6 #12 & 1 #10 in 3/4" EMT

Would you all mind double checking my figures. Let see if I can ask the question right.
Currently, I have 3 #12, with a #12 ground in 3/4" conduit. Two of the 3 are lights on different switches and the other one for a power outlet.
I used this website for the fill calculations. https://www.southwire.com/calculator-conduit

I may pull one of the light circuits out. It was a light that was on when the outlet that was for the portable air compress was on. I am adding a circuit for stationary air compressor. The motor tag says 17.2 FLA. I have the #10 laying around, so, for now, I am going to use that. I am extending the conduit along the wall for the compressor junction. I can pull out the #12 ground and replace it with the #10 ground.

So for the fill calculations, there are 6 #12 and 4 (L1,L2,N,G) #10. The fill for 3/4" is 26%. 26% less than 40%, good there.

The shop is currently not air condition. So the correction factor I am using here in Oklahoma is (96F to 104F) for THHN is .91. Maybe I should future proof for global warming and use the (105F to 118F) .87.

I think I read somewhere, for dereating you use the 90* column.
#12 CU =30amp
#10 CU = 40amp

30 X .87 (temp) X .80 (# of wires) = 20.88
40 X .87 (temp) X .80 (# of wires) = 27.84

Even being smart aleck, the #12 on 20amp breaker is ok, but I am a little shy on #10 for a 30amp. I would guess we are only 10 to 20 days a year over 100F and above 105F is rare. I would feel ok with a 30amp on the #10.

So, am I on track or is there something I am forgetting? Thoughts?
Do I need to change out the ground from a #12 to #10?

what is the HP rating on the motor nameplate?

FLA is meaningless because code requires conductors be sized by HP and FLC table.

wyliesdiesels said:

what is the HP rating on the motor nameplate?

FLA is meaningless because code requires conductors be sized by HP and FLC table.

Click to expand...

Man, I really thought I had done my research. Quoting Maxwell Smart, "missed it by that much".
The motor label had SPL in the HP box. I saw a lot of discussions that SPL does not mean much. There is 3.7 HP on the compressor.

You need to include the grounding wire for your conduit fill but not not for derating purposes, as it doesn't carry current.

After you do the ambient temp derating, you've got to further do it for the # of conductors.
The number of current carrying conductors determines the % to derate.
(7-9@ 70%, 10-20@ 50%)

wyliesdiesels said:

FLA is meaningless....

Click to expand...

Allow me to take your comments out of context.....but definitely not meaningless.

alfredeneuman said:

The number of current carrying conductors determines the % to derate.(7-9@ 70%, 10-20@ 50%)

Click to expand...

Thanks, that is what I needed. I thought it was 80%. So 3-6 is 80% correct?
Does the size of the wire make a difference in the derate?

So assuming I treat the #10 and #12 with the same percent.

Counting the neutral even though for now it will not be connected for the compressor, but I am running it would be 9 wires.

If I do not use the smart-aleck value

30 X .91 (temp) X .70 (# of wires) = 19.11
40 X .91 (temp) X .70 (# of wires) = 25.48

As I said, I will not need the compressor "switch on" light and I don't need to pull the #10 natural. That would move me back to 6 conductors and back to 80%.

I started to run a separate conduit.


The conduit going up and to the right is one I bent thinking I would run the compressor separately. It was just laying up there right now. If I do leave it I will add something across the unistruts to secure it.

Now, this may be another show stopper.
The conduit to the right, middle, behind tool box (above picture) is the power for outlets for the workbench and the light that will be over the workbench. That is where the 4 current-carrying conductors are coming from. The outlets are 4" boxes, not sure about the depth. I may need to add a spacer for fill reasons. I need to go back and read the fill rules for an outlet box. There are two duplex plugs. So there are the wires coming in, ones between plugs, and the one leaving. Does that affect the derating guidelines?

Let me add a couple of more pictures that might help make it clear.

Well, researching the box fill requirements was an eye-opener.
I think I am following up to where the grounds are calculated. So let me start with what I "maybe" understand, then do the grounds last.

Since I have two different wire sizes, I will have to calculate. The middlebox currently is the "fullest" because I was going to splice the bench light there before going up. Right now the so call bench light is wired into one of the duplex and the light is plugged into it. The light switch controls that outlet. I can pull it and rerun the wire to cut 2 out of the equation.

#12 = 2.25
#10 = 2.50

Outlet power (in) 2 #12 = 4.5
Outlet power (out) 2 #12 = 4.5
Two duplex (#12) 4 = 9.0
Two Light (in) 2 #12 = 4.5
Two Light (out) 2 #12 = 4.5
Three compress 3 #10 = 7.5
-----
34.5
Do I read right, that the ground counts as 1 and since I have #10 that would be 2.50.

So my total fill is 37. Does that look right?
So to meet code I need to add a 1 1/2" extender?

Edit
Last night I double checked and the 4" boxes are 2 1/8 square.

