UPS for 30A service to server racks

Question

Our server rack has two 208V 30A dedicated circuits running to it, each to a PDU mounted in the rack. Most of the equipment has redundant power supplies so one goes to each PDU. I'm not sure who had this installed but it seems like overkill for our relatively modest amount of equipment -- this is not a high-density data center.

Our building gets frequent power flickers and we'd like to get a UPS in there to keep things running smoothly. The rack currently houses our SAN, so losing power unexpectedly is not ideal.

The problem is that I'm having trouble finding a UPS for 208V/30A service. If we want to keep our dual power supply setup we're looking at dual 4kW UPS's at a total of $10k or so, which just seems silly when our power draw is closer to 1kW total.

Is this 208V/30A setup standard and I'm just not looking in the right place for power equipment? Should we have an electrician change the L6-30 connectors for L6-20 connectors and put in a 20A breaker instead? Our other server rack runs just fine off a single 120V/20A circuit.

Answer 1

Looking at APC, you can buy a 2.1kW online UPS (SURTD3000XLT) for about $2k each. Or a step-down transformer (AP9626) for about $500 each.

Electricians cost money as well. It would be a shame to downgrade your circuit and find you need it a couple years later.

Answer 2

Changing out the outlets to downgrade from 30A to 20A is not ideal. Remember that you'll want to calculate maximum draw from a particular leg and/or PDU. Maximum draw is presented when a server/equipment first starts up. Also, if a power supply goes bad or is unplugged, the load is solely on one leg of your supply.

We installed L6-30 outlets across our datacenter, even for the racks with low density. We're using a APC SymmetraPX. This unit delivers 3 legs/phases of 30A service. From there, we can essentially load balance between the 3 phases to even out the load.

One aspect we were calculating for in the wiring is the rare event that everything needs to be shutdown. When those servers come back online, they'll all be pulling quite a bit more amperage. Unless you're starting one at a time, you may need those 30A circuits.

When you're looking for a battery backup unit, always calculate max load for each systems; then give some more. As stated, APC makes a great product and they should be able to accommodate 5kw and below. Eaton is also another good product that can easily scale with lower end loads.