By Not Preparing for EMC Testing You are Preparing for Failure!
EMC testing can seem straight forward, but the truth is simple things can trip you up along the way. Some easy preparation before booking or attending the testing can save you a great deal of time, frustration and money. Not taking the time to prepare may mean a completely wasted day and possibly an unfavorable conversation with your peers the next morning when you explain why the units have not passed as expected!
Remember all your cables, input and output! Do not rely on the test house having an IEC connector that fits your device. The AC cabling will need to be a length of 1M for conductive radiated tests.
To add or change components it is highly likely you need to open the product to gain access to them - ensure that you have appropriate tooling with you and test the tooling before you go to be sure that you can open the unit up. If it is a sealed unit, it may be wise to leave it unsealed (unless it compromises EMC) if possible so that amendments can be made if necessary.
I would recommend arming yourself with a few different ferrites and a few IEC filters. They cost so little and should your UUT not perform as expected, these small inexpensive, but affective ancillaries can mean the difference between pass and fail on the day. There are a multitude of different filters and ferrites to choose from and it is hard to say which ones you will need to suppress the troublesome frequencies until you perform the test. Of course, remember that the ferrite(s) that you use will need a big enough ID to feed the cabling through, but also small enough to fit into the case of the product if required. If your unit has an AC-DC PSU, adding ferrites to both the DC and AC lines can make a difference. Experiment with looping the cables back through the ferrite core if one pass was not enough - this will not change the frequency of attenuation but will increase the attenuation at the ferrites active frequency.
IEC inlet filters
IEC inlet filters come in different styles; the inlet plug type, medical or ITE rated, class I or class II and different performance levels. Be sure to take a few different versions with you to swap out if required, they cost so little in comparison to re-booking a test house so best to have them and not use them, than need them and not have them!