3-Phase Installation Using 1200A Switchboard w Metering......

[dionysius]

This job is stretching my experience so I need some sanity checking. Important customer to me so I want to get it right. 480/277 3 phase Y.

This outside installation is spread over concrete wall of this old very large 200 ft high bldg.

The outside Switchboard will have outdoor conduit runs to 4 x 200A and 1 x 400A main breaker panels. Ground and neut will not be bonded in these.

The service disconnects will be in the Switchboard and will be moulded case cct breakers (4 x 200A; 1 x 400A).

This is a flat roof Switchboard. It will be mounted to the wall. Grd and neut will be bonded in this enclosure at point of service.

Q1:
Is it per code to exit these feeder conduits through the roof of Switchboard enclosure????

Neutrals will be same of gauge as current carrying conductor in all cases (just to be on safe side).

Do these following selections for sizing look good??. I always want to control the cost yet keep the installation not too stressful on moi or on the products.

Q2:
The 1000 kVA XFR secondary is connected to incoming side of Switchboard using 4 parallel feeds of 300A each. For each run will use:

3" plastic conduit​

500 MCM XHHW Al​

3 wires in cable​

Neutral​

Ground #2 Al

​

Q3:
The runs for the 200A panels will be:

480/277 V 3 ph 200 A​

300 MCM XHHW Al​

3 wires in cable​

Neutral ​

Grd #4 Al ​

3” plastic conduit

​

Q4:
The run for the 400A panel will be:

480/277 V 3 ph 400 A​

700 kcmil XHHW Al ​

3 wires in cable
Neutral ​

Grd #1 Al ​

4” plastic conduit​

I am so impressed with the sheer professionalism of this superb website. I hope to give back in the future.

 

[don_resqcapt19]

...
Q1:
Is it per code to exit these feeder conduits through the roof of Switchboard enclosure???? ...

That would be somewhat based on the design of the equipment. In general, I do not like top entry to equipment that is in a wet location.

Q2:
The 1000 kVA XFR secondary is connected to incoming side of Switchboard using 4 parallel feeds of 300A each. For each run will use:

3" plastic conduit​

500 MCM XHHW Al​

3 wires in cable​

Neutral
​

Ground #2 Al ​

Is the transformer on the line or load side of the service point?
If the transformer is on the load side of the service point, the three sets of 500 kcmil aluminum are not big enough...they only give you 930 amps. 240.4(B) does not apply because the circuit exceeds 800 amps....even if it was less than 800 amps, that section does not apply to transformer secondary conductors. In this case the ground conductor would really be a supply side bonding jumper and Table 250.102(C)(1) would require that conductor to be 4/0 aluminum.

I am not sure what you mean by 3 wires in cable and a neutral conductor....300.3(B) requires the phase conductors and the neutral to be in the same cable.

If the transformer is on the line side of the service point, or is the service point, there would be no "ground" conductor and the three sets or 500 kcmil would be permitted as long as the calculated load is 930 amps or less and there is more than one service OCPD. If you have a single main, you would have to have conductors that have an ampacity that is equal to or greater than the rating of the service OCPD.
Note that if you do have a 1,000 amp main in a 480Y/277 service the main will require ground fault protection per 250.95.

Q3:
The runs for the 200A panels will be:

480/277 V 3 ph 200 A​

300 MCM XHHW Al​

3 wires in cable​

Neutral ​

Grd #4 Al ​

3” plastic conduit
​

​

The code would permit the use of 250 kcmil aluminum for this application. You are using a larger conductor and 250.122(B) will require an increase in size of the EGC.

Q4:

The run for the 400A panel will be:

480/277 V 3 ph 400 A​

700 kcmil XHHW Al ​

3 wires in cable
Neutral ​

Grd #1 Al ​

4” plastic conduit ...​

The 700's are fine as long as the calculated load is less than 375 amps.
I try to avoid conductors larger than 500 or 600 kcmil, so I would probably install two sets of 250 kcmil for this application.

​

 

[dionysius]

Incorporating feedback.......

Incorporating feedback.......

Is the transformer on the line or load side of the service point?

It is on the line side. The old service is being torn out and this is a new and larger replacement.

I am not sure what you mean by 3 wires in cable and a neutral conductor....300.3(B) requires the phase conductors and the neutral to be in the same cable.

If the transformer is on the line side of the service point, or is the service point, there would be no "ground" conductor and the three sets or 500 kcmil would be permitted as long as the calculated load is 930 amps or less and there is more than one service OCPD.

Points well taken. I get that. I should have stated '4 wires in cable' and also deleted the Ground. I will repost a correction.

If you have a single main, you would have to have conductors that have an ampacity that is equal to or greater than the rating of the service OCPD.
Note that if you do have a 1,000 amp main in a 480Y/277 service the main will require ground fault protection per 250.95.The code would permit the use of 250 kcmil aluminum for this application. You are using a larger conductor and 250.122(B) will require an increase in size of the EGC.

I have purposely avoided having a single main to avoid the GFP and other implications plus it is what the customer has requested for other reasons.
[/QUOTE]

The 700's are fine as long as the calculated load is less than 375 amps.
I try to avoid conductors larger than 500 or 600 kcmil, so I would probably install two sets of 250 kcmil for this application.

[/QUOTE]
I am not sure if you are dividing this up correctly.