Consider G.657.A2 and G.657.B3 when the project calls for careful review of bend performance, particularly in constrained access or indoor routes. The B3 reference on this site includes a 5 mm radius test, while the A2 reference lists other radius conditions. These are published bare-fiber test conditions, not universal minimum installation radii for finished cables. Compare the exact wavelength, turns and allowed loss, then review mode field diameter, coating and other product limits. Before choosing B3 simply because it has a smaller test radius, confirm the required interfaces and the complete offered specification. Ask the cable designer or supplier to identify the conditions the final cable must meet and the evidence needed for approval.
Reference specification comparison
Values below are the same supplier reference data shown on the product pages. Different test conditions occupy separate rows; “Not listed” means the cited product table does not provide that entry.
| Parameter / condition | G.657.A2 | G.657.B3 |
|---|---|---|
| Attenuation at 1310 nm | ≤ 0.350 dB/km | Not listed in reference |
| Attenuation at 1550 nm | ≤ 0.210 dB/km | ≤ 0.210 dB/km |
| Cladding diameter | 125 ± 0.7 μm | 125 ± 0.7 μm |
| Coating diameter (table value) | 242 ± 7 μm / 200 ± 10 μm | Not listed in reference |
| Mode field diameter at 1310 nm | 8.6 ± 0.4 μm | 8.6 ± 0.4 μm |
| Macrobend: 7.5 mm radius, 1 turn, 1550 nm | ≤ 0.40 dB | Not listed in reference |
| Coating diameter | Not listed in reference | 242 ± 7 μm |
| Macrobend: 5 mm radius, 1 turn, 1550 nm | Not listed in reference | ≤ 0.15 dB |
| Macrobend: 5 mm radius, 1 turn, 1625 nm | Not listed in reference | ≤ 0.45 dB |
A smaller test radius is one part of the review
The listed B3 product includes a one-turn, 5 mm radius macrobend limit at 1550 nm and another at 1625 nm. The A2 table includes one-turn results at 10 mm and 7.5 mm at 1550 nm. Each line is meaningful only with all of those conditions attached.
Do not plot these limits as a measured loss curve or interpolate an unlisted radius. They describe source specifications under different conditions, not an experiment on a shared sample. Request the specific required test condition for a controlled comparison.
Keep geometry and interfaces in the decision
Review mode field diameter, cladding, coating and attenuation for the actual offered products. If a project joins a proposed fiber to existing material, confirm the joining and acceptance requirements instead of assuming that the grade names alone establish an acceptable connection.
The reference information here is intended to organize questions for the supplier. A final choice should use the complete offered specification and the qualification requirements of the network and cable design.
Translate indoor routing into requirements
Describe the enclosure, route and cable construction that create the space constraint. Ask for the finished cable installation and handling limits, including any conditions related to tension or routing. Keep these instructions separate from the bare-fiber optical test table.
Choose the product that meets the defined requirements with confirmed supporting information. If A2 already addresses the design requirements, a different grade is not automatically necessary. If a smaller-radius optical requirement is specified, discuss the relevant B3 reference and the exact offered option.
What to confirm
- Required radius, turns and wavelengths
- Loss limits under the required conditions
- Geometry, coating and joining requirements
- Cable construction and installation instructions
- Batch evidence for the offered grade
Frequently asked questions
Does the 5 mm test mean I can bend a finished cable to 5 mm?
No. It is a bare-fiber reference test condition. The finished cable has its own construction-dependent handling and installation limits.
Is B3 automatically a replacement for A2?
No automatic substitution is established here. Confirm optical, geometry, joining and cable-design requirements against the offered specification.
Why does wavelength matter in the bend table?
The source defines each result or limit at a particular wavelength. Preserve that condition and do not assume an unlisted wavelength has the same limit.
Sources & reference context
This guide is published by OpticFiberHub and summarizes the supplier literature identified below with editorial purchasing guidance. Product values describe the source grade, not a measured result or a conformity guarantee for a new order.
- G.657.A2 reference specifications — Jiangsu Nanfang Optical Fiber Product Manual, pages 7–8.
- G.657.B3 reference specifications — Jiangsu Nanfang Optical Fiber Product Manual, pages 9–10.
Quality & technical resources explains source selection, translated documents and the limits of historical batch records. Request the current specification and applicable records for the actual offered material.
Further terminology reference: The Fiber Optic Association: optical fiber fundamentals.
Single-mode standard references: ITU-T G.652 and ITU-T G.657. Supplier reference values above must not be mistaken for a reproduction of every requirement in those Recommendations.
