Multifamily dwelling units supplied by more than one feeder

[aaSpencer]

Thank you for allowing me to post here.

There is an existing apartment in which, each unit don't have its own electrical meter. thus the tenants pay by the 'averaged out' usage of the entire building.
The apartment has 8 floors with 10 units on each floor (thus 80 tenants).
The contractor has started working on this, and so this is the present condition:

For each floor, there is one - 42 space 400 amp panelboard in the electrical room to feed 3 appliances individually into each unit - 1 microwave oven, 1 food disposal and 1 dishwasher. Thus the panelboard uses up 30 spaces.

They used a 'feed-through' panel from the first to 8th floor (like 8 loads in parallel if that makes sense) and the conductor size used along the feed through is 250 kcmil from first to 8th floor.

The only thing they didn't do is to connect from the first floor panel to a 250 amp breaker in the MDP located in the basement.

The question is, how do we calculate the load with this set up?

This building was built in early 70s and have been in renovation for the last 3 years. I have been searching for answer but there is no crystal clear answer i can find.

By the way, some of the existing loads like the each A/C units are also tied up this way

Thanks for all the input and I hope I was able to make it clear enough.

AA

 

[charlie b]

I fear that you do have me a bit confused. If all the loads on any given floor come from one 42-circuit panel, and if 30 of those circuits are dedicated to those three types of appliances, that leaves only one circuit for each unit to feed any lights or receptacles. Is that right? How can that possibly be enough?

I also do not understand what you are saying with regard to the A/C units. Is there another source of power, other than that one 42-circuit panel?

In order to help you calculate the load, I would need to better understand the reason you need to do that in the first place. What kinds of renovations are taking place? Are loads being added? Are new panelboards being installed?

 

[Smart $]

...
The question is, how do we calculate the load with this set up?
...

Welcome. :thumbsup:

What is the system configuration, 120/240 or 208/120?

 

[gadfly56]

I fear that you do have me a bit confused. If all the loads on any given floor come from one 42-circuit panel, and if 30 of those circuits are dedicated to those three types of appliances, that leaves only one circuit for each unit to feed any lights or receptacles. Is that right? How can that possibly be enough?

I also do not understand what you are saying with regard to the A/C units. Is there another source of power, other than that one 42-circuit panel?

In order to help you calculate the load, I would need to better understand the reason you need to do that in the first place. What kinds of renovations are taking place? Are loads being added? Are new panelboards being installed?

Isn't there also a requirement that each tenant have access to the load center that supplies their apartment?

 

[Smart $]

Isn't there also a requirement that each tenant have access to the load center that supplies their apartment?

Yes, but it's dependent on building management provisions.

There are several requirements through the Code for occupant accessibility, but 240.24(B) pretty much covers all of them.

 

[aaSpencer]

I fear that you do have me a bit confused. If all the loads on any given floor come from one 42-circuit panel, and if 30 of those circuits are dedicated to those three types of appliances, that leaves only one circuit for each unit to feed any lights or receptacles. Is that right? How can that possibly be enough?

I also do not understand what you are saying with regard to the A/C units. Is there another source of power, other than that one 42-circuit panel?

In order to help you calculate the load, I would need to better understand the reason you need to do that in the first place. What kinds of renovations are taking place? Are loads being added? Are new panelboards being installed?

Hi Chuck,

Thanks for replying and sorry for the confusion.

I think the existing condition is this, for example, On each floor, lighting for all 10 units are bundled together into 1 panel. Receptacle for all 10 units are bundled together into another panel. A/C units for all 10 units on each floor are bundled into another separate panel. And all these panel are up and running right now.

They are upgrading this apartment for high end market. So for that, they are adding 3 new items for each unit, which are dishwasher, food disposal and microwave oven.

So just like pattern above, what the contractor did, on each floor, he installed a 42 circuit panel to feed these new items. And leaves 12 spaces unused.

The contractor and owner wants this to be fed with a 250 amp breaker from the MDP.

The owner came to us to design based on their set up, but I couldn’t give a load value.

Thanks,
AA

 

[aaSpencer]

Welcome. :thumbsup:

What is the system configuration, 120/240 or 208/120?

