multi-dwelling wih 208y/120

[baldie0217]

I need a good example of this so I know that I am doing it right. This is what I been working on.

10 units-208y/120 3-phase
1000 sq ft each
dishwasher-1.2kva
waste disp-1176va-motor
misc-.45kva
dryer-4.5kva
range-10kva
heat-10kva

I have 3 main questions

dryer-220-54 single phase dryer on a 3-phase system

range 220-55 single-phase ranges on a 3-phase system

220-61c1 prohibited reduction of the neutral load

I also need to size the transformer feeding the building I am taking the total kva rating and times it by 125% to get the kva of the transformer.
this would help me out alot on my next test in oregon.

thanks phil

 

[iwire]

While waiting for some more posts here you may find some good help in example D5(a) and D5(b) in information annex D at the rear of the NEC.

 

[Smart $]

...
I have 3 main questions

dryer-220-54 single phase dryer on a 3-phase system

range 220-55 single-phase ranges on a 3-phase system

220-61c1 prohibited reduction of the neutral load
...

These are questions???

I'll throw you a bone for the last one. In many situations where the service is 208Y/120V 3Ø 4W, each apartment is supplied with 120/208 1Ø 3W, which is exactly what is described in 220.61(C)(1). Where supplied as such, the grounded conductor has to be the same size as the ungrounded because it is technically not a neutral conductor when the third ungrounded conductor is not present. It will carry the same magnitude of 120V current as the higher of the two ungrounded conductors it is associated with.

On the other "questions", tell us what you think it means. The examples mentioned by iwire may help.

 

[baldie0217]

These are questions???

I'll throw you a bone for the last one. In many situations where the service is 208Y/120V 3Ø 4W, each apartment is supplied with 120/208 1Ø 3W, which is exactly what is described in 220.61(C)(1). Where supplied as such, the grounded conductor has to be the same size as the ungrounded because it is technically not a neutral conductor when the third ungrounded conductor is not present. It will carry the same magnitude of 120V current as the higher of the two ungrounded conductors it is associated with.

On the other "questions", tell us what you think it means. The examples mentioned by iwire may help.

for the neutral I think there should be no reduction for the appl dryers or range and the only reduction should be in the service at first 200 amps at 100% and the rest at 70%

dryer I think it should done -10/3=3.3 round up to 4 x 2=8
8 x 5kva x60%=24kva
24kva/2 x3=36k

 

[Smart $]

For the ranges?

Should other loads be balanced similar to clothes dryers and cooking appliances?

 

[baldie0217]

For the ranges?

Should other loads be balanced similar to clothes dryers and cooking appliances?

general Lighting 1k x 3va =3k
Small appl= 2 x 1500va =3k
Laundry= 1500va = 1500
total= 7500 x 10 =75k
1st 3k @100 -3k 3k
next 72k @ 35% 25200 main neutral
total 28200 28200 28200

Appliances
dishwasher 1.2kva
micro .45kva
disp 1176
total 2826 x10 =28260
water heater 4.5k
total 7326 x10 =73260 x 75% =54945 54945 28260

Dryer 10/3=3.33 =4 x 2 =8
8 x 5k x 60% =24kva
24k/2 x 3 =36k 36k 36k

Range 10/3 = 3.3=4 x 2
220-55 8 ranges = 23k/2 x 3 = 34.5k 34.5k 34.5k

heat = 10k x 10 = 100k 100k 0

total 253645va 126960
253645/208 x 1.732 =704 amps =800 amp overcurrent

704 amp/2 =352amps = 2 sets of 500kcm wire

neutral
126960va/208 x 1.732 = 352
-200 200
152 x 70%=106.4
total = 306 amp/2 =153.2 amps =2/o

optional method

lighting -3k
small app -3k
laundry -1500
diswasher -1.2k
micro -.45k
disp - 1176
water heater - 4.5k
heat -10k
dryer -4.5k
range -10k
total 39326 x 10 x 43% = 169101/208 x 1.732 = 469 amps (220-84)


each unit

lighting -3k
small app -3k
laundry -1500
diswasher -1.2k
micro -.45k
disp - 1176
water heater - 4.5k
dryer -4.5k
range - 10k
total 29326 - 10k
-10k
19326 x 40%= 7730
total = 17730
heat = 10k
total = 27730/208 =133 amp =150 amp breaker

 

[infinity]

I'll throw you a bone for the last one. In many situations where the service is 208Y/120V 3Ø 4W, each apartment is supplied with 120/208 1Ø 3W, which is exactly what is described in 220.61(C)(1). Where supplied as such, the grounded conductor has to be the same size as the ungrounded because it is technically not a neutral conductor when the third ungrounded conductor is not present. It will carry the same magnitude of 120V current as the higher of the two ungrounded conductors it is associated with.

