C7 Optical Fiber Cable Installation (NEC Article 770)

Question 1

What is the key difference between single-mode (OS2) and multimode (OM3/OM4) optical fiber that determines which type is used for a given installation?

Accepted Answer

Single-mode supports longer distances with a smaller core; multimode supports shorter distances with a larger core

Answer

Single-mode uses plastic fiber; multimode uses glass fiber

Answer

Single-mode is used for audio signals; multimode is used for data

Answer

Single-mode requires no connectors; multimode requires fusion splicing

Question 2

Per NEC Article 770, optical fiber cables installed in a riser (vertical shaft between floors) must be listed as which fiber cable type?

Accepted Answer

OFNR (optical fiber nonconductive riser)

Answer

OFN (optical fiber nonconductive)

Answer

OFNG (optical fiber nonconductive general purpose)

Answer

OFNP (optical fiber nonconductive plenum)

Question 3

When installing optical fiber, the minimum bend radius during and after installation must be respected. What is the general rule for the minimum post-installation bend radius of a typical indoor fiber optic cable?

Accepted Answer

No smaller than 10× the cable's outer diameter

Answer

No smaller than 1× the cable's outer diameter

Answer

No smaller than 30× the cable's outer diameter

Answer

Bend radius is not restricted for fiber since glass is flexible

Question 4

An OTDR (Optical Time Domain Reflectometer) is used after a fiber optic installation to:

Accepted Answer

Locate faults, measure splice loss, and verify end-to-end fiber attenuation

Answer

Verify copper continuity end-to-end

Answer

Test the PoE voltage on fiber-connected switches

Answer

Certify the fiber meets Category 6A standards

Question 5

What safety precaution is most critical when working with optical fiber, particularly during cleaving and splicing operations?

Accepted Answer

Ensuring all fiber shards are collected and properly disposed of — never left on surfaces or floors

Answer

Wearing rubber gloves to prevent electrical shock

Answer

Wearing arc flash PPE rated at 40 cal/cm²

Answer

Using only plastic-jacketed tools to avoid conductor damage

Question 6

A fiber optic link budget calculation shows a maximum allowable loss of 3.0 dB for a horizontal run. The installed link has two connectors (0.5 dB each) and one fusion splice (0.3 dB). What is the maximum allowable fiber attenuation for the cable segment itself?

Accepted Answer

1.7 dB

Answer

1.2 dB

Answer

2.3 dB

Answer

3.0 dB