She has been building panels for about 15 years and has worked for several different types of companies, machine builders and integrators including our own business. Usually specifications come from the customer rather than using our own, however sometimes when a customer didn’t have a written specification we would use our own.
Imagine her surprise when a panel showed up from Texas with all of the DC wiring in red. Of course she ended up rewiring that portion of the panel but then inquired as to what specification the Texas plant followed. Apparently no one really knew so she asked me if I would work up a sample specification for her to bring in as a starting point. With her input I started writing one yesterday. This is what I’ve got so far:
The purpose of this document is to define standards used in the fabrication, wiring and design of electrical control systems for [Company]. Exceptions to these standards must be approved in writing by the engineering department.
Table 1. Terminology and Definitions
1P Single Phase
3P 3 Phase
AC Alternating Current
COTS Commercial Off The Shelf
DC Direct Current
1.1.1 Standards and Handbooks
220.127.116.11 Table 2 details preferred components that should be considered prior to any other component selection. Any substitutions must be approved by [Company].
Table 2. Preferred Components
Commodity Brand Series Part Number /Example
Circuit Breakers for AC (UL489 Only) Eaton/Cutler Hammer WMZT, C trip
Circuit Breakers for DC Phoenix Contact TCP
Contactors Allen Bradley 100/700
Disconnect, NFPA79 type, or equivalent Allen Bradley 194R 194R-FJ030P3 for example
Emergency Stops, LED illuminated Allen Bradley, Illuminated 800T Series 800T-FXQH24RA1
Ethernet Switches, managed Allen-Bradley, Phoenix Contact Ethernet/IP certified
Ethernet Switches, unmanaged Phoenix Contact, Moxa (2nd) 2891929 for example
Ethernet Utility connections Wago 51205068
Fasteners SAE or Metric
Hookup Wire MTW or Stranded THHN
Light Curtain Banner (14mm preferred)
Photo electric Sensors Banner QS18 (Expert preferred)
PLC Allen Bradley CompactLogix or ControlLogix
Power Supplies (24V, 12V, 5V) Phoenix Contact SFB 2866763 for Example
Proximity Sensors, < 8mm Keyence EM series Proximity Sensors, >=8mm diameter Turck (Keyence) uProx preferred
Pushbuttons, Illuminated, LED Allen Bradley 800H Series 800H-QRAH24GD1 for Example
Pushbuttons, non-Illuminated Allen Bradley 800T Series 800T-A2D1 for example
Safety Contactors Allen Bradley 100S/700S 100S-C23DJ404C for example
Safety Scanners Sick, Keyence, Banner, STI
Safety Relays Allen Bradley 440R 440R-N23-120 for example
Status Light tower, LED Allen Bradley, Banner (TL50)
Switches, Pilot Lights, LED Allen Bradley, Banner 30mm
Terminal Blocks Phoenix Contact ST Series
Touchscreens Need to be approved
USB Utility Connections Wago 51205157
Wireway in enclosure (fingered) Panduit or Iboco
Wireway in enclosure (solid) Panduit or Iboco or Hoffman type
Delete or modify items in this table that do not apply
18.104.22.168 Table 3 below lists required methods associated with assembly of control systems.
Table 3. Required Documentation Methods
Schematic Format AutoCAD, ANSI Ladder
1.1.2 Regulatory Documents
Document Title Document Number, Issue Date
Electrical Standard for Industrial Machinery NFPA79, 2007
1.1.3 [Company] Documents
Document Title Document Number, Issue Date
System Safety XXXXXX-XX, 2011
Following are specifications for the fabrication of electrical controls and machine/system wiring.
2.1 Control Panel Wiring
2.1.1 Component Mounting
22.214.171.124 Component locating shall be done per drawings using appropriate measuring, marking and squaring techniques with straight edges, squares and tape measures.
126.96.36.199 Control components shall be attached to the enclosure backplane using tapped holes and appropriately sized machine screws. Exceptions may be made for components with specific manufacturer suggested mounting methods.
188.8.131.52 Din rail shall be attached to the enclosure backplane using tapped holes and 10-32 machine screws.
184.108.40.206 “Self-tapping” screws shall not be used for component mounting.
220.127.116.11 Plastic wireway may be attached to the enclosure backplane using tapped holes and appropriately sized machine screws, metal rivets or plastic rivets.
18.104.22.168 Standard pushbutton holes shall be made using an appropriately sized punch and die set.
22.214.171.124 Rectangular or square operator interface cutouts shall be closely sized to the component using manufacturer’s recommendations and deburred with no sharp edges.
126.96.36.199 Metal shavings shall be removed after drilling, cutting or deburring operations prior to further mounting of components.
188.8.131.52 Enclosures shall contain 20% spare capacity.
2.1.2 Component Wiring
184.108.40.206 DC wiring shall be blue TFFN, THHN or MTW.
220.127.116.11 AC 120V wiring shall be red TFFN, THHN or MTW for hot or fused wires and white THHN, TFFN or MTW for neutral wiring.
18.104.22.168 Ground wires shall be green TFFN, THHN or MTW. Ground wires shall be terminated by ground lug to the enclosure backplane and have a direct path to supplied power drop earth ground.
22.214.171.124 Wire shall be sized for appropriate current carrying capability per NEC or NFPA79 sizing charts.
126.96.36.199 Multiconductor wiring shall have their individual conductors terminated near each other.
188.8.131.52 Conductors shall be stripped to a length such that the conductor is inserted entirely into the terminal block or termination point with no more than 1/16” or 1.5mm of exposed copper visible.
184.108.40.206 Wiring shall be routed such that excess wire is not left in the wireway. Wiring shall also not be stretched tightly when rounding internal wireway corners.
220.127.116.11 All conductors must have ferrules for termination wherever practical. Not required for wires larger than 14AWG.
18.104.22.168 Cables entering through a metal space must be protected by a fitting or gland.
22.214.171.124 Wire nuts shall not be used inside of enclosures.
126.96.36.199 Wire extensions should be avoided whenever possible. If a wire must be extended, the extension wire must be the same color and gauge as the extended wire. It must be soldered and covered in shrinkable tubing.
188.8.131.52 Electrical tape shall not be used to cover wire or wiring splices.
184.108.40.206 Wireway shall be no more than 75% filled.
2.1.3 Wire Labeling
220.127.116.11 Wiring and cabling will be labeled using machine printed adhesive wrap around or heat shrinkable COTS labeling system.
18.104.22.168 All wires and cables shall be labeled on both ends and match the designation on the schematic.
22.214.171.124 Wire labels shall be clearly legible and oriented toward the front of the panel opening.
126.96.36.199 Wire labels shall all be oriented in the same direction; read bottom-top or left-right.
188.8.131.52 Wire labels shall be placed approximately 1/8” or 3mm from the terminal point and be consistent in appearance.
2.2 Machine Wiring
184.108.40.206 Wiring external to the control enclosure shall be contained in rigid conduit or EMT
220.127.116.11 Minimum conductor size for motors shall be #14AWG.
3 Drafting and Design
4 Programming and Software
I apologize for the somewhat disorganized look of the text; WordPress (the application used to post this blog) doesn’t lend itself to formating text like a word document. Much of the content of this specification is fairly standard stuff. The NEC handbook and NFPA79 is a good reference for electrical assemblies built in the US. If anyone would like a copy of the original Word document and associated tables and formatting let me know.
Anyway the theme of this post is that it really is necessary to generate some kind of written specification for whatever your product is. Amazingly, most smaller companys have little or no specifications written for their electrical equipment.