Grounding aluminum outdoor electrical boxes

[s14kev]

I'm wiring my barn with EMT and metallic boxes. Instead of the typical steel boxes, I'm using the outdoor aluminum boxes since they are fully sealed for dust ingress (horse barn). I typically won't run a ground with steel boxes and just ground to the conduit. Can I do the same with the aluminum boxes. Box selection is very limited in these as is space. The box in the attachment is one of the ones I'm using. It's 18cu in. If I run an outlet, two 12Ga conductors that pass through for a second light circuit and the four 12Ga wires that terminate on the outlet, I'm at the limit for 18cu in. If I run a separate ground conductor I'll go over. What's the normal consensus for these aluminum boxes? Are they appropriate without a separate ground conductor? I'll be using steel compression fittings with the EMT.

 

[rlitman]

Code allows for it. Just be sure to use weather resistant outlets, because they're less affected by corrosive environments.

 

[u2slow]

Do raintite/comp connectors constitute a proper bond?

 

[Norcal]

Do raintite/comp connectors constitute a proper bond?

Yes, but raintight & compression connectors are two different types of connectors which has been the case since UL changed the standard some years ago.

 

[u2slow]

Either way... I'm used locknuts or set-screw connectors making the bond. Raintite/comp not good enough for CEC, thought NEC would be more strict.

 

[mark flucke]

I'm wiring my barn with EMT and metallic boxes. Instead of the typical steel boxes, I'm using the outdoor aluminum boxes since they are fully sealed for dust ingress (horse barn). I typically won't run a ground with steel boxes and just ground to the conduit. Can I do the same with the aluminum boxes. Box selection is very limited in these as is space. The box in the attachment is one of the ones I'm using. It's 18cu in. If I run an outlet, two 12Ga conductors that pass through for a second light circuit and the four 12Ga wires that terminate on the outlet, I'm at the limit for 18cu in. If I run a separate ground conductor I'll go over. What's the normal consensus for these aluminum boxes? Are they appropriate without a separate ground conductor? I'll be using steel compression fittings with the EMT.

Animal confinement-have to run pvc-thus you have to run a ground-if you have a hayloft then emt and you dust resistant boxes are perfect-always run a ground in a barn because of bad grounding and the possibility of stray voltage-you need gfcis everywhere -

 

[alfredeneuman]

Animal confinement-have to run pvc

Do you have a Code reference for that?

 

[dscheidt]

Do you have a Code reference for that?

Article 547 covers agricultural buildings. I don't know it to quote from it, but there's a bunch of special requirements for them.

 

[s14kev]

Animal confinement-have to run pvc-thus you have to run a ground-if you have a hayloft then emt and you dust resistant boxes are perfect-always run a ground in a barn because of bad grounding and the possibility of stray voltage-you need gfcis everywhere -

This is correct. Agricultural use encompasses everything from commercial pig and chicken barns to small property horse barns. Code specifies PVC conduit for ag use only since pig/chicken barns produce tons of corrosive vapor and ammonia. EMT doesn't last long in that environment. Our horse barn is cleaner than most people's garages. Swept every day. Concrete flooring for the aisle. Foam mattress pads for the stalls. I built the stalls out of solid oak and they are finished in tung oil. It's nicer than my shop. See photo below of the barn interior.


Main concern is hay dust since we do have a hayloft and horse bedding can get dusty. Hence the decision to use outdoor waterproof metal boxes since they are dust proof. The barn was originally wired in the 80's/90's well before we bought it in romex and steel conduit for the drops. Hasn't burned down yet but I am converting it all since we can see areas where rodents have chewed the romex. Technically EMT is not to code in a horse barn but I feel safer with metal over PVC as horses are destructive and we've seen plenty of crushed or chewed PVC in horse barns. Panel has all AFCI/GFCI breakers. My main concern is sparking/fire from hay/bedding dust.

Ideally I would run a separate ground conductor and have no problem doing so except aluminum electrical box size is limiting. The single gang aluminum boxes are only 18.3cu in. The double gang aluminum boxes are large enough to not exceed box fill but they don't sell single device covers for the double gang boxes. Most of the boxes I just need a single switch or outlet. Adding two devices just puts me in the same situation as the second device takes up room. I would just get away with box fill on the single gang boxes without a ground but once I add a ground conductor I'm over fill. Any thoughts on a solution?

 

[rlitman]

...Ideally I would run a separate ground conductor and have no problem doing so except aluminum electrical box size is limiting. The single gang aluminum boxes are only 18.3cu in. The double gang aluminum boxes are large enough to not exceed box fill but they don't sell single device covers for the double gang boxes...

Box fill? Grounds aren't current carrying conductors, so you could have 27 ground wires in a box, but it still only counts as "1".

 

[alfredeneuman]

Code specifies PVC conduit for ag use only

There are 6 separate approved raceways and cables listed in Article 547. PVC conduit is just 1

 

[Yankeefarmer]

...but they don't sell single device covers for the double gang boxes. Most of the boxes I just need a single switch or outlet. Adding two devices just puts me in the same situation as the second device takes up room. I would just get away with box fill on the single gang boxes without a ground but once I add a ground conductor I'm over fill. Any thoughts on a solution?

I have multiple locations where I had to use two-gang boxes because I was installing a duplex receptacle and making a junction for other circuits. They make a filler plate that closes the opening for either a standard toggle type switch or a Decora style receptacle/switch. This allows you to use a two gang cover and install only one device.
Here’s an example: https://www.lowes.com/pd/Hubbell-1-Gang-White-Single-Blank-Toggle-Wall-Plate-Insert/1000050709

 

[s14kev]

Box fill? Grounds aren't current carrying conductors, so you could have 27 ground wires in a box, but it still only counts as "1".

Using 12GA THHN I have 4 conductors that terminate on the device, 2 conductors that pass through the box for another circuit, 1 device (outlet). That puts me at 18cu in. Adding 1cu in. for the ground conductor puts me at 19cu in. Those single gang aluminum boxes are 18.3cu in. I'm a stickler for following rules but maybe I should overlook this one!

 

[alfredeneuman]

That puts me at 18cu in. Adding 1cu in. for the ground conductor puts me at 19cu in. Those single gang aluminum boxes are 18.3cu in.

Deep version are available (2-5/8" instead of 2") that are 22.5 cu in
https://www.homedepot.com/p/BELL-1-...ree-3-4-in-Threaded-Outlets-5386-0B/315686619

 

[Engineer61]

Another option is to put your outlet boxes on a tee from the main conduit run, with a large double junction box on the conduit run. That removes your pair of pass through wires, and one set of wires to the outlet box, leaving just a single pair of wires to power the outlet. Large junction box has room for pair of pass through wires, plus the three pair of wires to power the outlet (1 pair into the junction box, one pair down to the outlet box, one pair out of junction box to next box on conduit run, connected together) together with all the ground wires you want.