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Service Upgrade for a 2-unit? #43677 10/20/04 12:56 PM
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
OK, here's the question...

I've done several panel upgrades / service upgrades, but they've all been single family homes up until now.

I've been asked by a friend of the family to upgrade the service and panels on his 2-apartment building (side-by-side units) to 200A.

Currently they have a single drop going to a 2 meter box, where it splits and runs to separate 100A panels in the basement of each unit(6 space Pushmatics... oh boy!).

He's got 1 1/2" RMC/IMC in place from the meters to the panels. I haven't pulled the meter covers or gone up to see what size the current drop is.

I know that per 310-15 I can run 2/0 cu from the meters to the new panels in each unit through the existing conduit. (He's happy 'cause he doesn't have to pay me to rip out his old pipe and install new. I'm happy 'cause I can get this job done faster... I'm doing this more as a favor to a friend than a money maker)

Do I need to run 400 kcmil (400A) as the new drop to the two meters, or it there a reduced conductor sizing FPN that I'm missing in reviewing the Code?

Thanks in advance,


Work Gear for Electricians and the Trades
Re: Service Upgrade for a 2-unit? #43678 10/20/04 10:18 PM
Joined: May 2003
Posts: 2,876
e57 Offline
Do they nessisarilly need to be 200A each? With load diversity and other factors of service calculation they may not need that much. (Unless AC units are involved.) I bring this up as a 2 meter base with 200A mains each will cost you plenty.

Each unit is calculated for service/feeder size individualy. The service itself, and the service conductors are calculated collectively In a multiple unit building.

Many 2-unit buildings in SF (NO AC UNITS) I can do a 100 and/or a 125 witha 40 -60a house panel, and service conductors sized at 200 or 225A.

[This message has been edited by e57 (edited 10-21-2004).]

Mark Heller
"Well - I oughta....." -Jackie Gleason
Re: Service Upgrade for a 2-unit? #43679 10/21/04 10:12 AM
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
They're planning to get A/C installed - that's why the upgrade was discussed.

I'll be running a line to a D/C Box outside for the HVAC guy to wire the compressor to.

Re: Service Upgrade for a 2-unit? #43680 10/21/04 02:06 PM
Joined: Dec 2003
Posts: 751
earlydean Offline
If you actually do the math, you may be pleasantly surprised. I have found that the service to multiple tenents is often much less than the sum of the panel mains.

Re: Service Upgrade for a 2-unit? #43681 10/21/04 10:09 PM
Joined: Apr 2001
Posts: 518
John Steinke Offline
Bear with me, I'm using the '99 code. Same info in 2002, just not sure of cite...

230-33 allows an alternate calculation. In the end, you may be able to use wire small enough to fit in that pipe. (Recently ran across the same problem).

Re: Service Upgrade for a 2-unit? #43682 10/21/04 10:37 PM
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
My table is out of the '96 - it's our AHJ adoted version...

Re: Service Upgrade for a 2-unit? #43683 10/25/04 12:46 AM
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
Update - pulled head out of rear. [Linked Image]

I was used to the (old) rule of the service having to be sized according to the sum of the main overcurrent device ratings.

Your prompting towards reviewing the Code helped me find the applicable sections (220-10 mostly). Had to take the time to so a quick service calculation (200A is real overkill for this small duplex, but an anticipated future sales point, and they were willing to pay for it)

I know I looked through there before... oops.

Thanks, guys.

[This message has been edited by DougW (edited 10-25-2004).]


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