[erickench]

What do you mean by purity of the material?

[erickench]

0.99 PF is a very good number.

[erickench]

One horsepower = 746 watts. For your problem the total HP = 746000 Watts. You can assume that this amount is consumed in one hour.

[erickench]

NEC 430.32 gives the rules for sizing motor overloads. You must either determine the service factor which should be on the nameplate or determine the marked temperature rise also on the nameplate.

 

Motors with a marked service factor 1.15 or greater                                           125%

Motors with a marked temperature rise 40'C or less                                            125%

All other motors                                                                                                  115%

[erickench]

Have you ever heard of this formula:

Resistance = K x L/A

 

The length L is in feet and the area A is in circular mils. K has two different values for copper and aluminum.

Copper K = 12.9

Aluminum K = 21.2

[erickench]

A short circuit occurs because an ungrounded conductor comes in contact with ground or neutal conductor or another ungrounded conductor such as a double line-to-ground fault. NEC 408.36 has rules for the protection of panelboards. They state:

a panelboard shall be protected by an overcurrent device having a rating not greater than that of the panelboard

 

If there is a fire or some other accident occurs then the panelboard is not protected properly. The main circuit breaker is supposed to trip whenever a short circuit or overload occurs. Perhaps the available short circuit current exceeds that of the AIC rating?

[erickench]

erickench said:

Transformers wil operate satisfactorily provided they have:

1) the same ratio of transformation

2) the same voltage ratings

3) approximately the same regulation

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Distribution tarnsformers are used at the customer interface i.e. spot networks.

[erickench]

Transformers wil operate satisfactorily provided they have:

1) the same ratio of transformation

2) the same voltage ratings

3) approximately the same regulation

[erickench]

18.4 amps can't be correct. You must always assume that the AC and the heater are not going to operate at the same time. You must take the higher of these two loads in your calculations.

[erickench]

Typical transformer impedances are around %6. Have you tried performing a short circuit test?

[erickench]

Are you sure it's three phase? It might be a single phase three wire 110/220 volt system. Picture a 220 volt transformer with a %50 center tap.

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What is the area in square feet? Is it just one apartment or the entire building?

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I would suggest using the KVA method in performing a short circuit calculation. You wouldn't have to use per units or complex numbers.

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Is it for a single apartment or foran entire multifamily building? NEC 220 has the procedures for calculating the load. What is the area in square feet?

[erickench]

It could very well be that power is being tapped upstream from the five submeters as you so call them and it's being used for something else. For instance hall and stairway lighting would not be charged to the tenants.

[Author]

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