ToftThis covers Square D, Schneider Electric, Homeline, QO. The serial number is on a separate date code, stamped or printed apart from the label numbers. On a breaker it's on the label near the wire end. On a panel it's on the wiring diagram or the box label. Type the date code, not the catalog number.
1956 to about 2013: a letter, two digits, another letter, then sometimes more digits. The first letter is the month (A is January, I is skipped). The two digits are the day. The next letter is the year. Square D skips I, O and Q, and the year letters start again every 21 years, so one code can mean more than one year.
Example: H25W0652 was made in August 1969 or August 1990 or August 2011.
Some codes are just two letters: the month, then the year. CN is March 2004, 1983 or 1962.
Example: CN was made in March 1962 or March 1983 or March 2004.
This is the date the unit was made. It was usually installed soon after, but it can be later. If a serial doesn’t fit any of these patterns, look on the label for a printed manufacture date.
Checked in October 2026.
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