Free TN-LLE Service and Feeder Sizing Questions and Answers

Question 1

What is the minimum ampacity for feeder conductors supplying a continuous load of 90 amps and a noncontinuous load of 40 amps?

Accepted Answer

152.5A

Answer

According to NEC 215.2(A)(1), feeder conductors must be sized to carry the noncontinuous load plus 125% of the continuous load. The calculation is (90A x 1.25) + 40A = 112.5A + 40A = 152.5A.

Question 2

Per NEC 230.71(B), what is the maximum number of service disconnects allowed to be grouped in a single location for each service?

Accepted Answer

Six

Answer

NEC 230.71(B) explicitly limits the number of service disconnecting means to a maximum of six for each service. This rule allows for a 'six-handle rule' where up to six switches or circuit breakers can serve as the service disconnect without a single main.

Question 3

According to NEC 230.70(A)(1), the service disconnecting means shall be installed at a readily accessible location:

Accepted Answer

Either outside or inside nearest the point of entrance

Answer

The code requires the service disconnect to be located where it can be accessed quickly in an emergency. This must be either outside the building or inside nearest the point where the service conductors enter.

Question 4

A 120/240V single-phase service for a dwelling unit has a calculated load of 95 amps. What is the minimum standard service size that can be installed according to NEC 230.79(C)?

Accepted Answer

100A

Answer

NEC 230.79(C) states that for a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire. Even though the calculated load is 95A, the minimum service size permitted for a modern dwelling is 100A.

Question 5

A feeder is installed to supply a subpanel in a detached garage. Which of the following is required for the feeder?

Accepted Answer

It must include an equipment grounding conductor.

Answer

NEC 215.6 requires that a feeder supplying a separate building include an equipment grounding conductor for grounding the non-current-carrying metal parts of equipment. This ensures a low-impedance path for fault current back to the source.

TN LLE - Tennessee Limited Licensed Electrician Practice Test

TN LLE - Tennessee Limited Licensed Electrician Practice Test

Free TN-LLE Service and Feeder Sizing Questions and Answers