3Ph wire/conduit sizing, receptacles, etc.

[SCLead]

I'm gradually but steadily making progress on my rotary phase converter install. Thanks to info in my other thread, I know which direction I'm moving with it.

Now normally I'd research to high hell, read the NEC, query the depths of the internet for days/weeks, and come up with a well-vetted solution through research. I just got an email that a local/regional hardware store chain is going out of business, so everything is 15-40% off until it's gone, so I'm hoping to run down and stock up on parts I know I'll need. Since I've never dabbled in 3ph power, I'm hoping some of you can help out with some more general questions, and I'll do the diligence of digging into NEC for specific answers before I actually execute my install.

A little reference: longest run will be <20ft. 240v 3ph from an RPC output source. Highest machine draw is 7.5a. Five machines total, going to put in one receptacle for each.

- How can I calculate the max capacity of EMT conduit, in terms of wire size, ampacity, etc? Obviously I'll run into physical limits of cramming more and more wire into one stick of EMT, but from my limited experience, you usually have to up-size your conduit to make pulling wire possible/easy before you actually reach ampacity limits.

- None of my machines currently have wire from the machines, nor plugs on them. Is there a "standard" receptacle/plug configuration? i.e. residential 120v mostly sees NEMA 1-15 15a receptacles, with 20a occasionally. Is it more common to see a certain amperage receptacle in shops on 3ph? I can run any of my current equipment on 15a receptacles, but if 30a NEMA 15-30R's are the ubiquitous "you see it everywhere" receptacle, then I'd rather invest in those for future compatibility in case I reconfigure my installation. Yes, I understand this will force upgrading wire and conduit size.

- Somewhat related - for in-wall installations of single-phase 240v, what's NEC require size-wise for a 40a run <40ft? I calculate 8awg, but I've come across situations where NEC has a minimum size requirement out to 100ft or whatever, so I want to be sure I'm kosher there, as I need to run two more single-phase outlets to the breaker box on top of the 3ph stuff.

[Carpenter84]

The simple question first. I don’t know where you are, so I go by Ontario rules.

40a is 8awg nmd-90, simple romex wire for in wall. 8awg is good to 50a with a non-resistive load up to 120’. Over 120’ then upsize.
Rule of thumb is upside to the first 120’ load, then regular gauge thereafter.

Do you plan to use a panel to distribute your 3ph power? Or just direct?
How many circuits do you plan on?
What’s the likelihood of ever running more than one machine at a time?

Ideal would be a dedicated circuit to each machine. Either a physical plug at the machine location, OR a disconnect switch. Plug is cheaper. Either are fine, just always have to have a means to physically disconnect the machine from the power source, cannot rely on breakers or fuses.
If max ampacity is less than 12a then 14awg is fine. 14awg is fine to 15a, but in most cases with large draw appliances or spike loads, you don’t want to exceed 80% of thr wires capacity.

As far as conduit size, just go big. There’s a whole calculation to determine fill, but don’t bother, just go bigger than you think you need. No rule against that. When I run conduit, it’s almost always 1 1/4” pvc (outdoors/inground), not too much commercial/industrial. Unless I’m running 4/0 services, then it’s 2”.

If you are running a single branch circuit in each conduit, go 3/4” for ease of use for all aspects. If you are going to daisy chain with one conduit, then just go big. 1 1/4”.

[Carpenter84]

As far as the plugs used, if you choose a physical plug over a hardwired disconnect, choose a plug that meets the correct amperage rating set by the machine and the circuit. You really should not “standardize” your plugs for “future use”. If you use a 30amp plug on a 15a circuit, and someone in the future comes along and thinks it’s a 30a circuit and plugs a 30a appliance in, it’ll trip. Or vise versa, standardize your shop with 30a circuits everywhere for “headroom” and put 15a plugs on, or plug in a 15a machine, you could wind up with some serious issues if there is a short. The circuit breaker won’t trip, and you could start a fire.

