A battery cable does not carry current in a laboratory label. It carries current beside other loaded cables, inside a battery box, near an inverter heatsink, behind insulation, across a warm engine compartment or under a protective sleeve. Those details determine how readily heat leaves the conductor. A cable described only by gauge, copper area and a large “amp rating” is therefore not ready for a purchasing decision.
The procurement question is not “How many amps can 2 AWG carry?” It is: Can this exact conductor, insulation, termination and route carry the defined duty without any controlled temperature being exceeded under the worst credible ambient, grouping and connection conditions? The answer needs a calculation or published rating whose installation assumptions match the project, followed by representative temperature-rise evidence.
This guide provides an RFQ method for that answer. It does not prescribe a universal ampacity, replace the applicable electrical code or approve a battery system. It also makes no unverified claim about a SINAWATTS cable size, insulation, listing, production process, thermal test capability, stock, price, MOQ, lead time or field result. Those facts must be confirmed for the offered part and project.
Direct answer: what must the bidder return?
Ask every bidder for one cable thermal schedule that identifies:
- exact cable part number, conductor material, strand construction, nominal and minimum conductor area, insulation and jacket construction;
- dry, wet and any application-specific temperature ratings, with the governing product standard and marking evidence;
- continuous, intermittent and peak current profiles, including duration, repetition and simultaneous neighboring circuits;
- maximum compartment air temperature and the method used to establish it;
- route segments, bundle count, loaded-conductor count, spacing, sleeve, conduit, gland, tray, insulation contact and ventilation;
- ampacity source or calculation method, every correction factor and the original assumptions behind any table value;
- terminal, lug, fuse holder, switch and equipment-terminal temperature limits that may be lower than the cable insulation limit;
- maximum permitted conductor, insulation-surface, terminal and local-air temperatures at named measurement points;
- a representative first-article temperature-rise report at the agreed current and ambient; and
- change-control triggers for conductor, insulation, color compound, lug, crimp, route, bundle, enclosure or duty changes.
Reject a single current number without conditions. The same cable can have different defensible ratings in free air, a tight bundle, a sealed conduit and an insulated battery box. A high insulation temperature rating does not grant permission to run a terminal, fuse or battery post at that temperature.
Keep this review separate from voltage drop and insulation selection
Ampacity is a thermal limit. Voltage drop is a performance limit. A large conductor may satisfy voltage drop while a tightly grouped route still creates a hot terminal; another route may remain thermally acceptable yet lose too much voltage for cranking or charging. Use the battery-cable voltage-drop guide for source voltage, route resistance and load-voltage acceptance. Use this article for continuous thermal behavior in the installed environment.
Likewise, the battery-cable insulation and jacket guide addresses oil, fuel, abrasion, flame, cold flexibility, wet use and marking. Those properties help define the cable, but they do not by themselves establish installed ampacity. An insulation marked for a high conductor temperature may still be unsuitable for a wet location, and a chemically resistant jacket may trap heat when placed inside another sleeve.
The official UL Solutions Wire and Cable Application Guide, checked on 2026-09-28, explains that wire markings distinguish temperature ratings for dry and wet locations and that Recognized Appliance Wiring Material is not automatically identified as an NEC wire type. It also shows why buyers must read the exact marking and certification scope rather than turning one insulation temperature into a universal installation ampacity. UL Solutions Wire and Cable Application Guide.
Freeze the load profile before choosing a cable
“Maximum current” is not a complete thermal input. Define current versus time for each operating state. A battery cable may experience a short starter pulse, a long inverter load, a charger plateau, regenerative current, a service overload and a low standby current. Heating depends on current squared, time and the thermal mass and cooling path. A peak that lasts seconds is not equivalent to the same current for hours, but repeated peaks can start before the cable has cooled.
