Question 1

Transformers may be operated in parallel and protected as a unit if their electrical characteristics are similar.

Accepted Answer

Transformers that have similar electrical characteristics can be operated in parallel and protected as a unit. This means that they must have the same ratios of voltage to turns and the same phase shift between the primary and secondary windings. This ensures that the total power output of the transformers is divided equally among them and that there are no imbalances that could cause damage or instability.

Question 2

How does the Code define a secondary tie?

Accepted Answer

The Code Article 450.6 defines a secondary tie as a circuit operating at 600 volts or less between phases. This circuit connects two power sources or power supply points such as the secondaries of two transformers.

Question 3

The fire hazard potential of oil-insulated transformers is greater than that of askarel-insulated transformers.

Accepted Answer

Oil is a flammable substance and thus increases the fire hazard potential of transformers. Askarel, on the other hand, is a non-flammable but toxic substance. Therefore, the fire hazard potential is greater for oil-insulated transformers compared to askarel-insulated transformers.

Question 4

According to Code Article 450.11, each transformer shall be provided with a nameplate including what information?

Accepted Answer

The answer of According to Code Article 450.11, each transformer...

Question 5

What should dry-type transformers installed outdoors have?

Accepted Answer

The answer of What should dry-type transformers installed outdoors have?...

Question 6

For a transformer of 600 volts or less, overcurrent protection is permitted.

Accepted Answer

According to NEC 450.3, overcurrent protection is permitted for transformers rated at 600 volts or less.

Question 7

When load taps are made in the tie circuit between transformers, the current-carrying capacity shall not be more than a stipulated percentage (200%) of the rated secondary current of the largest capacity transformer connected to the secondary tie.

Accepted Answer

The National Electrical Code (NEC) does not specify a 200% limit for the current-carrying capacity of load taps in the tie circuit between transformers. The actual requirements for transformer connections, including taps, are based on ensuring the system's safety and functionality without a specific percentage limit like 200% of the rated secondary current. The NEC and other standards focus on proper sizing based on load calculations, protection, and other electrical parameters.

Question 8

When transformers have similar electrical characteristics, they divide the load in proportion to their ____________________.

Accepted Answer

The answer of When transformers have similar electrical characteristics, they...

Question 9

The ____________________ is an indication of how much opposition the transformer offers to AC current.

Accepted Answer

The answer of The ____________________ is an indication of how...

Question 10

Describe "buck" and "boost" transformers.

Accepted Answer

The answer of Describe "buck" and "boost" transformers....

Question 11

The Code requires that instrument potential transformers have ____________________ if installed indoors or enclosed.

Accepted Answer

The answer of The Code requires that instrument potential transformers...

Question 12

Article ____________________ of the NEC covers the minimum requirements of the installations of electrical wiring and equipment within public or private buildings and their premises.

Accepted Answer

The answer of Article ____________________ of the NEC covers the...

Question 13

Transformers are required to have a disconnecting means located in sight from the transformer or in a remote location if the transformer is a class 2 or class 3 transformer.

Accepted Answer

Class 2 and Class 3 transformers are low voltage and low power, typically used for control circuits and do not require a disconnecting means in sight or remotely.

Question 14

What is an askarel-insulated transformer?

Accepted Answer

The answer of What is an askarel-insulated transformer?...

Question 15

The NEC requires that the metal cases and tanks of transformers be ____________________.

Accepted Answer

The answer of The NEC requires that the metal cases...

Quiz 22: National Electrical Code of Prime Concern Requirements for Transformer Installations