400 Amp Service

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kriverswaters

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I am planning on installing a 400A 120\240V single phase service to a four-plex apartment complex. The four pack meter base will have four 100A breakers to feed each apartment. Acording to my code book and calculations, the service feeder can be in a 3" metal rigid conduit with 2ea. 600MCM copper cables for the ungrounded conductors and a 500MCM for the grounded (neutral)conductor. Each indivdual apartment can be installed with #2 copper for the ungrounded conductors and a #3 for the grounded (neutral)conductor. According to NEC Table 250.66, the grounding cable to the electrode for this service should be a 1/0 copper conductor and each apartment 100A panel should be fed with a #6 copper wire. Am I correct in what I have described?
 
Re: 400 Amp Service

I think you can get by with a #8 EGC to each unit. But the rest looks good to me. That statement, of course, I must qualify by stating that I have not seen your calculations.
 
Re: 400 Amp Service

"Thank You" Charlie B! I'm kind of new to this code forum, but I really like to get feedback from fellow electricians to make sure I am on the right path. There always seems like there is so much room for error when laying out a project like this. Thanks again!
 
Re: 400 Amp Service

We have "the grounding cable"
and
"#8 EGC"
They are not the same thing.
If the 8 is a GEC then it has to be protected from damage and its just more practical to use a 6.
 
Re: 400 Amp Service

You might want to take advantage of Exception 3 of 230.90(A)

230.90(A)Exception No. 3: Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.
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What is the total calculated load?
 
Re: 400 Amp Service

Originally posted by kriverswaters: According to NEC Table 250.66, the grounding cable to the electrode for this service should be a 1/0 copper conductor and each apartment 100A panel should be fed with a #6 copper wire.
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Originally posted by tom baker: We have "the grounding cable" and "#8 EGC." They are not the same thing.
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Tom: I knew his use of terms was not precise. I interpreted his first ?grounding cable? to mean ?Grounding Electrode Conductor,? and his second ?should be fed with a #6? to mean ?Equipment Grounding Conductor.? I picked the #8 off of Table 250.122. I would not have known about a #6 being a more practical choice.
 
Re: 400 Amp Service

You guys now have me confused. I agree, I did use the wrong term when I wrote "grounding cable". I should have know better. The 1/0 I am planning on using is for the "Grounding Electrode Conductor" for the service(400A, fed with 600 MCM). This is according to Table 250.66. Each 100A apartment panel, (4ea.), will have a #8 "equipment grounding conductor" that will be installed in a schedule 40 pvc conduit between the meter pack and the distribution panel. This according to Table 250.122. It will be protected from damage, so I am confused by Mr. Baker's statement that it is more practical to use a #6?
My total calculated load for all four apartments was 44,170VA divided by 240V =185A.(+125%)=231A.
That is why I am installing a 400A service.
 
Re: 400 Amp Service

Originally posted by kriverswaters:
My total calculated load for all four apartments was 44,170VA divided by 240V =185A.(+125%)=231A.
That is why I am installing a 400A service.
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I know this was not the original question but if the connected load is 231 amps you could use 250 kcmil CU in place of the 600s for the service conductors you would be only 1 amp over using 4/0 CU.

I assume this meter bank does not have a 400 amp main, just the four 100 amp breakers?

I do not usually do service calcs maybe some one else can jump in but I do not think you need to add 125% to the 185 amp total, aren't the continuous loads already added into the individual units?

[ October 13, 2004, 08:55 PM: Message edited by: iwire ]
 
Re: 400 Amp Service

They currently have a gas heater that feeds all four apartments. The exisitng service is a 200A service. They want to install some electric heaters in each apartment in the near future. I am just planning ahead by going with the 600 MCM feeder. I agree, with the exisitng loads, I could get by with 250 KCMIL CU. I always try to plan ahead for future loads. There is no main disconnect for the 400A four unit meter pack, just the four 100A distribution breakers. I really appreciate your input.
 
Re: 400 Amp Service

I do not usually do service calcs maybe some one else can jump in but I do not think you need to add 125% to the 185 amp total, aren't the continuous loads already added into the individual units?
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That's right. Continuous loads are handled in the load calculations in Article 220.
 
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