120V Feeder to the Dwelling

[Kandela1992]

Hello,

I am an master electrician in NYC.
I have an potential job but conditions of it are concerning me.
So, client is combining 3 apartments on the top, 17th floor of the multifamily residential building.
Each apartment is fed by 120V 60A 2 wire feeder with 3 AWG conductors in steel conduit.
Building is old and they have installed 3 phase 4 wire feeders for 3 apartment on top of each other. Sharing the grounded conductor between those three apartments.
Distance from overcurrent protection to apartment panels is 250’ and as per my calculations voltage drop is exceeding allowable 4% drop as per 2011 NYC code.
Load calculations as per engineer is 60A on each feeder.
I just wanted your opinion if these installation, loading #3 wire on 250’ 3 phase system with 60A is allowed. Does it pose any overload or overheating of conductors?
Thank you very much!

 

[retirede]

I am very suspicious of the fact that the load calculation came out exactly the same as the current feeder rating.

 

[infinity]

So, client is combining 3 apartments on the top, 17th floor of the multifamily residential building.
Each apartment is fed by 120V 60A 2 wire feeder with 3 AWG conductors in steel conduit.
Building is old and they have installed 3 phase 4 wire feeders for 3 apartment on top of each other. Sharing the grounded conductor between those three apartments.

So you have (3)-1Ø, 120 volt panels for what will become one large apartment? Are they to remain as is or will you be converting those three panels into a single 3Ø, 208Y/120 volt panel?

 

[Kandela1992]

I am very suspicious of the fact that the load calculation came out exactly the same as the current feeder rating.

Yes, It is. but thats how an engineer calculated it.

 

[Kandela1992]

So you have (3)-1Ø, 120 volt panels for what will become one large apartment? Are they to remain as is or will you be converting those three panels into a single 3Ø, 208Y/120 volt panel?

No, as of now there is #3 AWG hot leg and 1 #3 AWG neutral. Neutral wire is shared between 3 apartments. 15th floor gets A phase, 16th floor B phase and 17th floor C phase. Building does not allow to upgrade a power to apartments.
Since distance of the wire is 250', we have a big voltage drop and I do not think conductors can be loaded with 60A.

 

[infinity]

No, as of now there is #3 AWG hot leg and 1 #3 AWG neutral. Neutral wire is shared between 3 apartments. 15th floor gets A phase, 16th floor B phase and 17th floor C phase. Building does not allow to upgrade a power to apartments.
Since distance of the wire is 250', we have a big voltage drop and I do not think conductors can be loaded with 60A.

So the new triplex apartment won't have any 208 volt loads all only 120 volts?

 

[kwired]

No, as of now there is #3 AWG hot leg and 1 #3 AWG neutral. Neutral wire is shared between 3 apartments. 15th floor gets A phase, 16th floor B phase and 17th floor C phase. Building does not allow to upgrade a power to apartments.
Since distance of the wire is 250', we have a big voltage drop and I do not think conductors can be loaded with 60A.

So is this essentially a three phase 4 wire feeder but with a single phase two wire tap off that to supply each floor?

Voltage drop may not be as bad as you thought if it is essentially a multiwire circuit, depending on how severely unbalanced it possibly can be, though still would likely been even better to have all three phases supplying each floor.

 

[infinity]

So is this essentially a three phase 4 wire feeder but with a single phase two wire tap off that to supply each floor?

Voltage drop may not be as bad as you thought if it is essentially a multiwire circuit, depending on how severely unbalanced it possibly can be, though still would likely been even better to have all three phases supplying each floor.

This is the very old school way with using a phase per apartment and 120 volt feeder. Modern apartments use the same 3Ø phase riser set up but with a 1Ø, 120/208 feeder to each apartment. Three apartment panels will share a single neutral. Since there is already a 3Ø riser to the first apartment it's pretty silly to leave three-120 volt panels when you could just use the riser for a new 3Ø panel and feed all three floors of the new single apartment.

