SV9100 Blowing CPU Cards

[zvanselow]

So we have the high voltage that feeds our substation get hit with lightning one night. The building our phone system is in has a dedicated back up generator. The phone system is also behind a large UPS. Somehow this outage blew our CPU card in our sv9100. We called our service campany for the phone system, Northeast IS, and they sent someone up with a new CPU card. Fearing our UPS was failing or just not good enough anymore, we plugged it into a new UPS. The other night we had another power outage and AGAIN our CPU card was blown. We are now on our third CPU card. The gentleman from Northeast IS thought i might be a failing transfer switch from the generator that might be put voltage over ground. However today we got with the Electrical department to meter the system during a switchover to the generator and have not found any voltage over ground.

Has anyone seen anything like this before? Or have any ideas? Anything would be greatly appreciated. Thanks in advance.

 

[CoralTech]

What's plugged into the CPU? Perhaps the voltage is coming from elsewhere?

 

[OzzieGeorge]

Unless your UPS is a double conversion UPS, it will not protect you against spikes. A normal UPS simply passes the power through whilst charging the batteries, then rapidly switches over to battery power if the power goes off. By the time it switches over any spike has already gone through.

A double conversion UPS constantly converts to extra low voltage (12V or 24V usually) and then back to low voltage (240 Vac or whatever your local system runs at), The batteries float across the middle of these conversions on the extra low voltage rail, This way the batteries absorb any spike rather than your CPU. Only problem is the higher cost of these units so unless you have lots of equipment that needs this level of protection, buy the smallest you can and sit it between your system and the existing UPS.

 

[zvanselow]

We have since taken the ground off to test. We have even had major power events since doing this. So far no damage to this new CPU card. We are guessing it IS a voltage to ground problem. This building our phone system is in is very old. We suspect the grounds are bonded in a way that makes it ineffective to try to meter. We are going to proceed with putting in a dedicated ground rod for the phone system to ensure it has its own ground that is not bonded to any other.

 

[OzzieGeorge]

I would check that with a suitably qualified engineer before doing that as you risk creating a ground loop which can be very dangerous.