22 Unit Multi -Family (Condos) Service Upgrade

[BobV3CORP]

Calculation is in next message.


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
house)
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.

 

[George Stolz]

Re: 22 Unit Multi -Family (Condos) Service Upgrade

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

Why don't you post your math, and we'll check it?

2)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.

Yes, you will have to derate. That doesn't necessarily mean there will be a change in plan. We would need to know specifics on the installation.

Am I correct in thinking that emt will surfice for a ground eliminating the need for this wire.

Technically, but I would strongly advise to pull a grounding conductor with these feeders.

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).

If you're upgrading the service, some AHJ's will require you to bring the existing panels to code (as in AFCI protection for the bedrooms, etc). You really should include fixing the neutral/ground mixing in your bid, either way. Otherwise, neutral current will be flowing on the grounding conductors back to the service. This is in violation of 250.6(A).

My two local supply houses don't have a lot of experience with this size project. Should I ask for "In House Sales", "Outside"?

Surely they can locate the service equipment you need. We get our stuff from a pretty seedy joint, and they don't have a problem getting what we need.

Any recommendations for best service equipment to use.

I've used Siemens and Square D. If space is an issue, Siemens is generally smaller. But, Square D's connections between modules is easier and more secure (IMO) than Siemen's "donut".

 

[BobV3CORP]

My calculations

My calculations

STANDARD CALCULATION

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

DRYER

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

A/C

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

LARGEST MOTOR

1920va x 25% = 480va

LOAD

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

NUETRAL

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?

 

[George Stolz]

Re: My calculations

Re: My calculations

I thought these were 22-plexes, not 23-plexes?

Also, aren't we dealing with two services per building? You should calculate the load for each seperately, IMO.

STANDARD CALCULATION
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
=207,168 va
Demand Factor
=207,168 va
First 3000va x 100% = 3000va
=3,000 va (204,168 remaining)
Next 117,000va x 35% = 40,950va
=43,950 va (87,168 remaining)
Next 79,968va x 25% = 19,992va Where'd the house panel go?
Next 87,168va x 25% = 21,792va
Subtotal = 63,942va 65,742 va

Fixed Appliances
Dishwasher 1,920va Double-check this: 16 amps?
Disposer 1,587va
Compactor 960va
Microwave 1,100va
Fridge 1,440va
Subtotal 7,007va
7,007 x 23 units x 75% =120,871va

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

A/C: 1920va x 100% x 19 = 36,480va Four units don't have A/C?
LARGEST MOTOR: 1920va x 25% = 480va

LOAD
65,742 + 120,871 + 40,250 + 36,480 + 480 = 263,823 va
I = 221,773va/240v= 924amps
I = 263,823 / 240 = 1099 amps
Four 4/0's for each phase
or
six 2/0's for each phase

Try four 300 MCM CU sets, or six 4/0 CU sets

Install in 1 four inch pipe.
In that case, make that four sets 600 MCM CU in a 6" RNC, or six sets of 300 MCM CU in a 6" RNC! :shock:

I'd definutely put your service conductors in seperate conduits.

 

[BobV3CORP]

STANDARD CALCULATION

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 OOps.
s.a. 1500va x 2 x 23 = 69,000va
Laundry 1500va x 23 = 34,500va
=207,168 va
Demand Factor
=207,168 va
First 3000va x 100% = 3000va
=3,000 va (204,168 remaining)
Next 117,000va x 35% = 40,950va
=43,950 va (87,168 remaining)
Next 79,968va x 25% = 19,992va Where'd the house panel go? :idea:
Next 87,168va x 25% = 21,792va
Subtotal = 63,942va 65,742 va

Fixed Appliances
Dishwasher 1,920va Double-check this: 16 amps? Actual is 8.6a or 1,032va
Disposer 1,587va Actual is 6.7a x 115v = 771va
Compactor 960va
Microwave 1,100va
Fridge 1,440va
Subtotal 7,007va 5,303va corrected
7,007 x 23 units x 75% =120,871va 91,477corrected

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

A/C: 1920va x 100% x 19 = 36,480va Four units don't have A/C?
LARGEST MOTOR: 1920va x 25% = 480va Four units are legal accessory units with their own electrical panels and meters. They don't have A/C.

