Looking for advice on datacenter electrical/generator


My organization is in a growth phase right now and within the next year will find ourselves having outgrown our current 16KVa Symmetra. We have comissioned an electrical engineer to make a recommendation as to what is required to install a new 130Kva Liebert nPower UPS along with a generator.

Our current plan is to purchase the UPS with a minimal amount of battery, approximately 15min worth; just enough to get the generator running. Is this the better way to go? Or should we consider more battery? What is everyone’s experience with the Liebert line of products? Any kudos or gripes? Our electrical engineer also recommended that we purchase a Generac generator and transfer switch. Any experiences with that company?

He also is strongly opposed to us purchasing a natural gas generator which seemed like a shoe-in for us. We have natual gas facilities and didn’t want to hassel with the diesel maintenance problems. Is a natual gas generator something that we should consider?

Additionally he recommneded that we place the HVAC and lighting upstream from the UPS and use some sort of junction box to supply both the UPS load and the HVAC. How do you “big guys” do it? Here is a link to the diagram that he gave us today. Your thoughts are appreciated!


Dan Lockwood
Microsoft Certified Professional
CompTIA Network+ Certified
Cisco Certified Network Associate

just how certain are you that your generator is always going to start
within 15 minutes?


Most places I hang around have only 5 to 10 minutes batter. We, NAC,
usually plan on 10 minutes at full load, sometimes a little more.

If your genset doesn't start and sync in 30 seconds, it's unlikely, that
even with really good planning, that you'd get a rollup there, hooked up,
etc., in time. Murphy wouldn't hear of it.

Yo Dan!

He also is strongly opposed to us purchasing a natural gas generator
which seemed like a shoe-in for us.

I know of several cases where the San Jose fire marshall turned off
natural gas as a precaution. You may wish to discuss with your local
fire marshall under what conditions they will turn off the gas.

Some places require auto-shutoff valves for NG as an earthquake


> He also is strongly opposed to us purchasing a natural gas generator
> which seemed like a shoe-in for us.

We currently have a 133 kwatt nat gas genset. It has performed flawlessly
-- they work well.

The point of the marshall shutting of gas is a valid one, but I've not run
across that. Also, if you are in a situation that the fire marshall need
sto shut of nat gas, it may be a moot issue.

-- Alex Rubenstein, AR97, K2AHR, alex@nac.net, latency, Al Reuben --
-- Net Access Corporation, 800-NET-ME-36, http://www.nac.net --

I don't know what policy is like in the USA, but before a fire crew even
breathes here in Toronto, they shut off the gas. Not to mention that in the
event of any political disaster, the supply of natural gas just cannot be

Although it took a lot of begging, we were able to put a 200KW diesel on top
of our wooden building. Wouldn't have it any other way.

On the topic of batteries, our rule of thumb has been to have enough
batteries around to cover a situation in which the genset does not start.
That most likely will happen when nobody is paying attention and everybody
competant is drunk at an office party. Even if you have a maintenance
contract on the genset with a 1 hour response time, odds are that something
is screwed up where the service guy will need a part that is somewhere else,
etc. etc.

Do a risk./benefit analysis. There is a point you reach where the cost of
redundancy outweighs the cost of downtime.


Alex Rubenstein wrote: