230V control circuit

Question

We've just taken delivery of a control panel that has switches controlling power to two pumps, a 9kW tank heater and an over-temperature trip. The control voltage is all 230V. Our maintenance engineer says that the control voltage, according to EIC 60204, should be stepped down to 24V. Is this mandatory? The panel is fully enclosed with an interlock cutting power when it's opened. There are no complex plc's involved, all very simple controls.

gkenyon · Accepted Answer

Chemenger said: he control voltage is all 230V. Our maintenance engineer says that the control voltage, according to EIC 60204, should be stepped down to 24V. Is this mandatory? 
 No, Clause 9.1.2 of BS EN 60204-1 :2018 (the current Designated standard) and BS EN 60204-1:2018+A1:2025 (likely to take over as the Designated standard by 30 April 2028) states: 
 9.1.2 Control circuit voltages The nominal value of the control voltage shall be consistent with the correct operation of the control circuit. The nominal voltage of AC control circuits should preferably not exceed &ndash; 230 V for circuits with 50 Hz nominal frequency, &ndash; 277 V for circuits with 60 Hz nominal frequency. The nominal voltage of DC control circuits should preferably not exceed 220 V. 
 I think that the confusion comes because where PELV is used (but it doesn't have to be, just if it is) there are different voltage limits to PELV in IEC 60204-1, i.e. 25 V AC or 60 V DC in BS EN 60204-1; 50 V AC or 120 V DC in BS 7671 ... unless, of course, there are lower limits in a relevant Section of Part 7). 
 There are specific wiring considerations in BS EN 60204-1 for panels that contain LV controls, and specific colour-coding where LV controls remain live when the panel isolator is in the "OFF" position to open the panel (e.g. so that electronic controllers can still relay status to other panels etc.).

Chemenger · Answer

Hi Mike, thanks for answering. 
 The wiring is properly installed inside an industrial enclosure rated to IK10 & IP66, with internal hinges and quarter turn locks. The wiring is all very professional looking (although hey, I'm just a chemical engineer so what do I know!), with the power supply coming from an independent isolator through a sealed gland into the enclosure. All terminals within the enclosure are labelled and the door is fitted with an isolator. It will be installed in a secure building inside a factory, with no exposure to rain or vandals! 
 The maintenance engineer is quoting Section 9.1.1 of the standard, that "where control circuits are supplied from an AC source, transformers having separate windings shall be used to separate the power supply from the control supply". But then Section 9.1.2 states that "The nominal voltage of AC control circuits should preferably not exceed 230V for circuits with 50Hz nominal frequency". These two statements seem to contradict each other, no?

230V control circuit

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