Paralleling slip rings

[jsmarotta]

I have a system which has a pedestal with slip rings to provide AC power to equipment mounted on a pedestal. The slip rings are rated at 10A each and the feeds to the pedestal are protected with 10A breakers. If I have a load on the pedestal that is 15A can / should I connect two of the 10A feeds at the top of the pedestal? Common sense and analysis shows me that an difference in the resistance between the two paths will result in proportional difference in current balance, with the potential of popping breakers if the 10A is exceeded. What I don't have a handle on is what the magnitude of the diffence in resistance may be by the time you go through slip rings a few circuit breakers, and some terminal blocks? Any help or guidance would be appreciated

 

[rbulsara]

Need more information to understand your system.

How many slip rings on a pedestal are there? What is the intended function of each slip ring?

Are all loads on a pedestal is single phase? 3 phase? How may circuit of each? Neutral wire. Can they be fed by a singel circuit?

 

[jsmarotta]

There are around 60 slip rings total in the system for various purposes. The intended purpose of each is beyond the scope of this discussion. The area I'm concerned with is the AC power distribution. The loads are single phase. In this particular enclosure I have two 10A circuits available which are split from one phase of a three phase wye system at the base of the pedestal.

 

[rbulsara]

There are a couple of things you can do:

1. This is a less desireable and eyebrow raising method: As you said, you can connect the two circuits together (after the slip rings) as long as you are 'aboslutely' sure that they are fed from the same phase and 'will remain so'. You obviously undestand what will happen if some one in the future switches the breakers to two diffrent phases. At any rate to your basic question, I do not think the connection reistance will make a significant difference as long as the lengths of the two circuits are more or less equal. You need to use #12 size minimum conductors all the way, specially after combining two circuits. Since you will be able to measure the amps after the modificaiton you will know if there is severe imbalance.

2. A much better way is to employ a 20A breaker, use #12 wire minimum, split the wires (using #12) at the slip ring and join them back to a single #12 wire and feed the 15 A load.

Please account for the voltage drop by upsizing the wire size.

 

[jsmarotta]

Thanks for the input. We had thought about just such an option, but I am worried that the slip rings would be the most significant contributer to a resistance difference over time? The slew rates are fairly slow so if it hit a higher resistance area it would not pass through it quickly and may cause a trip. There really is no way around it with the design constraints we have at this time. I'm looking into making the load 220 in which case I could go Line to Line.

 

[jbartos]

Suggestion: Unless some ingénues protection of slip rings is implemented, they will be vulnerable to the damage due to a short to the ground at one slip ring.