P
[email protected]
- Jan 1, 1970
- 0
Which of the following methods of wiring a large residential building
would be preferred between these two choices (there certainly are other
choices, but I'm focusing on these two right now).
The building is supplied by power at 480Y/277 volts, or at a higher
voltage stepped down in a secured electrical room to 480Y/277. One or
more large capacity 480Y/277 volts circuits feed through the vertical
core of the building to an electrical room on each floor. On each
floor, a dry-type transformer steps 480 volts down to service voltage
for each customer.
1.
Each floor is powered through a three phase transformer that steps the
480Y/277 volt subfeed down to 208Y/120 volts. Each tenant is supplied
with just TWO phases of the three phase service, with the choice of
phases approximately balanced.
2.
Each floor is powered through a single phase transformer that steps
just two legs of the 480Y/277 volt subfeed from 480 volts to 240/120
volts. Each tenant is supplied with this normal single split phase
voltage. The diversity of the floors are approximately balanced.
For both of these cases, assume the total load is within the capacity
of available transformers, or that multiple transformers could be used
to supply each floor when there is a greater load than one transformer
can supply. Also assume that special building-wide loads such as
elevators and centralized HVAC can be powered by 480Y/277 directly if
applicable, or by a voltage system derived from 480Y/277 as needed.
As a variation of choice #2, where more than one transformer is needed
for a building with large floors, these transformers can be balanced
as reasonably possible over the core subfeed phases. Also assume that
additional subfeed circuits can be separately wired if a single feed
would be inadequate, up to as many feeds as needed, such as one feed
separately to each floor.
I'm not specifying a particular size for this building. Instead, what
I want to focus on is the practicality of supplying 120/240 volts for
single phase tenants (and generally residential will be single phase)
instead of 120/208 volts.
Another question: would this preference be any different if some or
all of the tenants were light business use, such as lawyer offices,
corporate branch sales offices, recruiters, etc, with no unusual
electrical needs (but would have a small kitchen with normal cooking
facilities for employee use such as lunch breaks)?
would be preferred between these two choices (there certainly are other
choices, but I'm focusing on these two right now).
The building is supplied by power at 480Y/277 volts, or at a higher
voltage stepped down in a secured electrical room to 480Y/277. One or
more large capacity 480Y/277 volts circuits feed through the vertical
core of the building to an electrical room on each floor. On each
floor, a dry-type transformer steps 480 volts down to service voltage
for each customer.
1.
Each floor is powered through a three phase transformer that steps the
480Y/277 volt subfeed down to 208Y/120 volts. Each tenant is supplied
with just TWO phases of the three phase service, with the choice of
phases approximately balanced.
2.
Each floor is powered through a single phase transformer that steps
just two legs of the 480Y/277 volt subfeed from 480 volts to 240/120
volts. Each tenant is supplied with this normal single split phase
voltage. The diversity of the floors are approximately balanced.
For both of these cases, assume the total load is within the capacity
of available transformers, or that multiple transformers could be used
to supply each floor when there is a greater load than one transformer
can supply. Also assume that special building-wide loads such as
elevators and centralized HVAC can be powered by 480Y/277 directly if
applicable, or by a voltage system derived from 480Y/277 as needed.
As a variation of choice #2, where more than one transformer is needed
for a building with large floors, these transformers can be balanced
as reasonably possible over the core subfeed phases. Also assume that
additional subfeed circuits can be separately wired if a single feed
would be inadequate, up to as many feeds as needed, such as one feed
separately to each floor.
I'm not specifying a particular size for this building. Instead, what
I want to focus on is the practicality of supplying 120/240 volts for
single phase tenants (and generally residential will be single phase)
instead of 120/208 volts.
Another question: would this preference be any different if some or
all of the tenants were light business use, such as lawyer offices,
corporate branch sales offices, recruiters, etc, with no unusual
electrical needs (but would have a small kitchen with normal cooking
facilities for employee use such as lunch breaks)?