Create a duty table for every relevant conductor:
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Duty field | Required project value | Evidence expected |
|---|---|---|
| Normal continuous current | Highest sustained current and duration | Load study or equipment output limit |
| Cyclic load | Current, on-time, off-time and cycles | Operating sequence and thermal justification |
| Peak current | Magnitude, duration and repetition | Source/load data and protection coordination |
| Charge current | Maximum total from simultaneous sources | Charger settings and operating-state matrix |
| Neighbor circuits | Current in every cable sharing the thermal group | One-line, harness drawing and load schedule |
| Ambient | Local air range during worst operation | Compartment measurement or bounded analysis |
| Fault clearing | Prospective fault and protective-device time | Separate short-circuit withstand review |
Do not average positive and negative conductor currents as if they cancel heat. Both conductors dissipate resistive loss. Do not assume a nominal inverter rating is the continuous DC input current; efficiency, low battery voltage and overload behavior matter. If two chargers can operate together, include both unless a documented interlock prevents it.
Define the thermal route segment by segment
A single assembly can cross several thermal environments. Divide the route wherever cooling, ambient or grouping changes. Typical segments include an exposed battery lead, a close-spaced battery-box run, a grommeted wall passage, a sleeved harness, a cable tray and an equipment-terminal cavity. The most restrictive segment controls unless the design is changed.
For each segment, record:
- cable count and which conductors can be loaded simultaneously;
- cable outside diameter and center-to-center spacing;
- horizontal, vertical or coiled arrangement;
- length inside the restrictive condition;
- conduit, braid, corrugated tube, heat shrink or fire sleeve;
- direct contact with foam, carpet, insulation, battery cases or warm surfaces;
- air movement, vent openings and any fan dependency;
- radiant or conducted heat from engines, exhausts, chargers, inverters and sunlight;
- nearby terminal blocks, fuses and switches; and
- service conditions that can add another cable or close a vent.
Photographs are useful only when tied to a route drawing and dimensions. “Installed in free air” should not be accepted for a cable lying against a closed panel or sharing a dense harness. A short packed penetration can become the hottest location even when most of the run is exposed.
IEC 60287 addresses calculation of cable current ratings and losses under defined installation conditions. The official IEC 60287 series record available on 2026-09-28 contains current-rating, loss, thermal-resistance and operating-condition parts. IEC 60287-2-2 specifically addresses reduction factors for groups of equal cables in free air protected from solar radiation. These scopes demonstrate that grouping and thermal environment are explicit calculation inputs; they are not permission to apply a power-cable result blindly to a flexible battery lead. The responsible designer must select the applicable method and assumptions. IEC 60287 series official record and IEC 60287-2-2 official record.
Treat a bundle as a thermal system, not a cable count
Bundle derating is not determined by the number of visible jackets alone. Relevant variables include conductor losses, diameter, spacing, bundle geometry, load diversity, material thermal conductivity, sleeve construction and surrounding air. A center cable generally has a less favorable heat path than an outside cable. A mixed harness can place a small control wire beside a hot power conductor even when the control wire carries little current.
Require the supplier to identify whether its proposed factor comes from:
- the applicable installation code or product standard;
- a cable-manufacturer table with matching cable construction and arrangement;
- a recognized calculation method with listed inputs;
- a validated thermal model; or
- a representative test covering the offered assembly.
A factor copied from a different cable family is not adequate. Neither is a statement that only one polarity is “current carrying.” For a two-wire isolated DC circuit, outgoing and return conductors can both be loaded. For parallel cables, current sharing must be justified by conductor resistance, route symmetry and connection geometry; dividing total current by the number of parallels without tolerance analysis can hide an overloaded leg.
Specify how unused circuits and future additions are treated. If the project can add a second inverter or spare conductors can later become loaded, the original thermal calculation may no longer apply. Put maximum bundle occupancy and simultaneous loading on the controlled drawing.
Establish the real compartment ambient
Ambient is the air temperature surrounding the cable at the reviewed location, not a distant weather-station value. A closed battery or inverter compartment can continue warming after outside air stabilizes. Solar loading, charger losses, engine soak, restricted ventilation and recirculated fan air can create a local value far above room temperature.
