where to bond ground and neutral together

Status
Not open for further replies.
P

papa smurf

Member
Where should you bond the ground and neutral together at when you have a high voltage line pole feeding down to a high voltage feeder breaker that feeds a step down transformer and then a main breaker, then it goes to a double throw transfer switch for generator power and grid power, then it goes to a MDP.
 
Define high voltage, and are you asking about establishing a ground reference on the primary or secondary of the stepdown trans?

also is there a seperately derived system a feeding the trans sw ( does the sw break the neutral if there is one) ? What is the secondary voltage of the trans??

I would break the question down to several parts.
 
The neutral-ground bond normally occurs at your service disconenct and on the secondary side of a seperately derived system.
I wouod think in your scenerio, there woukd be a neutral ground bond at your hv breaker (if the neutral is present) and again at the secondary of your step-down transformer, probably at the main breaker.
There are varibles with different systems. You need to look at 250. Part X for voltages over 1kv and 250.24 for your lower voltage systems.
 
Last edited:
the voltage coming in is 11kv down the pole with three phases to a cabinet with a 11kv breaker. the pole has a ground coming down pole to a ground wire. The 11kv breaker feeds an adjacet transformer steping down to 400v, frame is grounded but not bonded to neutral at that point. From there it feeds a three pole 1000 amp beaker in cabinet. the ground and neutral is not bonded there either. From there it feeds the double throw transfer switch. Which has generator feed in transfer switch also. It is not bonded there either. From there it feeds a MDP ajacet with no bond there also. I believe the bond should take place at the MDP after the Tranfer switch but not positive. Hope this helps with the info.
 
As always the answer is not simple. From an NEC standpoint you need to look at the definition of "Service". At what point does the utility stop and premisis wiring begin ? Ahead of that, bonding grounding is POCO's problem. Once you define your service, if there is a neutral, it must be brought to your service equipmemt and a neutral-ground-bond established there. It would seem that would be your 1000 amp breaker.
Beyond that, there should be no grounded-grounding connection per 250.24(5) {250.24 is the "key" article for this discussion}
If the 11kv and transforemr are customer owned/maintained and not POCO responsibility then NEC Art 250 X for grounding on high-voltage needs to be addressed.
 
I do not see where you have mentioned a neutral conductor on the pri or sec. I'm thinking the 11kV breaker is the servie eq.???? and the sec is a seperately derived sys along with the generator. does the trans sw break a neutral??
 
Status
Not open for further replies.
Top