Load calculation for condo remodel

[R@rpe]

I wanted to post these questions again since I've not seen a response from Saturday's forum yet.
This condo shares a common 3/0 feeder with three other units protected by one 200 amp breaker located in a panel board below. The feeder runs through 2'' EMT into and through a 200 amp sub-panel located in each unit. The 3/0 feeder is tapped with a # 4 THHN that terminates on the main lugs of each sub-panel. We are bidding a remodel of one unit - they are adding a stackable washer dryer and two HVL's and additional lighting. The Heat and A/C are not factored in the calculation as the building has a water chilled system. Each original unit's load calc. is aprox. 52 amps (Optional calc)
and the aprox. calc for the remodel unit is 64.
Does table 220.84 apply to determine the feeder size for these units- If so the feeder would not need to be changed. What other code articles should be considered? 240.86 seems to indicate an Engineer's seal will be needed before any design can be determined but I am not sure if this applies in this situation. Also, the panel is shown on the drawings to be relocated further than 25' from original location. Any good advise will be greatly appreciated. -Rich

 

[George Stolz]

Does table 220.84 apply to determine the feeder size for these units- If so the feeder would not need to be changed.

I don't think so, because you said

The Heat and A/C are not factored in the calculation as the building has a water chilled system.

...and 220.84 says...

(A) Feeder or Service Load. It shall be permissible to calculate the load of a feeder or service that supplies three or more dwelling units of a multifamily dwelling in accordance with Table 220.84 instead of Part III of this article if all the following conditions are met:

(1) No dwelling unit is supplied by more than one feeder.
(2) Each dwelling unit is equipped with electric cooking equipment.​

(Exception)
(3) Each dwelling unit is equipped with either electric space heating or air conditioning, or both. Feeders and service conductors whose calculated load is determined by this optional calculation shall be permitted to have the neutral load determined by 220.61.​

I'd say you should confer with the AHJ and see if an engineer needs to get involved, or if you can upsize the feeder, IMO. It's the safest bet. But I am not a master of the nuances of multifamily load calcs either.

 

[George Stolz]

I just noticed, there was more to your original post in the first thread that I hadn't noticed.

Greetings,
We are bidding a remodel for one condo unit in a 14 story building.
The unit shares it's feeder with three other units. (one atop the next)
The feeder is 3/0 THHN and is protected by a 200 amp breaker. The feeder runs through the main lug sub-panel of each unit and is tapped w/ a # 4 THHN to the main lugs of panel.
The remodel unit has a load of aprox. 62 A and the remaining three units have an estimated load of 54 A. We are a residential company that specialize in new custom homes and this wiring method is something new to us. A builder we work with is involved in this project and has asked us to take it.
My first query is whether NEC 2005 220.84 applies for the feeder size and that my load should be aprox 100.8 after a 45% demand factor.
Secondly, the architect would like to re-locate this sub-panel more than 25' away. What advise can you share involving taps and splices?
Thanks in advance,
Rich

One thing I'd comment on:

The feeder is 3/0 THHN and is protected by a 200 amp breaker. The feeder runs through the main lug sub-panel of each unit and is tapped w/ a # 4 THHN to the main lugs of panel.

(snip)

Secondly, the architect would like to re-locate this sub-panel more than 25' away. What advise can you share involving taps and splices?

The tap conductors are the #4's, not the 3/0's - from the sound of it, your taps are extremely short, maybe a foot or two, correct? So 240.21(B)(1) would apply.

When was the original installation completed, you have an idea? I wonder if the load calculation back then made the unit's demanded load less than 52A.

 

[peter]

Shouldn't each condo unit have it's own meter?

_Peter

 

[R@rpe]

Peter-
The unit's have individual sub meters next to each sub-panel

George-
The tap conductors are in the sub panel itself now and 240.21 B-1 does apply however the relocation was going to be over 25' away and I don't think this is allowed per NEC since it not a high bay manufacturing building over 35'... At any rate the architect has chosen to install the new sub panel in it's currant location to save $:grin:
The building was built in the late fifties-early sixties so it is hard for me to say what was considered in the engineering.
I did speak to the AHJ today his opinion accepts 220.84 for the feeder determination- I see your point about the a/c and heat. Although the dwelling is equip with this provision and since it is not a considered load IMO it only helps to lesson the load calculation for the feeder. He also stated that since the scope of the work is less than 5000 sq ' - the engineer seal would not be required. I've heard different opinions on this but his will count the most.
Thank you very much for your thoughts and time and please continue to post any further thoughts and opinions - I can't say enough how much I enjoy this site. - Rich