The cable decides your PD test — and it is not on the test list
Every bench has a cable on it. Almost nobody writes down which one.
That cable is not a passive piece of copper in a PD system. It participates in the handshake. It reports what it can carry. It decides whether a negotiation ends at 20V/3A or at 20V/5A — and on that basis whether your unit is recorded as a pass or a fail.
What is the cable doing while you test the charger?
Inside a Type-C cable rated above 3A there is a small chip — the E-Marker. It sits on the CC line, and both ends read it before they agree on current. A 100W charger connected through a 3A cable will negotiate down, by design. Nothing is broken. The charger did exactly what the standard tells it to do.
This is the first place a bench goes wrong without anyone noticing: the tester is fine, the product is fine, the cable capped the result, and the number that lands in the report belongs to the cable.
Two wrong verdicts from the same cable
Most PD EPR and high-power profiles will not handshake at all without a properly marked cable. In practice we see two opposite mistakes:
- False fail. A good charger tested with an under-spec or damaged cable falls back to a lower profile or fails the handshake. The unit is marked bad, gets reworked or scrapped, and the real problem was a cable somebody grabbed from a drawer. If this happens a few times a month, a perfectly healthy batch takes a hit every month.
- False pass. A bench that always uses the same known-good cable never sees how the product behaves with a marginal one. That variation is exactly what the customer will experience, and it never appears on the test list.
What the cable is allowed to carry
| Cable rating | E-Marker required? | What a 100W charger does with it |
|---|---|---|
| Up to 3A (60W) | No | Negotiates within 3A — the charger behaves as a 60W charger |
| Above 3A (100W / 5A) | Yes | With a valid E-Marker the charger can offer its full profile |
| Above 3A, no E-Marker | — | Falls back to the lower profile, or the handshake fails |
Standard USB PD / Type-C behaviour: the cable's E-Marker reports its rating over the CC line, and both ends read it before agreeing on current. Source: USB-IF USB Charger / USB PD specification — usb.org/usb-charger-pd.
The flip problem
Type-C is reversible, which means both orientations have to work — and they are not electrically identical. Two CC pins run through the connector, and which one carries the handshake depends on how the plug is inserted. A cable with a damaged pin, a poor solder joint, or a mis-wired connector can pass in one orientation and fail in the other.
On a bench, this usually gets handled one of two ways. Either the operator physically flips the connector as a separate step — which is slow, easy to skip, and hard to prove afterwards — or the bench uses a dedicated test lead built for the job, which means buying and maintaining a second piece of hardware per station.
Testing the cable instead of assuming it
The cleaner answer is to let the bench handle both orientations itself. The GTI6031H carries a built-in E-Marker module, so Type-C cable front and back testing runs inside the test sequence: the unit cycles the orientation electrically rather than asking the operator to unplug and reinsert. No manual flipping step, and no dedicated test lead to buy per station.
That matters most where cables are part of what you ship. If you supply a cable in the box, its orientation behaviour is a product characteristic like any other — and it belongs in the same record as the charger that ships beside it, not in a separate manual check.
Three things worth recording per unit: which cable was used for the test, whether both CC orientations were exercised, and what current the negotiation actually settled at. Without the first, a failure cannot be reproduced. Without the second, a one-orientation cable passes. Without the third, a cable-capped 3A result looks identical to a genuine 3A product. If you already have the PD3.1 EPR profile on your line, the cable is the gate in front of it.
Where this fits on the line
Cable orientation and E-Marker behaviour are not incoming-inspection concerns only. They affect every high-power test you run, so the cable belongs in the station's own record — a fixed, identified lead for the bench, plus a periodic check that the lead still negotiates what it claims. The cheapest version of this is a bench that verifies the cable in the same pass as the product, which is what a built-in E-Marker module is for.