Critical Power Products

"Over 35 years' experience"
Telecommunications power
DC Power Products
uninterruptible power systems
ISDN Power Products
uninterruptible power systems
Telecom Power Services
Midspan Power Injectors
ISDN Network Termination Units

System Engineering International, Inc. (SEI) engineers, manufactures, and markets a complete line of uninterruptible DC UPSs and battery systems for use in communications, industrial and military applications, Digital Centrex (ISDN), and VoIP midspan power injectors for Power over Ethernet.

As part of its ISDN offerings, SEI also manufactures ISDN network termination units (NT1s) and ISDN terminals.

Our products can be purchased directly through us, or from authorized resellers and distributors.

A separate service company, SEI LLC, installs, maintains, and services a full range of critical (uninterruptible) power systems, both UPSs and DC plants, and batteries from all manufacturers.

For information and pricing on SEI's products, call us at 301-694-9601 or email us using our Contact Us form.

Introducing SNMP for ISDN Power Systems with the Power Management Package.

Click here for the announcement.

Do you need a replacement for Schweitzer Engineering Laboratories’ UPS? If your switchgear installation requires 48Vdc power with battery backup, the SEI 125/48-P is fast and easy to install in a cabinet, on a wall or rack. SEI also offers 24Vdc and 12Vdc output, expanded power and battery capacities. For more information, go to


System Engineering International, Inc. • 5115 Pegasus Court • Suite Q • Frederick, MD 21704
Voice: (301) 694-9601 • Fax: (301) 694-9608 • Email: