To the best of my knowledge it is electrical code complaint so long as
it is not considered a bedroom (it doesn't have arc-fault
protection.) There may also be more than 5% voltage drop if you fully
loaded the existing circuit (but that is a FPN).
Once again, I am feeling misunderstood.
My original question was not limited to NEC compliancy. I also asked
about egress and any other codes that might be applicable to the
intended use of the space: height of sloped walls, joist sizing for
live loads plus furniture, ventilation, etc.
I don't really care if it's code compliant in all areas - that's your
choice - and as I've said before, making it NEC compliant is
commendable, especially from a safety perspective. I'm just curious as
to whether or not you've put as much effort into all the other codes
that might apply as you seem to be to putting into the UPS
To answer your question I have put disproportional effort into this
posting. I have done so because I personally don't like it when I
spend the time to help someone out and they don't bother to reply. I
have also learned a little something and hopefully so have the other
participants. I consider the room reasonably safe for my family and
self in all regards. I apologize but I do not wish to revisit the
entire scope of the project.
Greetings Steve --- I believe my reply to Pete also addresses your
Your math is wrong. It uses prices for non-rackmount equipment and
generics. This is not the class of equipment which I am using for
this installation. I know you have strong pro-generic anti-rackmount
feelings but please try to put them aside. This is not what all my
clients like to see me use even in the dev environment and they are
right by definition.
Insisting on rack mount / name brand equipment does not equate to
cooking the books. Period. Your entire argument stems from the fact
that I could do it cheaper if I used non-rack mount generics. You
have not pointed out a math error! Lawyers could probably drastically
reduce their clothing / dry cleaning costs if they wore jeans and a
white t-shirt but clients wouldn't like it. When client perception is
taken into account it is cheaper to pay for the suits.
Yes. I have a backup generator and speaking of backup generators with
"central UPS" I can simply plug this generator into the power inlet in
the basement through the basement window (indirectly by plugging the
central UPS into the generator). Without "central UPS" I have to run
the generator cord in through the basement window and then snake it up
three flights of stairs with extension cords!
That said, thank you for your NEC notes.
The use of flexible cord as part of the permanent wiring system of a
building is tightly constrained by the US NEC. Connecting alternative
power sources to circuits is not a use the code writers permitted and in
the absence of a specific permitted use it may not be used as permanent
wiring. Here is how you do what you want to do and still be code
compliant. This is the same connection scheme that will pass inspection
for supplying hard wired appliances such as heating equipment from a
You install a box that is equipped with a double pole double throw
(DPDT) switch that has a center off position. The switch should be
rated for the ampacity of the circuit. The two center terminals on each
side of the switch are the commons of each pole. Those common terminals
will supply the circuit to the third floor which will terminate in an
appropriate receptacle outlet. The two terminals that are connected to
the common when the switch is in it's up position will be connected to
the circuits normal source of supply. The other two terminals will be
connected to a flanged inlet which is a recessed male plug that you will
install beside the DPDT switch either in the same J-box or one
immediately adjacent to it. A regular cord of the same configuration as
the UPS receptacle outlet will connect between the receptacle on the UPS
and the flanged inlet on the junction box. In that way the flexible
cord is not part of the permanent wiring and you can transfer the
circuit to it's regular supply when the UPS needs servicing.
It will be argued that the flanged inlet and the use of the double pole
switch is overkill and that the same function can be accomplished by
just terminating the flexible cord into the j-box and using a common
three way switch. That is not true however because the three way switch
will bypass the TVSS protection that is built into the UPS because the
circuits neutral will not pass through the UPS under UPS operation.
A common three way switch will also allow the transfer of the load from
regular power to UPS too quickly. If it is a continuous duty UPS it may
have an output waveform that is out of phase with the utility power.
Being only an electrician myself I can only tell you that we were taught
during apprenticeship training that could be harmful to some loads.
That information may not be up to date because modern computers may be
more tolerant of such power fluctuations then the ones in service when I
was in training low these many years ago.
Greetings Mr Horne:
a) I will try to limit the flexible cord length to 6 ft and run more
conduit if necessary.
b) I like the DPDT idea very much!
Thanks again Tom!
PS: At first glance this is an expensive switch: http://tinyurl.com/3altke
... but I am sure I can find a cheaper version. The appliance control
DPDT switches are very reasonable.
My assumption is that one uses a UPS to avoid power interruptions, giving
you a short time to safely save data and shut down. How is a system that you
have to manually throw a switch, assuming you are even there at the time,
going to help?
The addition of the DPDT switch makes the installation more
professional and more robust with increased applications and value
after the conclusion of the project with minimal extra work. Do you
think it is fair to call the flanged input and DPTP switch a "single
circuit generator input with manual transfer" when showing the house?
Do you think it will increase the home value more than the cost of the
I don't plan on ever flipping the switch in my installation. When the
power goes out I get notified on my phone. If it is out for very long
I have to plug the UPS into a generator or else the systems go into
hibernation. When the power comes back on the systems come out of
hibernation and continue as they were.
Hope this helps,
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