The alpha-numeric sequence is usually a stamp over the wiring diagram, as shown in the photo above. It would be more accurately described as a date-code system, since each panel box does not have a unique number. The diagram below is for panel manufactured from 1956 to approximately 2002.

So the date-code shown at the top of the page indicates that the panel was manufactured on December 15th of 1967 or 1988, by operator #924, on the first shift. Since the letter indicating year of manufacture can be one of several that are 21-years apart, you should evaluate the condition of the panel to determine which one that is most likely correct. Year of construction of the home, along with the year of any remodeling or electrical upgrades can further clarify it.

    Here’s another example, below, that was manufactured on September 29th of 1952, 1973, or 1994, by operator #462, on the first shift. In this case, since we knew that the home was built in 1995, it was easy to establish that 1994 was the year of manufacture.

    Panels from the late 1990s until the present most commonly use a five or six digit code, where the first two digits are the year, second two digits are the week. So “991731” would have been manufactured in 1999, on the 17th week of the year.

    To get date-code sequences for panels manufactured before 1956, download the Schneider Electric pdf document from this link: SquareDDate.pdf. 

    Also see our blog post Which Square D electric panels were recalled in 2022? And for the age of another manufacturer’s panel, go to How do I determine the age of an electrical panel?

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Field Guide for Home Inspectors, a quick reference for finding the age of 154 brands of HVAC systems, water heaters, and electrical panels, plus 210 code standards for site-built and manufactured homes, and the life expectancy rating of 195 home components. Available at amazon.com for $19.95.
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Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

• What causes copper wires to turn green or black in an electric panel?  

• What is the maximum number of circuit breakers allowed in an electric panel?

• When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

• What is a tandem circuit breaker? 

• When did arc fault circuit interrupter (AFCI) breakers first become required?

• Can an electric panel be located in a closet? 

• Can an electric panel be located in a bathroom? 

• Can you add circuit breakers by different manufacturers to an electric panel if they fit?

• My circuit breaker won't reset. What's wrong?  

• What is a split bus electric panel?

• How do I identify a combination AFCI (CAFCI) circuit breaker? 

• What does a circuit breaker with a yellow or white test button indicate? 

• What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

• What are the requirements for NM-cables entering an electric panel box?

• Why is a fuse box/panel an insurance problem for homebuyers? 

• Why is bundled wiring in an electric panel a defect?

• What is the difference between GFCI and AFCI circuit breakers? 

• Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

• What happens when you press the "TEST" button on a circuit breaker in an electric panel?

• What is a Dual Function Circuit Interrupter (DFCI)? 

• What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

• What is the difference between "grounded" and "grounding" electrical conductors? 

• What does it mean when a wire is "overstripped" at a circuit breaker?

• Why is an old fuse panel dangerous?  

• Who is the manufacturer of those "bad" electric panels?

• Why is the circuit breaker stuck in the middle? 

• What is a double tap at a circuit breaker?

• What is the right electric wire size for a circuit breaker in an electric panel?

• What is the life expectancy of a circuit breaker? 

• My circuit breaker won't reset. What's wrong? 

• Why do some breakers in my electric panel have a "TEST" button on them?

• What is the right size electric panel for a house? 

• What do I need to know about buying a whole house surge protector? 

• What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

• What is the main bonding jumper and where do it find it in an electric panel? 

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.