**Exhibit 31.2**

**CERTIFICATION**

I,Richard J. Thompson, certify that:

1.I have reviewed this quarterly report on Form 10-Q of American PowerConversion Corporation;

2.Based on my knowledge, this report does not contain any untrue statement of amaterial fact or omit to state a material fact necessary to make the statementsmade, in light of the circumstances under which such statements were made, notmisleading with respect to the period covered by this report;

3.Based on my knowledge, the financial statements, and other financialinformation included in this report, fairly present in all material respectsthe financial condition, results of operations and cash flows of the registrantas of, and for, the periods presented in this report;

4.The registrant’s other certifying officer(s) and I are responsible forestablishing and maintaining disclosure controls and procedures (as defined inExchange Act Rules 13a-15(e) and 15d-15(e)) and internalcontrol over financial reporting (as defined in Exchange Act Rules 13a-15(f) and15d-15(f)) for the registrant and have:

a) designed such disclosure controls and procedures, or caused suchdisclosure controls and procedures to be designed under our supervision, toensure that material information relating to the registrant, including itsconsolidated subsidiaries, is made known to us by others within those entities,particularly during the period in which this report is being prepared;

b) designed such internalcontrol over financial reporting, or caused such internal control overfinancial reporting to be designed under our supervision, to provide reasonableassurance regarding the reliability of financial reporting and the preparationof financial statements for external purposes in accordance with generallyaccepted accounting principles;

c) evaluated the effectiveness of the registrant’s disclosure controlsand procedures and presented in this report our conclusions about theeffectiveness of the disclosure controls and procedures, as of the end of theperiod covered by this report based on such evaluation; and

d) disclosed in this report any change in the registrant’s internalcontrol over financial reporting that occurred during the registrant’s mostrecent fiscal quarter (the registrant’s fourth fiscal quarter in the case of anannual report) that has materially affected, or is reasonably likely tomaterially affect, the registrant’s internal control over financial reporting;and

5. The registrant’s other certifying officer(s) and I havedisclosed, based on our most recent evaluation of internal control overfinancial reporting, to the registrant’s auditors and the audit committee ofregistrant’s Board of Directors (or persons performing the equivalentfunctions):

a) all significant deficiencies and material weaknesses in the design oroperation of internal control over financial reporting which are reasonablylikely to adversely affect the registrant’s ability to record, process,summarize and report financial information; and

b) any fraud, whether or not material, that involves management or otheremployees who have a significant role in the registrant’s internal control overfinancial reporting.
| Date: May 5, 2006                                       |
|--------------------------------------------------------------|
|                                                         |
| /s/ Richard J.  Thompson                                     |   |
|                                                         |
| Richard J.  Thompson                                         |
| Senior Vice  President, Finance, and Chief Financial Officer |

 

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