What's the cleanest way to wire this?

[rust buster]

I'm running electrical in metal conduit in my shop (surface mount on poured concrete walls). I want to put three different 50A welder outlets on the same circuit (only ever use one at a time, it's just spacing them strategically so I don't have to use a welder extension cord for my Miller 252). I've always only used a 4x4" deep metal box with the 5OR outlet, but never had daisy chained outlets. I'm using #6 wire, coopper. For the first outlet, I tried pigtailing the wires with the large blue wire nuts, but that was not happening both due to space and size of wires going in, so I purchased these multi connectors, but even they are too large to fit in the box along with the receptacle. What's the best way to get the incoming power, power to the receptacle, and power back out to the next box? I could buy a much large box and use a hole cutter to make a hole for the 50R, but is there a better way? The 50R only appears to allow one wire in each terminal, so I can't use the receptacle itself as a junction.

 

[Bert_]

I'll tell you what I usually do but the receptacles aren't rated for it.

I run #8thhn, since it's rated a full 50A with these devices, and I stick 2 wires in the lug on the outlet. Simple quick and never caused me a problem.

If I had to have a separate splice I would have a box just for the splice. Could be a box with a blank and put the welder plug right below it.

 

[mm08822]

If they will truelly be for welders, you may be able to get away with #10 thhn Cu. Depends on duty cycle. Still can't have 2 wires under a terminal. 8's are safer if heaters may ever be plugged in.

As Bert suggested another box to contain the splice and the recept has its own.

Also consider 4-11/16 sq boxes.

I suggest you pull your conductors straight through the boxes. Pull back enough to make a loop in the first 2 boxes. Without cutting the conductors, strip enough insulation from the looped conductor to get a split-bolt connector on. Add a tail in it to reach the recept.
Tape up when done. Last recept get wired directly.

If running EMT conduit, you could also eliminate pulling a ground and just use a jumper from recept to green screw in each box.