208/230 single phase on 277/480 systems

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desert designs

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Greetings folks,

I'm an architectural designer with enough EE experience (I started my career drafting at an EE's office) to do my electrical design as well......

I'm well versed in 120/208 design. I occasionally have a 277/480 project and that time is now.

My question is, is a 208/230V single phase hvac unit shown as 2-pole connection to a 277/480V panel, and do you multiply the amperage * 230 to get the VA, and divide it between the 2 poles ?

Thanks alot in advance guys,
Steve
'Desert Designs'
 
desert designs said:
Greetings folks,

I'm an architectural designer with enough EE experience (I started my career drafting at an EE's office) to do my electrical design as well......

I'm well versed in 120/208 design. I occasionally have a 277/480 project and that time is now.

My question is, is a 208/230V single phase hvac unit shown as 2-pole connection to a 277/480V panel, and do you multiply the amperage * 230 to get the VA, and divide it between the 2 poles ?

Thanks alot in advance guys,
Steve
'Desert Designs'
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Apparently you still require some EE experience. You simply do not connect 208/230 equipment to a 480/277 system [directly].
 
Connect the 120/208 single phase HVAC unit to the 277/480 panel. Then multiply the cost of the unit by 2(to replace the first one), and add in a dry pot XF to carry the second HVAC unit to replace the first one...
 
haha

you are correct sir......and Hv&Lv, I don't care how much this stuff costs maaaan

so, the 208/230 units are connected as a 2p/208V unit to the 120/208 system. thanks.

do still you multiply the FLA * 208 to get the VA ?
 
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Smart $ said:
Yes ...and sometimes times 125%...
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Not sure whay you are asking, but you should use 3.7 KW (4 KVA to be safe) per ton for load calculation purposes, not the actual load of one HVAC unit. Don't forget to add the circulating fan wattage to this as well. That is the figures I usually use. Newer HVAC systems are more energy efficient, but it is better to be safe than sorry.
 
Interesting.....

I've usually used 360.26*MCA or FLA for 3ph 208v units for example....




at any rate, hey, I wrote an autolisp panel schedule years ago, sold around 200 or so copies of it in san diego and LA back in the day to the likes of DMJM and some other heavies.....blah blah blah, if you use autocad and know how to add menu files to your system shoot me a PM and I'll send you the .lsp files, just a favor to MHF users, I may have other questions in the future. it's 3 pulldowns: inserting panels, setting voltage, and inserting breaker blocks. works at both 480/277 and 208/120 and calculates high phase as well.

418229_3035836066805_1590087125_32497381_966859125_n.jpg

steve
 
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desert designs said:
do still you multiply the FLA * 208 to get the VA ?
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No, that is not correct.

desert designs said:
I've usually used 360.26*MCA or FLA for 3ph 208v units for example....
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That is correct. But I am concerned as to whether you know why, and why you would have first asked about multiplying by 208 instead.

desert designs said:
. . . shoot me a PM and I'll send you the .lsp files, just a favor to MHF users
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No thank you. It looks like a panel schedule looks, and all of the math that I checked came out correct. But it has two errors that demonstrate a fundamental lack of understanding of the terms involved in electrical engineering design. I specifically refer to ?A.I.C.? and ?wattage.? The first of these terms does not apply to panels, and the second is simply the wrong word. You cannot add watts to watts and get watts, any more than you can add amps to amps and get amps. The physics does not work out that way.

 
well, I was talking about 1ph/2p when I said 208......

wattage....VA.....the first firm I worked at always had 14K AIC on 277/480V panels and 10K on 120/208 panels. I'm no electrical engineer though. I just know how to add VA to VA to get VA, do the voltage math, and design Title 24 compliant switching and pick neat looking light fixtures haha.

call it what you like, change the text to your liking delete the AIC rating etc.....

it's just one big macro that looks in each VA box, based on the scale the schedule is placed on the drawing, then determines the voltage you've selected and does the math.

again, a favor to anyone with the CAD .mnu file knowhow who would like to plug it in. It saves mega time instead of using your calculator or excel OLE or some such. when I was a young buck I drove all around LA selling that thing. Twas fun.

but thanks charlie, I think I'll change that wattage callout to VA. It's been that way for almost 20 years heh.

oh, btw, can anyone tell me how to determine the proper overcurrent rating of switchgear?

hahahahaha j/k
 
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Strathead said:
Don't you need to use 230V when calculating HVAC? On top of that, you generally need to use the Minimum Circuit ampacity as listed on the equipment label plate for actual draw.
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Not if you are connecting to a 208 system.

Yeh , MCA... if it has it. Not all do, which then you have to cal' your own... which was what my reply eluded to :blink:, but did not elaborate upon. Thanks for broadening the depth of response.
 
I have another question that maybe answerable, or debateable......


Is there a rule of thumb whether you specify Fused disconnects at the unit for HVAC units, or is simply a motor rated disconnect suitable for some units?

I usually indicate fused, but (probably) some get installed without, and have read that fused is more problematic than a hard requirement....
 
desert designs said:
. . . call it what you like, change the text to your liking delete the AIC rating etc.....
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AIC means "amps interrupting capacity." A breaker has the ability to interrupt the flow of current, and if a panel has a main breaker then that breaker can interrupt the flow of current, but the panel itself can not. That is why it is inappropriate to speak of AIC in connection with a panel?s rating.


 
charlie b said:
You cannot add watts to watts and get watts. . . .
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Since that statement appears to have confused one or more of my readers, let me clarify that if two or more loads have different power factors, then adding just the real power values (i.e., watts) is not going to give you the correct answer for the sum of their loads. You must also add their reactive power values (i.e., VARs), and then use vector addition of the watts and the VARs to get the total apparent power (i.e., VA).
 
As Charlie said, there is a difference. The proper term for panels would be Short Circuit Current Rating (SCCR).

AIC is a requirement of NEC 110.9, it relates to devices intended to interrupt fault currents.
SCCR is a requirement of NEC 110.10, it relates to equipment being able to withstand fault current until a protective device operates.
 
"would you be mind...?"

not at all mr. beck. my apologies. I use the hahaha in conjuction with joking to make sure it's understood that the comment should be taken with a grain of salt....like one of these :lol:..or in a manner in that we're all having fun.....but laughing at one's own jokes is annoying I'll try to refrain from it.

are you sure you're just not annoyed an architectural designer is treading into your respected profession?
just kidding again.

...I know that the fault current question is a long involved answer, so I was just kidding about it. And my Fused disconnect question is pretty broad as well; sometimes it's in the manufacturer's documentation and sometimes not though, and I've read varying opinions about it on the 'net.

The AIC indication on my panel schedule is a holdover from years and years ago, when one PE had deemed it appropriate to indicate that. I'll let you two fight it out, she was pretty nice for the most part but....

Isn't your explanation of the sum of loads and vectors, pardon the phrase, nitpicky and theoretical, when it's common practice to just add up the watts as VA and sum it up, add 125% where appropriate and call it a day ?

all fun aside, much respect charlie, and thanks jim as well for further explanation....I'll keep learning.
 
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