[4GSR]

In my garage shop, I have one 30 amp line with two L14-30 receptacles wired into the circuit.  Also a single 30 amp line with one L14-30 receptacle.  All my 120v plugs are on 20 amp services.   The only place I've used L15-30 plugs is on true 3-ph circuit, like on the output of a RPC, and I've done that, too.  I try to keep the Receptacle/plug arrangement in compliant to NEC code so that way it takes the guessing game out what that receptacle is putting out.  Size your wire according to code or what Shawn mentioned.

[woodchucker]

I will be going through this shortly. After I rebuild the surface grinder.
I have a rotary converter that I have never used. I'll need to learn as you.

I don't have any capacitors with mine, not sure if I need it. It's a Cedarburg unit.

[Carpenter84]

I don't know anything about the RPC units, but I do know the wiring down stream if anyone wants advice. Again, I only know Ontario code.

[firestopper]

On the RPC system, I ran 3/4" conduit. This allows for easy pulling and is not expensive. The standard cord cap I use on all machines are twist-lock NEMA  L-14-20P (plug) and L-14-20R (receptacle).  None of our machines come close to the 20 amp rating on these, these can be found in Leviton, Hubble etc. I buy mine at Home Depot without issues. The junction boxes and cover plates can also be sourced at your local hardware store.
If your machine requires a longer cord, then chart it accordingly for amperage drop, but 3 ph draws 1/2 the amps as single phase does so many machines come with smaller gauge wire. I use larger gauge 4 strand wire to accommodate the 20 amp plug.
 
 

[SCLead]

Great, thank you!

My (rough) plan is as follows:

Mount the RPC idler and box on the wall, with the converter box feeding a separate distribution box nearby (mounted above, next to, etc...details yet to be resolved). From the distribution box, each circuit will be fused inside the distribution panel, with conduit run to an individual receptacle for each machine. That will be a total of 5 circuits, ranging from immediately adjacent to the distribution panel, out to about 20' away at the farthest. Likelihood of running multiple machines at the same time is near zero, but the possibility is there, I suppose. Probably easiest to just plan to never run more than one at a time, which should be no issue as it's just a home shop. Daisy chaining the receptacles off one conduit would make for the cleanest install, but how does one terminate 1-1/4" EMT into a box? I can't imagine manually bending offsets is a task for the faint of heart.

I'm hoping to stick to one size conduit, because I don't own conduit benders in any size, and would prefer to only have to get my hands on one. That said, I'm not so eager to reduce costs that I'm willing to compromise the install in an unsafe manner. I've got a fair bit of background with 120/240v installations, but most of those were mobile applications using MC across the board, so EMT and 3Ph are a double-whammy of new beasts to me.

[PJB]

I used NEC 2008 when doing my RPC setup. 
Here are the few tables I believe are pertinent for conductor fill.  But be advised there's more to consider, not just # of X ga conductors in X size pipe. There's 30+ pages of rules and conditions to sort thru just to determine WHICH table actually applies and I can't post all of it.  Suffice to say going larger on the EMT won't hurt other than being nominally more $.   



 

[PJB]

Here's what I did if it helps any for referencing.   Bought everything on Ebay for pennies on the $ vs retail because boy it can get pricey quick buying new.

I have a 7.5HP RPC setup in my shop powering (4) machines.
 
Each machine has its own dedicated 3P breaker and pipe run to twist lock plug and receptacle.   

[SCLead]

Thanks PJB! I got a little chance to browse the NEC today and answered a lot of questions. Can anyone help me along the way in regards to fusing for 3ph motors? I left my work computer at work, so I mistakenly don't have the information in front of me to reference sections/numbers.

From what I read today, it was something like 175% the locked rotor draw for a slow-blow fuse on each of the three legs of 3ph power going to a motor - does that sound correct? I'm trying to nail down what types of fuzes I need, then figure out amperage. Am I correct to assume you don't fuse each leg at the full locked rotor amperage?

[PJB]

Watch this.... https://www.youtube.com/watch?v=Vc8vW826zmY

and this..  https://www.youtube.com/watch?v=nvJaaWGJMo0

Hope it helps you.