24 VDC, 120 VAC, 5 VDC frequency (all low power/current) in same conduit? 1

[PaulKraemer]

Hi,

I am working on a project for which my company will be providing a small machine that will perform a particular function. The controls for this machine will be located in a dedicated control panel that will not be mounted directly on the machine. A limited number of wires and cables will be required to connect the Control Panel to the machine. The intention is for the Control Panel to remain in a single location, but for the machine to be disconnected and removed when it is not in use.

For this reason, I would like to use multi-pin connectors at one end or the other for all of my interconnect wires and cables with the goal being to make the disconnection/separation of the Machine from the Control Panel as easy as possible. One of my interconnect cables will be for the power connection from a VFD to an AC induction motor. As this is a higher power / more likely to create noise connection, my plan is to run this cable all by itself. I've already received some good suggestions on this forum regarding the types of connectors I can use.

The remaining wires and cables that have to go from the Control Panel to the Machine are as follows:
(1) Two wires used to energize the 24 VDC coil of contactor (specs list the coil inrush power as 5.4W and the hold in power also at 5.4W
(2) Two wires used to energize the 120 VAC coil of a contactor (specs list the coil inrush power as 70 VA and the hold-in power at 7.5 VA
(3) Three wires used to engerize 24 VDC PLC inputs
(4) One three conductor shielded cable that provides frequency feedback (5 VDC signal) from a ring-kit speed sensor mounted on a motor)

Both of the contactors I mentioned in (1) and (2) above remain energized at all times while the equipment is in operation, and are only de-energized if someone hits an E-Stop pushbutton. (So these contactors do not switch ON and OFF during normal operation).

My gut feeling is that I most likely would not have a problem if I was to run all the above wires and cables ((1) - (4) above) through a single 3/4 inch liquid tight conduit and terminating them all on the same multi-pin connector.

I am just wondering if anyone here can tell me if my gut feeling might be wrong, or if there are any applicable codes that would make this a inadvisable. This equipment will be going to California. I am not specifically required to get it UL certified or CE marked, but when possible, I try to do my best to comply with these standards.

Any advice will be greatly appreciated.

Thanks in advance,
Paul

 

[itsmoked]

You are going to regret this silly design.

Install the controls on the machine like everyone else on the planet does for logical, historical reasons and only connect and disconnect the power to the system using proven, standard, approved, common, simple, inexpensive, non confusing, understood, readily available, and much more reliable means.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[PaulKraemer]

Hi Keith,

Thank you for your response. I think my attempt to simplify the description of my project resulted in my being unclear what exactly I am trying to accomplish. I will try to clarify by referencing the following illustration...

The "machine" I mentioned in my previous email is small module that will be used in conjunction with an existing machine. In my illustration, the existing machine is comprised of Module #1 and Module #2, which are separated by a Dryer. All of the controls for this machine are located in Control Panel 1-2. There is a single, dedicated 220 VAC power drop for this machine that goes into an approved disconnect in Control Panel 1-2. Inside this Control Panel 1-2, there is a transformer that transforms the 220 VAC down to 110 VAC, a 24 VDC power supply, a PLC, and a few DC drive boards (powered with 220 VAC) that drive 180 VDC motors. The motors and some operator controls (pushbuttons, selector switches, etc) are located in Module #1 and Module #2. All of the wires and cables that go from Control Panel 1-2 to Module #1 pass through Conduit A. All of the wires and cables that go from Control Panel 1-2 to Module #2 pass through Conduit B. These wires and cables are landed at terminal blocks in both locations. All power transmitted by these wires and cables is derived from the single 220 VAC power source and can be shut off using the Control Panel 1-2 disconnect.

Now, we will be building Module #3, which will perform a specific function which, when Module #3 is in place, will bypass Module #1. Module #3 will require its own Control Panel (Control Panel #3). Size, space, and access limitations make it impossible for me to mount Control Panel #3 directly on Module #3. Just like Control Panel 1-2, Control Panel #3 will have its own dedicated 220 VAC power source that will go into an approved disconnect. Control Panel #3 will have a PLC, a 24 VDC power supply, and two VFD's. The AC motors (controlled by the VFD) will be located in Module #3, as will a few operator controls (pushbuttons, selector switches, etc).

