12AWG and 30A circuit breakers

[kwired]

Correct. it is a large, LED Video display - something you would see at a NFL stadium or major College stadium. 55' x 120'.

Looking at your location, type of equipment and knowing of a company based there that does kinds of things you mentioned - I assume you work for that company and I find it a little hard to believe you don't somehow have listing on this equipment. Yes a lot of it is custom made for where it will be installed, that don't mean it can't be listed though. Does this equipment fall under NEC art 600? Likely yes. If so 600.3 does require it to be listed.

 

[Eddie702]

What about using a 30 amp breaker and feeding a 30 amp fused switch with 20amp TD fuses in it and then going with #12 from the switch? Maybe the fuses would hold better. Could try it on one and see if it works

 

[LarryFine]

What about using a 30 amp breaker and feeding a 30 amp fused switch with 20amp TD fuses in it and then going with #12 from the switch? Maybe the fuses would hold better. Could try it on one and see if it works

But, using what size wire in the feeder?

 

[ramsy]

This load for our display installation is not a motor, but we liken the situation to motor overcurrent circuit protection.

1. 220.18(A) requires conductors sized 125% of motor loads
2. 220.18(B) requires LED loads per NamePlate Amps, not Watts.

tables in NEC from 310.15 (2017 edition). The ampacity of 12 AWG THHN/THWN conductors in free air (which is what they are internal to our electronic display) is 40A.

1. Table 310.15x puts ** next to small conductors to reference 20A max fuse per 240.4(D)5, which can only be modified by specific exceptions listed in 240.4(G), such as inductive-motor loads w/ built-in thermal overload protection.
2. NEC tables require environment Adjustments. Ampacity must be reduced for ambient > 30°C for > 10% of length.

· Next higher standard overcurrent protection device rating allowed above the ampacity of the conductors being protected per 240.4 (B)

1. ** Small conductors are subject to 240.4(D). No next higher fuse.

· A case could be made for using 12 AWG with a 30A breaker according to the Tap rules in 240.21.

1. Branch-circuit tap conductors must comply with 210.19, which requires 125% Ampacity for continuous loads, and max 18 Inch luminaire taps.

· fixture wiring used with listed appliances in 240.5 B is also relevant

1. 240.5(B)2 refers to listed assemblies w/ fixture wire tested for the purpose.
2. #12 wire on 30A fuse w/ insulation listed for => 90° C would also require 90°C equipment lugs, terminals, and connectors, per 110.14(C).

· Table 240.4(G) is an entire list of applications where smaller conductors may be permitted.

1. If your equipment is not listed there, then you must have it designed under qualified engineering supervision, or listed / Approved by NRTL.

· 310.15 (C) is another carve out where under engineering supervision conductor ampacities are allowed to be calculated differently.

1. Yes, if both engineer and permit planning sign off on the design, and it passes AHJ inspection without requiring NRTL listing as an assembly.

We would appreciate your insight on how we can more clearly reference the NEC to assure the customer this installation is appropriate and safe.

1. Clients can demand permits and AHJ inspection per 90.4