Check this, please

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JDB3

Senior Member
3 phase 240/120 volt load for existing church:

What I came up with, but seems high!
2,000 sq.ft. @ 1 volt-amp = 2,000 @ 125% = 2,500
sign = 1,200 = 1,200
receptacles 15@ 180 = 2,700 = 2,700

non-dwelling demand first 10kVa @ 100% = 6,400

fixed electric heating 1 @ 15,000
1 @ 10,000 = 25,000
25,000 @ 125% = 31,250

total = 37,650

37,650 / 240 * 1.732 = 271.7 amps :jawdrop:

What did I do wrong? :slaphead:
 

charlie b

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37,650 / 240 * 1.732 = 271.7 amps
To add to David's response, if you punched the keys of your calculator in the order that the numerals and symbols are shown in your equation, the calculator will first divide 37650 by 240, and then it will multiply the result by 1.732, and it will give you the answer of 271.7. Calculators follow the order of precedence that multiplication and division operations are done left to right, unless any of the operations are shown within parentheses.

 

JDB3

Senior Member
Thanks guys, and to think that "math" was my best subject. :slaphead:
Probably need to figure a water heater also, so load will be around 104 amps!

Also want to check, because of 3 phase system, I need to grounded wire (neutral) full size as the current carrying (hot) conductors ??

This will be going from pole mounted disconnect, underground (around 150 feet) to an existing inside panel. So 4 current carrying conductors, therefore Table 310.15(B)(3)(a) {adjustment factors},
Using 1/0 Al. wire @ 150 amp @ 80% I should be good for 120 amp ? And, may fuse (or what ever the current disconnect type is) @ 125 amps ??
 

JDB3

Senior Member
Caution :jawdrop:
Something else did not seem right, that a 104 amp calculation was O.K., since there is a 15 & a 10 kw furnace (so I was told). These are SINGLE phase pieces of equipment equipment, which would mean, that extreme care would be needed to put them on: A & B -&- on B & C phases AND then make sure (as is possible, probable signage) that nothing else is on B phase.
I do not believe that there is a high phase involved, I will also need to verify this.

What is you'll thinking on this? :?
 

david luchini

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If you connect one heater A-B and the other B-C and the rest of your loads are A-N and C-N, you would expect to see approx. 90A on B. That would be your highest line current. But you are correct, you have to make sure the load are connected correctly.

edit: corrected typo
 
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JDB3

Senior Member
}} If you connect one heater A-B and the other A-C and the rest of your loads are A-N and C-N, you would expect to see approx. 90A on B. That would be your highest line current. But you are correct, you have to make sure the load are connected correctly. {{

David, did you mean to put A-B & B-C ?
 

david luchini

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}} If you connect one heater A-B and the other A-C and the rest of your loads are A-N and C-N, you would expect to see approx. 90A on B. That would be your highest line current. But you are correct, you have to make sure the load are connected correctly. {{

David, did you mean to put A-B & B-C ?

Yes, sorry...typo.
 

JDB3

Senior Member
Question off that subject? How do you'll copy another persons reply & have it show up with the blue/gray background & outlined? Not only do I learn electric here, but also computer stuff here.

I am from a town that supposedly had 300 people living there. Used memo-graph machine to make copies with, and remember when the first hand held adding machines came out (in my neck of the woods) that cost $30.00. And yes, in the first part of grade school, we used an outhouse!
 

david luchini

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Question off that subject? How do you'll copy another persons reply & have it show up with the blue/gray background & outlined? Not only do I learn electric here, but also computer stuff here.

I am from a town that supposedly had 300 people living there. Used memo-graph machine to make copies with, and remember when the first hand held adding machines came out (in my neck of the woods) that cost $30.00. And yes, in the first part of grade school, we used an outhouse!

In the bottom right of each post there is a button that says "reply with quote."

If you use that rather than the plain "post reply" button, it will add the other persons reply.
 

domnic

Senior Member
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Electrical Contractor
church

church

120/240 three phase. is this a corner grounded delta with a high leg?
 

JDB3

Senior Member
Can't be corner grounded if 240/120.


If 240/120V 3PH 4W, it has a high leg (B).

As such, you cannot use any 120/240 (aka slash-rated) breakers connected to the high leg.

:? But any 2 pole breaker, feeding 240 volt equipment, would be fine :?

Seems, like I have seen some "high leg" panels, that the high leg was on C phase ?
 

Smart $

Esteemed Member
Location
Ohio
:? But any 2 pole breaker, feeding 240 volt equipment, would be fine :?
Has to be straight-rated 240V if connected to high leg.

Seems, like I have seen some "high leg" panels, that the high leg was on C phase ?
There's an exception for meter panel combos because many older meters require high leg on C. But other than that, high leg is required to be B.
 

Smart $

Esteemed Member
Location
Ohio
}} Has to be straight-rated 240V if connected to high leg. {{

By that, do you mean, 240 volt with no neutral load what-so-ever?
Let's say high leg is B... as required other than by exception.

  • You can connect 120/240 slash-rated breakers A(N), C(N), AC, or A(N)C.
  • You CANNOT connect 120/240 slash-rated breakers B(N)*, AB, BC, ABC, BCA, or CAB.
  • You can connect 240 straight-rated breakers any way you like*.
Safest approach is to use all 240 straight-rated breakers.

*There should be no B(N) loads, period.
 
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junkhound

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Location
Renton, WA
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EE, power electronics specialty
3 phase 240/120 volt load for existing church:
What did I do wrong? :slaphead:

"Church" and '240/120' hit a note:
Do you not mean 208/120?

In that case, load is a little more complicated, as the 31.25 kW is likely powered by 208V - but but maybe the 31.25 kW is 240V nameplate? You can calc the lighting load based on 240 as they are all probably single phase 120, but the electric heating is probably connected line to line, and you need to verify what the wattage is at 208V. Many nameplates list both.

Note: the 'church' and '240' rang my bell - 40 years ago in our new church (208/120 3 phase) a member donated 2 electric stoves for the kitchen, residential type, so burners at 208 would not boil water fast enough to suit kitchen crew: had to add 208 to 240 autotransformers to the ranges.
 
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