Demand factor questions

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nickelec

Senior Member
Location
US
So I looked at a job today and need some help I lack a bit in this portion of the code

The building is 70 units

14 stories with 3 floors containg meter banks

The meter banks are fed with 400a 3 phase.

Each 400a meter bank feds 23 apartments with 60a mains

The reason I was called in is because the building wants to get rid of the gas lines and install Electric ovens 40a each

Each appointment currently has an electric hot water heater and Electric stackable washer and dryer both fed via 2 pole 30 amp breakers.

I'm pretty sure I need to upgrade the feds and panels in each apartment.

My concern is the 400a feeding the meter banks is not adequate. I know it should definitely be engineered but maybe some one here can help me figure out off the bat if it's big enough, if it may be obviously to small or close to adequate where an engineer is needed

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infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
From a shoot from the hip position without any engineering you could assume that the 60 amp is no longer large enough and move each apartment panel up to the next standard size panel of 100 amps and figure the feeder sizes from there. A true load calculation will yield a low number for the feeder size due to diversity. Having said that this method is pretty useless.
 

nickelec

Senior Member
Location
US
Regardless they want me to put in 100a feeder to each apartments. There is a demand factor for multi family dwelings, can you point me in that direction, how does an engineer go about a load calculation on an exsisting dwelling Poco data?

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david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Regardless they want me to put in 100a feeder to each apartments. There is a demand factor for multi family dwelings, can you point me in that direction, how does an engineer go about a load calculation on an exsisting dwelling Poco data?

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I would do a load calculation as if it was new. You didn't give the square footage of the apartments, you do the load calculation without that.

Also, you didn't mention air conditioning or electric space heating...without either of those, the optional calculation in 220.84 wouldn't apply, so you would have to use the standard calculation.

I can't imagine that a 400A meter bank would work for 23 apartments.
 

nickelec

Senior Member
Location
US
In NYC a dedicated 20a receptacle is required in every room for acs where a Central unit is not installed

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MyCleveland

Senior Member
Location
Cleveland, Ohio
In NYC a dedicated 20a receptacle is required in every room for acs where a Central unit is not installed


Nick
Had a few minutes so here are thoughts for your discussion.

220.82 (C)(1)...seem to comply. I used 1800w x 3 for the AC load.
220.84 (A)(3)...Article does not state "whole house" or "central" so I would think you comply.
Let you argue this if you agree.
If not, like "David" stated....you are left with the standard calc.

Each apartment: 120/208V-1P-3W, 4500W Elect Water heater, 6700W range even though I have never had one this small.

Standard Calc: No extra appliances added, ex: disposer, dishwasher, etc.
120 Amps
Optional Calc: No extra appliances added, ex: disposer, dishwasher, etc.
101 Amps (Probably get this under 100 by tweaking AC load)

23 Unit Meter Stack: 120/208V-3P-4W
669 Amps

VERIFY the range load and the electric water heater...make sure they understand the voltage is 208 and not 240.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
In NYC a dedicated 20a receptacle is required in every room for acs where a Central unit is not installed

Almost but not every room, an AC receptacle in the bathroom wouldn't get much use. :D

210.52(I) Outlet Requirements For Residential-Type Occupancies. In addition to the requirements set forth
in subsections (A) through (H) of this section, living rooms, bedrooms, dining rooms or similar rooms
shall have at least one receptacle outlet installed for air conditioners. Such outlets shall be supplied by an
individual branch circuit.
Exception: Buildings with central air conditioning systems that serve any of the above areas shall not
require separate outlets in those areas.
 

nickelec

Senior Member
Location
US
In NYC a dedicated 20a receptacle is required in every room for acs where a Central unit is not installed


Nick
Had a few minutes so here are thoughts for your discussion.

220.82 (C)(1)...seem to comply. I used 1800w x 3 for the AC load.
220.84 (A)(3)...Article does not state "whole house" or "central" so I would think you comply.
Let you argue this if you agree.
If not, like "David" stated....you are left with the standard calc.

Each apartment: 120/208V-1P-3W, 4500W Elect Water heater, 6700W range even though I have never had one this small.

Standard Calc: No extra appliances added, ex: disposer, dishwasher, etc.
120 Amps
Optional Calc: No extra appliances added, ex: disposer, dishwasher, etc.
101 Amps (Probably get this under 100 by tweaking AC load)

23 Unit Meter Stack: 120/208V-3P-4W
669 Amps

VERIFY the range load and the electric water heater...make sure they understand the voltage is 208 and not 240.
And with services I can round down to 600 or do I need to go up to the standard fuse of 700

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JFletcher

Senior Member
Location
Williamsburg, VA
Because the feeds are 3-phase 400 amps, the equivalent single phase amperage is almost 700, 692.8 to be precise.

Why can one not use table 220.55 to calculate the demand factor?

60 amp main and feeder are not going to cut it with electric dryer, water heater, and an electric oven. is your concern that the hundred amp panels and feeds that they want you to install will be too small? I know the following is not really a valid way of doing things, however if they are not tripping 60a mains now, the addition of an oven rated at roughly 30 amps should not be a problem for the hundred amp panels.

As far as data from the Poco, can one use customer bills to determine average hourly amperage draw?
 

nickelec

Senior Member
Location
US
I'm not really concerned I think the 100 a per apartment should be ok. I don't think the 400 meter Bank is sufficient is turning into a big job there's only a 4 inch pipe feeding them now I don't think I can fit eight 350s in it if I have to upgrade to 6

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WarrMann

Senior Member
Location
Atlanta, GA
I'm not really concerned I think the 100 a per apartment should be ok. I don't think the 400 meter Bank is sufficient is turning into a big job there's only a 4 inch pipe feeding them now I don't think I can fit eight 350s in it if I have to upgrade to 6

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Eight 350's in the same conduit isn't going to cut it for a 600 amp 3 phase service. That would be 70% of 620. That gives you 434 amps on a 450 amp over current device. Id avoid going that route.

Chances are the guy who designed that system put as much amperage through that conduit as possible. There's also the challenge of getting the old wire out.

Being that you have reached capacity, its possible that the poco and AHJ might allow another service to the building. But i realize that's a lot easier said than done.

How do you plan to upgrade the feeders? Are they in conduit, or are you running cables?

Be sure to let us know how it gets done if you do the job

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nickelec

Senior Member
Location
US
I'm not sure yet , were at the very preliminary stages an engineer definitely needs to get involved. We will see what he suggests.

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