System grounding and neutral-to-case bonding for each store in a mall

[alej27]

I have a question regarding grounding and bonding, in the case of a multi-store mall.

Consider a mall, with a dedicated transformer connected to the primary distribution lines on the HV side (say 13.8 kV). The LV side (say 240/120 V) conductors of the XFMR are then run to a set of cabinets. First, a main breaker (say 600 A) is encountered in a vertical cabinet. Then, the conductors are run to an adjacent horizontal cabinet with two-pole distribution breakers (say 70 A), one for each store. Then, the load-side of those breakers are connected to individual meters in another cabinet, again one for each store. Only the PoCo (power company) has access to the three previous cabinets. Finally, from the meters, conductors are run to another vertical cabinet with also two-pole distribution breakers, again one for each store, but now the mall owner has access to this cabinet; after each distribution breaker in this cabinet, conductors are run to the main panelboard of each store of the mall.

I'd like to know how should the grounding and bonding (only connections) be done in this scenario, in two cases: 1) private transformer (owned by the mall); 2) utility-owned transformer.

For case #1, I suppose that if it the transformer secondary neutral is not connected to the primary neutral, then the transformer is considered a SDS (separately derived system), hence the secondary neutral must be grounded and be bonded to the XFMR enclosure. Downstream of the XFMR enclosure, the neutral and ground wires are kept separate for each store. The main panelboard of each store must have the neutral and ground terminal bars separate. If each store owner want to, they can install more ground rods, connected to the ground (not neutral) terminal bar of their main panel. Is this correct? This is shown below.



For case #2, would the answer be the same? Or would somehow the main panel of each store receive the two hots plus neutral with no ground wire, and then require to bond and ground their neutral (for each store)?

 

[augie47]

Your diagram is basically correct for a POCO owned transformer installation. There would be a neutral to equipment ground link in the gear.

If it were a customer owned transformer 250.30 would apply although with the exceptions for SSJ and SSBJ the install would lilely be the same.

In either event you would run phase, neutral & grounding to each store.

 

[david]

Assuming the green conductor in your design is the SSBJ it would land in your 600 amp disconnect. Since your SBJ and your SSBJ originate in your exterior transformer. The neutral has to be run with your feeders so the neutral would also land in the 600 amp disconnect, however you would not bond the neutral in that disconnect. The SSBJ would bond to the grounding electrode conductor (system) to the equipment grounding and bond the enclosure for the 600 amp disconnect. Everything load side of that would be feeders and feeder taps

Now i have never seen utility owned meters on a feeder supplied building. Others here may have but i have not.

now if this was a service and the 600 amp disconnect was a service disconnect you could see utility owned neutral bonded meters on the load side of the service disconnect. ( adjacent to the service disconnect).

 

[david]

Your diagram is basically correct for a POCO owned transformer installation. There would be a neutral to equipment ground link in the gear.

If it were a customer owned transformer 250.30 would apply although with the exceptions for SSJ and SSBJ the install would lilely be the same.

In either event you would run phase, neutral & grounding to each store.

He is not showing the Neutral in his 600 amp disconnect and he not chowing the neutral with the conductors load side of that 600 amp disconnect,

are you thinking this is all one peace. (OP calls them out as separate cabinets)

 

[augie47]

He is not showing the Neutral in his 600 amp disconnect and he not chowing the neutral with the conductors load side of that 600 amp disconnect,

are you thinking this is all one peace. (OP calls them out as separate cabinets)

Yes. I was thinking it is a multisection distribution center as the drawing resembles such
If the 600 amp main is actually a separate enclosure I agree the neutral and bonding should all be done there.

 

[alej27]

Your diagram is basically correct for a POCO owned transformer installation. There would be a neutral to equipment ground link in the gear.

That would be the case because the 600-amp main would be the "service disconnect equipment", right?

Also, would this be in place of, or in addition to, the neutral-to-case bond inside the transformer enclosure I showed? Or would the answer be "maybe yes, maybe no", since the transformer in this case is utility-owned and hence doesn't have to follow NEC rules?

