Single vs. Separate Electrical Service Entrance

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jganser

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I'm working on a new elementary and middle school project where both schools will be located on the same site. We are in the very beginning of design and the owner has expressed interest in providing the site with a single point of service (electrical, sewer, gas, water, etc) rather than providing each building with its own services.

I'm wanting to put together a list of pros and cons pertaining to the idea of a single larger electrical service to be located at one of the schools and then sub-feeding the second school. They are currently planning on simultaneous construction of both schools so this should be feasible.

Any suggestions from those of you that have first hand experience on a project like this? As on owner, contractor, tax payer, or guy down the street, what are the benefits and disadvantage of a single service to the site and the same for two completely separate services?

Thanks in advance for your input and expertise everyone.
 
One of the Pro's to a combined service is that the school will likely have a lower electric bill. You would have to confirm this with the utility.
 
bob said:
One of the Pro's to a combined service is that the school will likely have a lower electric bill. You would have to confirm this with the utility.
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No doubt. Also lower install cost due to the fact that you can get POCO to CT at the pad mount. No PITA CT cans and meters on both buildings.
 
lets see a negative point..one point of service will require an investment in more expensive gear and a separate location from both facilities..plus an investment in a more qualified person to maintain the gear..this is project is going to be on an already tight budget..then you must consider the ascetics of the whole installation and the security required to be around children..as you can tell My first impression was not for a single point of service..schools are non-profit and get special rates from poco anyway..
 
As far a service sizes, we are looking at about 1450kVA for the middle school and about 1150kVA for the elementary school, both at 480V. My main concern right now is that if we combine the two services into one, we will be required to run everything, including the sub-feed, in a concrete encased trench duct which will drive cost way up. Also concerned with code issues related to disconnecting means and grounding systems. I?m starting to leaning toward separate systems?any thoughts?
 
Is this a contract job or a bid proposal design..Is your function to design the project for the bid proposal for the school district to present to the public..I am curious as to the design function purposes here...

I would lean toward the dual installation as the equipment will be more redundant and the materials used can be more common run materials which will in return cause the maintenance costs to be lower..so you can incorporate both aspects into the design..which will increase the ease of the sale of the project..
 
I would think if the buildings are connected you would use a single service, if there are separated I would use two services if allowed. How would you determine which service would supply the common areas?
 
chris kennedy said:
No doubt. Also lower install cost due to the fact that you can get POCO to CT at the pad mount. No PITA CT cans and meters on both buildings.
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I would call that a maybe.

Most of the local utilities in my area will no longer put CTs or meters at pad mounts. Slows them down to much during a transformer replacement .... they would have to send a meter crew out.
 
jmo, but unless the buildings are physically connected and shared an electric room I don't see what you would gain by having one service (in the absence of extraneous parameters which have gone unstated ?)
 
jganser,

After thinking it over, I can't think of one good reason to have just one service for both buildings.

One service for each building makes more sense for many good reasons. imo
 
iwire said:
I would call that a maybe.

Most of the local utilities in my area will no longer put CTs or meters at pad mounts. Slows them down to much during a transformer replacement .... they would have to send a meter crew out.
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Interesting, FPL doesn't seem to have a problem with it.
 
jganser said:
My main concern right now is that if we combine the two services into one, we will be required to run everything, including the sub-feed, in a concrete encased trench duct which will drive cost way up. Also concerned with code issues related to disconnecting means and grounding systems. I?m starting to leaning toward separate systems?any thoughts?
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Why would you have to install the duct in concrete? The electric cost savings
may be large enough to off set the extra expense. I think that question should be run by the customer.
 
Answers to some questions:

We are contracted by the school district to complete full bid docs to present to the public for bid. We have not yet reached schematic design at this point and the only reason we are entertaining the idea of a single feed to because the owner has suggested it. Also, the mechanical contractor is throwing around the idea of utilizing a central plant (separate from both buildings) for all mechanical equipment at which point we would provide the single point of service and sub-feed to the two buildings.

The two schools will not be physically connected. The only common space will be a bus drop off area set between the two schools, but all site lighting will be fed from the closes building, i.e. parking for elementary school will be fed from an electrical room at the building and vise versa.

We don't want to get into any medium voltage (4160V) work as that will drive up the costs and limit construction to certified medium voltage contractors.

Local AHJ requires any feed over 2000A to be installed in a concrete encases trench duct.

Ultimately, we as the electrical engineers will make this decision, but we want to be able to present a list of pros and cons to the entire design team and the owner.

Thanks for you help everyone!
 
that is what I thought you were doing..so do you want to stay 480 three phase all the way..have you thought of 480 to a transformer inside each building that drops it to 120/208 inside of each building..because if the mechanical is in separate mechanical room all your loads in the buildings are going to be small just lots of circuits..so you can keep the 480 in the mechanical rooms..that would limit the amount of conductors to each location..just a thought..
 
Can two _separate_ services (using the NEC definition of a service) be supplied using a _single_ meter and billed as a _single_ service (from the POCO perspective)?

-Jon
 
winnie said:
Can two _separate_ services (using the NEC definition of a service) be supplied using a _single_ meter and billed as a _single_ service (from the POCO perspective)?

-Jon
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If the entire site (with both buildings on it) is to receive a single service and single meter, there would be only one service as defined by the NEC. At that point, power would be distributed to the rest of the buildings on site by means of a feeder (as defined by the NEC).
 
jganser said:
If the entire site (with both buildings on it) is to receive a single service and single meter, there would be only one service as defined by the NEC.
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I guess that this is the issue that I'm trying to 'think outside the box' on. Where is _metering_ mentioned in the NEC definition of a service? If the power company wants to give away power, is a meter required?

As I understand it, everything 'upstream' of the service point is the domain of the power company, and governed by a different set of codes.

I guess my question really should have been phrased 'Can the power company supply _two_ services, but with a single point of metering that totals the power delivered to these two services?'

-Jon
 
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