Conductor transition to lower Voltage Drop

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stuartdmc

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Newport Beach, Irvine, CA
I have a 680 multi family apartment project that has 50 unit apt. approx 600ft. away from their meters, each unit has there own 125-amp load center. We are using 750 MC cables to feed the units to adjust the VD% to less then 5%. I want to use a transition box midway the run. I'm wanting to run from the meter/main to the transition box with EMT and 1000 kcmil, then transition to say, 250 MC cable taken it to each unit. Is this acceptable. taken the VD% workout at the end of the run?
 
We approve this a lot, where the conductors are to large to fit into the lugs, we allow them to use a transition box just outside of the panel (within 10ft) to decrease the conductor size to the size of lug, maintaining the ampacity of the OCPD.
 
Just some cheap advise, never, ever install 1000 kcmil use parallel sets of something smaller. Why are there any tap rules involved? Isn't there an OCPD at the meter for each apartment?
 
1000-kcmil was mentioned to simply covey the point I wanted to get across, I agree, no one in there right mind ever run that large of conductors without first consider parallel runs. The tap rule does however coming to play if the contractor runs MC cable the entire dentance, 750-kcmil doesn't come close in fitting in a 125 amp OCPD. but your right, parallel out of the meter main to a transition box then transition to MC then up 5 floors to each unit works for me.
 
stuartdmc said:
If I'm not mistaken, all unit panels are MLO.
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There's got to be an OCPD somewhere for each unit. Sounds like there's a meter-main involved, so there it is.

Is it like this?
(long multi 500kcmil run) -> (transition box with bus bars) -> (many smaller feeds, each shorter than 10') -> (lots of meter-mains) -> (MC or something feeders up to the individual units)
Is the long/large run service conductors or a feeder?

Where is the actual service point? Where are the meters? A drawing would really help.
 
stuartdmc said:
The tap rule does however coming to play if the contractor runs MC cable the entire dentance, 750-kcmil doesn't come close in fitting in a 125 amp OCPD. but your right, parallel out of the meter main to a transition box then transition to MC then up 5 floors to each unit works for me.
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You seem to be confusing a junction box to change wire sizes for voltage drop considerations with the tap rule that allows you to tap a larger conductor with a smaller conductor and feed a lower OCPD than the circuit you tapped allowing the new OCPD to protect the smaller conductor that was tapped to the larger conductor.

That is not your situation as I'm understanding you.

The way I'm understanding you, you have a service disconnect (at the meter main), then you leave with one size conductor into a junction box, up size the wire, go to a 2nd junction box then with smaller conductors to the 125 amp panel in the apartment. This is not using the tap rule.
 
oldsparky52 said:
You seem to be confusing a junction box to change wire sizes for voltage drop considerations with the tap rule that allows you to tap a larger conductor with a smaller conductor and feed a lower OCPD than the circuit you tapped allowing the new OCPD to protect the smaller conductor that was tapped to the larger conductor.

That is not your situation as I'm understanding you.

The way I'm understanding you, you have a service disconnect (at the meter main), then you leave with one size conductor into a junction box, up size the wire, go to a 2nd junction box then with smaller conductors to the 125 amp panel in the apartment. This is not using the tap rule.
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(y) This application has nothing to do with taps.
 
stuartdmc said:
1000-kcmil was mentioned to simply covey the point I wanted to get across, I agree, no one in there right mind ever run that large of conductors without first consider parallel runs. The tap rule does however coming to play if the contractor runs MC cable the entire dentance, 750-kcmil doesn't come close in fitting in a 125 amp OCPD. but your right, parallel out of the meter main to a transition box then transition to MC then up 5 floors to each unit works for me.
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You don't need to parallel at each end. All you need is one set of #2 CU at each end. These can connect to whatever parallel sets you have in the middle for voltage drop.
 
Our services consist of (4) 4000-amp service mains from there I feed 4 different meter rooms throughout the site each meter room houses approx 150, 100-125-amp 120/208v 1-phase meter mains, from there, we head out to the units, the furthest unit is like 600ft. we can't move the meters closer to the unit, we must beef up the wire to handle the VD. and this lies the problem How to lessen the wire sizes that affects the VD without relocating the meter mains closer to the units? beefing up the wire involves the lugs on both ends, one at the meters OCPD and two at the receiving end the unit panel. which is in this case a 200-amp panel to increase the log sizes. for all the units that require 750-kcmil MC cable, I want to show the installation of EMT from the main meter sections to a large gutter or transition box, 300 ft away(haft way) then from there run a lesser gage conductor to the unit.
 
stuartdmc said:
Our services consist of (4) 4000-amp service mains from there I feed 4 different meter rooms throughout the site each meter room houses approx 150, 100-125-amp 120/208v 1-phase meter mains, from there, we head out to the units, the furthest unit is like 600ft. we can't move the meters closer to the unit, we must beef up the wire to handle the VD. and this lies the problem How to lessen the wire sizes that affects the VD without relocating the meter mains closer to the units? beefing up the wire involves the lugs on both ends, one at the meters OCPD and two at the receiving end the unit panel. which is in this case a 200-amp panel to increase the log sizes. for all the units that require 750-kcmil MC cable, I want to show the installation of EMT from the main meter sections to a large gutter or transition box, 300 ft away(haft way) then from there run a lesser gage conductor to the unit.
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It seems to me you are making this more complicated than need be. This is a common thing to do for VD-just put a box at each each end fairly close to the panels at each end. All you need at each end is #2 CU for 125 amp and you can use 125 amp panels as you will only have #2 conductor terminating in them. Then just connect the #2's to your parallel sets for the middle section.
Why are you trying to change sizes in the middle as opposed to at each end?
 
What voltage drop are you trying to not exceed and what is the amperage you are using in your calculations?

I ask because @700', 125-amps, 208-volt, using 500 kcmil aluminum the voltage drop I see is about 2.75% .
 
oldsparky52 said:
What voltage drop are you trying to not exceed and what is the amperage you are using in your calculations?

I ask because @700', 125-amps, 208-volt, using 500 kcmil aluminum the voltage drop I see is about 2.75% .
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Using the full panel/feeder rating for the current is probably not even necessary. FYI I get 4% with your parameters. OP beware of some online calculators like the southwire one, they use 90% PF (which is very likely un-necessary as large resi loads will usually be resistive). That one gives 5% with the above parameters.
 
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