Two different power sources in 1 control cabinet

alive15

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Hello all,

We have an electrical cabinet which powers an okuma machining center (OMC) and also includes i/o module for robot. All devices related to OMC is powered from 480V, which is stepped down to 120V (NPN), which is then stepped down to 24V (NPN). The main breaker / disconnect is tied to the 480V 3 phase coming in.

Looks like few years down the line, they added a fanuc robot in front of the machine, so it was necessary to install an i/o module inside the same cabinet. However, for some reason, this was wired using PNP setup. So someone added a separate 120V power supply inside the cabinet, which is then stepped down to 24V pnp. The 120V is not connected to any switch / breaker, there are only fuses. It is actually coming from a power outlet next to the machine.

From my understanding, the idea was, in case the OMC went down, the robot i/o module was still powered on, and the robot could still run.

My task is to eliminate the safety issue where if someone turns the breaker off, they may assume there is no power in the machine, when actually there is still 120V / 24V pnp for the robot i/o module.

So I have figured out the wiring, and I can re-wire the robot module circuit to get fed by the original 480V coming in, so everything inside the panel would be tied to the OMC main breaker, but would lose the advantage of having the robot running in case the machine goes down.

Is it considered good practice for me to add a plexi-glass covering with holes around the robot i/o module power supply, and maybe change the wire colors to "orange" to showcase that power is still inside the machine, even though the main breaker is off? I want to figure out a way to keep the robot alive, even if the OMC breaker is turned off. I don't want to create a separate panel / junction box just for the robot i/o module power.

The reason I have recommended this idea, is I have seen something similar on different machine, were they used orange cable to denote power was still on the machine (it was backup battery for computer)

Any ideas are appreciated. Thanks,
 
alive15 said:
Hello all,

We have an electrical cabinet which powers an okuma machining center (OMC) and also includes i/o module for robot. All devices related to OMC is powered from 480V, which is stepped down to 120V (NPN), which is then stepped down to 24V (NPN). The main breaker / disconnect is tied to the 480V 3 phase coming in.

Looks like few years down the line, they added a fanuc robot in front of the machine, so it was necessary to install an i/o module inside the same cabinet. However, for some reason, this was wired using PNP setup. So someone added a separate 120V power supply inside the cabinet, which is then stepped down to 24V pnp. The 120V is not connected to any switch / breaker, there are only fuses. It is actually coming from a power outlet next to the machine.

From my understanding, the idea was, in case the OMC went down, the robot i/o module was still powered on, and the robot could still run.

My task is to eliminate the safety issue where if someone turns the breaker off, they may assume there is no power in the machine, when actually there is still 120V / 24V pnp for the robot i/o module.

So I have figured out the wiring, and I can re-wire the robot module circuit to get fed by the original 480V coming in, so everything inside the panel would be tied to the OMC main breaker, but would lose the advantage of having the robot running in case the machine goes down.

Is it considered good practice for me to add a plexi-glass covering with holes around the robot i/o module power supply, and maybe change the wire colors to "orange" to showcase that power is still inside the machine, even though the main breaker is off? I want to figure out a way to keep the robot alive, even if the OMC breaker is turned off. I don't want to create a separate panel / junction box just for the robot i/o module power.

The reason I have recommended this idea, is I have seen something similar on different machine, were they used orange cable to denote power was still on the machine (it was backup battery for computer)

Any ideas are appreciated. Thanks,
Click to expand...

I would add a local disconnect, a 6 pole switch, between the 3 phase power to the first panel (3 of the contacts) to the OMC as well as interrupting the 120V feed to the robot power supply (1 contact). That is a positive lockout point for 'the whole thing', but under normal operation the 120V power would stay on during an OMC trip.

But perhaps I mis-understood the question ;)
 
Is that acceptable practice? To have two separate disconnects on the same panel for two different power sources? This would require two lockouts on the machine, instead of one. See my sketch?
 
