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North American 10HP RPC - Questions about load center

Adair Orr

Aluminum
Joined
Apr 11, 2006
Location
Seattle
Hello,
I have ordered a CP-10 from North American. I am preparing to run my metal shaper with a 5hp motor (18 amps) and a power hammer with a 3hp motor(yet to document amperage). I have some questions that are identified on the attached drawing. My hope was that someone could either offer some direction for sizing the load center and circuit protection.
The questions on the drawing are as follows:
  1. Can the RPC plug into a 50 amp receptacle or do I need to abandon the outlet and hard wire the device?
  2. Do I need a disconnect between the RPC and a load center? I have a 30 amp fused disconnect, might that work?
  3. What gauge wire do I run between the RPC and the load center
  4. Is a 125 amp 12 space/24 circuit type BR 3 phase main lug load center the right distribution panel for a maximum of 4 three phase circuits?
  5. How do I size the wire between the protection in the load panel to the motor on the machine.
I'd happily pay an electrician for this input, but I have yet to find someone near me who is willing.
Best,
Adair
 

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1. Use the 50 A receptacle for testing. Later use conduit and wire. Either way works.
2. I use a disconnect between the RPC and the incoming power. My RPC has fuses and a breaker with a door interlock.
I would not use a disconnect between the RPC and load center. It doesn't hurt at first to have another part in the works that can fail later.
I would not use the main panel breaker as a permanent solution for turning the RPC on/off.
3. How long are the wires?
4. Not sure. Appears to be ok.
5. How long are the wires? I use a safety margin of 1.5 to 2X in current capacity.

Your drawing is excellent!
If everybody asking a question had a drawing like that then issues would be easier to figure out.
 
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You don’t need the disconnect. Just turn off the breakers in the panel.

Things typically work better with bigger wire. I personally would run #10 (good for 30 amps) to your machines.

The phase converter instructions should come with a minimum recommended wire size for both the panel and the idler. You don’t want to skimp on the wire size for that.

I believe going by memory that typically the single phase side of the wiring is seeing 1.73 times the amperage the 3phase side is.

My American rotary 75 had a minimum recommended wire size of 4/0 on the single phase side and a min 2awg going to the idler. Big difference in wire size.

Best bet is to get the instructions and see what they recommend as a minimum and go a bit bigger.
 
Eh, I'd NOT use the breakers.

Breakers are not switches. Unless specially rated, they have only a certain number of operations and then they fail.

Some are rated for switch duty, and those are OK. You probably do not have that type.
 
Thank you all for the feedback. This gives me a lot of confidence that I can install this safely.
I began pricing load centers and breakers. Great Scot! I'll be spending some money on this little project.

Unfortunately if I hardwire this RPC I will lose the outlet that powers my lathe. It runs on single phase. I'll have to figure that challenge out another time.
-A.
 
Nothing stops you from running a single phase out of the new box. Just connect to the incoming wires for the RPC, the "pass through".

It's not forbidden to do that, it's often done. You may want to label the outlet.
 
Nothing stops you from running a single phase out of the new box. Just connect to the incoming wires for the RPC, the "pass through".

It's not forbidden to do that, it's often done. You may want to label the outlet.

Wow, that's great. This is really going to add versatility to my shop.
-Adair
 
Hello again,
I found an Industrial Electric MFG load center that is 100 amps. It comes with 30 amp breakers which are perfect for my applications (1.25 x the maximum motor draw). How can I be certain that this is a load center that will work for me? I've attached a photo.
 

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It's marginal and not really "right".

You will have to be very careful about neutral to use that, and some (1/3) of the single phase breakers will not be useful, as they are intended for 120/208Y.

You are presumably going to have "stinger" or "high leg" 240VAC, which is a different thing entirely TThat is what RPCs make). Your line to neutral in that case will vary, being 120V for two lines, and from the third line, about 206VAC.
 
Diamond,
Hmm, now I'm in foreign language territory. I'm primarily concerned about the 30 amp three phase breakers, not the 20 amp single phase ones. I could save hundreds of dollars if this load center worked for my application. That said, I want to do it right and sensibly because my understanding is limited.
Edit - I see now that you are probably referring to the panel itself. On the sticker it says 208 Y/120. Is that the dilemma?
 
Not entirely. If the 208 is not a "hard" rating, that may be OK.

You have to look at the ratings for voltage to ground. Mostly things fall into classes of "300V or less to ground" and "150V or less to ground".

If this is rated only for 208 that would be 120V to ground, and so it is likely in the 150V maximum class, but your 206V is above that, and this panel would be disqualified.

The other issue I referred to was that every 3rd single phase breaker is actually supplying the generated leg, which is 206V to ground, a voltage that nothing runs at. You'd need to remove those breakers and blank off the breaker slots.
 
That panel is rated for 240volts. You will be fine using it. Just remove all the single phase breakers and put blank covers in the empty spots. Use it just for the RPC 3 phase loads, to avoid any issues and you will be good.
 
Depending on the location of all your boxes and RPC, you can feed the heavier 2 leads of your single phase panel supply directly to your 3 phase panel skipping the RPC. (thru a properly rated breaker of course) Then bring the single manufactured leg off your RPC back to fill in the 3rd spot on the 3 phase panel. This can make it easier and possibly cheaper to put the RPC in a location where you don't have to listen to it all day. Bringing only one wire back home helps that.

Back in the day I had my RPC in the basement fed off an existing sub-panel there. I only brought the Manufactured Leg back up to the garage to feed my 3 phase panel there. (The other two lines fed from the main single phase panel in the garage 1 ft away.) Worked perfect for over a decade.
 
