# 3 phase, 1200 amps



## Electric Al (Mar 13, 2010)

What size is the transformer???


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## Bob Badger (Apr 19, 2009)

Are there no inspections or permits? :blink:

To determine the existing load you should be following 220.87. If you can get the utilities demand data for the past year you can use that or the exception allows putting a recording meter on the service for 30 days.


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## pimpin electrician (May 2, 2009)

i haven't seen a transformer in the building. just the 120/208 switch gear. everything is fed off of that. a couple 400 amp panels, and 400 amp breakers going to meter banks.


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## pimpin electrician (May 2, 2009)

//


Bob Badger said:


> Are there no inspections or permits? :blink:
> 
> To determine the existing load you should be following 220.87. If you can get the utilities demand data for the past year you can use that or the exception allows putting a recording meter on the service for 30 days.



no inspections on this job. no permits. i will try and get demand data from the past year. That is a good idea. i also like the idea of the recording meter.

do you have any info on a brand of recording meter? is this like a current transformer? not too familiar with that.


thanks


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## brian john (Mar 11, 2007)

Typically you should have the demand for 30 days or in lieu of that you could install a load monitor for 30 days. You'll never know with your method if you are getting peak demand/usage.


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## Bob Badger (Apr 19, 2009)

brian john said:


> Typically you should have the demand for 30 days or in lieu of that you could install a load monitor for 30 days. You'll never know with your method if you are getting peak demand/usage.


The NEC requires the demand data for 1 year OR you can do a recording meter for 30 days. 

See 220.87


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## Toronto Sparky (Apr 12, 2009)

Problem may show up at Christmas or Thanksgiving when all the ovens come on line together


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## Magnettica (Jan 23, 2007)

Permit, or no permits, you need to know the calculated load. Because if ten of these units are being used to 'grow the weed' then those units are still going to draw from the connected load and if grandma's cooking a turkey for Thanksgiving dinner well then you're tempting fate and overloading that main breaker.


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## EJPHI (May 7, 2008)

I must be missing something. How are you getting 220V from the 208 service?

There must be a transformer hiding somewhere.

EJPHI


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## pimpin electrician (May 2, 2009)

EJPHI said:


> I must be missing something. How are you getting 220V from the 208 service?
> 
> There must be a transformer hiding somewhere.
> 
> EJPHI



There is no 220v. stoves and water heaters are gonna be receiving 208 power.


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## pimpin electrician (May 2, 2009)

brian john said:


> Typically you should have the demand for 30 days or in lieu of that you could install a load monitor for 30 days. You'll never know with your method if you are getting peak demand/usage.


where can i get a load monitor?


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## pimpin electrician (May 2, 2009)

Bob Badger said:


> The NEC requires the demand data for 1 year OR you can do a recording meter for 30 days.
> 
> See 220.87


where can i get a recording meter. is it a type of meter that i stick into the meter socket, or a device that needs to be hardwired?


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## Magnettica (Jan 23, 2007)

pimpin electrician said:


> There is no 220v. stoves and water heaters are gonna be receiving 208 power.


How many electric ranges? What's their kilowatt rating? 

How many hot water heaters? What's their kilowatt rating?


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## wildleg (Apr 12, 2009)

pimpin, are you really an electrical contractor ?


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## Innovative (Jan 26, 2010)

No permits....... Grow houses......... Do you have a license that you are concerned about????? Do you have insurance????


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## varmit (Apr 19, 2009)

The utility transformer is usually the load limiter for a service. Most POCO usually install the bare minimum for the original connected load.

Article 220 gives the procedure for sizing a service. You need more info as to the loads now connected and to be connected, in the future, in the additional units: unit square footage, type of HVAC, laundry facilities and any over all building loads.

Without knowing these details, I would guess that 1200 amp would be under sized for 24 units.


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## Toronto Sparky (Apr 12, 2009)

pimpin electrician said:


> There is no 220v. stoves and water heaters are gonna be receiving 208 power.


That helps to lower the load..

