The short answer: the ampere rating of residential wire in Taiwan depends on two things. One is the wire size (for solid wire, the diameter in mm; for stranded wire, the cross-sectional area in mm²). The other is how the wire is installed (in PVC conduit or metal conduit, how many conductors share one conduit, and how hot the environment is). The official chart is in the appendix tables to Article 25 of the Regulations for Installation of Customer Electrical Equipment (用戶用電設備裝置規則). Below, the wire sizes commonly found in homes are collected into one table, with an explanation of how to use it to work out your own circuits. But remember: replacing wire, changing circuits and adjusting breakers are all work for a qualified electrician. This article only helps you understand the numbers; it is not installation instructions.
Safety warning: Do not replace a breaker that trips often with a higher-rated one, and do not swap thin wire for thicker wire and then raise the protective breaker yourself. The breaker is the last line of protection for the wire. Once it is upsized, the wire can overheat and its insulation can degrade before the breaker ever trips.
Where this chart comes from: check the name of the regulation first
Many web pages still use the old name 屋內線路裝置規則 (the former indoor wiring rules). The current name of this regulation is Regulations for Installation of Customer Electrical Equipment (用戶用電設備裝置規則; formerly 屋內線路裝置規則), and the latest amendment date listed in the national laws and regulations database (全國法規資料庫) is 9 May 2025. The ampacity (安培容量) of conductors is set in Article 25, and the tables are attachments to Article 25:
- Table 25-1 (表二五～一): maximum allowable temperature of conductor insulation (60°C for PVC and rubber conductors, 75°C for heat-resistant PVC and similar, 90°C for cross-linked polyethylene and similar).
- Tables 25-2 to 25-4 (表二五～二 to 表二五～四): ampacity for metal conduit wiring (separate tables for 60°C, 75°C and 90°C).
- Table 25-5 (表二五～五): ampacity for PVC conduit wiring.
- Table 25-6 (表二五～六): correction factors when many current-carrying conductors share one conduit.
- Table 25-7 (表二五～七): correction factors when the ambient temperature is not 35°C.
The Regulations define "ampacity" as the maximum current a conductor can carry continuously under the conditions of use without exceeding the conductor's rated temperature. In plain terms, it is the upper limit of current at which a wire can stay energized for long periods without getting hot enough to damage its insulation.
Two ways to write wire size: "2.0" and "2.0 mm²" are very different
This is the easiest trap when reading drawings. The chart divides conductors into two types:
- Solid wire: one solid copper conductor, given by diameter (mm). The table has three sizes: 1.6, 2.0 and 2.6.
- Stranded wire: many fine strands twisted together, given by cross-sectional area (mm²). The table has 3.5, 5.5, 8, 14, 22, 30, 38 and so on.
So "2.0" on a drawing usually means solid wire 2.0 mm in diameter, not stranded wire of 2.0 mm². The units differ, so the two cannot be compared directly. If a wire size is written without a unit, ask the designer or electrician to add it; that is far cheaper than arguing about it afterward. For how to read other plumbing and electrical markings on design drawings, see how to read plumbing and electrical layout drawings.
The chart: ampacity of conductors in PVC conduit
Most concealed conduit in homes is PVC, so Table 25-5 is the main reference here. The conditions are a maximum allowable insulation temperature of 60°C and an ambient temperature of 35°C. "Number of current-carrying conductors" means how many energized wires are in the same conduit; ordinary outlet or lighting branch circuits use the "3 or fewer" column. With more wires in the conduit, the numbers fall toward the right.
| Type | Size | 3 or fewer (A) | 4 (A) | 5-6 (A) | 7-9 (A) |
|---|
| Solid | 1.6 mm | 13 | 12 | 10 | 9 |
| Solid | 2.0 mm | 18 | 16 | 14 | 12 |
| Solid | 2.6 mm | 24 | 22 | 19 | 16 |
| Stranded | 3.5 mm² | 19 | 16 | 14 | 12 |
| Stranded | 5.5 mm² | 25 | 23 | 20 | 17 |
| Stranded | 8 mm² | 33 | 30 | 25 | 20 |
| Stranded | 14 mm² | 50 | 40 | 35 | 30 |
| Stranded | 22 mm² | 60 | 55 | 50 | 40 |
| Stranded | 30 mm² | 75 | 65 | 55 | 50 |
| Stranded | 38 mm² | 85 | 75 | 65 | 55 |
Source: Table 25-5 (ampacity of conductors for PVC conduit wiring). Solid 1.6 mm wire has an ampacity of only 13 A, which is lower than a 15 A branch circuit, so it must not be paired with a 15 A breaker (the minimum wire size for a 15 A branch circuit in Table 40 (表四○) is solid 2.0 mm). The table also has sizes of 50 mm² and above, which are rarely used in homes and are omitted here. This table also applies to HDPE conduit, non-metallic flexible conduit and non-metallic wireways with a rated temperature withstand of 60°C.
