d receptacles. All of this will be included in the documentation for the power sup- ply, which is available on Cisco's web site. For example, the power cord for a power supply may come with a NEMA L6-20P plug. This will require NEMA L6-20R recep- tacles. The P and R on the ends of the part numbers describe whether the part is a plug or a receptacle. (The NEMA L6-20 is a twist-lock 250-volt AC 16-amp connector.) The power cables will connect to the power supplies via a large rectangular connec- tor. This plug will connect to a receptacle on the power supply, which will be surrounded by a clamp. Always tighten this clamp to avoid the cable popping out of the receptacle when stressed. Cooling On many chassis switches, cooling is done from side to side: the air is drawn in on one side, pulled across the modules, then blown out the other side. Usually, rack- mounting the switches allows plenty of airflow. Be careful if you will be placing these switches in cabinets, though. Cables are often run on the sides of the switches, and if there are a lot of them, they can impede the airflow. The NEBS-compliant 6509 switch moves air vertically, and the modules sit vertically in the chassis. With this switch, the air vents can plainly be seen on the front of the chassis. Take care to keep them clear. I once worked on a project where we needed to stage six 6506 switches. We pulled them out of their crates, and put them side by side on a series of pallets. We didn't stop to think that the heated exhaust of each switch was blowing directly into the input of the next switch. By the time the air got from the intake of the first switch to the exhaust of the last switch, it was SO hot that the last switch shut itself down. Always make sure you leave ample space between chassis switches when installing them. Installing and removing modules Modules for chassis-based switches are inserted into small channels on both sides of the slot. Be very careful when inserting modules, as it is very easy to miss the chan- nels and get the modules st