EGSA Automatic Transfer Switch Function 5

Question 1

What type of overcurrent protection is typically required ahead of an ATS in a distribution system?

Accepted Answer

Coordinated overcurrent protection sized per NEC 230.95 and ATS WCR rating

Answer

Overcurrent protection upstream of the ATS must be coordinated with the ATS withstand and closing rating to ensure the protective device clears faults before the ATS is damaged.

Question 2

Which NFPA standard governs the testing and maintenance intervals for ATS equipment in health care facilities?

Accepted Answer

NFPA 99

Answer

NFPA 99 (Health Care Facilities Code) establishes inspection, testing, and maintenance requirements for ATS equipment in hospitals and other health care occupancies.

Question 3

What is the purpose of 'peak shaving' mode in an advanced ATS controller?

Accepted Answer

To transfer critical loads to the generator during utility peak demand periods to reduce utility demand charges

Answer

Peak shaving mode uses the ATS to transfer loads to the generator during utility peak demand windows, reducing the facility's metered peak demand and lowering demand charges on the utility bill.

Question 4

What is a 'static transfer switch' (STS) and how does it differ from a mechanical ATS?

Accepted Answer

An STS uses solid-state thyristors (SCRs) to transfer load in less than one electrical cycle with no moving parts

Answer

A static transfer switch uses silicon-controlled rectifiers (SCRs) to switch between sources in under one AC cycle (< 4 ms at 60 Hz), far faster than mechanical ATS devices, with no physical contact wear.

Question 5

When sizing an ATS, which load characteristic most critically affects the ATS interrupting capability requirement?

Accepted Answer

Available short-circuit current at the ATS line terminals

Answer

The available short-circuit current at the ATS terminals determines the required interrupting and withstand ratings; the ATS must withstand fault current until upstream overcurrent devices operate.

(EGSA) Electrical Generating Systems Association Certified Practice Test

(EGSA) Electrical Generating Systems Association Certified Practice Test

EGSA Automatic Transfer Switch Function 5