The number an engineer of record actually asks for
Liquid filled distribution transformers over 600 volts sit under UL category control number XPLH. A company listed in that category has a file number in the form of the letter E followed by six digits, for example E342364. That number is what a consulting engineer, an inspector or a utility looks up in UL Product iQ to confirm the listing exists, what ratings and voltage classes it covers, and which plant built the unit. Without it, a submittal stalls.
A certificate number is a different document
Ask twelve factories for a file number and several will send something formatted like UL-US-26101188-1 or UL-CA-2427162-0 instead. Those are certificate or project identifiers tied to a particular assessment. They are not the listing reference and they do not look up. In our own sourcing, more than half the factories that said UL certified produced a certificate number when asked for a file number, and one, when pressed for a straight yes or no, confirmed it held no XPLH listing at all for the voltage class it had already quoted.
The listing is bounded, and the bounds matter
A file number is not a blanket. It covers stated kVA ranges and voltage classes, so a listing that genuinely covers 10 to 4000 kVA at 11 to 17 kV says nothing about a 34.5 kV class unit. That is exactly the gap that catches buyers out on 25 kV and 35 kV class jobs, where fewer factories are listed and the ones that are do not always advertise it. Ask for the file number and the covered range, per voltage class, as separate lines.
Certification arranged per order is not a listing
Watch for a quotation line reading excluding UL certification fee. That usually means the units are not listed and certification would be arranged, and charged, against your order. On a commercial project that is unworkable, because the engineer needs the listing before the submittal is approved, not a promise of one afterwards, and a certification cycle does not fit inside a construction schedule.
How to check it in five minutes
Take the file number, search UL Product iQ for it, and confirm three things. That the company name on the listing matches the company on your quotation, including the manufacturing location rather than a trading arm. That the category is XPLH. And that the kVA and voltage ranges on the listing include the unit you are buying. If any of the three does not match, you do not have what you think you have, whatever the quotation says.
Common questions
What is UL category XPLH?
XPLH is the UL category control number for liquid filled distribution transformers rated over 600 volts, which is where three phase pad mounted units sit. Listings in that category carry a file number in the form E plus six digits.
Is a UL certificate number the same as a UL file number?
No. A certificate number such as UL-US-26101188-1 refers to a specific assessment document. The file number, formatted as E followed by six digits, is the listing reference that can be looked up in UL Product iQ. Only the file number proves the listing.
Does a UL file number cover every rating a factory builds?
No. Each listing states the kVA range and voltage classes it covers. A file number covering 11 to 17 kV does not cover a 34.5 kV class unit, so ask for the covered range per voltage class rather than assuming the number is a blanket.
What does excluding UL certification fee mean on a quotation?
It usually means the units are not currently listed and that certification would be arranged and charged against your order. For a project that needs an approved submittal before installation, that is not the same as buying a listed unit and the schedule rarely survives it.
Is UL listing legally required for a pad mounted transformer?
It is not a federal requirement in itself, but the National Electrical Code and most authorities having jurisdiction require equipment to be listed by an approved testing laboratory, and utilities and inspectors routinely require it. In practice an unlisted unit does not get energised.
Free to cite with a link to this page. Work out current at any rating with the kVA to amps calculator.