Are there any suggestions on specific study materials (other than the NEC) to prepare for the exam? I'm only pursuing residential, not a master's license.

Thanks!

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A single-phase (B-phase) 75 kVA overhead transformer serves 17 single-family residential homes via overhead services, as seen in the attached feeder map. The three-phase primary feeder has distribution system voltage of 13.2GndY/7.62 kV.

- What is the most appropriate fuse size that most closely protects the single-phase transformer? ---------20T
- What is the most appropriate lateral fuse size that most closely protects the lateral
__and__coordinates with the downstream transformer fuse? -----40T

The closest upstream fuse to the lateral on B-phase is an 80T fuse link. The available list of fuses includes: 10T, 15T, 20T, 40T, 65T, 80T

I have searched up and down on a method to use to solve this problem, the only methods i can find use TCC graphs to determine values. That method requires calculating short circuit currents, i don't think there is enough info to do this.

So the last method i found pretty much said from the end of the line back to the main source the fuse values should increase to prevent un-necessary outages. The increase was suggested to be double.

Very unsure if this is correct, my answers are next to each question. I calculated the full load current of the 75kVA transformer to be 10A then doubled it to get 20T and used that to begin sizing the lateral at 40T which according to the rule of thumb coordinates with the upstream 80T fuse. Just seems wrong to do it this way, there has to be a better solution.

Winter = 50kVA * 1.40 = 70kVA Max

Summer = 50kVA * 1.10 = 55kVA Max

Primary full load current = 70kVA / 7.2kV = 9.72A

Secondary full load current = 70kVA / 240V = 291.6A

a.) 4/0 TX for secondary

b.) 4 for primary

I am an electrical engineer and ive recently been studying high power distribution, which i never studied in school. Can anyone check what ive done here and let me know if it is correct or how to better approach it.

What is the maximum full-load primary current that you could safely design for a three phase 500 kVA transformer bank to provide if it has a high-voltage winding of 25GndY/14.4 kV?

What does the notation 25GNDY/14.4kV really mean?

Is it 25kV L-L and 14.4kV L-NEU?

Full load current = VA / 1.73*Primary Voltage

Full load current = 500kVA / (1.73*25kV) = 11.56A *Assuming 25kV for primary voltage

Full load current = 500kVA / (1.73*14.4kV) = 20.07A *Assuming 14.4kV for primary voltage

Thanks everyone for your time.

Full load current = 500kVA / (1.73*25kV) = 11.56A *Assuming 25kV for primary voltage Full load current = 500kVA / (1.73*14.4kV) = 20.07A *Assuming 14.4kV for primary voltage ]]>

See any errors ?

For example, a 75 kva 3 phase 480 to 208Y/120 transformer can be protected with a primary

overcurrent device rated at 125 amps (75000/480 X 1.732 = 90 X 1.25 = 112 next size = 125) with no specified secondary protection

device rated at 225 amps (75000/480 X 11.732 = 90 X 2.5 = 225)

does not exceed 300 amps (75000/208 X 1.732 = 208 X 1.25 = 260 (300 = next size up) ]]>

Examples calculate water heater at nameplate rating. NEC 422.13 states water heaters (120Gal. or less) shall be calculated as a continuous load (125%) Should the 4500W nameplate rating in the example be increased by 125%? Why or why not? Thanks!! ]]>

I am interested in knowing if anyone makes or sells such a product?

Thanks.

Donald ]]>

I have a bachelor's degree in Electrical Engineering and have been in the consulting business (Commercial & Residential) for the pass 4 years, I also just passed the PE exam a few months ago. My questions is, do I have the required experience to apply for the test? ]]>

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For example>: (8) 2.5kw units plus (9) 8.5 kw units (unless I made a mistake the result would be 34 kw). If I had the same number of units (17) at 12 kw the Col C result would be 32 kw/

Makes no sense.. 17 ranges all less than 12kw give you a higher number than 17 units at 12 kw.

Am I looking at this wrong ? ]]>