Wouldn't it still be considered a neutral conductor since it meets the Article 100 definition even without the third ungrounded conductor?

Neutral Conductor. The conductor connected to the neutral point of a system that is intended to carry current under
normal conditions.

 

[GoldDigger]

It is definitely still a neutral as long as you consider it to be part of the four wire system. What it is not part of a three phase MWBC unless all three phases are present.
And it is always counted as a current carrying conductor, unlike the neutral when all three phases are sharing that neutral.

 

[GoldDigger]

And the current in the shared neutral will actually be more than the lower phase current but less than the higher current. Calling it equal to the higher is a conservative limit.
Oops, forgot that combinations of unequal power factor phase angles could make the neutral current higher than either phase current. (If the phase angle between the two currents is less than 120 degrees.)

 

[Smart $]

Wouldn't it still be considered a neutral conductor since it meets the Article 100 definition even without the third ungrounded conductor?

Yes it can still be called/considered the neutral conductor... but with respect to the two ungrounded conductors it is associated with, it is not a neutral conductor.

 

[infinity]

Yes it can still be called/considered the neutral conductor... but with respect to the two ungrounded conductors it is associated with, it is not a neutral conductor.

OK, but based on what? The NEC definition seems pretty clear that it doesn't matter if it's used with one, two, or three ungrounded conductors.

 

[Smart $]

OK, but based on what? The NEC definition seems pretty clear that it doesn't matter if it's used with one, two, or three ungrounded conductors.

Based on whether the neutral conductor current can be a nominal zero amperes when current is flowing in the two ungrounded conductors. In a 120/208 3-wire circuit it cannot.

 

[Smart $]

general Lighting 1k x 3va =3k
Small appl= 2 x 1500va =3k
Laundry= 1500va = 1500
total= 7500 x 10 =75k
1st 3k @100 -3k 3k
next 72k @ 35% 25200 main neutral
total 28200 28200 28200

Appliances
dishwasher 1.2kva
micro .45kva
disp 1176
total 2826 x10 =28260
water heater 4.5k
total 7326 x10 =73260 x 75% =54945 54945 28260

Dryer 10/3=3.33 =4 x 2 =8
8 x 5k x 60% =24kva
24k/2 x 3 =36k 36k 36k

Range 10/3 = 3.3=4 x 2
220-55 8 ranges = 23k/2 x 3 = 34.5k 34.5k 34.5k

heat = 10k x 10 = 100k 100k 0

total 253645va 126960
253645/208 x 1.732 =704 amps =800 amp overcurrent

704 amp/2 =352amps = 2 sets of 500kcm wire

neutral
126960va/208 x 1.732 = 352
-200 200
152 x 70%=106.4
total = 306 amp/2 =153.2 amps =2/o

optional method

lighting -3k
small app -3k
laundry -1500
diswasher -1.2k
micro -.45k
disp - 1176
water heater - 4.5k
heat -10k
dryer -4.5k
range -10k
total 39326 x 10 x 43% = 169101/208 x 1.732 = 469 amps (220-84)


each unit

lighting -3k
small app -3k
laundry -1500
diswasher -1.2k
micro -.45k
disp - 1176
water heater - 4.5k
dryer -4.5k
range - 10k
total 29326 - 10k
-10k
19326 x 40%= 7730
total = 17730
heat = 10k
total = 27730/208 =133 amp =150 amp breaker

Rather hard to decipher your calculation method. Do you have this in a tabular form, perhaps in excel or other spreadsheet format???

 

[GoldDigger]

Based on whether the neutral conductor current can be a nominal zero amperes when current is flowing in the two ungrounded conductors. In a 120/208 3-wire circuit it cannot.

I will still argue that it is always a neutral conductor under the definition. And it is almost always a current carrying conductor.
The explicit rules given in the code for whether or not it is included in the *count* of current carrying conductors are a different issue that does not depend on whether or not it is a neutral.

