Siamese Junction Boxes

jfunderburk · March 30, 2014, 7:23pm

Need a code please. What prohibits the practice of combining junction boxes?

Mike_Arbusto · March 30, 2014, 9:09pm

Hi Joe,
No issue here… Box extenders are not prohibited. The box attached to the top of the other one is just an extender – same kind of a box, but without a bottom. Peek inside if you want.
They are commonly used to avoid violating the box fill quota (too many conductors entering the box of too small a size), or just to make wiring easier with thicker gauge wires.

rmeier2 · March 30, 2014, 9:30pm

There isn’t one. Listed extension collars are permitted to increase the volume of a box. From the NEC:

314.16 Number of Conductors in Outlet, Device, and
Junction Boxes, and Conduit Bodies. Boxes and conduit
bodies shall be of sufficient size to provide free space for
all enclosed conductors. In no case shall the volume of the
box, as calculated in 314.16(A), be less than the fill calcu-
lation as calculated in 314.16(B). The minimum volume for
conduit bodies shall be as calculated in 314.16(C).
The provisions of this section shall not apply to termi-
nal housings supplied with motors or generators.
Informational Note: For volume requirements of motor or
generator terminal housings, see 430.12.
Boxes and conduit bodies enclosing conductors 4 AWG
or larger shall also comply with the provisions of 314.28.
(A) Box Volume Calculations. The volume of a wiring
enclosure (box) shall be the total volume of the assembled
sections and, where used, the space provided by plaster
rings, domed covers, extension rings, and so forth, that are
marked with their volume or are made from boxes the di-
mensions of which are listed in Table 314.16(A).

lkage · March 30, 2014, 9:34pm

Nothing prohibits that extension, that I know of…

jwicklander · March 30, 2014, 9:42pm

That’s a 1900 box extension.

Jeff

jfunderburk · March 30, 2014, 10:25pm

How 'bout this one?

Mike_Arbusto · March 31, 2014, 1:26am

[quote=“jfunderburk, post:6, topic:85693”]

How 'bout this one?

Yeah… this one takes the cake
NEC says:
NEC 110.12. Mechanical Execution of Work. “Electrical equipment shall be installed in a neat and workmanlike manner”
This one is neither neat nor workmanlike…

kbrittain · March 31, 2014, 1:53am

Thats the OCTAMOM of junction boxes and not the siamese!

mclark2 · March 31, 2014, 2:39am

lol. Nice one, Joe. I guess they had more J boxes than conduit!