Why a checklist, and not a rule of thumb
North American cord errors are rarely exotic. They are the same ten mistakes, made at speed, at the point where a quotation becomes a purchase order.
This list is short enough to run in two minutes and specific enough to catch the errors that actually reach the shipment. Run it before releasing the order, not after the goods are packed.
The ten checks
1. Is the rating the lowest of the three?
Plug, cable and connector each have a ceiling. The assembly takes the smallest.
If the quoted figure equals the plug’s rating, and the cable is lighter than that figure requires, the cord is overstated. Work the three numbers, then write the smallest.
2. In a three-conductor earthed plug, is the flat cable integrally moulded?
SPT-1 and SPT-2 are accepted in a three-conductor earthed plug only in the one-piece co-extruded construction. Non-integral flat cord is not accepted in that position. Confirm the construction, not just the cable family.
3. If the connector is C5 or C7, which voltage is the rating stated for?
C5 and C7 are 7 A at 125 V and 2.5 A at 250 V. A 250 V order labelled 7 A is wrong. Write 2.5 A.
4. Is the cable round if it is 17 AWG?
17 AWG exists only as round-jacketed SVT or SJT. There is no 17 AWG flat SPT cable. A 17 AWG flat-cord specification cannot be built.
5. Is 15 A on a 16 AWG cord backed by HPN?
Ordinary SPT and SJT at 16 AWG reach 13 A; only HPN reaches 15 A. If the order says 15 A on 16 AWG, the cable designation must read HPN. If it reads SJT or SPT-2, the figure is 13 A.
6. Are locking plugs and C19 free of flat cable?
Locking plugs (L5 / L6) and the C19 connector do not accept SPT flat cable. Both require round heavy-duty cord — SJT, ST or SO. C15 is likewise flat-cable free.
7. Is TPT excluded from the supply path?
TPT is 27 AWG tinsel, rated 0.5 A, for internal lamp wiring. It must never appear as a supply lead, however flexible it looks on a sample.
8. Does the plug match the supply system?
125 V configurations — 1-15P, 5-15P, 5-20P, L5 — must not be used on a 250 V circuit, and the 250 V family (6-15P, 6-20P, L6) must not be used on 125 V. The pin geometry prevents the mistake physically; the paperwork must not contradict it.
9. Do the conductor count and the earth match?
A two-blade plug takes 2-core cable; a grounded plug takes 3-core cable. A C7 or C17 connector is a 2-pole connector and belongs on 2-core cable. Cross-pairing is a defect, not a variant.
10. Does the label sit inside the certificate?
The label must not exceed the lowest of the three ratings, and the assembled combination must fall inside the UL file that covers it.
A rating that is arithmetically correct but outside the certificate scope is still wrong. Check the file, not only the arithmetic.
Quick reference
| # | Check | The failure it prevents |
|---|---|---|
| 1 | Rating = lowest of three | Overstated label |
| 2 | Flat cable integrally moulded (3-conductor) | Non-compliant construction |
| 3 | C5 / C7 at 250 V = 2.5 A | 7 A claimed where 2.5 A applies |
| 4 | 17 AWG = round only | Impossible build |
| 5 | 15 A on 16 AWG requires HPN | 13 A product sold as 15 A |
| 6 | Locking / C19 / C15 — no flat cable | Non-compliant construction |
| 7 | TPT never a supply lead | 0.5 A cable in a mains path |
| 8 | Plug matches the supply system | Voltage mismatch |
| 9 | Conductors match the earth | 2-core / 3-core cross-pairing |
| 10 | Label inside the certificate | Arithmetically correct, scope-invalid |
Using this list
The ten checks are ordered by how often they catch something, not by severity — in practice, items 1, 3 and 5 find most of the problems.
If you would like this as a printable one-page review sheet for your own purchasing team, ask us and we will send it.
本篇是「北美电源线」系列第 5 篇（完结）。系列总纲与快速索引见《北美电源线选型总纲》。
HENG-WELL supplies moulded power cords and cable assemblies, and reviews orders against these checks before production. Send us the equipment, the supply system and the required current and we will confirm the configuration.
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