Metal conduit has different numbers; do not mix the tables
Metal conduit wiring has its own Table 25-2 (表二五～二; also 60°C and 35°C). For the same wire size, the numbers in the "3 or fewer" column of the two tables are not the same:
| Wire size | PVC conduit (Table 25-5) | Metal conduit (Table 25-2) |
|---|
| 2.0 mm solid | 18 A | 18 A |
| 2.6 mm solid | 24 A | 27 A |
| 3.5 mm² stranded | 19 A | 19 A |
| 5.5 mm² stranded | 25 A | 28 A |
| 8 mm² stranded | 33 A | 36 A |
| 14 mm² stranded | 50 A | 52 A |
So when you see online claims that "a certain wire size can carry so many amps", first ask: which table does it use, what is the conduit material, and how many wires are in one conduit? Do not rely on numbers that give no conditions.
Ampacity, branch circuit rating and breaker: how the three numbers relate
- Branch circuit rating: determined by the ampere rating of the overcurrent protective device (that is, the breaker) on that circuit. Article 40 states plainly that even if thicker wire with a higher ampacity is used, the branch circuit rating is still determined by the breaker.
- Conductor ampacity: for a branch circuit serving outlets, the conductor ampacity must not be less than the branch circuit rating (Article 40); the same requirement applies to a branch circuit with two or more outlets for portable loads with plug-connected cords (Article 39).
- Upper limit for protective devices: Article 79 requires that the ampere rating of the protective device must not exceed the ampacity of the conductor (except where the Regulations provide otherwise), and specifically lists limits for small wire sizes: 2.0 mm wire must not exceed 15 A, 3.5 mm² must not exceed 20 A, and 5.5 mm² must not exceed 30 A.
Note that Article 79 lists "at most, no more than", not "can be paired up to this size". How large a breaker can actually be used also depends on the conduit material, the number of wires in the conduit, the ambient temperature and the purpose of the circuit, which is why the judgment should be left to an electrician.
Table 40: minimum wire size for branch circuits of 50 A or less
Article 40 provides that for branch circuits rated 50 A or less using metal conduit wiring, Table 40 applies; for non-metallic conduit wiring, or for branch circuits rated above 50 A, the minimum conductor size is selected under Article 25. The content of Table 40 (noted as applying to PVC conductors) is as follows:
| Branch circuit rating | 15 A | 20 A | 30 A | 40 A | 50 A |
|---|
| Minimum branch circuit conductor size | Solid 2.0 mm or stranded 3.5 mm² | Stranded 5.5 mm² | Stranded 8 mm² | Stranded 14 mm² | Stranded 14 mm² |
| Overcurrent protective device | 15 A | 20 A | 30 A | 40 A | 50 A |
| Receptacle rating | 15 A maximum | 15 A or 20 A | 30 A | 40 A or 50 A | 50 A |
When reading the table, note that in the 15 A column it lists solid 2.0 mm wire as the minimum size, while from the 20 A column onward all are stranded wire. This also explains why an older apartment that has only 2.0 mm wire but wants to connect a high-power 20 A appliance needs its circuits re-planned. For the fuller process of rewiring an older home and upgrading the main breaker, see rewiring an older apartment and upgrading the main breaker, and for a practical case of a dedicated kitchen circuit, see planning dedicated kitchen circuits.
Example: using the chart to work out how much a circuit has left
The following is a demonstration of reading the table, not a design basis. The conversion formula is simple: power (W) = voltage (V) × current (A). The Bureau of Standards, Metrology and Inspection (BSMI), Ministry of Economic Affairs (經濟部標準檢驗局) guide to buying extension cords labels an ordinary extension cord as 125 V, 15 A, 1650 W, which is 110 V multiplied by 15 A. Everything below is calculated at 110 V; check your own appliances' nameplates for their actual voltage.
Example 1: a 15 A outlet circuit (2.0 mm solid wire)
- Conductor: Table 25-5, 2.0 mm solid wire, 3 conductors or fewer, ampacity 18 A; breaker 15 A, which does not exceed the conductor's ampacity.
- Maximum circuit power: 15 A × 110 V = 1650 W.
- Continuous load (defined in the Regulations as a maximum current load that may continue for 3 hours or more): Article 38 provides that it must not exceed 80% of the branch circuit rating, which is 12 A, about 1320 W.