BTW 208 volt stoves are readily available. (In Canada anyway)

After all/most highrise apartments are 120/208


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## pimpin electrician (May 2, 2009)

Bob Badger said:


> The NEC requires the demand data for 1 year OR you can do a recording meter for 30 days.
> 
> See 220.87


im actually working out of 2002 code book. i guess it is time to update my code book.


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## kwired (Dec 20, 2009)

Why can't you find out the square footage of each apartment, and what appliances that are fastened in place and do a load calculation based on this information? Unless all apartments are drastically different from each other you should be able to come up with a fairly accurate calculation.

I have found that calculated load is usually higher than actual load in most dwellings.

BTW 1200 amps @ 120/208 3 phase is equal to about 43.2 kVA. That would be about 18kVA per apartment. Many single family dwellings do not calculate this high unless there is electric heat installed. And with that many apartments you get to apply more demand factors than you do with a single family dwelling.


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## pimpin electrician (May 2, 2009)

kwired said:


> Why can't you find out the square footage of each apartment, and what appliances that are fastened in place and do a load calculation based on this information? Unless all apartments are drastically different from each other you should be able to come up with a fairly accurate calculation.
> 
> I have found that calculated load is usually higher than actual load in most dwellings.
> 
> BTW 1200 amps @ 120/208 3 phase is equal to about 43.2 kVA. That would be about 18kVA per apartment. Many single family dwellings do not calculate this high unless there is electric heat installed. And with that many apartments you get to apply more demand factors than you do with a single family dwelling.


Thanks for your reply!

I just started doing a load calc. this is what im coming up with. 
I am figuring 24 units. Each with a clothes dryer, 5000 watts
electric stove, 8000 watts 
(2) small appliance circuits, 1500 w. each
(1) laundry circuit, 1500 watts
(1) water heater 2000 watts

I know not all of the units have laundry, or clothes dryers in them. It seems to me that the whole building shares just one washer and dryer. I am including it in my calculation that every unit has one, just to be safe. 

All of the above loads equal 19500watts. I am gonna use 22000 watts just because, and multiply by 24 for amount of units. T

So with that number i use the total demand factor of 35%. This is the demand factor for 24-25 multifamily dwelling units.

My total wattage after the demand factor is 184800. here is where i am a little stumped. The main service is 3phase 120/208v. Each unit is being fed 120/208 single phase. 

Do i take my total wattage after demand factor and just divide by 208? Or do i divide by the 208 3phase number? ( i actually forget how to work that one)

So i divide by 208 and i get 888 amps!! If this is correct, then i should be all good. There is a 1200 amp service, so i should be in the clear.

All of these units are loft type area's. Lotta weird people living there. 

Do you know what the formula is when you are looking for amperage of a 3 phase system. i know you need to multiply or divide something to the voltage, before you divide by the wattage. 

anywho... what do you think?


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## Mountain Electrician (Jan 22, 2007)

pimpin electrician said:


> Thanks for your reply!
> 
> I just started doing a load calc. this is what im coming up with.
> I am figuring 24 units. Each with a clothes dryer, 5000 watts
> ...


X 1.73 :thumbsup:


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## kwired (Dec 20, 2009)

pimpin electrician said:


> Thanks for your reply!
> 
> I just started doing a load calc. this is what im coming up with.
> I am figuring 24 units. Each with a clothes dryer, 5000 watts
> ...


For the individual units if only single phase just divide by voltage to get amps

For the service or any three phase feeders divide by voltage and divide again by square root of 3 (1.732) and try to get loads as balanced as possible across all three phases.

double check your wattages of appliances operating at 208 volts, many of the figures you presented are common values for equipment operating at 240 volts and will draw less at 208 volts.


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## Toronto Sparky (Apr 12, 2009)

BTW 1.73 is square root of 3


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## pimpin electrician (May 2, 2009)

kwired said:


> For the individual units if only single phase just divide by voltage to get amps
> 
> try to get loads as balanced as possible across all three phases.
> 
> double check your wattages of appliances operating at 208 volts, many of the figures you presented are common values for equipment operating at 240 volts and will draw less at 208 volts.