Define the ambient envelope with one of three evidence paths:
- Measured: instrument a representative compartment at the worst credible operating state, load, ventilation state and outside condition.
- Calculated: use a reviewed enclosure heat balance or thermal model with stated losses, surfaces, airflow and uncertainty.
- Conservative boundary: select a documented design ambient that bounds the installation and verify it during the first article.
Place ambient sensors away from direct contact with a conductor, heat sink or enclosure wall unless that location is intentionally being measured. Record sensor accuracy, response, shielding and sample interval. Capture start-up, steady operation and heat soak after a heavy load stops. If acceptable temperature depends on a fan, include blocked-filter, failed-fan or reduced-speed behavior in the system safety analysis rather than silently assuming full airflow forever.
The official IEC 60287-2-1 record defines steady state as continuous constant current sufficient to approach maximum conductor temperature under constant surrounding ambient conditions. That boundary is useful: a steady-state calculation is not automatically a transient-cycle calculation, and a measured short run that never reaches equilibrium cannot prove continuous capacity. IEC 60287-2-1:2023 official record.
Build a temperature-limit stack
List every component limit in the current path. The permitted operating current is governed by the lowest applicable limit after considering measurement location and uncertainty.
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Limit layer | Evidence | Procurement question |
|---|---|---|
| Conductor/insulation | Cable datasheet, marking and certification scope | Is the rating valid for the exact environment? |
| Jacket or sleeve | Material/product instructions | Does an outer layer have a lower temperature limit? |
| Lug barrel and palm | Lug specification and qualification | Is the conductor range and temperature scope matched? |
| Equipment terminal | Device instructions and certification | What conductor temperature and tightening method are permitted? |
| Fuse holder or switch | Product rating and temperature-rise conditions | Does it impose a lower current or ambient limit? |
| Battery post | Battery installation manual | What temperature, stack and torque restrictions apply? |
| Adjacent material | Grommet, enclosure, label or foam data | Can it tolerate local cable temperature? |
The cable’s 105°C marking, for example, does not mean a nearby terminal certified with 75°C conductors may be operated at 105°C. Conversely, measuring a cool outer jacket does not prove the conductor beneath thick insulation is below its limit. The test plan needs a correlation or conservative acceptance value for each measurement point.
Connector current ratings also depend on test arrangement. TE Connectivity’s official Power Key connector product specification, checked on 2026-09-28, notes that its current rating is based on temperature-rise testing and that shorter wire lengths can reduce current-carrying ability because less heat is conducted away from the connector. That statement applies to the named product family, not a battery cable generally, but it illustrates why the terminal and attached wire form one thermal system. TE Power Key product specification.
Review resistance and tolerances without substituting voltage drop
Conductor loss for a uniform segment is approximately P = I²R. Resistance rises with conductor temperature, so an iteration may be required: current causes heating, heating increases resistance, and increased resistance adds loss. Use minimum conductor area, maximum permitted resistance or a justified production distribution rather than the most favorable nominal value.
Terminations add localized resistance. A milliohm that looks small can be significant at battery current. At 200 A, a hypothetical 0.5 mΩ joint dissipates:
P = 200² × 0.0005 = 20 W.
That fictional example is not an acceptance limit. It shows why cable-only loss can miss a hot lug. The Kelvin resistance testing guide explains four-wire measurement boundaries for complete assemblies. Use resistance data to diagnose consistency and support a thermal model, while retaining a temperature-rise test for the installed condition.
Include conductor cross-section tolerance, stranding compaction, plating, length, crimp resistance, parallel-leg imbalance and contact resistance. Ask whether the supplier’s stated resistance is maximum, typical, initial or after conditioning. “Pure copper” is not a numerical resistance guarantee.
Use a bounded worked comparison
Assume a fictional project has four identical positive/negative cable pairs sharing a sleeve for 1.5 m inside a compartment. Three circuits can carry 80 A continuously while the fourth is idle. A table shows 100 A for one isolated cable at a stated ambient. The buyer must not conclude that every cable has 20 A of margin.