- Suppose you want to run a 1200 W electric heater continuously: the current is 1200 ÷ 110 ≈ 10.9 A, below 12 A. On the conductor side, Article 39 requires a factor of 1.25, so 10.9 × 1.25 ≈ 13.6 A, below 18 A, and by the Regulations' method the limit is not exceeded. But this circuit then has only about 120 W of margin left, and adding one slightly larger appliance will trip it.
Example 2: a 20 A dedicated circuit (5.5 mm² stranded wire)
- Conductor: Table 25-5, 5.5 mm² stranded wire, 3 conductors or fewer, ampacity 25 A; breaker 20 A.
- Maximum circuit power: 20 A × 110 V = 2200 W; the continuous load limit of 80% is 16 A, about 1760 W.
- For a continuous load of 16 A, a factor of 1.25 gives 20 A, still below 25 A.
Temperature also eats into the margin
Table 25-7 (表二五～七) requires correction when the ambient temperature is not 35°C. For a conductor with 60°C insulation, the factor is 0.89 at an ambient temperature of 36 to 40°C and 0.77 at 41 to 45°C. The 18 A of 2.0 mm solid wire multiplied by 0.89 is about 16 A. In a stuffy rooftop add-on structure (頂樓加蓋), inside a ceiling, or on a sun-baked wall, the actual environment can be hotter than 35°C, which is one reason wiring in older homes is more sensitive to heat. Under Article 25, when 10 or more current-carrying conductors share one conduit, the factor from Table 25-6 (表二五～六) must also be applied.
Five things to ask when you receive drawings or an electrician's quote
- The wire size and unit of each circuit (mm for solid wire, mm² for stranded wire).
- The breaker amperage for each circuit, and whether the panel labels each circuit.
- Whether the conduit is PVC, metal or something else, and how many wires are in one conduit.
- Whether the wire carries the required markings and has a ground wire. For grounding and leakage protection, see breaker layout in the distribution panel.
- Whether terminals and connections are tightened and polarity is correct; for details see distribution panel screw torque and outlet polarity.
When buying a second-hand home or inspecting a new one, you can use the DIY home inspection checklist to tick off the plumbing and electrical items one by one, and then have an electrician double-check. For how to add up loads when several electric heaters and a microwave run at the same time and whether they will trip the breaker, see also extension cord and outlet overload wattage and electric heater electrical safety in winter.
When you must call a qualified electrician
- A breaker trips often, or an outlet or switch plate feels hot or smells burnt.
- You need to add 220 V equipment, a large kitchen appliance or an electric water heater, which requires a new dedicated circuit.
- You only know the wire is thin and old, but are not sure of its size, or the panel has no circuit labels.
- You want to replace a breaker with a larger one, or lengthen or extend existing wiring. Do not do any of these yourself, ever.
The numbers in this article are for reading the table only; actual installation and acceptance depend on the on-site judgment of a qualified electrician and the regulations currently in force.
Last updated: 2026-10-26
Sources
- National laws and regulations database (全國法規資料庫): Regulations for Installation of Customer Electrical Equipment (in Chinese): supports the name of the regulation, the amendment date, the definition of ampacity, and the content of Articles 25, 38, 39, 40 and 79.
- Table 25-5, ampacity of conductors for PVC conduit wiring (表二五～五; in Chinese): supports the numbers in the main chart.
- Table 25-2, ampacity of conductors for metal conduit wiring (表二五～二; in Chinese): supports the comparison showing PVC and metal conduit numbers differ.
- Table 25-1, maximum allowable temperature of conductor insulation (表二五～一; in Chinese): supports the insulation temperature classes for each type of conductor.
- Table 25-6, correction factors for the number of current-carrying conductors (表二五～六; in Chinese): supports the derating when a conduit holds too many wires.
- Table 25-7, correction factors for ambient temperature (表二五～七; in Chinese): supports the numbers for ambient temperature correction.
- Table 40, installation of branch circuits (表四○; in Chinese): supports the minimum wire sizes and receptacle ratings for branch circuits of 50 A or less.
- Regulations for Installation of Customer Electrical Equipment, Article 79 (in Chinese): supports the rule that a protective device must not exceed the conductor's ampacity, and the protective device limits for 2.0 mm, 3.5 mm² and 5.5 mm².
- Bureau of Standards, Metrology and Inspection (BSMI), Ministry of Economic Affairs: guide to buying and using extension cords (in Chinese): supports the 125 V, 15 A, 1650 W marking on ordinary extension cords.