So, assuming so far I am right and now that I know I have 2 1/8", I have 30.3"
So I need to lose 6.7"

If I re-pull the bench light that would drop 2 of the #12 since they would be passing through and spliced. There is 5"
Also, I don't need the neutral for the compressor, there another 2.5"

Now the plugs are high enough above the bench that another 1 1/2" extension would not be horrible and I could splice the light and keep the #10 neutral.

Thoughts?

I'm not a fan of extension boxes, but when you need them, you need them.

In your case, since the box will be front and center, I would consider a RACO#256. It's a 4" sq box @ 3.5" deep.

penright said:

Outlet power (in) 2 #12 = 4.5
Outlet power (out) 2 #12 = 4.5
Two duplex (#12) 4 = 9.0
Two Light (in) 2 #12 = 4.5
Two Light (out) 2 #12 = 4.5
Three compress 3 #10 = 7.5
-----
34.5

Click to expand...

If the wires pass straight through the box, without a splice (wirenut), they only count once. So, don't splice your lighting and compressor wires, and you'll save a lot of cubic inches.

And yes, multiple grounds only count as one ( the largest AWG ) and each device counts as 2, (based on wire size connected to it)

Also, don't forget the raised box cover also has a cubic inch capacity stamped on it. So, add that to your box capacity

Steve

mm08822 said:

I'm not a fan of extension boxes, but when you need them, you need them.

In your case, since the box will be front and center, I would consider a RACO#256. It's a 4" sq box @ 3.5" deep.

Click to expand...

That's the ticket. I am with you, I don't like the way extension fit. I used one on a light switch that had outlet and duplex switch (if that how you say it.). No one around here stocks them. HD has them in a qty 25 box. I did find one on Amazon for $15 counting shipping.

Question, I did not see the fill listed on the NEC. Did I just miss it?

Did I read right that if it is not listed on the chart, then it has to be stamped on the box?

I tried to zoom in on the one picture I had of the light switch and it is very pixelated, but you get the idea.

penright said:

That's the ticket. I am with you, I don't like the way extension fit. I used one on a light switch that had outlet and duplex switch (if that how you say it.). No one around here stocks them. HD has them in a qty 25 box. I did find one on Amazon for $15 counting shipping.

Question, I did not see the fill listed on the NEC. Did I just miss it?

Did I read right that if it is not listed on the chart, then it has to be stamped on the box?

I tried to zoom in on the one picture I had of the light switch and it is very pixelated, but you get the idea.

Click to expand...

It's 40.5 cu in from mfr specs. See pic.



That table would be massive if every box size were included in it.

I believe only raised covers/mudrings require cu in stamp.

I still have the option of going up, over, then down like how I started.

It just would have been cleaner to go down that middle girt. Looking back at the picture I had to kick back go behind the post, then kick back out to the box. What if that was low enough that I could run a conduit just about it. Then I could use the knock out that is above it on the distribution panel. Kick back behind the post, then go behind the boxes above the bench down to the compressor outlet.

My question is how do you support two conduits stacked so that one conduit is not supporting the other? Can that be done?

Also, in researching EMT support, my straight conduit between outlets are not up to code. I guess there is no minimum distance between boxes that do not require support. Are support and strap used interchangeably?

If the girt is deep enough to run the 3/4" conduit in it, remove the conduit and place into the channel of the girt with the offsets rolling the conduit upward. Use the same ko's in the panel and jbox. If the offsets are too deep to get the conduit into the girt, cut it in the middle and use a coupling.
Doing that should give you enough room for a strap in the girt. Locate the strap directly in front of a siding rib so the siding doesn't take a hole!

Conduit has to be secured within 3' of a box. If less than 3' between boxes, then it is considered secured by the other box.

mm08822 said:

If the girt is deep enough to run the 3/4" conduit in it, remove the conduit and place into the channel of the girt with the offsets rolling the conduit upward. Use the same ko's in the panel and jbox.

Click to expand...

Yes, I will have to try that. As you said, I will have to pull it to move it. Also, there are 3 other boxes after that one, so depending on slack, that could be a chore, needs to be done, but not easy.


Before I read your post, I did take a picture of dropping the current conduit down and sliding the new one over it. I stuck couple of short pieces on top just for a visual reference. So is there a way of supporting the two on top of each other?

The question is - does the girt accept 3/4"C behind the post?

For the future, will you be able to pass 3/4"c behind the 4" sq boxes?

mm08822 said:

The question is - does the girt accept 3/4"C behind the post?

Click to expand...

Yes. The trick is where they screw the siding. Most of that row is toward the top. If I did hit a screw, I could grind it down some. On my way home tonight I am going to pick up a few sticks. I am thinking out loud, I could let the compressor run inside the girt and leave the current run the way it is. Then kick it out to the box. The outlet will be on the same girt, about 10-12' down.

mm08822 said:

For the future, will you be able to pass 3/4"c behind the 4" sq boxes?

Click to expand...

