When burying multiple runs of electrical conduit in concrete, they need to have specific spacing between each other to ensure the integrity of the resulting concrete pour. Too close together and the concrete slab won't have sufficient rigidity. Too far apart and the installation may not be possible or efficient. Spacers are therefore used to keep the proper distance between conduits and to support them as the concrete is slushing and being compacted around them.The installation uses two types of spacers: Base and Intermediate. The Base spacer, sometimes called a chair, goes at the very bottom of the pile and the first conduit is laid inside it. The intermediate spacers go on top of each conduit and form both the top of one and the bottom of the next. That is why they are sometimes called the ladder.