Pull box sizing and 314.28

[LarryFine]

I am trying to size a pull box for a new installation. The desire is to run a single 4" EMT to house a feeder to one panel now, and room to feed an additional panel in the future. The largest conductors will be four 250mcm.

I'm looking for the minimum size allowable for the pull box. The feed will be the 4" EMT coming into one end (shorter) wall, and both the present 3" and unknown (2" or 3") future EMTs will come out of one side (longer) wall.

I want to use a 24" long box so it's long enough to straddle past the center knockouts on two panels on 16" centers. I'm thinking a 24" x 12" x 6" box will do, but the NEC sizing seems to indicate a 24" x 18" x 6" box is necessary.

This will hall under the angle-pull rules. They call for 6x the largest opening, so the 24" is necessary anyway, if I'm correct. But, with only a 3" on the side wall (for now), is the 18" adequate? Your opinions are requested, please.

 

[ActionDave]

Going off of memory but it should be six times the diameter of your largest conduit plus the diameter of each additional conduit.

 

[augie47]

The key may well be the "in the same row" clause. If your 3" is in the same row as the unknown conduits then the 18" would not meet Code. Different row, it would.

 

[LarryFine]

As of now, there is no additional conduit, so its not a concern now.

Incoming 4" x 6 = 24"
Outgoing 3" x 6 = 18"

A 24" x 16" box would comply, and be the next guy's problem.


Now, about the depth. Is 6" enough, or as long as the fittings fit?

 

[Dennis Alwon]

Is this what you are looking at

 

[LarryFine]

Is this what you are looking at

Yes, the 3" run in this drawing. A 4" coming from the left, and a 3" going out of the bottom. Only the single angle pull.

If anything is ever added, it would come in in the same 4" and leave through a new hole. I'm only concerned with now.

I'm only sizing for what I'm installing. The customer is the GC and builder, and is doing the rest of the wiring himself.

In fact, I'm working under his permit, as a sub, and doing only the service. He's even providing the wire, so I'm happy.

 

[don_resqcapt19]

Is this what you are looking at

Item C is often overlooked by electricians when sizing a pull box.

 

[LarryFine]

Item C is often overlooked by electricians when sizing a pull box.

Won't be an issue for me. I'll be following the outside L of the box, near each outside corner.

 

[LarryFine]

How is 314.28(A)(3) implemented? A 2.5" EMT would be large enough for the conductors.

 

[don_resqcapt19]

How is 314.28(A)(3) implemented? A 2.5" EMT would be large enough for the conductors.

You have to use the actual size of the raceway that has been installed.

 

[LarryFine]

You have to use the actual size of the raceway that has been installed.

314.28(A)(3) seems to allow exceptions, but I'm not clear how, unless the box listing must specify conductors like a conduit body.

 

[don_resqcapt19]

314.28(A)(3) seems to allow exceptions, but I'm not clear how, unless the box listing must specify conductors like a conduit body.

I have never seen a box so marked, but yes, if it was so marked, you could use that box size.

 

[LarryFine]

I took a pic of the outside today, after we ran the 4" conduit inside.

Notes:
1. Both conduits originally went through the wall to the upper-left of the 4" elbow, where the brick was patched and painted. I shortened the distance the lower LB sticks out of the switch. And, no, I haven't installed the strut and straps yet.

2. We didn't remove the original work, but we did reuse both LBs and the painted conduit and connectors. We didn't install the 2" run. (I would have used a single piece.) They're using it for temp power, so I have one coupling to put in.

3. The lower LB must be steel. It weighs about five times as much as the other one!

 

[don_resqcapt19]

The rules in 314.28 also apply to the LBs. Since you are using smaller conductors than you would normally see in 4", the LBs may be large enough, but you will have to do a calculation as conduit bodies that are marked are marked for "3 size XX conductors" so any time you have more than 3 conductors you have to do the calculations found in the last sentence of 314.28(A)(3).

 

[augie47]

Looks like one of the older pulling LBs and may not be marked. Hopefully it is or 314.28 will be a problem.

 

[don_resqcapt19]

Looks like one of the older pulling LBs and may not be marked. Hopefully it is or 314.28 will be a problem.

Looks too short to be a pulling LB to me.

 

[oldsparky52]

Are the LBs marked? What's the markings say?

 

[Carultch]

You have to use the actual size of the raceway that has been installed.

Suppose the raceway is oversized, possibly because you are unifying sizes with other unrelated circuits, or possibly because you are using a spare conduit that was sized without your work in mind. Can you cleverly get around this rule, by using reducing fittings to locally reduce its size, and using the reduced size for this calculation?

 

[LarryFine]

I will be going back tomorrow. I'll look in them, and take a pic of the pull box we got installed today.

We'll be pulling in four 250 MCMs and a #4.

 

[don_resqcapt19]

Suppose the raceway is oversized, possibly because you are unifying sizes with other unrelated circuits, or possibly because you are using a spare conduit that was sized without your work in mind. Can you cleverly get around this rule, by using reducing fittings to locally reduce its size, and using the reduced size for this calculation?

That would be up to your AHJ. I might accept that, but not without looking at the installation.