3 Phase range question and Sign

[AC\DC]

Hello, Been studing for my test and I just got " Tom Henry 2017 Calculations" Book. In his book he states
Section 220.55: Where Two or more single-phase Ranges are supplied by a 3-Phase,4-Wire feeder, the total load shall be computed on the basis of twice the maximum number between any two phases

One of his examples says " 30 Single-phase ranges at 12kw each are supplied by a 3-phase, 4-wire,120/208 feeder. What is the demand on the feeder for these ranges?

Solution
A Phase B Phase C Phase
10 10 10

10x2=20 appliances. Column C 20 appliance =35kw

That is the answer


In annex D and mike holt it shows it should be

The demand load for each two phases is 35/2 = 17.5 KW.The total demand load is 3 x 17.5 = 52.5 KWThe line current is:I = 52,500 / (1.732 x 208) = 52,500 / 360.3 = 145.7 amperes

Been jamming information in and this kind of messed me up. Every 3 Phase range calc I was getting wrong doing it like Annex D does.


Also Don't know if I should start a new topic but it should be brief answer. Its about including a Sign Circuit in commercial calculations. In Toms book he says don't assume Commercial Building are accessible to Pedestrians. Mike's books have always included even if it did not state.
How should I go about it. Only include it, or see if they state "accessible to pedestrians"

Thanks
​

 

[kwired]

Hello, Been studing for my test and I just got " Tom Henry 2017 Calculations" Book. In his book he states
Section 220.55: Where Two or more single-phase Ranges are supplied by a 3-Phase,4-Wire feeder, the total load shall be computed on the basis of twice the maximum number between any two phases

One of his examples says " 30 Single-phase ranges at 12kw each are supplied by a 3-phase, 4-wire,120/208 feeder. What is the demand on the feeder for these ranges?

Solution
A Phase B Phase C Phase
10 10 10

10x2=20 appliances. Column C 20 appliance =35kw

That is the answer


In annex D and mike holt it shows it should be

The demand load for each two phases is 35/2 = 17.5 KW.The total demand load is 3 x 17.5 = 52.5 KWThe line current is:I = 52,500 / (1.732 x 208) = 52,500 / 360.3 = 145.7 amperes

Been jamming information in and this kind of messed me up. Every 3 Phase range calc I was getting wrong doing it like Annex D does.


Also Don't know if I should start a new topic but it should be brief answer. Its about including a Sign Circuit in commercial calculations. In Toms book he says don't assume Commercial Building are accessible to Pedestrians. Mike's books have always included even if it did not state.
How should I go about it. Only include it, or see if they state "accessible to pedestrians"

Thanks
​

I agree that the examples in the annex seem to include more steps than what is mentioned in 220.55. All it says there is what you mentioned: the total load shall be calculated on the basis of twice the maximum number connected between any two phases.

For single phase applications the answer would be the value in the table for the number of ranges with no other functions applied to it, yet the example seems to think what 220.55 calls the "total load" is now only the total load per phase. I don't know what is right. Never have really had to do this calculation for a real world application though.

I will say that 35 kVA demand seems a little low for 30 ranges though so maybe what is in the annex is how they intend it, if so I think 220.55 needs better wording to reflect that. I guess if the supply were only single phase and you had 30 ranges the demand should be 45kVA, still less than 52.5 that the annex came up with.

 

[synchro]

I will say that 35 kVA demand seems a little low for 30 ranges though so maybe what is in the annex is how they intend it, if so I think 220.55 needs better wording to reflect that. I guess if the supply were only single phase and you had 30 ranges the demand should be 45kVA, still less than 52.5 that the annex came up with.

I agree that the annex shows the proper way to do the demand calculation. I believe the intent of the wording "shall be calculated on the basis of" does not mean that the kW from the table is the final result, but instead should be used as a starting point in the calculation. I think they try to keep the wording as short as they can, but I agree that more clarification is necessary in this case.

As Einstein said: "Everything should be made as simple as possible, but not simpler."