express drop as a percentage of supply voltage to compare it with the code limit.
• Copper has lower resistance than aluminum for the same size.

Study tip

Check the current version of the Canadian Electrical Code for the percentage limits your exam expects.

Try these

1. Doubling a run's length while keeping the same wire and load will:

   1. Halve the drop
   2. Double the drop
   3. Not change it
   4. Quadruple it
   Show answer

   B. Double the drop Drop is proportional to length.

2. To reduce voltage drop on a long run you would:

   1. Use a smaller conductor
   2. Use a larger conductor
   3. Raise the load
   4. Use aluminum of the same size
   Show answer

   B. Use a larger conductor Larger conductors have less resistance.

3. A 6 V drop on a 240 V circuit is:

   1. 1.5%
   2. 2.5%
   3. 4%
   4. 6%
   Show answer

   B. 2.5% 6 / 240 = 2.5%.

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