Fastening to tension concrete can be tricky. Typically you are not allowed to go beyond 3/4″ depth with your fastener. That really limits what you can use! Tapcon and wedge anchors will require at least a 1″ embedment so they are out. Shooting into post tension concrete is really a bad idea for two reasons. First off, most pins are 1″ length and if you hit a void or soft spot they could easily go in deep enough to hit a cable. Secondly, the concrete is usually so hard you will end up blowing out chunks of concrete. So how are you supposed to mount a j hook or bridle ring or other hanger? For these type of applications we are recommending a 1/4″ shallow or mini drop in that requires only a 3/4″ depth.
Installation is easy following these steps. First drill a 3/8″ diameter hole using what is called a stop bit. A stop bit has a shoulder on it preventing you from drilling too deep and hitting a post tension cable in the concrete. This is a key part of the process that will really protect you. You simply can’t drill too deep. Now tap the shallow or mini drop in anchor into the hole and set with the included set tool. You will need to hammer until the shoulder of the tool comes in contact with the anchor to achieve full setting of the anchor. Now you have 1/4″ diameter threads in the concrete so you can screw in a standard bridle ring. If you want to use a j hook, buy one with an angle bracket attached and use a 1/4-20 screw 3/8″ in length. If you need to drop your hangers, a j hook tree or a 1/4″ threaded rod could be used as well.
While using a drop in anchor really is over kill for something as simple as a cable run, when fastening into post tension concrete, it really is your best option, simply because it is the only concrete anchor with such a shallow embedment and that is approved for overhead use. The smaller size of 1/4″ mini drop in makes it a little easier to set over the larger 3/8″ sizes.
So to recap, when faced with fastening your j hooks, bridle rings or other hangers to post tension concrete, you will want to stick with an anchor and a system designed for that purpose. Shallow embedment or “mini” drop ins fit the bill. Use them in conjunction with a stop bit and you will be good to go.