A friend has a factory where the incoming municipality cables are regularly cut and stolen. When the municipality reconnects very often the phase rotation is incorrect. The genset and solar system are setup to sync and share with the Mains.

The idea is to have an incoming DB board with the phase correction contactors and rotation sensing relays.

Is it safe to have a pair of incoming contactors designated 1 & 2 with a pair of phase rotation and voltage sensing relays designated A & B.

The output of contactor 2 is reversed A/C/B to the output terminals.

Relay A picks up contactor 1 when the incoming rotation is correct.

Relay B sensing is reversed and picks up contactor 2 when the rotation is incorrect. The coils of both are interlocked via the NC auxiliary contacts.

This would ensure that the rotation into the main DB is always A/B/C regardless of the incoming rotation.

Using 2 phase rotation relays & their NO contacts to only select the appropriate contactor when the values are in spec ensures it's fail-safe.

Looking for better solutions or ideas.

1 hour ago, paulsabatier said:

A friend has a factory where the incoming municipality cables are regularly cut and stolen. When the municipality reconnects very often the phase rotation is incorrect. The genset and solar system are setup to sync and share with the Mains.

The idea is to have an incoming DB board with the phase correction contactors and rotation sensing relays.

Is it safe to have a pair of incoming contactors designated 1 & 2 with a pair of phase rotation and voltage sensing relays designated A & B.

The output of contactor 2 is reversed A/C/B to the output terminals.

Relay A picks up contactor 1 when the incoming rotation is correct.

Relay B sensing is reversed and picks up contactor 2 when the rotation is incorrect. The coils of both are interlocked via the NC auxiliary contacts.

This would ensure that the rotation into the main DB is always A/B/C regardless of the incoming rotation.

Using 2 phase rotation relays & their NO contacts to only select the appropriate contactor when the values are in spec ensures it's fail-safe.

Looking for better solutions or ideas.

A very high risk method without a mechanical interlock with the electrical interlock. If the N/C on one contactor melts close you can get a nasty surprise.

Is there someone on the site to correct the phase rotation if for instance the phase rotation just gives an audible alarm to correct it?

5 minutes ago, Scorp007 said:

A very high risk method without a mechanical interlock with the electrical interlock. If the N/C on one contactor melts close you can get a nasty surprise.

Is there someone on the site to correct the phase rotation if for instance the phase rotation just gives an audible alarm to correct it?

Great feedback Sir.

Mechanical interlocked they will be.

Site is usually unattended after hours.

Panel is built and tested.

Contactors are mechanically and electrically interlocked. Timer to prevent the common reconnect flickering.