What are the difference: indoor cable, outdoor cable, and indoor outdoor optical cable?
According to the applicable scenarios, optical cables are divided into several categories: outdoor, indoor, indoor and outdoor cable. What are the differences between these categories of optical cables?
Outdoor cable
The outdoor cables that we come into contact with the most in communication engineering are usually GYTA and GYTS cables. The models of outdoor cables start with GY. To meet the needs of outdoor environments, outdoor optical cables generally have good mechanical performance and commonly use moisture-proof and water-resistant structures. To improve the mechanical performance of optical cables, outdoor fiber optic cables usually use metal components such as metal center reinforcements and metal armor layers. The plastic coated aluminum or steel strip protective layer outside the cable core has good moisture-proof performance. The waterproofing function is mainly achieved by adding fillers such as oil paste or water-resistant yarn in the cable core.
The outdoor cable sheath is generally made of polyethylene (PE). Polyethylene sheath has excellent physical properties, corrosion resistance, long service life, good toughness, etc., but it is not flame retardant. Additives such as carbon black are usually added to the sheath to enhance its UV resistance, so the outdoor cables we see are often black.
Indoor cable
Indoor cables are generally non-metallic structures, and aramid is often used as reinforcement for the cables, which makes them more flexible. The model of indoor optical cables starts with GJ.
The mechanical performance of indoor cable is lower than that of outdoor cable. For example, the allowable tensile and compressive forces of indoor vertical cable with better mechanical performance vs outdoor pipelines and non self-supporting overhead cables with weaker mechanical performance, as shown in Table 1.
| Cable type | Min. allowable tension(N) | Min. allowable crush(N/100mm) | |||
| Short term | Long term | Short term | Long term | ||
| Indoor(vertical wiring) | ≤12 cores | 660 | 200 | 1000 | 300 |
| >12 cores | 1320 | 400 | 1000 | 300 | |
| Outdoor（duct,non self-supporting aerial） | 1500 | 600 | 1000 | 300 | |
Indoor cables generally do not need to consider moisture resistance, water resistance, or UV protection, so the structure is much simpler than outdoor cables. The colors of indoor cable sheaths are more diverse, usually corresponding to the types of optical fibers, as shown in Table 2.
| Fiber type | Sheath color | |
| Single mode | G.652 | Yellow |
| G.657 | Yellow or green | |
| Multimode | OM1 | Orange |
| OM2 | Orange | |
| OM3 | Aqua | |
| OM4 | Purple | |
| OM54 | Lemon green | |
Compared to outdoor cables, indoor cables have shorter segments and often require termination at both ends. Therefore, indoor cables often appear in the form of jumper or pigtails, as shown in Figure 3. The middle part of the patch cord is the indoor cable. To facilitate termination, the core of indoor cables usually uses tight buffer with a diameter of 900um (outdoor cables usually use colored bare fiber with a diameter of 250um)
SC patch cord
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FTTH patch cord
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Armored patch cord
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But indoor cable are required be to have a certain degree of flame retardancy. Depending on the flame retardant level, different flame retardant materials are used for the cable sheath, such as PE,PVC,LSZH,TPU,OFNR, etc
Indoor Outdoor Cable
Indoor outdoor cable, also known as indoor and outdoor universal cable, is a type of optical cable that is introduced from outdoors to indoors. It can be used both outdoors and indoors.The models of indoor and outdoor optical cables start with GJY. For example, the self-supporting drop cable cable with model GJYXFCH, is a type of indoor and outdoor cable, as shown in Figure 5.
Indoor outdoor cables need to have the advantages of moisture resistance, water resistance, good mechanical performance, and UV protection of outdoor cable, as well as the flame retardant and electrical disconnection characteristics of indoor cables. The indoor outdoor cables have made the following improvements on the basis of outdoor cables:
(1) The sheath is made of flame-retardant material;
(2) The structure does not contain metal components or uses metal reinforcement components that are easy to electrically disconnect (such as suspension wires for self-supporting optical cables);
(3) Adopting dry water blocking measures to prevent grease dripping when the optical cable is vertically laid. In conventional communication engineering, indoor and outdoor optical cables are rarely used, except for FTTH indoor optical cables. However, in comprehensive cabling engineering, the use of indoor and outdoor optical cables is quite common due to the widespread occurrence of optical cables entering indoors from outdoors. Figure 6 shows two commonly used indoor and outdoor fiber optic cable structures in comprehensive cabling engineering. The fiber optic cable in the left figure is a loose tube structure, while the one in the right figure uses a tight fitting fiber optic cable.
Can outdoor cables be used indoors?
In conventional communication engineering, due to the vast majority of optical cables are laid outdoors, the indoor part is often only a few dozen to tens of meters long. It is very common for outdoor cables to be directly laid indoors without changing the model. Even some core computer rooms’ incoming cables and communication cables in different floors also use outdoor cables, which poses great hidden dangers to the fire safety of buildings. In the existing engineering specifications, there is no specification that allows the direct use of outdoor cables indoors when it comes to the selection of indoor cables. The clauses regarding indoor fiber optic cable selection in some specifications are shown in Table 3.
| Standard Number | Specification | Clause Name | Clause Content |
| GB 51158-2015 | Design Specification for Communication Line Engineering | 4.2.3-5 | For indoor and outdoor optical cables, it is recommended to use non combustible materials for the outer protective layer structure |
| GB 51158-2015 | Design Specification for Communication Line Engineerin | 6.6.2-1 | Indoor optical cables should use non combustible outer sheath optical cables; When outdoor optical cables are directly introduced into the computer room, strict fire prevention measures should be taken. |
| GB 50311-2016 | Design Specification for Integrated Cabling System Engineering | 9.0.2 | The cables and optical cables selected for the comprehensive cabling engineering design should be comprehensively considered from the height, area, function, importance, and other aspects of the building, and the corresponding level of flame-retardant cables should be selected. |
| GB 51348-2020 | Electrical Design Standards for Civil Buildings | 13.9.3 | The communication cables and optical cables of the comprehensive cabling system should be selected based on the importance of the building, and the corresponding combustion performance level of the communication cables and optical cables should comply with the provisions of Table 13.9.3. |
Suggestions for selecting optical cables in buildings
From Table 3, it can be seen that the national standard has very clear requirements for flame retardancy of indoor cables, and non flame retardant outdoor cables are not allowed to be used indoors. Fire accidents caused by improper cable selection have occurred repeatedly both domestically and internationally. The power cables and comprehensive wiring cables in buildings are all flame-retardant cables. Therefore, it is recommended to:
(1) Fiber optic cable sections that require both outdoor and indoor deployment should use indoor outdoor fiber optic cables, such as incoming fiber optic cables and building entry fiber optic cables;
(2) All fiber optic cable sections installed indoors should use indoor or outdoor optical cables
(3) Indoor and outdoor optical cables and indoor optical cables with corresponding flame retardant levels should be used according to GB 51348.