 

[kwired]

This is the very old school way with using a phase per apartment and 120 volt feeder. Modern apartments use the same 3Ø phase riser set up but with a 1Ø, 120/208 feeder to each apartment. Three apartment panels will share a single neutral. Since there is already a 3Ø riser to the first apartment it's pretty silly to leave three-120 volt panels when you could just use the riser for a new 3Ø panel and feed all three floors of the new single apartment.

Maybe I misunderstood OP but I thought he was combining three existing apartments on just one floor, and all three of them currently are on one phase with each of the two floors below each being on one other phase of the same feeder, if more work were being done then it would make sense to better balance things but sounds like they don't want to touch the others not involved with remodeling.

 

[infinity]

Maybe I misunderstood OP but I thought he was combining three existing apartments on just one floor, and all three of them currently are on one phase with each of the two floors below each being on one other phase of the same feeder, if more work were being done then it would make sense to better balance things but sounds like they don't want to touch the others not involved with remodeling.

I think that you're correct. All three existing panels are on the same phase of the 3Ø riser. Having said that we can ignore my initial suggestions.

 

[Kandela1992]

So the new triplex apartment won't have any 208 volt loads all only 120 volts?

Yea, that is correct. They found 120V heat pump Air Conditioning units. All loads 120V

 

[MyCleveland]

This is the very old school way with using a phase per apartment and 120 volt feeder. Modern apartments use the same 3Ø phase riser set up but with a 1Ø, 120/208 feeder to each apartment. Three apartment panels will share a single neutral. Since there is already a 3Ø riser to the first apartment it's pretty silly to leave three-120 volt panels when you could just use the riser for a new 3Ø panel and feed all three floors of the new single apartment.

Not disagreeing with anything said....just clarifying it is being done with any quantity from 3-9 apartments sharing the same neutral of the 3P feeder where the OCPD is anything between 100A - 200A.

Curious here if the cooking is just a microwave and the HVAC is on the house service?
If just lights and plugs and the two kitchen SABC's....you can come up with a fairly large sq ft apartment.

 

[Kandela1992]

This is the very old school way with using a phase per apartment and 120 volt feeder. Modern apartments use the same 3Ø phase riser set up but with a 1Ø, 120/208 feeder to each apartment. Three apartment panels will share a single neutral. Since there is already a 3Ø riser to the first apartment it's pretty silly to leave three-120 volt panels when you could just use the riser for a new 3Ø panel and feed all three floors of the new single apartment.

There is no 3/Ø wires. From the cellar we have #3 AWG to all three apartments

 

[mikeames]

Just curious how they heat water or cook? Is it gas? Sounds like a pricey place not to have a double oven.

Is this the situation

 

[Kandela1992]

Just curious how they heat water or cook? Is it gas? Sounds like a pricey place not to have a double oven.

Is this the situation
View attachment 2573861

This is exactly how it is.
Hot water is from the building.
No electric ovens. Gas range.
But they want washing machine, 120V heat pump (not gas) dryer, radiant floor heating, 2 dish washers, 2 het pump condenses units with air handlers, 2 in wall AC units and other small appliances.
Total square footage of the unit will be 3,000 sq foot.

 

[mikeames]

If that's the case then what Infinity said in post 8 makes sense. Should be enough power there total but, how its distributed among the three is the critical detail. How will the loads be distributed? Kind of constrained where things have to go, No? The 250 foot distance is not a problem depending on how its distributed. Unbalanced and abused and it could be.

 

[Kandela1992]

If that's the case then what Infinity said in post 8 makes sense. Should be enough power there total but, how its distributed among the three is the critical detail. How will the loads be distributed? Kind of constrained where things have to go, No? The 250 foot distance is not a problem depending on how its distributed. Unbalanced and abused and it could be.

 

[Kandela1992]

I did a voltage drop calculation and this is what I came up with.
I just want to know if I am doing it correctly.