Grounding 400 Amp Service with 2 Meter Cans

[Mdgator56]

We are doing a big job upgrading a duplex's service from 200 amps to 400 amps. We have an overhead service which feeds into a gutter(400 MCM), then into 2 separate meter cans for each unit. Each Meter can feeds it's own separate disconnect. There is no existing grounding system. What is the proper way to ground this service? I was thinking 4 ground rods total with #4 Bare Cu going into each disconnect? What do you guys think?

 

[Dennis Alwon]

Hello, you don't need 4 rods.... 2 rods & #6 not #4 to the rods. Bring the grounding electrode conductor that connects the 2 rods into the gutter. The power company will make the connection to the neutral or you may need to.

The other option is to run one #6 copper conductor from one meter base to the two rods and then the same for the other meter base.

If the power company will not allow the grounding electrode conductor in the meter base or in the gutter ten you will need to run it to each disconnect

 

[electrofelon]

Just to expand a little on what Dennis said, 250.64(D) is where you find how to connect the grounding electrode conductor to services with multiple enclosures. It is very clearly spelled out. As Dennis said, the common location method is probably the simplest, and hit the neutral in the gutter. Do you have any other electrodes? Metal water pipe?

 

[Mdgator56]

Hello, you don't need 4 rods.... 2 rods & #6 not #4 to the rods. Bring the grounding electrode conductor that connects the 2 rods into the gutter. The power company will make the connection to the neutral or you may need to.

The other option is to run one #6 copper conductor from one meter base to the two rods and then the same for the other meter base.

If the power company will not allow the grounding electrode conductor in the meter base or in the gutter ten you will need to run it to each disconnect

If I do have to run it to each disconnect, Can I share the two ground rods? Run one set of wire to the Rods, then hit Cold water Bond in Unit A, then disconnect. Then run another set to the same two ground rods, hit the cold water Bond in Unit B, then up to the Unit B disconnect?

 

[Mdgator56]

Just to expand a little on what Dennis said, 250.64(D) is where you find how to connect the grounding electrode conductor to services with multiple enclosures. It is very clearly spelled out. As Dennis said, the common location method is probably the simplest, and hit the neutral in the gutter. Do you have any other electrodes? Metal water pipe?

The Outside Service has the two meter cans and both disconnects in the back of Unit A. Unit B is right next to it, with a fence separating the two. I can hit the Metal water pipe for both units. I would just have to run wire around that fence onto Unit B's Metal water pipe.

 

[electrofelon]

If I do have to run it to each disconnect, Can I share the two ground rods? Run one set of wire to the Rods, then hit Cold water Bond in Unit A, then disconnect. Then run another set to the same two ground rods, hit the cold water Bond in Unit B, then up to the Unit B disconnect?

Have you looked at 250.64(D)?

 

[marmathsen]

I came here to ask a very similar question, so I guess I'll ask it in this thread.

What if those two meters feed separate buildings, as in my case with a back yard cottage (DADU). Or in the OPs scenario maybe there is a firewall such that it's considered separate buildings. One meter feeds the building it's attached to, the second feeds a separate building.

Would you install main bonding jumpers at both disconnects and run the GEC into both (or the gutter in the OPs post).

Or since the second meter doesn't feed that building it's mounted to, would you install 2 meter+2 disconnects, with the first disconnect labeled "EMERGENCY DISCONNECT, SERVICE DISCONNECT" and the second labeled "EMERGENCY DISCONNECT, NOT SERVICE EQUIPMENT". The first meter feeds the first unit conventionally with H/H/N/G, but the second feeds the second building underground with H/H/N and then you have all the required main bonding jumper and GES at the second building. If option 2 then would you need to run the first building's GEC into both disconnects? Am I incorrect in thinking you could run to the second building without an EGC?

Forgive my ignorance, I don't deal with multi unit services very often. And with the addition of the Emergency Disconnect, it adds additional confusion.

 

[electrofelon]

Ignore the meters, they have nothing to do with it. It is just one service regardless of the meter quantity. The service needs a grounding electrode system. If you have multiple service disconnects, again see 250.64(D) for your options.

 

[electrofelon]

.

Would you install main bonding jumpers at both disconnects and run the GEC into both (or the gutter in the OPs post).

You can run into both service disconnects using the tap method. Or you can use the common location method into the gutter. There's probably no point in saying anything else until everyone reads 250.64 (D)!

 

[Dennis Alwon]

I came here to ask a very similar question, so I guess I'll ask it in this thread.

What if those two meters feed separate buildings, as in my case with a back yard cottage (DADU). Or in the OPs scenario maybe there is a firewall such that it's considered separate buildings. One meter feeds the building it's attached to, the second feeds a separate building.

Would you install main bonding jumpers at both disconnects and run the GEC into both (or the gutter in the OPs post).

Or since the second meter doesn't feed that building it's mounted to, would you install 2 meter+2 disconnects, with the first disconnect labeled "EMERGENCY DISCONNECT, SERVICE DISCONNECT" and the second labeled "EMERGENCY DISCONNECT, NOT SERVICE EQUIPMENT". The first meter feeds the first unit conventionally with H/H/N/G, but the second feeds the second building underground with H/H/N and then you have all the required main bonding jumper and GES at the second building. If option 2 then would you need to run the first building's GEC into both disconnects? Am I incorrect in thinking you could run to the second building without an EGC?

