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I need help witha load letter residential interior

Customer Question
Hi I need help witha...
Hi I need help witha load letter for a residential interior
Submitted: 2 years ago.Category: Electrical
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Answered in 45 minutes by:
8/25/2015
Electrician: AssuredElectrical, Master Electrician replied 2 years ago
AssuredElectrical
AssuredElectrical, Master Electrician
Category: Electrical
Satisfied Customers: 4,241
Experience: Contractor-42+ Years in the ElectricalTrade
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Welcome. My name is ***** ***** would be glad to assist.

Is this for an entire new home or service upgrade?

Or an electrical addition to the home?

I assume the local jurisdiction provided one to you to fill out and return.

Can you post it here so it can be reviewed?

Jurisdictions all have there own and best to go with their criteria instead of generic.

Let me know and we can continue

Thanks

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Customer reply replied 2 years ago
Hi Tommy, This is a renovation of an apartment in a loft building in NYC - I am the architect. The electrical service to the apartment needs to be upgraded and the building architect has requested a load letter and the size of the service, panel and conduit. We got one from an electrician but then the building architect said it needed to be NEC format and our electrician has balked. I did some work on the file and I think I have it correct, but I have some questions and I wanted to get confirmation. am adding the Excel file here.
Customer reply replied 2 years ago
I am happy to have a call instead of writing if that is better.
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

Ok, got the sheet.

Never seen a municipality give an excel sheet for the calculations. Always just a piece of paper, very interesting.

So, pretty much the standard, so you have to supply the information needed:

Since you have been working on it, what are the specific questions?

I do see you are using amperage on the appliances. That will work, but not normal as the appliance may be on a 20 amp circuit breaker, it does not use that amount.

The actual nameplate gives the amperage and normally 50-75% of the circuit in many cases.

We can use the standard numbers if needed, but actually is best in a remodel situation. It will lower the load and the size of the service. I would not over do the situation personally when not needed.

Not sure which way you want to go with them?

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Customer reply replied 2 years ago
The questions I have are about if this is correct. The load letter the electrician sent said we would need a 120 amp board and that we would actually use 80 amps. But when I look at the load letter that I sent you it looks more like 140 amps are needed! So I am confused. Also I don't understand items #14 and #15 either... Maybe best to have a call.
Customer reply replied 2 years ago
BTW - the excel chart is from the building architect. To say that they are extremely overbearing is an understatement!
Customer reply replied 2 years ago
The questions I have are about if this is correct. The load letter the electrician sent said we would need a 120 amp board and that we would actually use 80 amps. But when I look at the load letter that I sent you it looks more like 140 amps are needed! So I am confused. Also I don't understand items #14 and #15 either - what are they for and how do I fill them out?
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

I did not have excel on my new PC just purchased, so had to borrow the better halfs to view the spreadsheet in detail.

I only have reader on mine, so I could not see the programming of each cell.

Item 14 and 15 are math cells, you do nothing with them. The #14 is the total amperage needed on a service based on the number in #13 which is total watts and then either 240 volts or 208 volts depending on your utility power available.

Now, looking at the sheet, it is flawed and has errors in the math.

The sheet totals the wattage of both heat and air conditioning, which is incorrect.

You do the greater of the two. not both.

What is the service you have right now? Need that to determine how much more is needed.

In cell #8 you show an oven, what is that?

In cell #10 for ranges, you have 12000 watts, did you get that off the nameplate of the unit?

Where did you get the numbers for the heating and air in #11?

Lets start there as I am still sifting through the spreadsheet calculations

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Customer reply replied 2 years ago
Hi - first of all thanks for your help - I think we can hammer this out and I am excited.I looked further and have some revisions to the loads, but specifically answers to your questions are:
Service now - I don't know the answer and it does not matter much since it will be entirely replaced, not augmented. The electric for the whole building is being redone.OVEN - in #8 - we have 1 cooktop (gas - 2Amps /120V), 1 double oven (7200 VA per the spec), and 1 microwave oven (120V 60hz, 15 Amp)I wasn't sure why #10 is listing ovens and also # ***** listing ovens. Is there a duplication?For #11 - I am revising per the spec. We will have 2 Compressors at 7,280VA each. and 2 Air Handlers at 3,600 VA each.Does that make sense?How can we fix the spreadsheet? Can you send me what to change the equations to?Thank you!
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

Ok, thanks.

Will try to go one at a time here:

1. Sounds like you have the oven at 7200 and not the 12000, correct?

2. The microwave, what is the wattage? It will not pull 15 amps, do not do the math for the wattage.

Most are 1000-1500 max

3.Air Handler will not use 3600 watts. That is a huge motor at 30 amps if 120 volts.

It has a nameplate rating and will list the motors amperage or wattage on the label.

