Upgrading Existing Electrical Service

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amzngsurf

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Here's the situation:

An existing apartment building is fed as follows

Main service is fed from a pole mounted 120/240V 50KVA utility transformer single-phase
The service is tapped by two 400A disconnects each feeding a meter bank consisting of 19 meters - each one rated for

120/240V single phase

Part of the basement is being renvoated for 8 new apartments. The demand for which need to be calculated per NEC.

The new service can't be sized with the existing demand becasue you can't get the demand for residential meters so we have

to size the existing per NEC.

The total demand calcualted per NEC is too large for a sinle-phase service so we have to size the service for 120/208V

3-phase and back feed the 400A disconnects for 120/208V single-phase...which should not be a big deal.

We are going to call for a new 800A tap box with a new meter bank consisting of 8 meters and for the existing 400A feeders

to be extended and connected into the new tap (located within 25ft of the existing disconnects).

We looked into bringing in a serperate service but adding a fire wall was an issue.

I was just wondering - with the information given above - what others on here have done or would do for this type of

situation...looking forward to your replies.
 
You said you can't get the demand for a residential meter? why? I would start at the poco to get the history for at least 12 months for connected load if you do not want to do the calcs.
 
For commercial projects we always ask for 12 months of bills. However residential bills do not show the demand on them and the utility company, for some reason, are not allowed to give out that information. The only thing we could do was to calculate the total dwelling load of 46 units (38 existing - 8 new) and size the service that-a-way.

It's hard to explain to an owner when he's only renovating for an additional 8 apartments with no washers, dryers or dishwahers that the service needs to be upgraded so much but we need to follow the NEC. And we all know the units will not draw nearly that high a load.
 
Is it possible to apply second service for the additional 8 appartment? Explain your situation to Poco. I think NEC allows second service. If you change the existing 120/240v service to 120/208 service as mentioned in you post, some appliance rated 240V only may not be able to work properly. You have to check with existing tenants before you make the change.
 
Yes...the 208V is one issue we spoke about. We also spoke about the second service and they would allow it with the addition of a fire wall. The architect did not want to add a fire wall so we were stuck with this option. Fun isn't it?!?!?!
 
Look at 230.2(c)(2) for the exception. You can have more than one service for a building (with out firewall) if:
"the load requirements of a single-phase installation are greater than the serving agency normally supplies through one service."

Just make sure you provide identification per 230.2(E).

Who is "they would allow it"? The NEC allows for it, and it could be argued with the AHJ.
 
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How about renting a data logging meter and using 220.87 (1) exception 1? Would take a month, but may save a lot of headaches.
 
"they" would be the utility company. We proposed the additional service first however they wouldn't provide it without a firewall separating the two services. We thought labeling the services per NEC would be acceptable...guess not. The utility company goes by 'you want power, you do as we say'.

Hooking up a data meter is a good idea but the summer months usually draw a larger demand.
 
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