Machine control unit: on-machine electrical control box to IEC 60204-1

01

Build it to IEC 60204-1 as part of the machine

IEC's abstract for IEC 60204-1:2016 says it applies to electrical, electronic and programmable electronic equipment and systems of machines not portable by hand while working, including groups of machines working together, and that the equipment it covers starts at the point where the supply connects to the machine's electrical equipment. The sixth edition added requirements for power drive systems, revised EMC and protective bonding requirements, clarified overcurrent protection, added determination of the short-circuit current rating and reorganised Clause 9 on safe torque off, emergency stop and control circuit protection. [1]

Siemens' guidance for control panel builders treats IEC 60204-1 as the starting point for control panels that are part of a machine, applying from the connection to the grid to equipment with rated voltages up to 1,000 V AC and 1,500 V DC, and recommends a risk analysis, with IEC 61439-1/2 consulted where risks are not covered. It notes that the revised IEC 60204-1 from late 2016 applies in Germany through DIN EN 60204-1 published in June 2019. [2]

Editorial note: because the control unit is part of the machine, its circuit diagrams, terminal lists and parts list belong in the machine's technical documentation; ask for them in the language of the operating site and for the risk assessment that covers the electrical equipment.

Give the supplier the machine and its functions, the supply voltage, frequency and earthing system, the prospective short-circuit current at the supply point, the motors, valves and sensors to connect, the controller and protocol required, emergency stop and safety functions, the mounting position and environment, and the documentation and standards (IEC 60204-1, NFPA 79 or others) to be met.

02

Check the short-circuit level and the enclosure rating

Siemens notes that IEC 60204-1 does not itself include a proof of short-circuit strength: it requires the rated short-circuit breaking capacity of protective devices to be at least the fault current expected where they are installed, and the short-circuit current to be considered when sizing conductors. Under IEC 61439-1, Siemens lists cases where short-circuit verification is not needed, including assemblies with a rated short-time or conditional current of no more than 10 kA rms, and circuits protected by current-limiting devices whose let-through current does not exceed 17 kA. [2]

For auxiliary circuits Siemens lists the same exemption where the supply transformer is at least 110 V and up to 10 kVA, or below 110 V and up to 1.6 kVA, with an impedance voltage of at least 4%. [2] Editorial calculation: a 1.6 kVA, 24 V control transformer has a rated current of 1,600 / 24 ≈ 67 A, and at 4% impedance voltage its secondary short-circuit current is at most about 67 / 0.04 ≈ 1.7 kA before cable impedance. [2]

For the enclosure, Hoffman's EU declaration for its Type 12 large industrial control enclosure states IP55 under EN 60529 and lists EN 60204-1 and the Low Voltage Directive as applied. [3] Editorial note: a box bolted to a machine frame sees vibration, splashes and wash-down that a cabinet in an electrical room does not, so state the mounting position and cleaning method and ask for the enclosure's tested IP or NEMA rating.

03

A spray-gun maker's control cabinets, and the standard and ratings to confirm

The linked listing is a coating-equipment maker selling control units and central control cabinets for its spray guns. Ask any supplier which standard the unit is built to, the supply and short-circuit ratings, the enclosure rating and the documentation delivered.

04

Supply disconnect, control transformer, controller I/O, emergency stop circuit, drives and enclosure

05

Supply voltage, fault current, I/O count and enclosure rating for an on-machine control box

State the prospective short-circuit current at the supply point: IEC 60204-1 requires protective devices to break at least that fault current. [2]

06

Send the machine, supply and environment together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Machine: [type; functions; motors, valves and sensors]
Supply: [voltage; frequency; earthing; prospective short-circuit current]
Control: [controller; I/O count; protocol]
Safety: [emergency stop; safety functions; STO]
Enclosure: [mounting; IP or NEMA rating; cleaning]
Standards: [IEC 60204-1; NFPA 79; others]
Documents: [circuit diagrams; terminal list; parts list; risk assessment]

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