The correct review asks whether the table covers the exact conductor and insulation, whether both poles are counted, what grouping factor applies to six simultaneously loaded conductors, whether the stated ambient matches the compartment, and whether lug and device limits are lower. If a documented method produced a fictional grouping factor of 0.72 and an ambient correction of 0.88, simple multiplication would yield 100 × 0.72 × 0.88 = 63.4 A, below the 80 A requirement. Those invented factors are teaching inputs only; they must never be copied into a real design.
Options would include a larger conductor, spacing the circuits, separating polarities into approved arrangements, shortening the restrictive segment, using a validated ventilated route, lowering continuous current or changing duty. Increasing insulation temperature alone may not solve lower-rated terminals or adjacent components.
This example illustrates another important rule: apply factors according to the governing method. Some tables already incorporate ambient, installation or conductor-count assumptions. Multiplying unrelated factors can be as wrong as applying none. Require the bidder to show the source table and full calculation chain.
Specify a representative temperature-rise test
The first-article test should reproduce the thermally controlling configuration, not lay one cable on a bench. Freeze cable lengths, bundle geometry, sleeve, enclosure, ventilation, terminal hardware and neighboring loads. Condition the assembly as required by the applicable specification and use calibrated current and temperature measurement.
Record at least:
- exact cable, lug, device and enclosure identities;
- conductor and assembly resistance before the test at a stated temperature;
- ambient sensors at inlet, local bundle and enclosure locations;
- temperature points on center and outer bundle cables;
- lug barrel, lug palm, stud, fuse holder, switch and equipment-terminal temperatures;
- current in every parallel leg and neighboring circuit;
- voltage at useful diagnostic points;
- airflow or fan state where relevant;
- time-series data through thermal stabilization or the complete duty cycle; and
- post-test inspection for discoloration, softening, loosening or insulation movement.
Use thin, secured sensors that do not materially improve cooling or disturb contact pressure. Infrared images can locate anomalies, but shiny metals have emissivity and line-of-sight limitations. Pair thermal imaging with contact sensors or another justified method. Report temperature rise and absolute temperature; a safe-looking rise at an incorrectly low test ambient can still exceed a limit in service.
Define stabilization before testing. A practical criterion must come from the governing procedure or approved plan, such as a sufficiently small rate of change over a defined interval. “Ran for 30 minutes” is not proof of steady state. For cyclic duty, begin from the specified initial temperature and run enough cycles to reveal heat accumulation.
Compare suppliers with an evidence matrix
On small screens, swipe or scroll sideways to read every column. Keyboard users can focus the table and use the arrow keys.
| Decision field | Strong return | Hold point |
|---|---|---|
| Cable identity | Controlled drawing and exact markings | Generic gauge description |
| Duty | Current-time states and simultaneous loads | One unexplained maximum current |
| Route | Segment drawing with bundle and environment | “Harness installation” only |
| Ampacity basis | Applicable source and transparent factors | Vendor chart without conditions |
| Ambient | Measured or bounded local temperature | Room temperature assumption |
| Termination limits | Lug/device/battery documentation | Cable insulation used as only limit |
| Parallel sharing | Maximum leg imbalance evidence | Total current divided equally |
| Thermal test | Representative geometry and time series | One free-air spot measurement |
| Production control | Resistance, crimp and BOM controls | First sample only, no monitoring |
| Change control | Defined re-analysis and retest triggers | Material substitutions allowed silently |
Score evidence completeness separately from cable size. A thick cable with an undocumented lug, dense bundle and unsuitable terminal can present more risk than a smaller cable used within a fully supported installation limit.
Control production and field changes
A qualified first article is valid only for its controlled configuration. Require notice before changing conductor source, strand count, plating, insulation compound, wall thickness, color concentrate, jacket, lug, crimp tooling, heat shrink, cable length or terminal hardware. Changes to route, bundle population, enclosure, ventilation or load can also invalidate the thermal result even if the cable part number stays the same.