It's a 480V 3 phase cable coming down from a bus bar into the cabinet. You can unplug it outside the cabinet if you want. So even if you turn the disconnect off, there is still 480V 3 phase inside the cabinet, on the top side of the breaker. I don't even know if this practice is allowed also, seems weird to lockout the breaker, even though the 3 phase is still on the top and inside the cabinet.
 
There is not a separate junction box for the 480V. The disconnect switch is right next to the door of the cabinet. Old machine (20 years), maybe that was acceptable back then, I don't know about today.
 
is the door interlocked with the 480 disconnect?

Is the disconnect with reach of the cabinet?
I am only asking because without seeing the set up it sounds like was done a long time ago and cludged together (i apologize if i'm wrong)..
I'm far from a safety expert or up on all codes but nowadays you have be very careful. If you touch it you own it.
 
please refer to NFPA 79 - electrical standard for industrial machinery.

if you keep the additional 120 volt power, you will need the following
(2) voltage stickers for the disconnect power 480 and 120
(1) this enclosure has more than one source of power
(1) 120 volt sticker below the sticker just mentioned.

the external 120 volt wire color will need to be yellow or orange ( sorry, I don't have my copy with me) and also be finger safe.

i'm not sure of the current rules for dual power past the finger safe part.

hope this helps.
james
 
No, opening the door will not cut power off. Yes, the disconnect is right at the cabinet door.

I will go ahead and just add another disconnect, seems like the easiest and best option for me. I'll just require the techs to use two locks, and add the stickers as James mentioned. And change the red wire for 120V to orange color for the robot module.

Thanks!
 
James Mcquade said:
please refer to NFPA 79 - electrical standard for industrial machinery.

if you keep the additional 120 volt power, you will need the following
(2) voltage stickers for the disconnect power 480 and 120
(1) this enclosure has more than one source of power
(1) 120 volt sticker below the sticker just mentioned.

the external 120 volt wire color will need to be yellow or orange ( sorry, I don't have my copy with me) and also be finger safe.

i'm not sure of the current rules for dual power past the finger safe part.

hope this helps.
james
Click to expand...

This is what i was going to recommend as well.
Also add the second lockout location to your LOTO placard that should be posted on the machining center, for the new disconnect you install.

Most the time everybody wants the cell to keep running if 1 machining center goes down, so you try to keep it at externally feeding the I/O module in the CNC only at 24Vdc, supplied by the robot/cell PLC. Not supplying module power from the CNC.

But in your case it seems like they grabbed 120V and introduced it into the panel.
 
Current code is now Orange for wires that are not de-energized with the control panel's disconnect - no longer yellow. Of course, that depends on what NFPA your state is currently enforcing
NFPA enforcement map (scroll down half way)
Typically, use Orange with a red stripe for AC power from an outside source, and orange with a blue stripe for DC power from an outside source.

As mentioned above, if it is AC voltage, it probably should have a disconnecting means at the panel. If there is room, a disconnect inside the panel would work, or you can get an external disconnect like the ones below:
External disconnect enclosure
 
Rson said:
Current code is now Orange for wires that are not de-energized with the control panel's disconnect - no longer yellow. Of course, that depends on what NFPA your state is currently enforcing
NFPA enforcement map (scroll down half way)
Typically, use Orange with a red stripe for AC power from an outside source, and orange with a blue stripe for DC power from an outside source.

As mentioned above, if it is AC voltage, it probably should have a disconnecting means at the panel. If there is room, a disconnect inside the panel would work, or you can get an external disconnect like the ones below:
External disconnect enclosure
Click to expand...

I thought the wire code had to do with the voltage not if it was always energized.

name the five colors associated with a 120/280V Y three phase panel - red, blue, black, green, white neutral

name the five colors associated with a 277/480V Y three phase panel - brown, orange, yellow, green, gray neutral
 
Van,

is this your color standard or is there a code for these colors?

By the way, green doesn't always mean ground !
no, i'm not joking. my previous plant used green as 120 volt output wire because it was all they had on the weekend to get a machine running.
No, the wire did not get replaced. I found that out the hard way and lost the battle to replace the wire when I brought it up to the engineering manager.
it has been running for years and no one has complained yet was his answer.

james
 

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