office wiring

The following web page:
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describes an office setup for software developers. Well into the page it
tells about how the offices have 20 outlets powered through UPSes located
in the server room.
What I'd like to know is what code compliance wiring issues might be
involved in connecting the office outlets back to the UPSes. I would
think that whenever power emerges from a separately derived system and
then becomes building wiring again, it must meet all code requirements
including proper overcurrent protection (not the supplementary type of
protection found in the UPS units).
Reply to
phil-news-nospam
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The bionic office described in your link has one anomaly that I have noted as stated in the following:
"Power. Every desk has twenty, that's right, twenty outlets. Four of them are colored orange and have uninterruptible power coming off of a UPS in the server closet, so you don't need a UPS in every office. The outlets are right below desk level in a special trough which runs the entire length of the desk, about six inches deep and six inches wide. The trough is a place to hide all your cables neatly and has a handy cover which blends in with the desk."
Comment: Flexible cords must be exposed and cannot be run in troughs as described in the bionic office. There is a reason for this. Several decades ago as a State of Alaska electrical inspector I wrote up a 450 tent type temporary man camp at the Red Dog Mine near Kotzebue, Alaska for using flexible cords for wiring and running them through walls, under floors and you name it. My supervisor at the time objected to my report and requested a justification other than the code sections. (As I later learned the tent city as it became known was sold to the Cominco Red Dog Mine owners by a relative of my supervisor.) I obtained the UL standards for flexible cords and for nonmetallic sheathed cable and proceeded to compare the two standards. After all what was so great about NM cable that it could be run concealed and what was so detrimental about flexible cords that they could not be run concealed? My discovery was quite astonishing. Flexible cord is tested to a much lower standard and is primarily made for flexibility, not durability. On the other hand, NM cable is tested to 13 different standards that are quite impressive. One such standard required that 40 amperes be run through No. 12 and No. 14 AWG cable for 1 hour while two 50 pound weights are suspended from the ends of the cable that is held up by a mandrel. The cable is then taken down and tested for 5000 volts breakdown while immersed in water. Flexible cord on the other hand is tested to flex 15,000 times using a machine and then is tested for continuity only, and for a 2000 volt breakdown. Presumably, flexible cords must be exposed so that any damage can be identified and if they smoke, at least we know they are smoking.
Ref: 400.8 Uses Not Permitted. Unless specifically permitted in 400.7, flexible cords and cables shall not be used for the following: (1) As a substitute for the fixed wiring of a structure (2) Where run through holes in walls, structural ceilings, suspended ceilings, dropped ceilings, or floors (3) Where run through doorways, windows, or similar openings (4) Where attached to building surfaces Exception to (4): Flexible cord and cable shall be permitted to be attached to building surfaces in accordance with the provisions of 368.56(B) (5) Where concealed by walls, floors, or ceilings or located above suspended or dropped ceilings (6) Where installed in raceways, except as otherwise permitted in this Code (7) Where subject to physical damage
Reply to
electrician
| "Power. Every desk has twenty, that's right, twenty outlets. Four of | them are colored orange and have uninterruptible power coming off of a | UPS in the server closet, so you don't need a UPS in every office. | The outlets are right below desk level in a special trough which runs | the entire length of the desk, about six inches deep and six inches | wide. The trough is a place to hide all your cables neatly and has a | handy cover which blends in with the desk." | | Comment: | Flexible cords must be exposed and cannot be run in troughs as | described in the bionic office. There is a reason for this. Several
Would it really be classified as a trough if it's just an area behind the desk where the receptacles are? When I envisioned from this is a space for the cords to lay out of the way, effectively protected from most causes of damage. Basically the desk would have a platform for the cords to lay on, instead of dangling to the floor. If the cords are reachable from the under-desk area when dangling, there is now the added hazard of feet causing either direct damage, or damage due to be ing pulled by entanglement with feet (shoes on, preventing the sensation of knowing that the cord is entangled).
So I would think that what still might officially be a trough could in this case actually be safer by providing added protection to the cords.
Reply to
phil-news-nospam
The solution is to obtain either a listing or a field certification from a NRTL such as UL. I do not think an inspector enforcing the NEC as written can accept this installation. Perhaps a waiver could be obtained from an individual jurisdiction, but if these offices are going on the market, the listing option would sound prudent to me.