 

[augie47]

Since it is a POCO transformer this would be service (as opposed to a SDS) and they (POCO) would provide the grounding electrode system at the transformer.
Your phases, neutral, main bonding jumper and building grounding electrode system should all connect in your 600 amp main
(In the event the main/meters etc are all a part of a manufactured switchboard then there should be a factory diagram showing termination points).
The feeders would consist of phases, neutral & equipment ground conductors.

 

[alej27]

He is not showing the Neutral in his 600 amp disconnect and he not chowing the neutral with the conductors load side of that 600 amp disconnect,

are you thinking this is all one peace. (OP calls them out as separate cabinets)

Sorry my original post gave that impression. I meant all the cabinets are assembled as one unit. I know they're called "metering center" (literal translation from Spanish), but perhaps they're called "multisection distribution center" as @augie47 said.

 

[alej27]

Since it is a POCO transformer this would be service (as opposed to a SDS) and they (POCO) would provide the grounding electrode system at the transformer.
Your phases, neutral, main bonding jumper and building grounding electrode system should all connect in your 600 amp main
(In the event the main/meters etc are all a part of a manufactured switchboard then there should be a factory diagram showing termination points).
The feeders would consist of phases, neutral & equipment ground conductors.

So, just to be clear, my first diagram (for mall-owned XFMR, a SDS) is correct. And for a utility-owned XFMR, a service, it'd be as follows:



The neutral is bonded to case, as well as grounded, through the ground terminal bar, at the main breaker cabinet, as required by the NEC. Furthermore, the utility company, following the NESC, grounds the neutral and bonds it to the casing also at the transformer; lastly, the secondary neutral is bonded to the primary neutral in the transformer (since it is my understanding this is the most typical distribution configuration in the US, see this post in another forum). Is that correct?

 

[david]

So, just to be clear, my first diagram (for mall-owned XFMR, a SDS) is correct.

im not sure anyone said that

 

[alej27]

im not sure anyone said that

Ups, my bad for not answering your first post.

Since your SBJ and your SSBJ originate in your exterior transformer. The neutral has to be run with your feeders so the neutral would also land in the 600 amp disconnect, however you would not bond the neutral in that disconnect.

In my first diagram, the neutral is indeed run with the phase conductors. It lands on a terminal bar adjacent to the main breaker, which is in the same cabinet. And, the neutral is not shown bonded to the main breaker enclosure/cabinet. So I think I have this one correct. Please correct me if mistaken.

Assuming the green conductor in your design is the SSBJ it would land in your 600 amp disconnect.

The SSBJ would bond to the grounding electrode conductor (system) to the equipment grounding and bond the enclosure for the 600 amp disconnect

So, if I move the ground terminal bar, along with the ground wire that bonds the cabinet enclosure to the ground terminal bar, from the rightmost cabinet (where it is currently drawn) to the leftmost cabinet (where the main is) in my diagram, as shown below, would both of these errors be fixed?

 

[augie47]

Someone else may spot a problem but it looks correct to me.
You would need to address a GES at the building.
If you read the exceptions to 250.30 {(A)I(1) Exception 2 & (A)(2) exception) } you may find you can install the SDS in the same manner as you do a utility transformer

 

[david]

Ups, my bad for not answering your first post.

In my first diagram, the neutral is indeed run with the phase conductors. It lands on a terminal bar adjacent to the main breaker, which is in the same cabinet. And, the neutral is not shown bonded to the main breaker enclosure/cabinet. So I think I have this one correct. Please correct me if mistaken.


So, if I move the ground terminal bar, along with the ground wire that bonds the cabinet enclosure to the ground terminal bar, from the rightmost cabinet (where it is currently drawn) to the leftmost cabinet (where the main is) in my diagram, as shown below, would both of these errors be fixed?


View attachment 2572797

To me. Since the meters are factory bonded. Both the mall owned and the utility owned drawings would be identical

I still have a big question mark about the utility sealing meters supplied by a mall owned transformer

No one else is questioning that, so maybe it's something a utility would do.

 

[alej27]

I still have a big question mark about the utility sealing meters supplied by a mall owned transformer

No one else is questioning that, so maybe it's something a utility would do.

I've realized my hypothetical case of what you're trying to say (my first case: mall-owned transformer with utility-owned meters) doesn't make sense and is not common, is true. I'm a bit of a newbie regarding these types of installations. Only the second case (utility-owned transfomer with utility-owned meters) is common/seen. Thanks!