Hello,
I have ordered a CP-10 from North American. I am preparing to run my metal shaper with a 5hp motor (18 amps) and a power hammer with a 3hp motor(yet to document amperage). I have some questions that are identified on the attached drawing. My hope was that someone could either offer some direction for sizing the load center and circuit protection.
The questions on the drawing are as follows:
  1. Can the RPC plug into a 50 amp receptacle or do I need to abandon the outlet and hard wire the device?
ID reccomend hard wiring it only, less chance for failure when under load and it pulls more then 50A and melts the plug.
  1. Do I need a disconnect between the RPC and a load center? I have a 30 amp fused disconnect, might that work?
NO, 30A wont cover it. 10HP is about 30A 3 phase, multiply by 1.73 and you are 51.9A single phase. so pull down 60A disconnect is better after a 60A breaker.
  1. What gauge wire do I run between the RPC and the load center
Rate for 60A so short run (under 150 ft)8-3 is probably good.
  1. Is a 125 amp 12 space/24 circuit type BR 3 phase main lug load center the right distribution panel for a maximum of 4 three phase circuits?
sure, depends on various factors.
  1. How do I size the wire between the protection in the load panel to the motor on the machine.
Biggest you can afford or the lugs will fit. i went a size up in copper as its a short run.
I'd happily pay an electrician for this input, but I have yet to find someone near me who is willing.
most should be able to, trades are a weird bunch
Best,
Adair
 
I guess there are more variable than I imagined.
I decided to sell some tools to fund this wiring project.
I would buy a proper 3 phase load center like the one attached below (12 Spaces, 125 A Amps, 208Y/120/240V AC, QO Circuit Breaker Type)


Won't I have the same problem with the "High Leg" in any load center if I want to have one single phase, 240 outlet? There will be one bus bar that is 206V rather than 120V, correct?

Depending on the location of all your boxes and RPC, you can feed the heavier 2 leads of your single phase panel supply directly to your 3 phase panel skipping the RPC. (thru a properly rated breaker of course) Then bring the single manufactured leg off your RPC back to fill in the 3rd spot on the 3 phase panel. This can make it easier and possibly cheaper to put the RPC in a location where you don't have to listen to it all day. Bringing only one wire back home helps that.

Back in the day I had my RPC in the basement fed off an existing sub-panel there. I only brought the Manufactured Leg back up to the garage to feed my 3 phase panel there. (The other two lines fed from the main single phase panel in the garage 1 ft away.) Worked perfect for over a decade.
13 engines:
My RPC will hang on an interior partition wall. I can put the idler motor directly behind that wall and reduce the noise if that is a problem. The run would be very short.
 

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Hello again,
I decided to take a look at the IEM panel that I first posted. It was built so stoutly and it had copper busses so I talked them down to a ridiculous price and bought it. It sure seems like it should work.

I've updated my wiring diagram per previous discussion and with wire sizes from the RPC Panel manufacturer. I increased the wire size by 1 AWG for the 3 phase loads, from 10 AWG TO 8 AWG. I left the split phase supply at 6 AWG because that is what is supplying my existing 50 amp outlet.

If anyone cares to take a look and comment, I sure would appreciate it. I'm showing one split phase load on the 3 phase load center. It will draw only from the L1 and L2 busses of the panel, avoiding the manufactured leg L3. Will that work?

I have a couple questions:

1. What happens to the neutral (white) wire from the split phase supply to the RPC panel?
2. What do I ground the RPC panel, the idler motor, and the 3 phase load center to?
3. What do I do with the neutral from the split phase load going to the 3 phase load center?

If this is too specific, or presents a liability problem, please just let me know. This is a fun learning process for me.
Many thanks.
-Adair
 

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1) Nothing. There will be no white wire in anything you do as far as hooking up machine tools goes.

2) I'd say carry a ground over from your single phase panel. Then ground your machines to the new panel. Seeing as that's where all the other wires feeding your machines will come from.

3) Again... forget you ever saw a white (neutral) wire.
 
1) Nothing. There will be no white wire in anything you do as far as hooking up machine tools goes.
Roger that. In that case, do I just cap the neutral (white) wire and tuck it into a junction box?
2) I'd say carry a ground over from your single phase panel. Then ground your machines to the new panel. Seeing as that's where all the other wires feeding your machines will come from.
Thank you, that makes sense to me.
3) Again... forget you ever saw a white (neutral) wire.
I will do just that. I've omitted any reference from my drawing.
 

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You really won't have any white wires in the cables or connections you run. If you do, and need it for one of the three power wires feeding your machine, just color code it with tape at the end point(s). Again... forget all about white neutral wires.

For instance... you have a 3 conductor chord w/ground and one of the conductors is white, just tape it black or one of the standard 3 phase colors.

Try to set up a system and stick to it so you always know which lead is your manufactured phase. Then just keep that off of any Machine Tool transformer connections you run into.

If you want to run 110 volt stuff for computers and such, (which will have a neutral white) feed that out of your single phase panel as a separate deal.

If you run your conductors in EMT or Rigid conduit, you don't need to run a ground. Though if at any point you switch to flex or water tight or anything else, a ground will have to be carried from that point on. Not sure if this last paragraph is true in every state.
 
Oh my gosh, I just realized that I have been misrepresenting my power source. The 50 amp outlets in my shop are all NEMA 6-50. I had it in my head that they were NEMA 14-50. Therefore, yes, there are no white neutrals to deal with at all.

Is there any other way to branch off of the split phase circuit with a (edit: single phase) 240V 20 amp outlet than what I have shown in my diagram (using two poles of the 3 phase load center)? This load is for my Lathe and I'd hate to run the RPC just to power it.

-Adair
 
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