Disconnect Mounted by Transformer

[Ron Poehlmann]

I've come to a point were I need some help on a clubhouse project. I'm the EE on this project. 208V, three phase system, 1400A. We had the transformer pad close to the building and disconnect installed right outside the building. The MDP was MLO 30 ft inside the building. One of the owners dropped in to take a look and said the transformer and disconnect must be moved.

Architect and EC have worked with POCO to move the transformer and disconnect to a new location about 230 feet away from building. All conductors underground.

My question is about where the bonding jumper between the neutral and ground should happen in the new arrangement. Originally I landed the GEC in the outside disconnect and ran a ground conductor (with the phase conductors & neutral) from the SD to the MDP.

With the service disconnect so far away, I want to treat the conductors from the disconnect to the MDP as if they were service entrance conductors. Can I do this and not install a ground conductor with the phase conductors? IE only phase conductors and neutral.

The GEC will have to be landed in the MDP now. It doesn't make sense to me to run ground conductors between the Service Disconnect in this instance, but I can't find an exception in the code that will allow me not to.

Does anyone see the fallacy in my thinking?

 

[charlie b]

I am wondering whether having the service disconnect that far away would satisfy the requirement that it be "readily accessible." The definition of that phrase includes the notion of being able to be reached quickly.

 

[iwire]

In my opinion you will have to have a 1,200 amp disconnect located at the club house with the GECs running to that.

VI. Service Equipment ? Disconnecting Means
230.70 General. Means shall be provided to disconnect all
conductors in a building or other structure from the service entrance
conductors.

(A) Location. The service disconnecting means shall be
installed in accordance with 230.70(A)(1), (A)(2), and
(A)(3).

(1) Readily Accessible Location. The service disconnecting
means shall be installed at a readily accessible location
either outside of a building or structure or inside nearest the
point of entrance of the service conductors.

You might be able to use this section to overcome the disconecting means issue.

230.71(A)(3) Remote Control. Where a remote control device(s) is
used to actuate the service disconnecting means, the service
disconnecting means shall be located in accordance with
230.70(A)(1).

But that section does nothing to solve the GEC issue.

 

[Ron Poehlmann]

Thanks for the comments.
The fire Marshall has already signed off on the location and told them to put a plackard at the Chinese finger about the disconnect. Given the layout I was considering it readily accessible myself.

If we consider that issue settled, then it seems like to require the ground and neutral to be connected in the disconnect instead of the MDP does two bad things. In a fault situation it requires the fault current to travel 230 feet on smaller conductors (the ground conductor instead of the neutral conductor), and it would give the possibility of a potential difference between the neutral and the ground at the building by adding more impedance.

If my MDP only had 6 breakers in it, I would be able to use it as the service disconnect, but it does not. The requirement of 250.24(A)(1) requires the GEC to be landed at the service disconnecting means. This again would not make sense to have to run the GEC an extra 230 feet, that would seem like it should violate other parts of the code.

The best option would be to put another disconnect inside the building, but there is simply no room, at this point in the project everything has been landed.

 

[petersonra]

The best option would be to put another disconnect inside the building, but there is simply no room, at this point in the project everything has been landed.

Is there no way to add a main breaker to the MLO panel?

Didn't they add "within 50 feet" to the definition of "readily accessible" a few cycles ago?

 

[don_resqcapt19]

I see the disconnect as a "structure" that is feeding a second structure and the installation to the second structure will have to comply with Part II of Article 225 and 250.32.

 

[augie47]

To me your 6 breaker disconnect would serve as your building service rated panel, but I agree with Don that since you have the disconnect at the transformer Art 225 has to be addressed and you need a EGC from that disconnect (250.32).
If you had the choice and the location of the MDP allowed, I would have eliminated the disconenct altogether.

 

[Ron Poehlmann]

In this jurisdiction the Fire Marshall is requiring an outside disconnect. So that is why I did not put a main in the MDP origiannly. The EC said that the way that the GE gear is built there is no way to put a main the MDP.

I need to clarify. The MDP has more than 6 breakers in it. That is part of the reason that I am having this trouble knowing what to do.

I had never thought of the disconnect as a structure. By calling it a structure, then 225.32 would require another disconnect either inside or outside the building. This puts me right back where I started.

If we call the Disconnect a structure and I am able to somehow get a main in the MDP or disconnect in the building, do I need to run a ground wire with the phase conductors and the neutral? (I think I know the answer), and If yes, then can I bond the neutral and the ground together in the inside disconnect or MDP?

 

[tryinghard]

I see the disconnect as a "structure" that is feeding a second structure and the installation to the second structure will have to comply with Part II of Article 225 and 250.32.

I see it this way as well, meaning it's a premises "feeder" past the utility secondary service disconnect 230' upstream - separate equipment ground & neutral heading out (no bonding the neutral past the service disconnect unless exceptions are met 250.24(A)(5) & 250.142(B)). The utility determines their "Service Point" (point of service).

A premises disconnect will most likely be required at building, most likely only because we've had acceptable installations where the exterior building disconnect was long distance away but in sight and sufficed. Either case requires earth grounding the structures but the rule is only bonding at the service disconnect.

 

[tommyrice]

using 3 wires between disconnects

using 3 wires between disconnects

why is it legit to run 3 wires between discs. in a trailer park and 4 wire between last disc. and panel,but not in this situation?

 

[tryinghard]

why is it legit to run 3 wires between discs. in a trailer park and 4 wire between last disc. and panel,but not in this situation?

Maybe these are utility service or at one time met the exceptions of 250.32(B)(1)? In premises wiring we are not supposed to install in a way that puts current on items it does not belong on, if bonding the neutral happens incorrectly current will travel to its source (usually a transformer) on all common conductive paths according to level of resistance. Example if the bonding takes place at the service disconnect and again at a downstream panel, and there are common conductive items in between like pipes, cables, metal building, earth?every time 120v circuitry is used the unbalance load will travel all conductive paths back to its source ? yet it should only travel solely on the grounded conductor. This is why the rule is to not bond the grounded conductor past the service disconnect.