Reply to
electrician
A UPS is not a separately derived source. The neutral passes straight through. If the UPS is large, as I expect this one is, it will have output breakers. If it is really large, which is likely, it probably feeds a PDU (power distribution unit) which is basically a breaker panel for a UPS.
Charles Perry P.E.
Reply to
Charles Perry
Interesting -- in the UK, you are not permitted to assume any supply side connections remain intact, i.e. the UPS can't assume that its neutral or ground connections to the supply still work. (One reason it might come on is if someone were to cut through all of them.) UPS's usually have provision for a separate ground connection for this reason.
People sometimes overlook a UPS's [in]ability to supply enough current to cause a breaker to trip in a fault condition.
Reply to
Andrew Gabriel
|
|> The following web page: |> |>
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|> |> describes an office setup for software developers. Well into the page it |> tells about how the offices have 20 outlets powered through UPSes located |> in the server room. |> |> What I'd like to know is what code compliance wiring issues might be |> involved in connecting the office outlets back to the UPSes. I would |> think that whenever power emerges from a separately derived system and |> then becomes building wiring again, it must meet all code requirements |> including proper overcurrent protection (not the supplementary type of |> protection found in the UPS units). | | A UPS is not a separately derived source. The neutral passes straight | through. If the UPS is large, as I expect this one is, it will have output | breakers. If it is really large, which is likely, it probably feeds a PDU | (power distribution unit) which is basically a breaker panel for a UPS.
This is not true with all UPSes. I've talked with tech support engineers at a couple UPS makers who indicate that this aspect (neutral passing through) varies by model. Specifically they said ALL 230 volt units do NOT pass neutral through because of the variations of wiring that are standard in the world. But even many 120 volt units do not pass neutral through.
And then there's the matter of when there is no power. It certainly is a separately derived system if the source supply is cut off.
Reply to
phil-news-nospam
| People sometimes overlook a UPS's [in]ability to supply enough | current to cause a breaker to trip in a fault condition.
Having seem this happen a couple times, at least I know the internal breaker they provide can trip on the current available. In one case a sysadmin working for me had rewired a power switch incorrectly on an older AT-style power supply, and short circuited the power which was being fed from a UPS. It tripped virtually instantly. The UPS was a 10 kVA three phase 120/208 version, so it probably had the umph to do the job. I then made a new rule for the shop: all rewired computers are to be first tested on a non-UPS circuit.
Reply to
phil-news-nospam
Powerware 9125, neutral straight through. I have a lab full of european spec UPS that pass the neutral straight through. I have them from several manufacturers and in sizes from 2kVA up to 50kVA, single phase and three phase. Some do have a contactor to open the neutral when the UPS is turned off.
Charles Perry P.E.
Reply to
Charles Perry
|
|> |> |
|> |> The following web page: |> |> |> |>
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|> |> |> |> describes an office setup for software developers. Well into the page |> it |> |> tells about how the offices have 20 outlets powered through UPSes |> located |> |> in the server room. |> |> |> |> What I'd like to know is what code compliance wiring issues might be |> |> involved in connecting the office outlets back to the UPSes. I would |> |> think that whenever power emerges from a separately derived system and |> |> then becomes building wiring again, it must meet all code requirements |> |> including proper overcurrent protection (not the supplementary type of |> |> protection found in the UPS units). |> | |> | A UPS is not a separately derived source. The neutral passes straight |> | through. If the UPS is large, as I expect this one is, it will have |> output |> | breakers. If it is really large, which is likely, it probably feeds a |> PDU |> | (power distribution unit) which is basically a breaker panel for a UPS. |> |> This is not true with all UPSes. I've talked with tech support engineers |> at a couple UPS makers who indicate that this aspect (neutral passing |> through) varies by model. Specifically they said ALL 230 volt units do |> NOT pass neutral through because of the variations of wiring that are |> standard in the world. But even many 120 volt units do not pass neutral |> through. | | Powerware 9125, neutral straight through. I have a lab full of european | spec UPS that pass the neutral straight through. I have them from several | manufacturers and in sizes from 2kVA up to 50kVA, single phase and three | phase. Some do have a contactor to open the neutral when the UPS is turned | off.
Is that a 120 volt or 240 volt model?
