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Old February 15th, 2021, 09:50 PM   #1
Ltpriyank
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PLC panel standards

What are some of the standards and common practices that are followed while designing a PLC panel ?
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Old February 16th, 2021, 12:22 PM   #2
Robb B
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Put the controller at the opposite end of the cabinet from where the majority of cables/wires will come in. Put terminal blocks in between rack and entry points, use the biggest, deepest wireduct that is reasonable. Assume there will be double the wires than the initial build.
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Old February 16th, 2021, 12:29 PM   #3
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Minimum of 25% free space for future expansion, if this is for anything other than a machine specific control panel.

On most big plants now that will likely be there for 30+ years I ask for / allow for 50%.

Then the project manager kicks and screams and we negotiate down to to 40% so he feels like he wins something.
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Old February 16th, 2021, 12:46 PM   #4
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Mount heat producing components like VFDs at the top of the cabinet.
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Old February 16th, 2021, 01:43 PM   #5
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Mount heat producing components like VFDs at the top of the cabinet.
Since the VFD is probably also the most heat sensitive component, it can be wise to put it in the buttom. Better to put heat resistant components at the top if you ask me
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Old February 16th, 2021, 01:54 PM   #6
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If cabinet is possible to reach over 40 Celsius, advise putting active cooling in. Heat is electronics' enemy.
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Old February 16th, 2021, 01:59 PM   #7
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(1) Depending on the plant/facility and how much they enforce Arc Flash rules, have a separate cabinet for all AC voltage (120/480) and put the PLC in a cabinet with only 24VDC. The cabinet can then be opened/accessed without having to suit up.

(2) Generally speaking, a place to plug in a laptop is nice to have. Put a plug on your power enclosure for programming.

(3) Unless the project is very small, allow space for 'maximum rack' - so if you have to add modules / terminals there is room

(4) Don't use relay cards. Use digital output cards and wire to a terminal block relay (like these: https://www.automationdirect.com/adc...-sce-24vacdc-1

(5) Use a 3 tier terminal block for Digital inputs. This allows you to land the sensor & power (+)/(-) in one spot. If you don't use the power terminals - no worries, they are there for future considerations.

Those are just off the top of my head.
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Old February 16th, 2021, 02:07 PM   #8
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"Standards" is a relative term. Relative to where the install is. In the USA, NFPA 79 and UL508A are the "standards" for industrial control panels.
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Old February 16th, 2021, 02:42 PM   #9
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Quote:
Originally Posted by Rson View Post

(5) Use a 3 tier terminal block for Digital inputs. This allows you to land the sensor & power (+)/(-) in one spot. If you don't use the power terminals - no worries, they are there for future considerations.

Those are just off the top of my head.
This is always appreciated by the installers. Seen way too many panels where there's one fused +24V terminal for the positive feed of the field I/O. Cool... expect me to land 16 wires into that do ya?

I tend to do the same for analogs for things such as level or pressure sensors which may be 2 or 3 wire. Much easier to change something in the middle of the night if you've got +24V, 0V and the analog input + and - right there. 2 wire to 3 wire, no problem.
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Old February 16th, 2021, 02:52 PM   #10
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(4) Don't use relay cards. Use digital output cards and wire to a terminal block relay (like these: https://www.automationdirect.com/adc...-sce-24vacdc-1
Would you care to expand as to why to not use relay cards? Aside from the card costing more then a digital output card, about double in the 5000IO line from AB.
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Old February 16th, 2021, 03:00 PM   #11
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In addition to what was said by others:

Check the devices manual about how much free space it need around, but never less than 25 mm between the devices and the cable duct. This space is necessary to identify the cables.

Try to separate the power cables as much as possible from those with weak signals, for example put the power terminals in the lower left zone and the power devices also towards the left side.

Same with weak signal cables and devices on the right side.

Highly recommended to draw a plan before.
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Old February 16th, 2021, 03:31 PM   #12
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Would you care to expand as to why to not use relay cards? Aside from the card costing more then a digital output card, about double in the 5000IO line from AB.
This is usually a convenience to those in the plant a few years after the machine has been installed. Relays have a limited life. Digital outputs, if used properly, will last many, many times longer (likely the life of the machine).

If one particular relay on your output card turns on/off very often and dies, you have to replace the whole relay I/O card. If you run to slim interface relays, you only have to replace the one relay (and usually not the base - just the 'cube').
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Old February 16th, 2021, 07:43 PM   #13
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Don't place the panel thermostat on the DIN rail next to a device that will keep it cosy, despite the outside temperature !!
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Old February 16th, 2021, 07:55 PM   #14
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Quote:
Originally Posted by rQx View Post
Since the VFD is probably also the most heat sensitive component, it can be wise to put it in the buttom. Better to put heat resistant components at the top if you ask me
Disagree, a VFD is most likely not "heat sensitive" by design, and it will almost certainly protect itself. Putting it in the bottom of the enclosure is just gonna add stress to the other inhabitants above it.

It makes sense to put the devices producing the most heat "top to bottom" thereby protecting the devices with lower temperature ratings below them. Even with forced ventilation !
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Last edited by daba; February 16th, 2021 at 08:08 PM.
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Old February 17th, 2021, 12:41 AM   #15
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Quote:
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Disagree, a VFD is most likely not "heat sensitive" by design, and it will almost certainly protect itself. Putting it in the bottom of the enclosure is just gonna add stress to the other inhabitants above it.

It makes sense to put the devices producing the most heat "top to bottom" thereby protecting the devices with lower temperature ratings below them. Even with forced ventilation !
The VFD we use are rated at 40C enviromental, other components can have 70-80C. I still claim VFD should be in the buttom
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