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Joined: Feb 2006
Posts: 22
Units are 1530 Sq ft.
gas furnaces
gas ranges
elect. dryers
240v 20amp Central AC
Dish washers
Garbage Disposals
Some (eight) w/ 120v 20amp whirlpool tubs
Some (seven) w/ 120v 5.6amp trash compactors

1 House panel for outside lighting and outlet power for maintenance
Load is approximately 30-50 amps not continuous.

There are two seperate 22 unit buildings. The meters are currently located outside and they will remain outside. One buildings meters will be relocated to a new location on the other end of the building. The other buildings meter location will not change unless new service equipment cannot meet clearances. The space is 47 inches deep with a window above at approximately 8 feet.

1) Just checking my math.
What is the demand for each unit?
What is the service size?

2) From the service equipment there are long runs to each panel location.
Can I put multiple feeders in one pipe. Do I have to derate or does
the standard wire size for services allow me to maintain that size wire
not needing to account for derating.
Am I correct in thinking that emt will surfice for a ground eliminating
the need for this wire.

3) The owners would like to keep their existing panels as most of them
are rated 125amps. Those that are not will be changed (apprx.6).
They are existing equipment so would this pass code requirements
despite the neutrals and grounds being mixed together and the age
of the equipment (20-30yrs).

4) Where would you price out the meter bank (national/local supply
My two local supply houses don't have a lot of experience with this
size project. Should I ask for "In House Sales", "Outside"?
Any recommendations for best service equipment to use.

Thanks in advance.

Joined: Feb 2005
Posts: 219
From the questions you are asking, I would question if this is a project you can handle.

It is also alot to ask from someone who has no vested intrest in this project.

Joined: Feb 2002
Posts: 182
Bob Offline
Why don't you put you caculations in the post and let someone check it out. Just follow Art 220. Its all in there.

Joined: Feb 2006
Posts: 22
I'll post the calculations I came up with tomorrow in hopes that someone would be able to give me some valuable reply. Sierra is correct in thinking I don't have any experience with a project this size however I have only been self employeed for a year and would appreciate any help from those willing.

Anyone able to give me their perspective on the other questions with code or experience insight I would be appreciative of their response.

Joined: Feb 2006
Posts: 22

19 units x 1532 sq.ft. x 3va = 87,324va

4 units x 762 sq.ft. x 3va = 9,144va

1 house panel outside lites= 7,200va

s.a. 1500va x 2 x 23 = 69,000va

Laundry 1500va x 23 = 34,500va

Demand Factor

First 3000va x 100% = 3000va

Next 117,000va x 35% = 40,950va

Next 79,968va x 25% = 19,992va

Subtotal = 63,942va

Fixed Appliances
Dishwasher 1,920va
Disposer 1,587va
Compactor 960va
Microwave 1,100va
Fridge 1,440va
Subtotal 7,007va
7,007 x 23 units x 75% =120,871va


5000VA x 23 x 35% = 40,250va


1920va x 100% x 19 = 36,480va


1920va x 25% = 480va


I = 221,773va/240v= 924amps
Four 4/0's for each phase
six 2/0's for each phase


I = 185,293va/240v = 772amps
First 200amps x 100% = 200amps
Remaining 572x 70% = 400amps
Subtotal = 600amps
Four 4/0's
six 2/0's

Install in 1 four inch pipe.
Rigid metallic or PVC yes/no?

Joined: May 2003
Posts: 2,876
e57 Offline
I did not check all the math, but it appears Ok....

Now for the challenge of building it. And, how to keep everyone happy while changing it over.

You'll need to coordinate that well ahead of time, and would advise both services be built in new locations (Preferably closer to the existing as possible), inspected, and ready for change over. Make a good friend in your POCO reps, and let them know what you're doing and plan it out well with them. So you can make sure all of thier requirements are met.

Most of the services that I have done in this type of size were new in empty buildings. Only one was an up-grade of an existing. And the POCO was nice enough to leave both energized for change over.

Either way most of your time on this will be hand shaking and site meetings that you will need to pay yourself for.

And before you even shop for gear, it would be wise to get an EE to spec your feeders and AIC ratings. So you can double and triple check to see if what your ordering will be sufficient.

Put some beefy allowances in contract for those... Sounds like fun?

Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Jan 2003
Posts: 1,429
LK Offline
"And before you even shop for gear, it would be wise to get an EE to spec your feeders and AIC ratings. So you can double and triple check to see if what your ordering will be sufficient."

We get an EE that has a track record, with this type of job, to work with us, and it makes life a lot easer, the cost is well worth it.

Joined: Jun 2005
Posts: 91
Hey fellas, check my math ? [Linked Image]

[This message has been edited by Just George (edited 03-05-2006).]

Joined: Feb 2006
Posts: 22
Thank you all for the info. George I further cleaned up a couple of errors that you pointed out and had a couple more questions on the type of wire and derating on the "linked" site.
Any suggestions on where to find an electrical engineer. The Yellow pages, supply house word of mouth?

One of the buildings is located in such a way that I think I can only replace at the existing location but I check yet again. I was starting to wonder how I was going to keep power on in that building.

Thank you all for your comments.

Joined: May 2003
Posts: 2,876
e57 Offline
Take a picture of the old one.... What's wrong with it by the way? [Linked Image]

Mark Heller
"Well - I oughta....." -Jackie Gleason
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