PAT testing in an office is usually reasonably straight forward as most of the testing in a modern office is IT (PCs, Monitors, Printers and Communications Equipment etc) either class I or II. The biggest danger when testing IT and Communications equipment is not damaging the electronic circuits with the test, it is loss of data. Best practice to prevent loss of data is to seek permission from the responsible person (The person in charge of the area). Better still, get them to shut the systems down and make sure they bring them back up after the test to prove the system. However there can be problems of access particularly under desks etc. If you have a mains powered tester, access to a mains source under the desk can also be a problem. When testing offices you might like to consider a battery operated PAT tester which for the earth continuity test and insulation test will not require a mains source. However, if you wish to use the load leakage or touch current test where the appliance has to be powered up, you will need to plug the tester into a mains socket and not all battery testers have this feature. When testing modern IT equipment it is not normal to performed a leakage or touch current test; these tests are usually used on older equipment in place of the 500 Volt insulation test.