Douglas Krantz - Technical Writer - Describing How It Works

Does it Void the UL Rating to Drill Conduit Holes?

It sounds like a simple question, but it's a question of practicality, UL rating, and the acceptance by the AHJ. Unless it's a go in all three ways, it's not a good idea to drill conduit holes in equipment boxes.

Does it Void the UL Rating to Drill Conduit Holes?

Greetings Douglas,

Does drilling a 3/4 holes into the enclosure void the UL listing of the power supply? I would appreciate your input.

There are several levels to your question: Practicality, UL Rating, Acceptance.


  • Will the power-limited wires (low voltage wires) be routed through spaces in the box reserved for power-unlimited wiring (utility power or battery power)?
  • Will the power-unlimited wiring be routed through spaces reserved for power-limited wiring?
  • Will the hole, conduit connector or bushing, or wiring be placed in the space reserved for the batteries?
  • Will the added wiring prevent proper servicing and access to the circuit boards?

If the answer is yes to any of these questions, then, from a standpoint of what is practical, drilling holes for wires isn't a good idea.

UL Rating

Questions about the actual UL rating for the box can be best answered by the technical support people at the power supply's manufacturer.


Even if it is practical to drill holes, even if technical support says that the UL rating won't be violated, it may not be acceptable to the Authority Having Jurisdiction to drill holes.

Read: Just Who Is the Authority Having Jurisdiction (AHJ)? to get an understanding about who actually makes decisions about the fire alarm system.

Remember, if it's the fire marshal or the electrical inspector that says you can't drill holes, that person is a representative of the government. It isn't a non-profit publishing house like the National Fire Protection Association (NFPA) that makes laws, it isn't a private company like UL that makes laws, it's the government that makes the laws that we have to live by. Being a representative of the government, if the fire marshal or electrical inspector doesn't accept drilled holes, that's the final authority.

Douglas Krantz
Life Safety
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