Oh yes, I forgot to add that in, its 208/120v

 

[GoldDigger]

Isn't there also a requirement that each tenant have access to the load center that supplies their apartment?

It is true that the circuits in one unit cannot originate at a load center in another unit, but if the building is actively managed, as defined in the code, then the panels may be somewhere accessible only to management.

 

[gadfly56]

It is true that the circuits in one unit cannot originate at a load center in another unit, but if the building is actively managed, as defined in the code, then the panels may be somewhere accessible only to management.

I've never had to look closely at this issue. Is the "actively managed" part relatively recent or has it been in a while?

 

[dmxtothemax]

none of these three loads seem unusual or large and not continuese.
are there no other circuits in these units apart from these three ?
one light circuit for the whole floor ?
so if one person blows the breaker, the entire floor losses lights ???

Sound like a basket case to me !
walk away !

 

[Smart $]

H...
The contractor and owner wants this to be fed with a 250 amp breaker from the MDP.

The owner came to us to design based on their set up, but I couldn’t give a load value.

Oh yes, I forgot to add that in, its 208/120v

Let's say we put the micro's on SBAC's because that will give us the lowest calculated demand under dwelling unit general lighting demand.

1500VA/SABC × 80 units = 120,000VA
First 3,000 at 100% = 3,000VA
Next 117,000 at 35% = 40,950VA
Total = 43,950VA

Next we have DW's and GD's... lets say 1200VA and 960VA respectively... and put the demand at 75% per 220.53.

(1200VA + 960VA) × 80 units × 75% = 129,600VA

129,600VA + 43,950VA = 173,550VA
170,550VA ÷ 208V ÷ 1.732 = 482A


I do not believe 250A circuit is going to cover it. You may want to try the optional method...

 

[Smart $]

I've never had to look closely at this issue. Is the "actively managed" part relatively recent or has it been in a while?

Code doesn't use those exact words, but the concept has been there for quite some time... seemingly forever to me.

 

[Smart $]

...
1500VA/SABC × 80 units = 120,000VA
(1200VA + 960VA) × 80 units = 172,800VA

... You may want to try the optional method...

292,800VA x 23% demand ÷ 208V ÷ 1.732 = 187A

 

[Smart $]

292,800VA x 23% demand ÷ 208V ÷ 1.732 = 187A

Have to retract last post.

You can only use the optional method if dwelling units are supplied by no more than one feeder... and your units are supplied by several.

 

[aaSpencer]

Have to retract last post.

You can only use the optional method if dwelling units are supplied by no more than one feeder... and your units are supplied by several.

Hi Smart $

Sorry for not replying sooner, we are here in the east coast.

Thank you for last few posts. I did consider that 220.42, and just like the you mentioned as well, the units are supplied by more than 1 feeder so can't use that.

The calculation you did that resulted with 482 AMP is how I would have approached it, but wasn't quite sure, because it is as if I am treating the whole building like a huge single dwelling unit.

but since there is no mention ( or I might have missed it) in NEC if a dwelling is supplied by more than 1 feeder. That what's throwing me off.

 

[Smart $]

...
The calculation you did that resulted with 482 AMP is how I would have approached it, but wasn't quite sure, because it is as if I am treating the whole building like a huge single dwelling unit.

but since there is no mention ( or I might have missed it) in NEC if a dwelling is supplied by more than 1 feeder. That what's throwing me off.

Once you are "inside" a building there's hardly any rules on the number of feeders, or where they must go. Just the fact that 220.84(A)(1) states no dwelling can be supplied by more than one feeder to use the optional method is essentially a testament that a multifamily dwelling can have more than one feeder to each unit...

 

[aaSpencer]

Once you are "inside" a building there's hardly any rules on the number of feeders, or where they must go. Just the fact that 220.84(A)(1) states no dwelling can be supplied by more than one feeder to use the optional method is essentially a testament that a multifamily dwelling can have more than one feeder to each unit...

Thanks so much, this truly helps.

 

[charlie b]

I've never had to look closely at this issue. Is the "actively managed" part relatively recent or has it been in a while?

It's in the 1999 edition. That's the oldest edition that I have at my desk. The phrase in the 2014 edition is "under continuous building management supervision." 240.24(B)(2).