UL674 specification for an NPT threaded hole for conduit

[renasis]

Hello,

I am little confused by a note in the UL674 "Electric Motors and Generators for use in Division 1 Hazardous Locations" standard. It is under the section "Connections for conduit". The specific section is detailing the requirements for a threaded conduit entry into an electric motor.

The statement is specified below:
18.1.1.1 .."NPT threaded entries shall conform to ANSI/ASME B1.20.1 except that entries shall gauge with +1/2 to +3-1/2 turns beyond the L-1 gauging notch in lieu of the +/-1 turns described in ANSI/ASME B1.20.1."

Note that this statement is the last line of section 18.1.1.1, the statement stands alone, no additional context needed. ANSI/ASME B1.20.1 does specify that NPT tapped hole shall gauge +/-1 turn, where +1 turn means the hole is large and -1 turn means the hole is small. The problem is with the "+1/2 to +3-1/2" turns. I believe what UL is trying to specify is that they want the L-1 gauge to stay within +/-1/2 a turn. I am not sure where +3-1/2 turn comes in. If the L-1 gauge had a value of +3-1/2, then the hole would be over sized. I am going to discuss with UL, but I am curious if someone on this forum can help me understand what they are trying to specify.

Thanks

 

[racookpe1978]

NOT an official, nor a correct answer, but I'd claim they're trying to say, "We want to use the same fittings and threads as the pipefitters, but we don't trust electricians not to leak water into our motors, so turn it tighter than the pipefitters by at least 1/2 turns more than they do." 8<)

 

[Compositepro]

I believe they saying they want more thread engagement (+1/2 to +3-1/2 turns) than for standard pipe (+/- 1/2 turn).
Note that female conduit threads are not tapered and thread sealant is not used on conduit. The small gap in the threads is too small for a flame to pass.

 

[renasis]

Compositepro,

The ANSI/ASME B1.20.1 indicates that NPT threads are tapered .75 in/ft in 3.1.5. ANSI/ASME B1.20.1 specifies that the L-1 gauge should stay within +/-1 turn. Since the threaded hole is tapered, +3-1/2 turn would mean the hole is oversized, a positive value indicates the gauge went farther into the threaded hole than it was supposed to. So, a fitting may bottom out before proper thread engagement is reached.