Maximum number of POTS lines

Answered Question
Apr 6th, 2009


We are currently quoting a customer for a UC520 to replace a legacy PBX installed with 18 POTS lines.

I have been finding contradictory info in regards to the max # of POTS lines for the UC520.

This document says 12 max POTS lines:

But the SBCS Pricing tool says that the max is 8 with the additional 4 port FXO card.

  1. What is the total number of POTS lines available?
  2. What can we offer this customer if they insist on keeping their 19 inbound phones lines?



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0 votes
Correct Answer by Steven Smith about 7 years 6 months ago


It has 8FXO built in, and an expansion slot left for 4 more FXO.


It has 8FXO built in, and the expansion slot is filled with a 4 FXO card.

Look near the bottom of that link.

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Overall Rating: 5 (1 ratings)
Steven DiStefano Mon, 04/06/2009 - 06:41

What are the total number of PSTN interfaces that the UC500 can support?

Depending on the UC500 model or SKU - can have any of the below:

    • 4 to 12 FXO ports or 2 to 6 BRI ports (VIC slot can be used to add interfaces in certain model)
    • T1/E1 VWIC interface card for use in the 8-, 16-, and 32-user UC500 SKUs (VIC slot can be used to add this T1/E1 interface card)
    • UC500 48-user SKU is also available with integrated T1/E1 interface.
jaydien1358 Mon, 04/06/2009 - 08:06


So what model/sku UC520 would accept 8 additional FXO ports? I am only aware of the form factor for the UC520 that has 1 expansion slot.




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