Control panel design

[cornbread]

Recieved a new piece of equipment and the control panel has 480V sprinkled thru out the panel. There is a 480v drive next to the PLC. I know its a crappy design but are there any standards for building panels? I plan on modifying the panel so the controls group can access the PLC with out opening the panel door, but i would think this would be a safety design standard to avoid the problem in the first place?

I should mention the panel was built by a German company (I'm sure built to IEC standards).

As alway, I apprciate the informed opinions expressed by all.

 

[augie47]

There are standards and there are also Nationally Recognized Testing Labs (NRTL) such as U.L., CSA, ETL, etc.
THe NRTLs have the responsibility of assuring the equip met meets the standards prior to applying their stickers.
Some jurisdictions (such as the State of TN) and OSHA require the equipment bear the label of a NRTL before being place in service.
A lot of foreign equipment will have a "C-E" label. C=E is not a NRTL.

 

[jim dungar]

I know of no standard that would prohibit the 'intermingling' of voltages within a panel. There are some that restrict voltages on the doors.

Dividing the panel into "line" and" control" sections is a design decision.

 

[petersonra]

I agree that it is a design decision. And arranging control panels in the way you describe is often more trouble then it is worth to the builder, and does not always do all that much for the end user. Worse yet, it almost always ends up making the thing physically larger. A lot of times there are different voltage levels on the same device, like a VFD for instance. it is not unusual to have 480VAC, 120VAC, and 24VDC on the same device. There is just not a practical way to seperate them.

I like having a door mounted comm port for the PLC. It reduces the need to get inside the cabinet at very little cost.

Keep in mind very little of the inards of such a control panel is actually covered by the NEC.

 

[pfalcon]

Voluntary consensus standard NFPA79:2007:11.2.2 addresses the issue.

Control devices mounted within the control enclosure and connected to the supply voltage, or to both supply and control voltages, shall be grouped separately from those connected only to the control voltages.

There's more but not a lot more. Since my company requires compliance to NFPA79 as part of the purchase that company would be real unhappy if they started building the panel before allowing me to review.

We've never had a problem with panel sizes growing on us. It doesn't really prohibit the VFD from being mounted next to the PLC. But it does require that someone does more than slop stuff in. If I find the PLC between the 480 disconnect and the VFD then I'll ding them on the inspection. A decent layout on the panel will also typically take the 480V to the top panduit and the 24V to the bottom. Or vice versa. Or left-right. The standard specifies grouping not separation.

 

[tallgirl]

There are control devices that are next to impossible to separate between two different voltage levels. I'm having a control panel designed for devices that operate between 0.333 VAC and 208/120Y. And that range is in one particular device -- the CT inputs are 0.333 VAC and the voltage inputs are anything up to 480/277. Kinda hard to put a divider in the middle of a device ...

That said, I'd push back on the layout -- it sounds like someone opened a box of parts and poured them into the control panel.

 

[augie47]

............................................................ That said, I'd push back on the layout -- it sounds like someone opened a box of parts and poured them into the control panel.

 

[kwired]

You can't avoid having power wiring and control wiring on a magnetic motor starter, or any other magnetic power contactor. Even solid state power controllers will have this issue. What about current sensing relays, or current transformers? With the last two at least you usually don't have to remove insulation from the power conductor.

 

[pfalcon]

You can't avoid having power wiring and control wiring on a magnetic motor starter, or any other magnetic power contactor. Even solid state power controllers will have this issue. What about current sensing relays, or current transformers? With the last two at least you usually don't have to remove insulation from the power conductor.

But what can you do?
You can stick all the 100% low voltage (24V) stuff in the bottom left of the panel.
You can stick all the pure 480V stuff in the top right of the panel.
You can stick the mixed 480V/24V stuff in the top left, run the 480V across the top and the 24V across the bottom.

Don't for a moment believe that I'll accept a panel where I have to unbraid the 480V from the Ethernet cable.
Just because my VFD uses Ethernet/IP for control doesn't mean you get to run the Cat 6 in the same channel as the power circuit.

 

[kwired]

But what can you do?
You can stick all the 100% low voltage (24V) stuff in the bottom left of the panel.
You can stick all the pure 480V stuff in the top right of the panel.
You can stick the mixed 480V/24V stuff in the top left, run the 480V across the top and the 24V across the bottom.

Don't for a moment believe that I'll accept a panel where I have to unbraid the 480V from the Ethernet cable.
Just because my VFD uses Ethernet/IP for control doesn't mean you get to run the Cat 6 in the same channel as the power circuit.

