 John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | reply to Jack_in_VA
Re: OK, What is this? Once again...this:
quote:
480 volt single phase (2 legs) to 277/240/120 single phase.
isn't done anymore...just like no one installs high-leg systems anymore. |
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 Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | said by John Galt:Once again...this:
quote:
480 volt single phase (2 legs) to 277/240/120 single phase.
isn't done anymore...just like no one installs high-leg systems anymore. Really? No one installs 277 volt 1-ph lighting anymore? That's news to me since it's so simple to take any one leg of a 480 volt 3-phase circuit for a lighting circuit.
What do you think they do run a bunch of 120 volt circuits for multiple high wattage lighting? |
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John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | Perhaps you can explain how your 480v single phase gets to be 120v... |
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 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6
 ·SONIC.NET
| reply to Jack_in_VA
I don't know about elsewhere in this country but here the utility penalizes commercial users for unbalanced loads. Therefore standard practice for industrial/office lighting is a 3 phase 480V/277V panel that feeds all 3 legs into the same area.
The light fixtures themselves are single phase 277V but each row of lights is on a different leg then the rows immediately next to it (every 3rd row is on the same leg).
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Got some spare cpu cycles ? Join Team Helix or Team Starfire! |
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John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | Precisely...balanced systems. Scabbing on a single phase transformer makes the system unbalanced.
To a maintenance man, it's no big deal. To those who have to design and run efficient systems, it -is- a big deal. |
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Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | reply to John Galt
said by John Galt:Perhaps you can explain how your 480v single phase gets to be 120v...
480 volt to 240/120 transformers. How do you think it's done? |
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Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | reply to leibold
said by leibold:I don't know about elsewhere in this country but here the utility penalizes commercial users for unbalanced loads. Therefore standard practice for industrial/office lighting is a 3 phase 480V/277V panel that feeds all 3 legs into the same area.
The light fixtures themselves are single phase 277V but each row of lights is on a different leg then the rows immediately next to it (every 3rd row is on the same leg).
Really? how about 1, 2 and 3 etc in the same row? Every 3rd light fixture is the same 277 volt circuit. There are many ways designers lay out their loads. |
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leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6 Reviews:
·SONIC.NET
| said by Jack_in_VA:Really? how about 1, 2 and 3 etc in the same row? Every 3rd light fixture is the same 277 volt circuit. There are many ways designers lay out their loads. Electrically it would make no difference whatsoever but because of labor and material costs nobody does it that way (2 versus 4 wires in each row).
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Got some spare cpu cycles ? Join Team Helix or Team Starfire! |
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Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1 | said by leibold:Electrically it would make no difference whatsoever but because of labor and material costs nobody does it that way (2 versus 4 wires in each row).
Really? You can quantify that statement? In some cases the added cost doesn't make any difference. The safety aspect of not having a whole row of lights go out has merit. Not only does each row have three feeds every third light is also on the emergency system. To say "nobody" does it........
Evidently you haven't worked much industrial applications that have critical considerations that are not necessarily cost effective but required for safety. |
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sk1939Premium
join:2010-10-23
Washington, DC
kudos:9 Reviews:
 ·T-Mobile US
| reply to Jack_in_VA
said by Jack_in_VA:The incoming feed may be 3-phase but it has to be stepped down and split into single phase circuits. I don't think I've seen any 3-phase lights and computers.
Nope, feeds a 3 phase 120/240V panel (Siemens, like this one: »www.ebay.com/itm/Siemens-120-240···4wt_1163). |
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Jack_in_VAPremium
join:2007-11-26
Mathews, VA
kudos:1
1 edit | said by sk1939:said by Jack_in_VA:The incoming feed may be 3-phase but it has to be stepped down and split into single phase circuits. I don't think I've seen any 3-phase lights and computers.
Nope, feeds a 3 phase 120/240V panel (Siemens, like this one: » www.ebay.com/itm/Siemens-120-240···4wt_1163). What does that have to do with my statement about 3 phase lights and computers? It still requires a transformer to step the voltage down to usable single phase 240 and 120 volt circuits.
It matters little if it's 3-Ph or single phase. It all depends on the installation requirements. |
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 AVDRespice, Adspice, ProspicePremium
join:2003-02-06
Onion, NJ
kudos:1 | I've seen 600V DC lighting and if you think about it, most computers run on DC power too. |
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sk1939Premium
join:2010-10-23
Washington, DC
kudos:9 Reviews:
·T-Mobile US
| reply to Jack_in_VA
480V 3 Phase to 240V 3 Phase transformer to that panel, which allows for 120V 1 Phase circuits.
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 whizkid3Premium,MVM
join:2002-02-21
Queens, NY
kudos:9
2 edits | said by sk1939:480V 3 Phase to 240V 3 Phase transformer to that panel, which allows for 120V 1 Phase circuits. If the transformer had a 240V wye-wound secondary, such a configuration would provide:
240V / 1.732 = 138.5 volts.
So, no. You don't have such a transformer. Its a 480V to 208/120V transformer. The laws of physics prevent it. 208V / 1.732 = 120V.
(e-Bay is not the best place to get electrical specs from)
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As for 277V lighting, its pretty standard in the design field to alternate 1 phase to each row. It saves on install & materials costs, which is the primary reason for using 277V lighting in the first place (more fixtures on less circuits).
Where emergency lighting circuits are needed / desired; yeah the emergency circuit may go to every third, fourth or fifth light fixture; but it doesn't make any sense at all to use one of the phases from the same system/transformer. You would just lose all of your lighting. If its code-required emergency lighting, this would be prohibited by both the NEC and NFPA-110 which require separate or at least isolated systems providing the emergency circuits (or battery packs). To my knowledge, no one is running 3 hots & 1 neutral to every row of 277V lighting, to alternate phases - at least not any skilled professional in the building design industry.
I also don't know of anyone employing single-phase transformers on a regular basis in general building design, other than where the building only has single-phase power or a special application requires it. (Excluding the one-phase of high-leg delta systems, which are becoming rarer in the US. With such systems, the use of single-phase transformers for general lighting & power are a lot more common.) Using multiple single-phase transformers and much more than the minimum quantity of wiring needed to achieve balance in the overall system, would incur unnecessary costs and labor, require more equipment & maintenance, and more physical space. Its just not done. Don't beat on me - these are just my daily experiences in the industry. |
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sk1939Premium
join:2010-10-23
Washington, DC
kudos:9 | I regularly confuse the two for some reason, I guess its because I see both daily. |
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