Well if the appliances operating at 208 volts will draw less current, then i suppose i am even more better off. if my calcs are high and it still shows i have enough power to add these units, then that is what i want.

I will do my best to jumble things around to balance the load, if need be. And if i divide by 208 volts instead of 360, then i should get an even better answer.

sorry if you dont understand, this guy wants to add a bunch more units to this building, and i just want to make sure it is safe. if i use high numbers, and it still allows the extra's, then that's great!


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## pimpin electrician (May 2, 2009)

kwired said:


> For the individual units if only single phase just divide by voltage to get amps
> 
> For the service or any three phase feeders divide by voltage and divide again by square root of 3 (1.732)


There is the 1200 amp switch gear. 3 phase 120 208.

Then out of that there are 3 sets of feeders. (2) going to meter banks, and (1) going to a distribution panel. 3 phase feeders.

These all go to feed the units. Nothing else. So if i just divide everything by 208, it will show more draw then if i did the 3 phase feeders separately. 

i want to show more draw, then there actually is.


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## Murphy (Dec 10, 2009)

pimpin electrician said:


> There is the 1200 amp switch gear. 3 phase 120 208.
> 
> Then out of that there are 3 sets of feeders. (2) going to meter banks, and (1) going to a distribution panel. 3 phase feeders.
> 
> ...


 
so then there isnt any single phase at all.. you are using two phases of the 3 phase in each unit?


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## varmit (Apr 19, 2009)

Your total service demand will be based on three phase in this case. Even if all of the connected load is single phase, you still have a three phase service with a three phase transformer or transformer bank. Therefore, your loads would be calculated as a load on a three phase system. (Load/208) x 1.73)

The same wattage load on 208 volts, will draw more amps than the same load on 230 volt.
(10,000 watts / (208 VAC x 0.9 PF x 1.73)) = 30.88 AMPS
(10,000 watts / (230 VAC x 0.9 PF x 1.73)) = 29.92 AMPS

However, on a resistance only load, as the voltage decreases, the wattage also will decrease. This does lessen the heat produced by the appliance and the current required.
(208 x 208) /50 ohm = 865 watts
(230 x 230) /50 ohm =1058 watts


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## Bob Badger (Apr 19, 2009)

Murphy said:


> so then there isnt any single phase at all.. you are using two phases of the 3 phase in each unit?


Two phases of three phase is commonly called single phase. But it is important to know when wiring single phase loads from 3 phase sources. The calculations for the neutral loading and current carrying conductor count for derating can change.


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## pimpin electrician (May 2, 2009)

varmit said:


> Your total service demand will be based on three phase in this case. Even if all of the connected load is single phase, you still have a three phase service with a three phase transformer or transformer bank. Therefore, your loads would be calculated as a load on a three phase system. (Load/208) x 1.73)
> 
> The same wattage load on 208 volts, will draw more amps than the same load on 230 volt.
> (10,000 watts / (208 VAC x 0.9 PF x 1.73)) = 30.88 AMPS
> ...



Thank you! your information is very helpful.


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## pimpin electrician (May 2, 2009)

Bob Badger said:


> Two phases of three phase is commonly called single phase. But it is important to know when wiring single phase loads from 3 phase sources. The calculations for the neutral loading and current carrying conductor count for derating can change.


Thanks for your reply. i will have to check out the nuetral load. i am counting neutral as current carrying for my derating. i count it always anyway.

Thanks again.


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## kwired (Dec 20, 2009)

pimpin electrician said:


> There is the 1200 amp switch gear. 3 phase 120 208.
> 
> Then out of that there are 3 sets of feeders. (2) going to meter banks, and (1) going to a distribution panel. 3 phase feeders.
> 
> ...


 
If you are bringing only single phase to individual units then all calculations for that unit and its feeder are based on 208 volt only, the 1.73 factor comes into play on your service and any three phase feeders and you want to include it here or your numbers will get large faster than you want them to. Remember it is giving you 1.73 times more capacity by adding the third phase. 

