4 meter banks, 1 Service Rated ATS

[Dylankjsutice]

I am working on a project where the customer wants to add generator backup power to an existing building that currently has 31 apartments. Additionally, they are planning an expansion that will include 10 more apartments. The existing 31 apartments are fed from two separate meter banks. Meter Bank 1 has 15 meters, while Meter Bank 2 has 16 meters, and both are equipped with a 1200A main breaker.

The new addition will have two more meter banks (referred to as Meter Banks 3 and 4), each with 5 meters. Based on load calculations, each of these new meter banks will require a main breaker rated at 400A.

The utility company, however, will not allow an ATS (Automatic Transfer Switch) to be installed between their transformer and the four meter banks. Instead, they will be installing a single meter to serve all 41 apartments.

The challenge I am facing is determining how to connect all four meter banks to a single service-rated ATS. The primary issue is that the ATS manufacturer does not recommend using the eight conductors per phase needed to feed all four meter banks due to "space" limitations inside the ATS enclosure.

I considered the option of tapping the conductors for the existing and new meter banks, but this is not possible since tap conductors are not allowed for overcurrent devices rated 800A or less. Below is a breakdown of the feeds I have identified for this setup.

Primary Line Side:
Utility to ATS – (4) Parallel Sets – (2) 500 MCM AL (1) 350 MCM AL N (1) 250 MCM G

Secondary Line Side:
Gen to ATS – (4) Parallel Sets - (2) 250 MCM AL (1) 3/0 N, (1) 3/0 G

Load Side:
From ATS to Meter Bank 1 - (2) Parallel Sets – (2) 250 MCM AL (1) 3/0 N, (1) #1 AL G
From ATS to Meter Bank 2 - (2) Parallel Sets – (2) 250 MCM AL (1) 3/0 N, (1) #1 AL G
From ATS to Meter Bank 3 - (2) Parallel Sets – (2) 500 MCM AL, (1) 250 MCM AL N, (1) 2/0 G
From ATS to Meter Bank 4 - (2) Parallel Sets – (2) 500 MCM AL, (1) 250 MCM AL N, (1) 2/0 G

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Line Side: (4) 500 MCM AL – *Per Leg

Load Side: (4) 250 MCM AL, (4) 500 MCM AL – *Per Leg

Neutral will have: (4) 350 MCM AL, (9) 250 MCM AL, (8) 3/0 AL, (4) 2/0, (4) #1 (includes bonded grounds)
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[electrofelon]

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I considered the option of tapping the conductors for the existing and new meter banks, but this is not possible since tap conductors are not allowed for overcurrent devices rated 800A or less.-----------------------------------

Where are you getting this from?

 

[Dylankjsutice]

NEC code section 240.21 (B) says... "Section 240.4 (B) shall not be permitted for tap conductors"

240.4 (B) Overcurrent Devices Rated 800 Amperes or Less

 

[jaggedben]

NEC code section 240.21 (B) says... "Section 240.4 (B) shall not be permitted for tap conductors"

240.4 (B) Overcurrent Devices Rated 800 Amperes or Less

That just means that you cannot use the 'next size up rule' in that section when sizing an OCPD at the end of a tap. It does not mean you can't have tap conductors under 800A.

 

[electrofelon]

Looking over this again, a couple things are not clear. Where is the service disconnect(s)? IS there a breaker in the ATS? If so what size? Also Take a look at 240.21(B)(1)(1) or 240.21(B)(2)(2) regarding the two existing banks with the 1200A breaker. Regarding the specific issue of making all the taps, you may want to consider a bussed gutter.