Transformer Connection

[ctrane]

Any and all help will be most appreciated. On a Low-Voltage General Purpose Transformer, what are the proper connections in terms of grounding? On the transformer chasis ground lug, should it be connected to the Primary side ground, Secondary side ground, or both? Also, is it appropriate to run a Ground Electrode Conductor (sized according to secondary over-current protection) from the Primary Ground bar (assuming it is point of service and ground bar is directly tied to ground system) and use that as the grounding of the separatley derived system, i.e. the secondary of the transformer, which in turn is tied to my Neutral (XO, assuming this whole question relates to a three phase, four wire system on the secondary). Is this grounding point of the secondary usually a lug that will accept multiple wires, or is this something that must be specified, because I will also have to run my equipment ground to the downstream panel from this lug.
Thanks

 

[raider1]

Take a look at 250.30 in the NEC. This section deals with grounding of separately derived systems.

Chris

 

[RUWired]

On the transformer chasis ground lug, should it be connected to the Primary side ground, Secondary side ground, or both?

The equipment ground lug on the frame of the transformer when the bonding jumper is made at the transformer can be made up a couple different ways. One way if using mechanical lugs, is to use a four hole lug.1 primary ground, 2 secondary ground, 3 system bonding jumper to xo, 4 grounding electrode conductor. the other way is to use a 3 hole lug and put put the grounding elctrode conductor with the neutral ox conductor.

Also, is it appropriate to run a Ground Electrode Conductor (sized according to secondary over-current protection)....

Thr grounding electrode conductor is sized according to the table in 250.66 based on the size of the secondary conductors,

.....from the Primary Ground bar (assuming it is point of service and ground bar is directly tied to ground system) and use that as the grounding of the separatley derived system, i.e. the secondary of the transformer, which in turn is tied to my Neutral

If your saying you want to use the grounding electrode conductor, run it through the equipment ground lug and then onto the ox without a splice for the jumper. Yes you can do it if the GEC is rated for the SBJ. Sometimes it looks a little tacky because of the bolt holding the lug to the frame.

. Is this grounding point of the secondary usually a lug that will accept multiple wires, or is this something that must be specified, because I will also have to run my equipment ground to the downstream panel from this lug.
Thanks

Typically a multi hole lug is used as described above .

rick