Seasonal or all-year? What UL 588 Supplement SD means for outdoor string lights in the US
If the string stays up beyond a season, a US buyer asks for an all-year product rather than a seasonal one. UL 588 Supplement SD covers factory-assembled string lights intended for year-round use at a maximum input voltage rating of 120 V, and the Listing sits in UL category DGZW. Ask which of the two the listing card names.
The two categories side by side
| What differs | Seasonal: "lighting strings" | All-year: "string lights" |
|---|---|---|
| Intended use | Temporary installation and use, not more than 90 days under NEC Article 590 | Left in place year round |
| Where it sits | UL 588 itself | Supplement SD, added to UL 588 on 15 September 2017 |
| Product covered | Lighting strings for seasonal use | Factory-assembled, parallel-connected string lights, maximum input voltage rating 120 V |
| UL product category | — | DGZW, "String Lights for All-Year Use"; a string light may alternatively be Listed to UL 153 |
| Cord | — | Hard-usage cord, SJW or equivalent |
| Markings on the goods | — | "This product is intended for all-year use"; a cord tag in black on yellow giving the string's wattage rating and the maximum total wattage that may be joined end to end; a holographic UL Certification label |
UL 588 Supplement SD, category DGZW and the marking requirements above are stated as they stood on 9 September 2026.
What decides the answer for your order
- How long it hangs. A four-week display and a café terrace that never comes down are two different products. The 90-day line in NEC Article 590 is what separates them.
- Which market. Supplement SD stops at a maximum input voltage rating of 120 V, so a 230 V version sits outside it and is specified against the rules of the market it ships to.
- What is printed on the goods. The all-year wording, the black-on-yellow wattage tag and the holographic label are part of what Supplement SD calls for, so they are checkable on the product itself rather than on a carton.
- What your customer's paperwork asks for. A distributor's document pack names a standard and a model. Match the model on the document to the model on your quotation, and settle it before tooling or artwork is cut.
Which models this bears on
iLamp Technology (Shenzhen iLamp Technology Co., Ltd, 深圳市兰谱芯科技有限公司) prints a plug type and a voltage on every mains string. The S14 strings run as 120 V US 2-prong versions and as 230 V versions with EU and UK plugs; the G40 globe strings are 120 V US 2-prong; the ST38 strings print 120/230 V and 120/240 V. Supplement SD reaches 120 V and no further, so only a 120 V configuration can sit inside it.
The cable type is printed per model as well: 18AWG and 20AWG SJTW on the 120 V S14 strings, SJTW again on the 230 V S14 strings, SPT-1 on the ST38 strings and SPT-1W on the G40 strings. Read those against the hard-usage cord Supplement SD calls for, and confirm the conductor size and the exact construction on your quotation.
Ask for the listing card, and read four things on it
An all-year claim is only as good as the document behind it. Ask for the listing card itself, not a logo on a carton or a line in a specification sheet.
- The company holding the file. Read the name on the card and compare it with the company that will invoice you. A card held by another company covers that company's product.
- The category. For an all-year outdoor string that is DGZW, "String Lights for All-Year Use". A card written for a seasonal product answers a different question.
- The models. The card names what it covers. Check that your model appears on it character for character, and that the same model appears on the quotation and on the product label.
- The finished string, not a part inside it. A document issued for a driver, a lampholder or a cordset covers that part. Check that the document names the assembled string light.
What the factory states about its marks
The factory states its string lights carry an ETL listing and CE and RoHS markings; the listing card, the declaration of conformity and the test reports are requested and will be published here when received. Until then, ask for them with your quotation and treat the marks as the factory's statement.
Which route a model qualifies for, seasonal or all-year, is settled by the card and not by a specification sheet. Name your destination market and the way the string will be installed in your first message, and the card can be requested against the model you are quoting.
What to check on the sample
- Read the cord tag. If the string is built to Supplement SD, the wattage rating and the end-to-end total are printed on it in black on yellow.
- Look for the all-year wording on the product and for the holographic label.
- Read the print on the cord jacket. The type letters and the conductor size run along the jacket; they should match the model you were quoted.
- Compare the model on the label with the model on the quotation and on the card. One character of difference is a different product.