Ring Terminals

[john8791]

Working in a manufacturing plant on a 480V (Wye) supplied cabinet that has a PLC controller for a nickel plating line along with a various control relays, etc. On the outside of the cabinet is mounted a 480V-120V transformer (2 wire secondary) that supplies control circuits as well as a boiler circulation motor.

The secondary of this transformer is not grounded (which is what I am going to do). I noticed rather than using a ground bus bar, the person who wired it took all the grounds to a 1/2" stud on the galvanized base plate in the cabinet. There are about 5 ground wires ranging 14 to 10ga crimped into ring terminals and put on the one stud. Is there any restriction that limits how many ring terminals on one stud? I have not found anything in the NEC handbook. I am inclined to put in two bus bars; one for the grounds, and one for the "neutral" of the transformer and then bond the two together. Any thoughts? Thanks

 

[weressl]

Working in a manufacturing plant on a 480V (Wye) supplied cabinet that has a PLC controller for a nickel plating line along with a various control relays, etc. On the outside of the cabinet is mounted a 480V-120V transformer (2 wire secondary) that supplies control circuits as well as a boiler circulation motor.

The secondary of this transformer is not grounded (which is what I am going to do). I noticed rather than using a ground bus bar, the person who wired it took all the grounds to a 1/2" stud on the galvanized base plate in the cabinet. There are about 5 ground wires ranging 14 to 10ga crimped into ring terminals and put on the one stud. Is there any restriction that limits how many ring terminals on one stud? I have not found anything in the NEC handbook. I am inclined to put in two bus bars; one for the grounds, and one for the "neutral" of the transformer and then bond the two together. Any thoughts? Thanks

In my design I usually use two identical busbars, with equal number of connection provisions - since I carry a grounding conductor to each circuit - and install the neutral bar on standoff insulators to maintain the single point of ground/neutral bonding. If you have many internal users, you may end up with extra, unused grounding connection, but there is no harm in that.

The other way I deal with this, when using terminal strips only, is that I provide regular terminal blocks grouped together for the neutrals and put a power distribution insulated busbar that clamps into each lineside neutral terminal. Ground/bond at one point. Then provide grouped grounding terminal blocks where the terminal blocks attachment provision to the DIN rail BONDS the terminal connection to the common DIN rail, thus the DIN rail becomes a 'grounding' bar. If you want to group each circuit L/N/G, you can still do the same thing.

 

[SG-1]

Old School

Old School

What you are seeing is the Old School way of grounding. Westinghouse Electric's last version of medium voltage air-magnetic switchgear was DHP. All the CT,PT, relay case, etc... grounding was done in this manner. All the wires were terminated with ring terminals & taken to a single 10-32 screw that was fasten to the ground bus. The wires would be at angles to each other so as not to bend the terminals, it looked like a wire flower if many ground wires were present.

What you are considering is an up-grade.

 

[john8791]

Thanks for the input guys.