Yes, no problem. Hard to tell from the picture but the one is behind the JBox. Besides the width of the grit, you can press into the insulations some.


This may seem I am overthinking this, if all I wanted was to just wire it up, I just would have used the way I started. I have learned a lot from this exercise.

One thing I learned, I may be out of code when I am adding a device to make a "dumb" switch "smart". If you replace a dumb with smart then there is no fill change. When you splice in a device and use the existing dumb switch then since none of the wires exits the box they don't add, but you are adding something, a gadget of some sort. Would it be a second switch even though it is not on the outside? Should you count 2 wires? Getting way off thread here. This rabbit hole started with me explaining how these questions help me learn and I appreciate the community time.

penright said:

Yes. The trick is where they screw the siding. Most of that row is toward the top. If I did hit a screw, I could grind it down some. On my way home tonight I am going to pick up a few sticks. I am thinking out loud, I could let the compressor run inside the girt and leave the current run the way it is. Then kick it out to the box. The outlet will be on the same girt, about 10-12' down.

Yes, no problem. Hard to tell from the picture but the one is behind the JBox. Besides the width of the grit, you can press into the insulations some.

This may seem I am overthinking this, if all I wanted was to just wire it up, I just would have used the way I started. I have learned a lot from this exercise.

One thing I learned, I may be out of code when I am adding a device to make a "dumb" switch "smart". If you replace a dumb with smart then there is no fill change. When you splice in a device and use the existing dumb switch then since none of the wires exits the box they don't add, but you are adding something, a gadget of some sort. Would it be a second switch even though it is not on the outside? Should you count 2 wires? Getting way off thread here. This rabbit hole started with me explaining how these questions help me learn and I appreciate the community time.

Click to expand...

I would have used the girt as the "raceway for the raceways". One conduit high in the girt and the other one low in the girt. Straps would secure in the middle of the girt. (Ok, the siding screws easily screw this idea up!)
Then offset out of the girt into the jboxes straddling the returns of the girt.

Each device (or strap or yoke) requires a 2 wire allowance.

grounded-b said:

Also, don't forget the raised box cover also has a cubic inch capacity stamped on it. So, add that to your box capacity

Steve

Click to expand...

Steve, you called it. I pulled out a box cover last night. It was 6.5CU. So with my 30.3 from the box, that gives me 36.8.

Outlet power (in) 2 #12 = 4.5
Outlet power (out) 2 #12 = 4.5
Two duplex (#12 connected) 4 #12 = 9.0
Two Light (in) 2 #12 = 4.5
Two Light (out) 2 #12 = 4.5
Three compressor (L1, L2, N, G) 4 #10 = 10.0
-----
37.0
Missed it by .2.

So I can drop that box to a single duplex and keep my light splice or pull a new un-spliced light wire. Single duplex is not a huge deal, I have plenty of outlets anyway.

Warning !!! Rabbit hole ...
The three boxes number 1-3 left to right, box number two, one of the outlets is split and I have the current bench light plugged into it. I am building a shelf over the bench and has two C-channel sistered back to back (horizontal beam) for support. I will have two boxes mounted to them. The conduit will go up using the window support between the two girts. So that is why I have to either splice or pull new. Also, I was thinking about adding an outlet up there. Right now I am welding the beam up. I am adding tabs for the light boxed and something to screw the conduit's supports. That way I am not putting holes into the beam. I thought about adding a small drop-down shelf for the DeWalt battery changers. And someplace to set charged batteries. I dropped that because I would need to splice another wire for the outlet above. Now if I drop to single duplex and pull new light, I can have the overhead battery charger shelf.

Here is a picture to help picture what I am talking about.
Pay no attention to the disorganize bench. I am pulling the "spoiler light". I will be using some metal shelves for shelving. The beam will be down the middle with a post on each end. The shelving is not wide enough to span the girt to the front beam. You can see where I have sistered some C-channel for the post in the background.

mm08822 said:

I would have used the girt as the "raceway for the raceways". One conduit high in the girt and the other one low in the girt. Straps would secure in the middle of the girt. (Ok, the siding screws easily screw this idea up!)
Then offset out of the girt into the jboxes straddling the returns of the girt.

Click to expand...

@mm08822, Thanks for your thoughts. As I said, I am not trying to make something more complicated, just my way of learning. I am glad I did, I learned a lot. Not only did the screws from the outside cause an issue with using the inside and the other issue of screwing into the back part would be penetrating the outside also. That is why I am using the split part of the C-channel. I never did find a clamp that would hold two conduits one of top of the other. Somewhat a moot point now, but you never know when it might be needed again.

mm08822 said:

Each device (or strap or yoke) requires a 2 wire allowance.

Click to expand...

So my 3 gang box is 57ish CU. I bet they used #14 for lights, but worse case I will use #12. L, N, G is 6.75. Then 3 light switches. 27. And 3 devices 27. That is 60.5 if all 3 were automated. Actually, I only automated two of the lights so I am ok. But if I would not have learned what I did and I would have been in trouble. Thanks again.