Forgive my ignorance, I don't deal with multi unit services very often. And with the addition of the Emergency Disconnect, it adds additional confusion.

You cannot run a feeder to the second building with just 3 wires. You need an equipment grounding conductor. Now if you left the meter without a disconnect on the building then IMO, you can run 3 wires to the second building

 

[Joe Villani]

Does the incoming water service qualify as a grounding electrode conductor?

You might not have to bring the water bond back to the service disconnects.

 

[marmathsen]

You can run into both service disconnects using the tap method. Or you can use the common location method into the gutter.

I was actually asking if it would be required or best practice to install an equipment grounding conductor (and thus main bonding at the meter/disconnect) from meter/disconnect #2 to the separate building. Now that I think about it, if not required then probably best practice in case there are continuous metallic paths now or in the future between the buildings.

There's probably no point in saying anything else until everyone reads 250.64 (D)!

I think where I got hung up with that section is that is starts off with,

"If a building or structure is supplied by a service or feeder with two or more disconnecting means in separate enclosures..."

Does it make any difference whatsoever if one of the meters is merely mounted there and then goes on to feed a separate building with it's own GES? I'm not seeing that distinction in 250.64 (D) or anywhere else for that matter.

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Maybe this is my mistake but I'm considering the service to be everything between the service point and the service disconnect. And I'm considering the service disconnect to be where the main bonding jumper is. If the main bonding jumper is at another building, then obviously you wouldn't run an GEC to from meter #2 to the second building and this wouldn't be considered a feeder as @Dennis Alwon mentions.

In 230.85(E)(1) where is gives you the option for EMERGENCY DISCONNECT, NOT SERVICE EQUIPMENT, doesn't that not give you the flexibility have your main bonding jumper and service disconnect downstream, or even at a separate building provided you have no other distribution between the Emergency Disconnect and the Service Disconnect?

 

[electrofelon]

I was actually asking if it would be required or best practice to install an equipment grounding conductor (and thus main bonding at the meter/disconnect) from meter/disconnect #2 to the separate building. Now that I think about it, if not required then probably best practice in case there are continuous metallic paths now or in the future between the buildings.



I think where I got hung up with that section is that is starts off with,

"If a building or structure is supplied by a service or feeder with two or more disconnecting means in separate enclosures..."

Does it make any difference whatsoever if one of the meters is merely mounted there and then goes on to feed a separate building with it's own GES? I'm not seeing that distinction in 250.64 (D) or anywhere else for that matter.

Take a look at 230.40:


230.40 Number of Service-Entrance Conductor Sets. Each service drop, set of overhead service conductors, set of under‐ ground service conductors, or service lateral shall supply only one set of service-entrance conductors.

There are exceptions, and if this is a residential property, then you could use Ex #3 run service conductors over to the other building without a disconnect

 

[electrofelon]

I think where I got hung up with that section is that is starts off with,

"If a building or structure is supplied by a service or feeder with two or more disconnecting means in separate enclosures..."

Does it make any difference whatsoever if one of the meters is merely mounted there and then goes on to feed a separate building with it's own GES? I'm not seeing that distinction in 250.64 (D) or anywhere else for that matter.

---

Maybe this is my mistake but I'm considering the service to be everything between the service point and the service disconnect. And I'm considering the service disconnect to be where the main bonding jumper is. If the main bonding jumper is at another building, then obviously you wouldn't run an GEC to from meter #2 to the second building and this wouldn't be considered a feeder as @Dennis Alwon mentions.

In 230.85(E)(1) where is gives you the option for EMERGENCY DISCONNECT, NOT SERVICE EQUIPMENT, doesn't that not give you the flexibility have your main bonding jumper and service disconnect downstream, or even at a separate building provided you have no other distribution between the Emergency Disconnect and the Service Disconnect?

I think you bring up an interesting question. Ok lets say you have two meters. The meters are fed from a trough which is fed with 2 sets of 250 AL as a riser. Each meter is fed from a single set of 250 AL tapped in the trough. Lets say meter A has a 200A service disconnect right next to it. Lets say meter B just feeds a set of service conductors that goes to a remote building which has a 200A service disconnect. It seems to me that 250.64(D) does not apply because there is only a single service disconnect at the main building. So how are the GEC's for the main building and the remote building sized? I would say the main building is sized for the paralell 250's so#2 CU. Sizing for the remote structure is not realy clear IMO. 250.66 says:

250.66 Size of Alternating-Current Grounding Electrode Conductor. The size of the grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system of a grounded or ungrounded ac system shall not be less than given in Table 250.66, except as permitted in 250.66(A) through (C).

The remote building is not supplied by a feeder or branch circuit so the only option is to size it per the "at the service" clause, and I am not really sure what that means. I Am tempted to say size it to the conductors only in the set feeding the remote building, but that is not stated. Does note #1 in table 250.66 apply so I have to size it to the parallel 250's?

 

[david]

230.40 was mentioned, assuming this is not a single family dwelling and an accessory building

You see this set up a lot on pedestal in mobile home parks

You might even see this mounted to a utility garage in a mobile home park with one meter of several supplying the utility garage.

The point is you would treat what is being describe similar to a pedestal as far as the remote building is concerned

The NEC does not dictate if a building can or cannot be the structure that supports a meter bank