USB-C 5m Charge Cable: Power Delivery Voltage Drop and Current Selection
A five-metre USB-C charge cable is the longest length at which charging-only cables are commonly deployed, and it sits precisely where conductor resistance begins to matter for Power Delivery. At this distance, the difference between a well-specified cable and an ordinary one is not subtle: a laptop that charges at full rate on one cable may charge at two-thirds rate on another, with no error reported and no visible indication of why. The explanation lies entirely in the interaction between conductor gauge, the E-Marker, and the negotiated Power Delivery profile.
Quick Answer / Technical Summary
For a USB-C 5m charge cable, the two governing specifications are conductor gauge and E-Marker rating. To deliver 5 A at 20V over five metres, the cable requires 20 AWG power conductors, which limits the round-trip drop to approximately 0.25V, and a 5 A E-Marker, without which the source will limit current to 3 A and deliver about 60W instead of 100W. For 3 A operation, 22 AWG is sufficient. Where 240W extended power range is required, the cable must be rated for the higher voltage profile as well as 5 A.
Voltage Drop Arithmetic Over Five Metres
The calculation follows the same method as any resistive circuit: drop equals current multiplied by the round-trip resistance of the power conductors. Five metres of 24 AWG conductor has roughly 0.85 ohms of round-trip resistance, so 5 A produces about 4.25V of drop, which is catastrophic for a 5V rail and still substantial for a 20V profile. Five metres of 20 AWG has roughly 0.33 ohms round trip, so 5 A produces about 1.65V of drop, which is significant but manageable at 20V and becomes the reason Power Delivery operates at higher voltage in the first place.
This is the key insight for a c 5m charge cable: the higher voltage profiles exist partly because they reduce the current required for a given wattage, and therefore reduce the drop that the cable causes. Delivering 100W at 20V requires 5 A, but delivering the same 100W at 5V would require 20 A, which no practical cable could carry over five metres. Selecting a cable that supports the highest voltage the devices can negotiate is therefore as important as selecting the gauge.
Conductor Gauge and E-Marker Selection by Current
For 3 A operation, which covers devices charging at up to 60W, 22 AWG power conductors are adequate over five metres, producing roughly 0.8V of drop at 3 A on a 20V profile and considerably less on a 5V profile where the current would be lower at the same wattage. Most laptops and tablets fall into this category, and a 3 A rated cable is entirely sufficient.
For 5 A operation, which covers charging at up to 100W, 20 AWG is required, and the cable must contain an E-Marker declaring 5 A capability. The E-Marker is not optional: the source reads it over the configuration channel before negotiating, and in its absence it will cap the current at 3 A regardless of how substantial the conductors are. This is the single most common reason a user with a 100W charger observes 60W charging, and it is resolved only by replacing the cable with one that declares 5 A.
Extended Power Range and Higher Voltage Profiles
The newer Power Delivery specification defines Extended Power Range, which raises the maximum to 240W by allowing negotiation up to 48V at 5 A. For a five-metre cable, this is a meaningful development because the higher voltage keeps the current at 5 A even as wattage more than doubles, so the voltage drop relative to the delivered power remains similar to the 100W case. Cables intended for this must be rated for the extended power range and must contain an E-Marker declaring the appropriate capability.
Two practical cautions apply. First, both the source and the sink must support the extended range; if either does not, the negotiation settles at a lower profile and the cable’s higher rating yields no benefit. Second, the power supply must be capable of the required wattage, since a 100W adapter cannot deliver 240W regardless of the cable and device. For the great majority of current deployments, a 5 A E-Marked cable covering up to 100W is the correct and sufficient specification, and extended range is relevant only to high-power workstations and specialised equipment.
Technical Specifications & Performance Benchmarks
| Charging Target | Required Current | Minimum Gauge at 5m | E-Marker Required | Approx. Drop at 20V | Observed Outcome If Under-Specified |
|---|---|---|---|---|---|
| Up to 45W | 3 A at 15V | 24 AWG | No | Approx. 0.6V | Charges correctly at the negotiated rate |
| Up to 60W | 3 A at 20V | 22 AWG | No | Approx. 0.8V | Charges correctly at the negotiated rate |
| Up to 100W | 5 A at 20V | 20 AWG | Yes, 5 A rated | Approx. 1.65V | Charging limited to about 60W if the E-Marker is absent |
| Up to 240W extended range | 5 A at 48V | 20 AWG | Yes, rated for the extended profile | Approx. 1.65V | Falls back to a lower profile if either device lacks support |
Industrial & Enterprise Application Scenarios
- Wall Panel Charging Installation: Running a five-metre charging cable from a floor box to a wall-mounted tablet, specifying 22 AWG conductors and confirming the device’s 45W requirement is met without unnecessary bulk.
- Laptop Charging from a Floor Box: Reaching a desk laptop from a floor-mounted 100W supply over five metres, specifying 20 AWG conductors and a 5 A E-Marker so that charging occurs at full rate rather than being capped at 60W.
- Test Bench Power Delivery Verification: Confirming that a candidate five-metre cable declares a 5 A capability by reading the negotiated current at the device end, rather than relying on the product description, before approving it for a fleet purchase.
System Integration & Recommended Connectivity Infrastructure
To complete a single-cable workstation, charging, or equipment-cabinet connectivity stack, pair these USB cable products with our certified interconnect range:
- usb-c power hub: Where multiple devices must charge from one point, review how a usb-c power hub allocates its power budget.
- type c to audio/video cable: Where the same run must also carry audio and video, see our type c to audio/video cable range.
- type c-hub: Add data ports and display output at the far end with a type c-hub.
- adapter series: Convert legacy connectors at either end with our adapter series.
Frequently Asked Questions (FAQ)
Q: Why does my 100W charger only deliver 60W over a five-metre cable?
The cable almost certainly lacks a 5 A E-Marker. USB-C cables rated above 3 A must contain an E-Marker chip that declares their capability, and when the source does not detect one it limits the negotiated current to 3 A. At 20V that gives 60W. Specify a cable explicitly rated for 5 A with an E-Marker to obtain the full 100W over five metres.
Q: What gauge wire should a five-metre USB-C charging cable use?
For charging up to 60W at 3 A, 22 AWG power conductors are adequate. For charging up to 100W at 5 A, 20 AWG is required to keep the round-trip voltage drop near 1.65V at the 20V profile, which is acceptable when the source provides a properly regulated supply. Cables of 24 AWG or thinner will produce excessive drop at 5 A and should not be used for high-current charging at this length.
Q: Does a longer charging cable reduce charging speed even if the wattage rating is correct?
Yes, if the conductor gauge is inadequate for the length. Resistance increases with length, so a cable rated at 5 A over one metre may produce unacceptable drop over five metres if its conductors are thin. The rating is only meaningful in combination with the length. Where a cable’s documentation states a wattage without stating the conductor gauge or the length at which the rating applies, treat the figure with caution and verify actual charging current at the device end.