So _why_ does the neutral need to be passed through on models that are dual conversion continuous online? Since not all models do this, there must be some reason that varies depending on targeted uses for various models.
Reply to
phil-news-nospam
It makes the bypass simpler since it only has to switch the line conductors.
Reply to
Matthew Beasley
|
|> [...]
|> | Powerware 9125, neutral straight through. I have a lab full of european |> | spec UPS that pass the neutral straight through. I have them from |> several |> | manufacturers and in sizes from 2kVA up to 50kVA, single phase and three |> | phase. Some do have a contactor to open the neutral when the UPS is |> turned |> | off. |> |> Is that a 120 volt or 240 volt model? |> |> So _why_ does the neutral need to be passed through on models that are |> dual conversion continuous online? Since not all models do this, there |> must be some reason that varies depending on targeted uses for various |> models. |> | | It makes the bypass simpler since it only has to switch the line conductors.
You used plural. Are you assuming TWO line conductors?
In some locations, 220 to 240 volts is carried with two conductors where each is about equal distant from ground potential, sometimes at 180 degrees phase vector, sometimes at 120 degrees (and possibly even at 60 degrees in an uncommon setup). In other locations, 220 to 240 volts is carried with two conductors where one of the is grounded. Some of those locations may have a correctly wired polarized outlet and plug which identifies which of the two conductors is grounded. Others may have unpolarized plugs making it possible that either is grounded.
If the UPS assumes one of the input lines is grounded, and makes a new hot voltage relative to it, it could result in as much as 360 volts to ground on the output in the case of a split 120/240 volt system coming in, and it could result in as much as 480 volts to ground on the output in the case of straight 240 volts in where it assumed the neutral on wrong conductor, depending on the phase angle of input and produced voltages.
I talked to a support engineer at one of the UPS companies, which I beleive was Powerware, who told me that indeed most, but not all, 120 volt models did indeed pass the neutral through, and the 220-240 volt models specifically did not due to the variety of electrical systems around the world. Much of the world that normally utilizes 220 volts still does so with a L-L connection, either from a single phase 110/220 volt system, or from a three phase 127/220 volt system where usually just two of the phases are used. The only way to make a 220-240 volt UPS work in all locations, even if North America is not considered, is to NOT pass the neutral through, and switch all conductors in a bypass switch.
Reply to
phil-news-nospam
They pass it through, they do not assume it is grounded. Check european equipment requirements. Unlike the US it is unusual to find any connection between neutral and ground (such as filters).
I can say with 100% certainty that the Powerware 9125 European spec, 240V, UPS passes the neutral straight through. We test them, open then up, etc.
Charles Perry P.E.
Reply to
Charles Perry
| They pass it through, they do not assume it is grounded. Check european | equipment requirements. Unlike the US it is unusual to find any connection | between neutral and ground (such as filters).
That's not the assumption I am talking about. They CANNOT pass it through unless they are passing BOTH wires through.
|> I talked to a support engineer at one of the UPS companies, which I |> beleive was Powerware, who told me that indeed most, but not all, 120 |> volt models did indeed pass the neutral through, and the 220-240 volt |> models specifically did not due to the variety of electrical systems |> around the world. Much of the world that normally utilizes 220 volts |> still does so with a L-L connection, either from a single phase 110/220 |> volt system, or from a three phase 127/220 volt system where usually |> just two of the phases are used. The only way to make a 220-240 volt |> UPS work in all locations, even if North America is not considered, is |> to NOT pass the neutral through, and switch all conductors in a bypass |> switch. | | I can say with 100% certainty that the Powerware 9125 European spec, 240V, | UPS passes the neutral straight through. We test them, open then up, etc.
Well, you are contradicting explicit information from the support engineer who said: (1) the neutral is not and cannot be passed through because not all electrical systems in the world are the same ... (2) the unit operates correctly in continental Europe when the plug is rotated 180 degrees.
So what kind of tests did you do on this model? Did you test it with a Schuko plug into a Schuko outlet in both way the plug could fit? Did you test this with the same kind of electrical service in some rural parts of Europe, including in Spain, Norway, and Russia, as well as in countries like Saudi Arabia where the 220 volt mains has 2 hots at 127 volts to ground?
Are your test reports available to the manufacturer? How can I cite your reports to them the next time I call them up to confirm this?
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phil-news-nospam

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