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A system consisting of various electrical components is desired. Required supply voltages to power these components include the following: three-phase 240 V AC (directly through the supply), 24 V DC, 5 V DC. Are there any reasons in particular one may be hesitant to regulate power through this single available three-phase 240 V AC supply? Is it dangerous to step down from such a high voltage to reach 5 V DC? Are there potential stability issues? Does it not make sense to convert between three-phase and single-phase power?

If this option is indeed viable in practice by what means could it be regarded as both safe and effective to provide voltage regulation? Could a power supply simply be connected directly to the 240 V AC source? Or possibly some sort of custom step-down transformer?

This is a convenient powering option since no other power supply outlet lies within proximity of the system.

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  • \$\begingroup\$ If you need to convert 240VAC to 24VDC or 5VDC, use a wall wart. They are cheap, easy to use, and designed to be safe and compliant with regulations. \$\endgroup\$ – Li-aung Yip Dec 3 '13 at 9:10
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Is it dangerous to step down from such a high voltage to reach 5 V DC?

No, this is very common. All "wall-wart" adapters do this. Use a properly certified product to do this.

Are there potential stability issues?

No, but you'll have slight imbalance between usage of phases, this won't cause any issues. If your application requires a 3-phase supply then that will certainly dominate (I assume your 24V DC and 5V DC parts draw relatively little current)

As an example, the house in which I live is in a country where almost all houses have a single phase 240 V AC supply. This house had a three-phase supply fitted as it was intended to install an electric home heating system that needed a three-phase supply. However one of those phases would additionally supply all the other household appliances, including 32 A circuits for electric ovens, showers etc. In fact I have gas powered heating installed and only use one of those three electrical phases, the other two have 0 A drawn from them. That's a fairly extreme imbalance. I encounter no stability issues.

Does it not make sense to convert between three-phase and single-phase power?

If you have a device that works from a three-phase supply it is entirely appropriate to use a three-phase supply.

Could a power supply simply be connected directly to the 240 V AC source?

Yes. This is normal. By directly I assume you mean through an appropriate distribution panel with RCD/GFCI protection and permanently wired to a suitable outlet conforming to all local regulations.

Or possibly some sort of custom step-down transformer?

That's just one particular type of power supply. So yes.

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  • \$\begingroup\$ If phase balance is a real issue (if your DC supplies are really chunky) you can rectify 3-phase, although you're then moving away from cheap common single-phase PSU's. \$\endgroup\$ – John U Dec 3 '13 at 11:00
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Assuming the three phase outlet contains a neutral pin ...

Conversion from three phase with neutral to single phase is a matter of wiring.

Use an electrician to prepare a three phase plug to single phase socket assembly. This can be done off site.

The electrician is to choose one of the three phase active terminals on the plug, connecting it to the active terminal on the socket. The neutral terminal of the plug is to connect to the neutral terminal of the socket. The earth terminal of the plug is to connect to the earth terminal of the socket. Insulation and conductor correspondence tests are to be done, for safety.

There may be other regulatory constraints, check with an electrician in your area.

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