I will require some interconnect wires and cables to go from Control Panel #3 to Module #3 (to support the Module #3 operator controls and AC motors) and also from Control Panel #3 to Control Panel 1-2 (to support some limited hand-shaking between the existing machine and Module #3).

I plan to run dedicated cables for the AC motors (as these are the higher power, higher noise connections), but everything else is low power (5 VDC, 24 VDC, and 110 VAC; all at low current). I know I can install hard-conduits for Conduit C and Conduit D and land wires at terminal blocks just like on the existing machine, but being Module #3 will have to be removed occasionally, I was thinking removal would be easier if I used multi-pin connectors rather than landing at terminal blocks.

Do you think this is a bad idea? (Or an idea that might lead to violation of applicable codes)?

I appreciate your help.

Best regards,
Paul

 

[itsmoked]

OK I see it now.

Control Panel #3 will have a PLC, a 24 VDC power supply, and two VFD's. The AC motors (controlled by the VFD) will be located in Module #3, as will a few operator controls (pushbuttons, selector switches, etc).

No chance you can mount the two VFDs on Module #3? Even Nema 4 VFDs? It constrains the VFD power waveforms to the shortest paths.

I will require some interconnect wires and cables to go from Control Panel #3 to Module #3 (to support the Module #3 operator controls and AC motors) and also from Control Panel #3 to Control Panel 1-2 (to support some limited hand-shaking between the existing machine and Module #3).

The standard is this type connector:
Amphenol Industrial Operations Type connectors.

Note: Hold your mouse cursor over the picture column to call up larger photos. (Nice!)

Often referred to as Mil-Spec connectors.

Note: They come in both sexes, reverse numbering, bulkhead, free-hanging, plastic, cheap metal, cripplingly expensive metal, solder pins, and crimp pins.

Be aware that you may need very expensive crimping tools if you go the crimp route and especially since you'll have power and control sizes (2).

Typically Module #3 would have bulkhead connectors where all the wires converge to the bulkhead connector. This eliminates strain failures on the machine side.

Use all available strain-relief options with the free hanging cable side.

They take a bit of understanding but can reliably interconnect a lot of wires. Make sure they key differently or are incompatible sexs or sizes so it forces them to be correctly connected.

Do you think this is a bad idea? (Or an idea that might lead to violation of applicable codes)?

Nope. Nope. As long as the connectors are voltage and current rated appropriately.


Use separate cables/connectors for motor power, VFD nastiness, and any control wiring. (Even if the same destination is involved.)
The plastic shells are cheap and adequate unless you expect abuse via yanking, or walking-on. Consider using metal for the VFD output cables.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[PaulKraemer]

Hi Keith,

Thank you for your response. Unfortunately, I really do have no space to put the VFD's on Module #3. I will take every precaution to use a dedicated cable/connector for the motor power cable and to use a high quality, symmetrically grounded cable as recommended by the drive manufacturer. For my control wiring, I will read up on what AMP has to offer. I have actually used the type of connector shown below before in temperature control applications in which I used the same connector to pass a heater power connection (only about 3-4 amps) and an RTD connection. I did have to buy the expensive crimp tool. The toughest part was that I used 18 AWG high temp wire for the power wires and the RTD was a much smaller gage. The 18 AWG was easy to crimp, but the smaller gage was a challenge with the same size pins/sockets. I ended up getting it to crimp quite nicely by stripping a little more insulation off the RTD wires and bending them back over themselves before crimping.

Anyway, I really appreciate your help.

Best regards,
Paul

 

[mc5w]

Contact Electronics makes 4 pin power plugs and 4 to to a kajillion pin control plugs that can be ordered with a famale NPT conduit hub and can be used with liquidtight flexible metal conduit to solve some of your noise problems with the 120 volts and the VFD. These can also be ordered with mechanical pins to keep 2 seemingly identical plugs from being swapped.