If you want your load calculation to be high don't do it by omitting the 1.73 three phase factor do it by factoring in higher loads than you have, round things up, add additional square feet or higher VA per square foot. Do not omit demand factors for things like ranges and dryers or they will kill your capacity pretty fast. Not everyone will use the ranges and dryers at same time (especially to their full capacity) plus they will not draw a continuous amount of current, they cycle on and off as needed to maintain temperature that is why there is demand factors for them.


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## pimpin electrician (May 2, 2009)

Thanks a bunch Kwired! 

i am gonna do my calc over. it's looking like i am gonna have no problem doing what my customer wants.

Thanks everyone else for your help as well.


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## pimpin electrician (May 2, 2009)

*Finally!!*



kwired;232169
If you want your load calculation to be high don't do it by omitting the 1.73 three phase factor do it by factoring in higher loads than you have said:


> Thanks a bunch. I just finished my calc. i used annex D, for multifamily dwelling.
> 
> i put every unit at 2000 sq ft. (which i know they are smaller) at 3VA
> and i put every unit with a dryer, range, and water heater. which there is not
> ...


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## pimpin electrician (May 2, 2009)

Bob Badger said:


> Are there no inspections or permits? :blink:
> 
> To determine the existing load you should be following 220.87. If you can get the utilities demand data for the past year you can use that or the exception allows putting a recording meter on the service for 30 days.



i just got the demand data for the last 6 months. is there a formula that helps me figure out how much power is being used at one time? The bill just shows usage in KWh.

The usage ranges from 60,000KWh to 90,000KWh.

service feed is 12,000 amps. 120/208 3 phase.

my friend is also going to let me borrow this amprobe meter thing.

it measures current for 24hrs. keeps track of it on paper. kinda like the things that measure earthquakes.

i plan on measuring current of the a,b, and c phase for at least 24 hours to see what kind of readings i get.

Any formula to figure out it i can add more distribution panels with my existing service by looking at electric bills?


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## pimpin electrician (May 2, 2009)

brian john said:


> Typically you should have the demand for 30 days or in lieu of that you could install a load monitor for 30 days. You'll never know with your method if you are getting peak demand/usage.


hey brian. i got the load demad for the past 6 months on this building. i also have gained access to a load monitor.

i am going to start monitoring the load on thursday. 

how do i use the electric bills in order to figure out if my existing service can handle extra load from a few new units that my customer wants to install?
is there some kind of formula?

electric bill just shows how many kw used per month.KWh

got anymore advice for me?


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## edcoho (May 23, 2010)

Toronto Sparky said:


> That helps to lower the load..
> 
> BTW 208 volt stoves are readily available. (In Canada anyway)
> 
> After all/most highrise apartments are 120/208


Ya but if the appliances are rated 230 volt, which is highly likely, load is increased. Unless there is a transformer stepping the 120/208 to 120/240.:thumbup:


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## Toronto Sparky (Apr 12, 2009)

edcoho said:


> Ya but if the appliances are rated 230 volt, which is highly likely, load is increased. Unless there is a transformer stepping the 120/208 to 120/240.:thumbup:


A 230 stove connected to 208 has a lower load and lower wattage and less heat.


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## edcoho (May 23, 2010)

Toronto Sparky said:


> A 230 stove connected to 208 has a lower load and lower wattage and less heat.


 It'll draw more current if the supply voltage is 208 not the rated appliance 230 volt.....big shooter.:thumbsup:


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## kwired (Dec 20, 2009)

edcoho said:


> It'll draw more current if the supply voltage is 208 not the rated appliance 230 volt.....big shooter.:thumbsup:


Ohms law does not say this.

If the resistance remains the same (still same elements) and the voltage is lowered the current will also be lowered.


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## Toronto Sparky (Apr 12, 2009)

edcoho said:


> It'll draw more current if the supply voltage is 208 not the rated appliance 230 volt.....big shooter.:thumbsup:


And why would it? Voltage drops Resistance stays the same.. Hmmm

Take a look at the name plate on a base board heater 1500W @ 240 ...1250W @ 208


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