In certain slip ring applications, it makes sense to use more than one bore size range in a combination or 'piggy-back' unit. This is not possible where a through passage, with the clearance of a larger bore slip ring is required completely through the assembly. However, if the slip ring mounts on the end of a shaft, it can often be the most practical solution because it often provides a less expensive package. In most instances, the cost per circuit increases with the diameter of the circuits involved in United Equipment Accessories slip ring assemblies'. As an example, building a slip ring with only the high power (150 amps plus) circuits in a 2.50”-4.00” bore size range and assembling the lower powered signal, communication, etc. circuits in a 1.50” bore size slip ring would be less expensive than a slip ring with the same combination of circuits built entirely in the larger bore size. UEA also has a wider variety of brush and ring materials, as well as brush ratings, available in the 1.50” bore assemblies than in larger bore assemblies. In some instances, this can provide an assembly with a shorter height than the same assembly built entirely with the larger bore components.
Another advantage of the 'piggy-back' assemblies is that it is much easier to provide increased electrical isolation for circuits potentially sensitive to electrical noise, such as noise provided by VFD (Variable Frequency Drive) circuits passing through the slip ring. Good isolation can be obtained by enclosing the sensitive circuits within an all metal enclosure, separate from the overall enclosure, with these circuits having both inputs and outputs through shielded cables. The electrical noise from VFD circuits is most likely to affect sensitive circuits where the cables from both types of circuits are run closely parallel for more than a few inches. Where this is a potential problem, a center mounting tube for the upper (signal and communications) slip ring can be furnished with a steel tube that passes completely through the center of the lower (power), and larger bore, slip ring. This provides another isolation 'shield' around the signal or communication circuits cable(s).
While not a solution for all applications, the UEA 'piggy-back' style slip ring can be used for certain applications to save cost, space and provide needed electrical isolation.