IEC designation letters

Rson

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Jun 2017
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Michigan
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So, first of all, I've spent a year or so working with some IEC software.

We don't typically do 'true' IEC style drawings - but we use IEC symbols in replacement of standard NFPA symbols and continue to do everything with top-to-bottom ladders.

I have found after trying some true IEC drawings that I prefer it over NFPA drawings, but I do have a few questions on the designations:

We typically label our enclosures/panels as P-1, P-2, JB-1, JB-2, etc. Would these fall under a -A designation for multiple purpose in IEC?

What about VFDs? We typically use VFD for the letter code. I'm not sure what letter code would be appropriate.

How about PLCs and HMIs? I've seen -A on some drawings and -K on others. Then again, we just use PLC and HMI.
 
Generally:

Components ("-") must strictly follow the letter codes. I.e. wire "-W1", terminal "-X2", control relay "-K20", contactor "-Q3", etc.

A VFD would be a "-T" for conversion of energy by maintaining the type of energy.
PLC is a "-K" for control element.
An operator panel can be a "-P".

Functions ("=") and locations ("+") can follow the IEC letter codes, but do not have to. If they do not, simply document the functions and locations in the begining of your diagrams. Just make a list, or for the locations an overview sketch.
IMO it just makes a mess to try and squeze functions and locations into the IEC letter codes. Make your own functional and locational designators, keep them short (!) and document them.
Pro-tip: Think about the order in which you want the functions to appear in your diagrams. Then assign letters to the functions so that the diagrams becomes easy to navigate alphabetically.

Enclosures, cabinets:

A complete enclosure would usually be a "location", i.e. it would have a "+" designator.

An enclosure can have a functional designator ("=") as well, but usually not as it is almost always used for many functions.
If there is a structure of functions and sub-functions (=BD1.C1, =BD1.C2, =BD1.A5 etc) and the top-level function is for a complete machine, and the control cabinet is for that one machine, then the control cabinet could have the top-level function and the location.
The locations for that machine could also have a top-level location, i.e. the cabinet becomes=BD1+BD1.CC1.
A control cabinet can be, but does not have to be, divided into sub-locations for sections, i.e. =BD1+BD1.CC1.1, =BD1+BD1.CC1.2 for multiple sections within the samce cabinet.

The panel itself would not have a "-" designator. The only exception as far as my experience is terminal boxes with only 1 terminal strip inside. The complete terminal box and terminals then get an "-X" designation, i.e. =BD1.C1+F2-X100

Another tip: You do not have to put the long names on all components inside a cabinet. If there is a label on the outside of the cabinet "=BD1+BD1.CC1", then a component inside with the full label "=BD1.C1+BD1.CC1-Q2" can be cut down to "=.C1-Q2"

edit: Another tip: Beginners to the system of functions, locations and components some times goes overboard and define way too deep a structure. i.e. =BD1.C1.F3.K1.L8 etc.
Keep the structure to 1 top-level and 1 sub-level. Only occasionally use an additional sub-level if there is a special problem that can only be solved by adding the sub-level.
 
Last edited:
Thank you, this makes a lot of sense.

If the operator panel and the main enclosure are one and the same, would you use a -P or still use a location code?
 
If the operator panel is in the main enclodure, then I would NOT give it a separate location. One should not just add locations for the sake of it.

edit: I have seen some use a sub-level location for every mounting plate, including the cabinet door, in each section.
One could argue that for the operator panel you could use the location for the door.
But IMO that is overkill. I argue that if you have a label on a section door, i.e. "=BD1+CC1.1" then when you open the door it is assumed that everything inside the door has that reference.

That being said, a control cabinet would most definitely have its own location code.
I argue that whenever you have a number of cables that have to go from cabinet to cabinet, or from cabinet to field, then it falls neatly into place if the cabinets and field locations all have their locations. Then when you must document the cables, there will be a "from" location and "to" location in the cable list. Any decent electrical diagramming software will automatically create such lists and using the locations for the to/from information.
 
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So let's say I have the following:

1. A control panel - with five pushbuttons and a disconnect
2. Two motors
3. A level switch

I would probably do four locations since I would be running cables/conduit between all:
-Control Panel (+QS1 since it has a disconnect?)
-Motor 1 (+M1)
-Motor 2 (+M2)
-Level Switch (+SL1)

And for each location it would have a connection (-X1) and my panel would connect to them (-X1 on Control panel to -X1 of Motor 1, -X2 on control panel to -X1 of Motor 2, etc)

Is my thinking correct in this situation? Is it a fairly blanket statement to think of anything you have to run wires between as separate locations?
 
If it is a small machine, I would use one location for the control cabinet and one for field.
Each device do not have to have its own location. Only if it makes sense.

Usually you do not have to add an X for the connections on a device. I would not consider the terminals in the junction box on a motor as a separate device.

I would call the control cabinet +CC1.
I would call the disconnect =G1+CC1-QS1 (=G1 would be for main power distribution).
I would call each motor -M1, -M2.
The connections for one cable to one motor would go to -M1:U, -M1:V, -M1:W, -M1:pE
 

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