Useful production evidence includes conductor resistance, strip length, crimp height or compression index, pull testing where applicable, visual criteria, finished length and traceability. Trend resistance rather than accepting only a broad limit; a shift can reveal conductor-area, crimp or length changes. Do not use a low assembly resistance to waive dimensional or material requirements.
Field instructions should prohibit coiling excess high-current cable, adding unreviewed circuits to the bundle, covering cables with insulation, blocking vents or replacing a high-temperature component with an unverified alternative. Maintenance should look for discoloration, hardened insulation, loose supports, damaged sleeves, corrosion and hot-joint evidence. A thermal alarm, if used, needs sensor location, threshold, delay, failure response and test procedure.
Send a complete battery-cable thermal RFQ
Attach the one-line diagram, load-state table, route drawing, compartment environment, applicable rules, cable interfaces and evidence matrix. Ask for exact order codes and a deviation list. Commercial terms such as price, MOQ, sample availability and lead time should be supplier responses, not assumptions embedded in a technical guide.
For a focused inquiry, include:
- system nominal and maximum voltage;
- continuous, cyclic, peak and fault-clearing current duties;
- cable lengths, number of parallels and allowed voltage drop;
- local ambient and nearby heat sources;
- bundle, sleeve, conduit, penetration and enclosure details;
- mating lugs, studs, fuses, switches and equipment terminals;
- temperature limits and required measurement points;
- first-article quantity and thermal test plan;
- required reports, certificates and traceability; and
- destination, quantity, schedule and requested quotation validity.
Use the AWG-versus-mm² cable sizing guide to normalize conductor descriptions and the cable-lug geometry guide to freeze the termination interface. When the inputs are complete, send the project-specific RFQ with the thermal route schedule. Ask the bidder to return assumptions and deviations beside each requirement.
Buyer FAQ
Can one AWG or mm² size have one universal amp rating?
No. Current capacity depends on conductor construction, insulation, allowable temperature, ambient, grouping, route, terminations and duty. Use an applicable rating or calculation whose assumptions match the installation, then verify the representative assembly.
Does a 105°C cable permit every joint to operate at 105°C?
No. Lugs, device terminals, fuse holders, battery posts, sleeves and adjacent materials can have lower limits. The lowest applicable limit controls, with measurement uncertainty and hot-spot location considered.
Must both positive and negative battery cables be counted in a bundle?
If both carry the circuit current and share the thermal environment, both produce heat. The governing method determines the precise conductor count, but a buyer should not remove the return conductor from the review merely because currents flow in opposite directions.
Can voltage-drop compliance prove ampacity?
No. Voltage drop and ampacity are related through resistance but answer different questions. A route can pass one and fail the other. Review load voltage, continuous temperature and termination hot spots separately.
Is a short starter pulse irrelevant to thermal design?
No. Its duration and repetition determine its contribution. A single brief pulse differs from continuous current, but repeated cranking or a stalled load can accumulate heat. Define the full current-time duty and protective clearing.
How should parallel battery cables be assessed?
Require route and connection symmetry, individual-leg current measurements and a tolerance-based sharing analysis. Do not assume equal current merely because the cables share gauge and nominal length.
Is thermal imaging enough for first-article approval?
Usually not by itself. It is useful for finding anomalies, but emissivity, reflections and hidden conductor temperature require a documented method and often contact measurements. Record time series, ambient and current, not only one image.
What is the most common bundle evidence gap?
It is a factor quoted without its source conditions. Ask for the original table or method, cable arrangement, loaded-conductor count, ambient and whether other correction factors are already included.
When must the temperature-rise test be repeated?
Repeat or justify the affected portion after changes to cable materials, conductor resistance, lug or crimp, length, bundle, sleeve, route, enclosure, ventilation, ambient or load duty. A different color compound can also require review if it changes the controlled insulation system.
What should be included in a useful quotation?
Require exact cable and lug order codes, construction and markings, ampacity basis, route assumptions, all temperature limits, first-article test deliverables, production controls, deviations, price, MOQ, sample plan and lead time. A quotation that states only gauge, length and amps is incomplete.