Service Neutral Load Question

[GingerZap]

I am in an Electrical Program taking an NEC 1 class and my teacher is no help. I am trying to wrap my mind around service neutral loads and am wanting to check my work to make sure I am on the right track. Below is the question and how I solved it. Can anyone verify if my answer is correct?

An eighteen-unit multifamily dwelling contains the following appliances in each unit: a 1-kVA, 115-volt dishwasher; a 1/3 HP, 115-volt in-sink waste disposer; and a 4500-watt, 230-volt water heater. Using the standard method, what is the service neutral load contribution, in volt-amperes, for these appliances? (Assume water heater watt rating equivalent to volt-ampere.)
85,428 Volt-Amperes

Service Neutral Load is the maximum unbalance of the load determined. The maximum unbalanced load shall be the maximum net calculated load between the neutral conductor and any one ungrounded conductor as per 220.61(A). (Is this the Line 10 Calculation?)

Using the Standard Method Load Calculation for Multifamily Dwellings, Line 10 Fastened-In-Place Appliances Rated ¼ hp or 500 Watts or Greater 220.53.

Dishwashers 1000 VA x 18 = 18,000 VA

In-Sink Waste Disposers 1/3 hp (7.2amp) x 115V = 828 VA x 18 = 14,904 VA

Water Heaters 4,500 x 18 = 81,000 VA

18,000 + 14,904 + 81,000 = 113,904 VA (Derate to 75% because there are more than four)

113,904 x .75 = 85,428 Volt-Amperes

 

[david luchini]

The water heaters are line-to-line loads, and would not be part of the neutral load calculation.

 

[ptonsparky]

I see you've had a least a couple questions where your instructor is no help. Perhaps the instructor wants you to think it thru for yourself.

You've been doing well. Keep at it.

 

[kwired]

Information too vague to come up with any kind of exact answer.

Yes line to line loads are not going to contribute to neutral loading. I'm also pretty certain there is much more line to neutral loads in such an installation than just DW, DISP.

Question does say "for these appliances" so I guess that makes it somewhat legitimate question though.

But you also need to know if single or three phase and how balanced said appliances are connected across the lines.

Worst case is if you have all units mentioned on same phase. Again ignoring the WH as it doesn't contribute to neutral current.

 

[GingerZap]

Thank You for the advise. I haven't read yet about line to line loads not contributing to the neutral loading. I have a lot to learn.

 

[kwired]

Thank You for the advise. I haven't read yet about line to line loads not contributing to the neutral loading. I have a lot to learn.

Think about it. Current flows into a 240 volt load via L1 and out through L2, neutral is not even involved therefore neutral has no current associated with this particular load.

 

[Tulsa Electrician]

"An eighteen-unit multifamily dwelling contains the following appliances in each unit: a 1-kVA, 115-volt dishwasher; a 1/3 HP, 115-volt in-sink waste disposer; and a 4500-watt, 230-volt water heater. Using the standard method, what is the service neutral load contribution, in volt-amperes, for these appliances? (Assume water heater watt rating equivalent to volt-ampere.)
85,428 Volt-Amperes"

Was 85,428 the ansawer given or is that what you came up with.

In you 2/0 ansawer in previous post I assumed it was the one given.

I just want to be sure I am reading it correctly.
Thank you

 

[GingerZap]

Tulsa Electrician 85,428 VA is the answer that I got, but it was incorrect because I included the water heater loads in my calculations. After recalculating I came up with 24,678 VA.

 

[GingerZap]

Ya kwired that makes sense.

 

[Tulsa Electrician]

Tulsa Electrician 85,428 VA is the answer that I got, but it was incorrect because I included the water heater loads in my calculations. After recalculating I came up with 24,678 VA.

Thanks I'm following correctly now.
Keep up the good work. It's nice to see some one doing the math.
There some examples in the annex D at back of book.

 

[david luchini]

Tulsa Electrician 85,428 VA is the answer that I got, but it was incorrect because I included the water heater loads in my calculations. After recalculating I came up with 24,678 VA.

I'd say 25,164 VA would be the correct answer.

 

[Tulsa Electrician]

I did not get either ansawer.
18* 1000 =18000
1/3 a 115v table 430.248
7.2*115= 828
7.2*115*18= 14904
Largest motor 430.24
1000*.25=250
.25 for largest motor 250
18000+14904= 32904
32904*.75= 24678
24678+250= 24928 va

 

[JEFF MILLAR]

I like your attitude, and your passion to learn. " Everything is easy when you understand it "
Mike Holt is a fantastic teacher. And i learn on this wonderful forum.
You will learn. There is a common neutral allowed with 3 hot wires, i.e 3 circuits, balanced load.
This is the neutral where only the unbalanced load flows,
There is the circuit where a one neutral and one hot wire is run in a circuit .
An equipment ground wire should always be included in each circuit.
Be patient, with your passion to learn you will learn all of this and much much more.

 

[Jpflex]

Don’t you also need to provide square foot of each dwelling for lighting and general load calculation?

 

[wwhitney]

Don’t you also need to provide square foot of each dwelling for lighting and general load calculation?

To find the total load on the service. But the question was just about the contribution from those specific appliances.

Cheers, Wayne

 

[Dennis Alwon]

I see you've had a least a couple questions where your instructor is no help. Perhaps the instructor wants you to think it thru for yourself.

You've been doing well. Keep at it.

Are you his teacher?

 

[ptonsparky]

Are you his teacher?

I'm usually no help, so I could be.