Milne Computer Center UPS Information

Circuit Breaker listings

Note: Please contact Andy Morgan before any UPS circuit changes are made so that this documentation can be kept up to date.

Current draw for common servers

Server	Steady State Current
Dell PowerEdge 2550	2.0A
Dell PowerEdge 4300	2.5A

Note: These are a little on the high side, so you should feel safe using these as guidelines

Rack guidelines

In general, each Dell rack should have two 20A UPS circuits assigned to it. Dell provided PDUs have a 16A rating, so two circuits with two Dell PDUs will provide a total of 32A per rack. However, only 80% of the available capacity should be used, to allow for current spikes during initial power-up of servers. This leaves approximately 26A for steady state current draw.

A 42U Dell rack will physically hold at most 6 PowerEdge 4300 servers, drawing a total of 6 * 2.5A = 15A, well within the 26A recommended maximum. However, only 13 PowerEdge 2550 servers can be placed in a 42U Dell rack and still keep the current draw below 26A (26A / 2.0A = 13), although the rack is physically capable of holding 21 PowerEdge 2550 servers.