Control Power Supply of E3 (or E3 Plus) Relay

Yes, the E3 and E3+ get their control power from the DevieNet terminal, and yes, when the DeviceNet goes down, the device ceases to be an OL relay. It's a commonly known flaw to the DeviceNet scheme when it comes to OL relays. Many loyal A-B users have been shocked when they discover this, which is usually right after they lose a motor when the network goes down,

There are a couple of work-arounds;

1. Install LOTS of power supplies in the DeviceNet circuit. This does not guaratee continuous operation, but it lowers the chances of a sytem wide loss.

2. Install a separate power supply capable of powering just the E3's in your system and wire it to every motor starter through selector switches so that if the network crashes and you must continue to run, someone can flip the switch into "LOCAL" mode to power the E3s. You must also deal with the change in control command structure if the E3s were doing direct network control.

By the way, this is a MAJOR diference between DeviceNet and Profibus. Profibus does NOT power the devices. So if a Profibus network crashes, the devices still function normally. Most Profibus OL relays I have seen have the ability to monitor the network and if it doesn't see it, automatically switch to a "Local" control mode, i.e. if the network had been in control, it then puts local pilot devices in control (assuming they are installed of course).