CME Electrical Systems Design & Installation 3

Question 1

When installing a 1000 kVA, 480-208Y/120V transformer, what minimum clearance must be maintained from combustible material per NEC 450.21(A)?

Accepted Answer

No clearance required if ventilated

Answer

NEC 450.21(A) permits dry-type transformers rated 112.5 kVA or less to be installed with no separation from combustible material if enclosed; larger units require 12 inches or fire-resistant construction.

Question 2

Per NEC 220.87, what method allows an existing service or feeder to be evaluated for additional load without full load calculation?

Accepted Answer

Measured demand method using 12-month data

Answer

NEC 220.87 permits using the maximum demand data from the previous 12-month period measured at the meter to determine available capacity for new loads.

Question 3

In a switchboard installation, what is the minimum headroom required in front of the equipment per NEC 110.26(A)(3)?

Accepted Answer

6.5 feet

Answer

NEC 110.26(A)(3) requires a minimum headroom of 6.5 feet (2.0 m) in front of electrical equipment 600V or less.

Question 4

A photovoltaic system is connected to a 200A residential service panel. Per NEC 705.12(B)(3), what is the maximum breaker size allowed for the PV interconnection?

Accepted Answer

40A

Answer

NEC 705.12(B)(3) limits the PV supply breaker to 120% of the bus rating minus the main breaker; for a 200A panel with 200A bus, maximum PV breaker = (200A × 120%) - 200A = 40A.

Question 5

What is the purpose of an equipment bonding jumper in an electrical system per NEC Article 250?

Accepted Answer

Bond non-current-carrying metal parts to the grounding system

Answer

Equipment bonding jumpers connect non-current-carrying metal parts (conduit, enclosures, equipment frames) to the equipment grounding conductor to ensure fault current can flow safely.

(CME) Certified Master Electrician Practice Test

(CME) Certified Master Electrician Practice Test

CME Electrical Systems Design & Installation 3