 

[Smart $]

I will still argue that it is always a neutral conductor under the definition. And it is almost always a current carrying conductor.
The explicit rules given in the code for whether or not it is included in the *count* of current carrying conductors are a different issue that does not depend on whether or not it is a neutral.

You/we can call the conductor whatever we wish (outside technical NEC speak, of course). What matters is the current can never be zero through this conductor while a line to neutral conductor load is powered, and this is the reason it is always counted as a current carrying conductor.

The reason why it should never qualify for size reduction compared to the other circuit conductors is because the current magnitude is always at least that of the greater of 120V loading on either of the other circuit conductors. This magnitude cannot realistically be reduced by any other load on the circuit.

 

[Smart $]

general Lighting 1k x 3va =3k
Small appl= 2 x 1500va =3k
Laundry= 1500va = 1500
total= 7500 x 10 =75k
1st 3k @100 -3k 3k
next 72k @ 35% 25200 main neutral
total 28200 28200 28200

Appliances
dishwasher 1.2kva
micro .45kva
disp 1176
total 2826 x10 =28260
water heater 4.5k
total 7326 x10 =73260 x 75% =54945 54945 28260

Dryer 10/3=3.33 =4 x 2 =8
8 x 5k x 60% =24kva
24k/2 x 3 =36k 36k 36k

Range 10/3 = 3.3=4 x 2
220-55 8 ranges = 23k/2 x 3 = 34.5k 34.5k 34.5k

heat = 10k x 10 = 100k 100k 0

total 253645va 126960
253645/208 x 1.732 =704 amps =800 amp overcurrent

704 amp/2 =352amps = 2 sets of 500kcm wire

neutral
126960va/208 x 1.732 = 352
-200 200
152 x 70%=106.4
total = 306 amp/2 =153.2 amps =2/o

...

I had to calculate it out with my method to compare. I took the micro' out of appliances because at 450VA it should be supplied by an SABC (though there are other possibilities). Your result appears to be okay until you get to the neutral part... and even that might be okay if I just don't understand your method. I don't see how you get 126960va of neutral load, and then I don't understand why you divide by 2 in the total line...???

Anyway here's how I did the standard load calculation (conductor sizing not included):

 

[Smart $]

... and then I don't understand why you divide by 2 in the total line...???

Okay, I figured that part out... it's because you are running 2 sets.

(Note this is where math falters as the universal language :lol

 

[baldie0217]

general Lighting 1k x 3va =3k
Small appl= 2 x 1500va =3k
Laundry= 1500va = 1500
total= 7500 x 10 =75k
1st 3k @100 -3k 3k
next 72k @ 35% 25200 main neutral
total 28200 28200 28200

Appliances
dishwasher 1.2kva
micro .45kva
disp 1176
total 2826 x10 =28260
water heater 4.5k
total 7326 x10 =73260 x 75% =54945 54945 28260

Dryer 10/3=3.33 =4 x 2 =8
8 x 5k x 60% =24kva
24k/2 x 3 =36k 36k 36k

Range 10/3 = 3.3=4 x 2
220-55 8 ranges = 23k/2 x 3 = 34.5k 34.5k 34.5k

heat = 10k x 10 = 100k 100k 0

total 253645va 126960
253645/208 x 1.732 =704 amps =800 amp overcurrent

704 amp/2 =352amps = 2 sets of 500kcm wire

neutral
126960va/208 x 1.732 = 352
-200 200
152 x 70%=106.4
total = 306 amp/2 =153.2 amps =2/o

optional method

lighting -3k
small app -3k
laundry -1500
diswasher -1.2k
micro -.45k
disp - 1176
water heater - 4.5k
heat -10k
dryer -4.5k
range -10k
total 39326 x 10 x 43% = 169101/208 x 1.732 = 469 amps (220-84)


each unit

lighting -3k
small app -3k
laundry -1500
diswasher -1.2k
micro -.45k
disp - 1176
water heater - 4.5k
dryer -4.5k
range - 10k
total 29326 - 10k
-10k
19326 x 40%= 7730
total = 17730
heat = 10k
total = 27730/208 =133 amp =150 amp breaker[/QUOTE

i had main and nuetral to the right but when i submitted it moved everything to the left.