LOAD
65,742 + 91,477 + 40,250 + 36,480 + 480 = 234,429va corrected
65,742 + 120,871 + 40,250 + 36,480 + 480 = 263,823 va
I = 221,773va/240v= 924amps I = 234,429/240 = 977amps corrected
I = 263,823 / 240 = 1099 amps
Four 4/0's for each phase I assumed 75 deg.THWN cu what are you using? 977/4=244amps each or 4# - 250mcm corrected
or
six 2/0's for each phase Using 75 deg.THWN cu 977/6=163amps each or 6# - 2/0's corrected

Try four 300 MCM CU sets, or six 4/0 CU sets
In your example(before I cleaned up my corrections) Would you have
put these sets all in seperate pipe. Otherwise would you have had to derate for more than 3 current carrying or do they only count as three since they're parrallel? I will not meet clearance to the side of the window with 4 seperate pipe runs.

Install in 1 four inch pipe.
In that case, make that four sets 600 MCM CU in a 6" RNC, or six sets of 300 MCM CU in a 6" RNC! Corrected it is four sets 500 or six sets 250 mcm cu right?
I imagine that this must answer my question on derating......would this 6" rigid pvc be heavy with this much copper in it if the pipe were 20' long and the wires extended out 4' on one end and 6' on the other? It sure sounds heavy even with my reduced calc of 977amps.

Very much obliged George.[/list]

 

[BobV3CORP]

George apologies for the vagary. I didn't anticipate I would get such in depth assistance. It is a pleasant surprise. I thought I would just get an example across and see if I was accurate with it and then apply it to the real quote. I have been doing small residential work and minor equipment installations in light commercial buildings for the past 12 years mostly 1-3 families and condo's and am now moving forward with bigger and better things. This project will kick off in September so I plan on being well prepared before then so as to perform at a high level.

 

[George Stolz]

I assumed 75 deg.THWN cu what are you using?

Same thing. Your original wire sizes were too small by 4 amps a conductor, by your original post, unless I was cross-eyed at the time, which happens.

(four 250mcm's) or (six 2/0's for each phase)

Yes, before derating.

In your example(before I cleaned up my corrections) Would you have put these sets all in seperate pipe. Otherwise would you have had to derate for more than 3 current carrying or do they only count as three since they're parrallel?

By 310.15(B)(2)(a), you have to derate parallel conductors.

... Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

I will not meet clearance to the side of the window with 4 seperate pipe runs.

Are these overheads, or underground? Why not upgrade, go underground, if possible?

Corrected it is four sets 500 ... (Yes)
...or six sets 250 mcm cu right?
No. Six sets of conductors is 12 current carrying conductors - they're derated at 50%. I made that goof in my last post, I had them both at 70%. Six sets would have to be CU 400's.

I'd say yeah, it sounds heavy. Hope you have help, whether you can go underground or not!

• So, are these services going to be separate?
• How many units, for sure?
• Why do 4 units have their own meters? They're not getting included in the calc, you've already figured out whatever's happening there?

Glad to be some help. 8)

 

[BobV3CORP]

Thanks again George
.
You asked how many units, for sure?
Why do 4 units have their own meters? They're not getting included in the calc, you've already figured out whatever's happening there?

The building that we have calculated has 19 1532 sq.ft.units and 4 units that are 762 sq.ft. as indicated in the beginning of the calculations from my last post. Total there are 23. I'm not sure what you are saying about my not calculation four units. Am I missing something here?
So the service for all 23 of these units will be at one location with a single disconnect to comply with code unless I find equipment that makes for better application.

I do have three other electricians to work with me on this but wont I need some sort of small crane to lift a single pipe into place if we go that root. I will be meeting with the supply houses later this week or next to discuss the meter equipment and I assumed I would find I would need a crane to lift that into place as well.

Thanks again for the advice. Once things have settled down here over the next couple years I'll have to compile a list of "Georges" to thank as I am amazed about how helpful this site is. Any idea if there are other professions such as General Contractors and Realtors who have similar support/discussion sites?



You replied

... Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

Thanks for directing me to this

 

[George Stolz]

Thanks again George

No sweat.

I'm not sure what you are saying about my not calculation four units. Am I missing something here?

The A/C's. So 4 units have two meters? That's what I'm not seeing.

I do have three other electricians to work with me on this but wont I need some sort of small crane to lift a single pipe into place if we go that root.

I don't go overhead often, but wouldn't it be easier to get the pipe up, and then install the conductors?

I have no idea about the other trade's sites.

 

[BobV3CORP]

George if you are referring to the original 22 unit statement it was an error. There are 19 1352 sq.ft. units, 4 762 sq.ft. units and a house panel.
So a total of 24 meters on this building. The small units are garden level units and have no A/C. Does this clear up the confusion?


Thanks again for the help.

 

[George Stolz]

It sure does. Good luck in your project.