Question: For soldering a wire into a connector fillet, what is the minimum space/area between the wire and the connector walls? Is there a standard for this?
Answer: Based upon the question, I’m making the assumption that the connector fillet is in a Cup Terminal and my answer is based upon this assumption.
Regardless of the wire size, when soldering a wire into a connector, the acceptable conditions are the same. Check IPC-A-610E, on page 6-51, where it states that the wire will be inserted to the full depth of the cup and in contact with the back wall of the cup. If the wire is not in contact with the back wall of the cup then it is a process indicator and does not have to be fixed, by that I mean the solder joint does not have to be reflowed to reposition the wire.
If the wire is not in contact with the back wall of the cup and it interferes with subsequent assembly steps, then it is a defect for all three Classes of products.
Therefore to answer the question: Is there a standard for this? Reference IPC-A-610 page 6-51, or IPC/WHMA-A-620A, page 4-41, to get the pictures of what the acceptable conditions are for a wire into a cup terminal. There is no dimensional criterion for the space between the wire and the connector walls, only that each wire when inserted into the cup will not interfere with the installation of the other wires and their proximity or closeness will not impact or reduce minimum electrical clearances.