4W vs 3W wire main, what does service entrance rated mean?

[elmatador]

Hi Everyone,

I am new to this forum. I am a junior engineer so please pardon me for the basic questions.

I have a 2MVA 25kV/600v Y-Y transformer. The secondary neutral is resistor grounded 5A. The client requires that our main incoming on our MCC be service entrance rated. The MCC vendor has quoted a Four Wire main incoming section and a Three wire MCC. The questions are as follows :

1. Does service entrance just mean that a neutral lug or neutral bus is provided in the main incoming?
2. I was going to run seven runs of 3c 750mcm cables for the secondary. The Wye point of the transformer would connect to the NGR which in turn will be grounded to the MCC ground bus. Is it okay to leave the neutral bus on the main incoming section unconnected to anything? It would basically be not in use. Based o. My understanding this shouldn't be a problem.
3. The vendor shows the neutral bus as tied to ground on the main incoming. Is this ok? I also have a surge arrestor and power meter. The vendor shows the neutral wired to both devices. Is this going to be an issue with the Surge arrestor since the neutral is tied to ground in the vendor drawings? What would the meter see if nothing is Connected to the neutral?

I hope I have explained things properly. Thank you in advance

 

[Smart $]

Welcome :thumbsup:

1. Does service entrance just mean that a neutral lug or neutral bus is provided in the main incoming?

The actual term is "suitable for use as service equipment". Click the following link for more info and post again if you have additional questions:

http://www.neca-neis.org/newsletter/report.cfm?articleID=11114

2. I was going to run seven runs of 3c 750mcm cables for the secondary. The Wye point of the transformer would connect to the NGR which in turn will be grounded to the MCC ground bus. Is it okay to leave the neutral bus on the main incoming section unconnected to anything? It would basically be not in use. Based o. My understanding this shouldn't be a problem.

Is this a service (POCO owns transformer) or an SDS (separately derived system, consumer-owned transformer)?

If a service, the grounded conductor (neutral) is required to be brought to the service disconnecting means. Once connected to the main, it can remain unconnected to anything on the load side. If SDS, you obviously have to connect the neutral to the NGR, and the NGR to the GES. The neutral is not required to be run to disconnecting means, but you may need to for your metering and fault detection scheme.

3. The vendor shows the neutral bus as tied to ground on the main incoming. Is this ok? I also have a surge arrestor and power meter. The vendor shows the neutral wired to both devices. Is this going to be an issue with the Surge arrestor since the neutral is tied to ground in the vendor drawings? What would the meter see if nothing is Connected to the neutral?

In addition to my last comment above, with an High-Impedance Grounded Neutral System, the neutral will have to be unbonded from the GES/GEC/EGC. See 250.36 for more info on connections and routing.

 

[elmatador]

Hello Smart $!

Thank you for your response.

The transformer is a SDS. The power meter I was referring to in my post was not a Utility Meter, only a local MCC meter for display purposes. I will leave the neutral unconnected and not bond it to ground. I will make sure the vendor corrects this along with the power meter and lightning arrestor wiring.