AP7723 Automatic Transfer Switch Chassis Earth Bond - yes or no?

[Rooster_apc]

This was originally posted on APC forums on 2/23/2016

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I recently suffered a destroyed AP7723 ATS and UPS (SURT2000) during commissioning/testing. The defect occurred having just added the ATS to an existing UPS system whilst manually switching between 2 x UPS input supplies (2 x SURT2000) whilst on load (approx 1100W). The UPS generated an 'over-voltage' error and is now stuck in permanent bypass mode. Trouble is, I don't know if the ATS destroyed the UPS or the other way-round. 

Having replaced both the UPS and APS, I then attached an earth bond to the chassis of the ATS. I then continually repeated the ATS input selection testing and the install worked seamlessly as designed.

I have no idea if I was just unlucky with the first failure, or if the addition of an earth bond made any difference in terms of voltage suppression during switch-over. 

I assume the previous earth path was only via the 2 x UPS inputs, so I have no idea how these are referenced to each other - or to chassis ground. The brief ATS instructions refer to fitting an earth bond if fault current is unknown (or greater than a certain figure) but could the lack of earth-bond have contributed to the original failure?

[BillP]

This reply was originally posted by Bill on APC forums on 2/25/2016

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Hi,

The ATS would be using the ground of the source (the UPS in the first case) - did you do any configuration to the ATS before deploying it? Is it possible to send us the configuration files/event logs/event counts of the ATS?

[Rooster_apc]

This was originally posted on APC forums on 3/3/2016

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Hi Bill. The only thing I did prior to fitment was upgrade the firmware to 3.9.0, select 'no source preference' and lock-out the front panel button. No other parameters were changed.

[BillP]

This reply was originally posted by Bill on APC forums on 3/7/2016

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Hi,

Without the logs it is difficult to say what may have caused the issue. As mentioned earlier the ATS should have been grounded while plugged into a UPS assuming the UPS was grounded. 

[Rooster_apc · Accepted solution]

This was originally posted on APC forums on 3/7/2016

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Hi Bill,

I've checked the faulty ATS again and can confirm that the Source A 24V PSU is dead i.e. reading 0V via serial or Ethernet with an input supply present. You can hear a relay 'click' when the lead is inserted into Source A, but you have to power the unit up via Source B.

I've attached a text version of the log file, which shows many 'over frequency violation Source A' errors. In this case, both sources were from SURT2K UPS' - albeit the one feeding Source A failed simultaneously to the ATS input failure.