Usually 10 amps max or so for air handling.

4. On the AC, again they have nameplates that should always be used for calculations.

It will list the entire condensing unit as a whole for FLA and may list the compressor and the fan separately. 2 motors on a condenser.

5. The big issue on the sheet, look at cell P48

You will see that it adds up cells P21,P34,P36,P37,P38,P39,P40, P41 and P45

But look at those and you will see that 38, 39, 40 and 41 are heating AND AC.

You only use the greater of the 2 in calculations because you cannot run heat and air at the same time.

To cure the problem, you might use some blank cells as calculations where you add up the AC , then another where you add up the heat, then use one cell to hold the greater value and add it to the total

Its called a Logical IF

You would Highlight a cell then use the Logical formula and enter the below:

IF P38>P41

Value if True P38

Value if False P41

Now your total will not contain both AC and Heat but the greater of the 2.

Remember also, the AC uses the blower on the furnace too, just no heat strips.

But the blower is minimal in wattage.

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Customer reply replied 2 years ago
Again - thank you for your help. I will answer in same order.
1. Yes we now have the oven listed in #10 as 7200.
2. Microwave - yes it is a 1000 watt Kitchen Aide - how should that be listed?
Here is the specifications: http://www.kitchenaid.com/shop/major-appliances-1/microwaves-2/microwaves-3/-[KMBS104ESS]-5539096/KMBS104ESS/3. Again - you are correct - here is a photo of the model sheet. (uploaded)4. For the condensers we will use 2 units of THDC-48 LX Series ( I uploaded a cut sheet) Clearly I read this incorrectly - or dd my math incorrectly.5. For this I should just to the math myself and submit the report after manually entering the amount. The apartment HAS heat from a building boiler, so the max load should be AC I would expect.
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

1. I would list the microwave as 1000 watts ( 1 KW)

2. Air Handler Just use the highest motor amperage for yours, since I dont know your model or voltage on the unit.

It is still a small number

3. On the AC units, again I do not know your model size (like the look of those units though)

Use the FLA column on the blower
Add that to the column Compressor RLA for your total amperage to calculate the wattage

Since you have boiler heat, the AC is definitely the one to use

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Customer reply replied 2 years ago
Ok - but Where to I put in 1000 Watts? Is Watts equal to VA? I though that was something else...
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

Ok, sorry.

Yes, the VA is the same as wattage

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Customer reply replied 2 years ago
AH - GREAT - that helps a lot.
Also - so the electrician who I had discussed this with said that the letter would show the total to be about 80 Amps. How can I see what the total Watts is in terms of the Amps in the service. We are allowed to request up to 208 Amp 3 phase service and I guess we were going to ask for 120 Amp 3 phase service to be delivered to the floor.
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

Ok,

All that is on the sheet

P48 is your wattage and P51 is the amperage

What does your sheet show now since the changes?

It would be wise to get what you can irrelevant to what you need now.

The work is there anyway and the cost is minimal to go higher while they are now upgrading, not later.

I would go the full 200 myself or at least 150

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Customer reply replied 2 years ago
My sheet is showing 247.0, 214.1, and 142.6A for the 3 numbers under #14.For the Compressor - The chart I saw said that the Model we were using had VOLTAGE - (208/3/60) and Max Fuse of 35 AMPS. I thought that would mean 35 Amps at 208 3 phase. This is how I got 7280 for the watts. Meanwhile in another part of the PDF it says that the motor will draw 4.3Amps. So this is why I am confused as to what to use in that box.
Customer reply replied 2 years ago
OK that makes sense - getting the most service. So you would get ask for a 208 Volt, 200 Amp, 3 phase riser and then have a 200 amp panel in the unit? And that riser would not noticibly larger or more complex to install than a smaller one?
Electrician: AssuredElectrical, Master Electrician replied 2 years ago

Ok,

Something I did not realize , you are installing 3 phase power, there is a difference

Here is how to calculate the wattage (same as VA) on 3 phase

Whatever equipment is 3 phase only

volts x amps x 1.732 = watts

DO NOT USE max fuse size. Look at my posts. Use the Compressor RLA and the blower FLA

Add them together for the total

Ask what the difference is in a 150 sand 200 amp.

Surely they can give that to you and then make the decision.

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Electrician: AssuredElectrical, Master Electrician replied 2 years ago

One other item in your sheet.
It duplicates the AC in the largest motor load.
It needs to be removed, you are counting one AC twice.

Also, click on the link below and you can download a much better worksheet for Residential
load calculations.
From one of the most repected individuals in the electrical industry
nationwide.
Free too.

CLICK HERE for the Load Calc Program

See the below picture and save it, print it out to better understand the Load Calculation worksheet

from the NEC

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