These days, multiple power sources can be present in a single building or structure. Many of these are what the National Electrical Code (NEC) calls separately derived systems. Transformers, batteries, fuel cells and generators can supply these systems. An electrical system produced by a generator is either required to be grounded as a separately derived system or it is not, and the key to this is the transfer equipment.
Created by: Michael Johnston
1. If a transfer switch is installed with a generator, and it includes a switching action in the grounded conductor, the generator must be grounded as a separately derived system.
2. If an auxiliary (supplementary) grounding electrode (ground rod) is installed for a generator, what is the maximum size grounding electrode conductor from the frame of the generator to the ground rod?
A. 8 AWG copper
B. 6 AWG copper
C. 2 AWG copper
D. 12.5 percent of the largest ungrounded system conductor supplied by the generator
3. What size copper grounding electrode conductor is required for a generator’s separately derived system, if the grounding electrode is a metal water pipe and the largest ungrounded derived phase conductor supplied by the system is 750 kcmil copper?
A. 4 AWG
B. 2 AWG
C. 1/0 AWG
D. 2/0 AWG
4. A generator is grounded as a separately derived system, and the largest output ungrounded derived phase conductor is 1,000 kcmil copper (two 500 kcmil copper conductors in parallel). What is the minimum size required for a copper system bonding jumper?
A. 1 AWG
B. 1/0 AWG
C. 2/0 AWG
D. 3/0 AWG
5. The feeder from a generator routed to a building is sized at 250 kcmil copper and is protected by a 225-ampere (A) breaker installed on the generator. What minimum size copper equipment grounding conductor is required from the generator to the transfer equipment in the building or structure served?
A. 2 AWG
B. 3 AWG
C. 4 AWG
D. 6 AWG
6. If a generator is installed with transfer equipment that does not switch the grounded conductor, the generator system is required to be grounded in accordance with 250.30(A).
7. A generator is installed using 400 kcmil copper ungrounded phase conductors. If no overcurrent protective device is installed, the copper equipment-bonding conductor installed from the generator to the transfer equipment in the building must not be smaller than _____ AWG copper.
8. An autotransformer is a separately derived system and must be grounded in accordance with 250.30(A).
9. A panelboard is supplied by the secondary of a transformer separately derived system. The size of the largest ungrounded feeder conductor routed from the transformer to the 200A overcurrent device in the panelboard is 4/0 copper. What is the minimum size required for the supply-side bonding jumper installed with the feeder conductors?
A. 6 AWG
B. 4 AWG
C. 2 AWG
D. 1/0 AWG
10. A system bonding jumper for a separately derived system is required to be installed at the source enclosure only.