I never said you can't try to reduce mixing up power and controls I said there are certain devices that will have both power and control on the device. It is unavoidable if you want to control power. If you want to check to see if a relay coil is receiving voltage you may have to stick your meter probes near the power circuit to do so.

 

[petersonra]

But what can you do?
You can stick all the 100% low voltage (24V) stuff in the bottom left of the panel.
You can stick all the pure 480V stuff in the top right of the panel.
You can stick the mixed 480V/24V stuff in the top left, run the 480V across the top and the 24V across the bottom.

Don't for a moment believe that I'll accept a panel where I have to unbraid the 480V from the Ethernet cable.
Just because my VFD uses Ethernet/IP for control doesn't mean you get to run the Cat 6 in the same channel as the power circuit.

A lot of VFDs have all the power and control connections coming out the bottom. Others have line power coming in the top and motor power going out the bottom, with control power usually out the bottom, but sometimes out the sides.

Sometimes the same brands and even same model numbers in different sizes are not consistent.

I have tried conventions like you suggest and they rarely work very well.

We do try to separate things as best we can, but it is nowhere near as easy as you are trying to claim it is.

We are unlikely to wrap an Ethernet cable around a 480V wire, but it is not unusual for them to come out of the bottom of a small VFD within an inch of each other just because that is where the openings in the VFD are physically located. If you have two such VFDs adjacent to each other, there is no way not to have the Ethernet cable of one cross the power wiring of the other, and often there are dozens of VFDs lined up side by side.

As for putting the "pure" 480V stuff together, usually the only things we have that are pure 480V in a cabinet are the fuses and distribution blocks. Most often we put the distribution block directly under the disconnect switch to reduce the run of large wires. I like to try to put the fuses associated with a drive in some logical relationship to the drive to make it easier to find them, rather than having them arbitrarily placed in some corner of the cabinet.

 

[pfalcon]

... And arranging control panels in the way you describe is often more trouble then it is worth to the builder, and does not always do all that much for the end user. Worse yet, it almost always ends up making the thing physically larger... There is just not a practical way to seperate them...I have tried conventions like you suggest and they rarely work very well.

We do try to separate things as best we can, but it is nowhere near as easy as you are trying to claim it is...

See, we aren't disagreeing about what to do. We are disagreeing about the attitude we bring to the problem. I have never found it to be "more trouble then it is worth" nor do I find it to "always end up making the thing physically larger". I approach the panel with the attitude that I can. Then I accept what can't. And that makes the job pretty easy.

 

[Jraef]

I think there is general agreement here on "best practices" but there are few hard and fast rules about separating voltage levels inside of a panel. That NFPA rule is essentially toothless in my opinion, because it acknowledges up front "mixed" devices, such as oh, let's see, contactors, motor starters, relays, solid state power controllers, drives, power supplies, transformers, servo controllers, stepper amplifiers, .... oh wait, that's EVERYTHING inside the panels I build!

Best Practices are something best enforced UP FRONT in a design specification, such as a simple statement in the tender offer like "Control panel components shall be arranged and wired so as to minimize EMI/RFI interference and the possible intermingling of voltage levels wherever practical."

But that said, the new(ish) revisions to NFPA 70E regarding Arc Flash protection do pertain to the safety aspects of having access to interior components that need to be energized when adjusting them. If there is sufficient energy available inside the panel, it becomes very impractical to expect a PLC or VFD geek to "suit up" to tweak the program, lending to control panel designs that will effectively separate equipment or at least use external access points for those that need programming.

 

[cornbread]

What?s extremely aggravating is most of these issues were talked about early on in the project and the ball was dropped. In addressing the design issue I have effectively pissed off engineering and the shops. (Engineering for the poor design & shop for having to wear additional PPE). I feel somewhat good in the fact that we have made everyone aware of the safety issue but still feel bad that we are missing some low hanging fruit in the design phase of our projects.

 

[pfalcon]

I wouldn't go so far as to call it toothless. It's something that requires judgement to be applied. And I doubt anyone could perfect wording that would replace that judgement and be rational. At least until they figure out how to mount a 24V control in one panel and the 480V contact in separate panel while still working together. :blink:

 

[jimbo123]

Just mounted a control box with 24volt relays , 120 volt for plc , 4-20 ma devices . On the safety side a outside door mounted ethernet plug with single 120v plug for the tech's laptop keeps him from entering box for programing and such.