Service Feeders and Branch Circuits - Section 8

Question 1

What is a “demand factor”?

What is a demand?

Why do we use them?

Answer 1

A percentage of the total demand of an electrical feeder circuit determined from statistical data.

A base wattage value of the expected average load put on a feeder or branch circuit.

Because not all loads (or components within a load) will operate at once.

Question 2

When determining living area, what percentage of the basement is counted?

Answer 2

75%

Question 3

What is a basic load based on?

How is it calculated?

Answer 3

Living area.

Living area divided by 90 m² rounded up, plus 4 - all multiplied by 1000 W.

Question 4

How would a service load be calculated for an electric range?

Answer 4

6000 W plus 40% of any demand exceeding 12000 W.

Question 5

How would a branch circuit load be calculated for an electric range?

Answer 5

8000 W plus 40% of any demand exceeding 12000 W.

Question 6

If a range is not provided for, how should the miscellaneous loads of the house be calculated?

Answer 6

100% of the total sum of demand (only counting loads exceeding 1500 W) up to 6000 W plus 25% of the demand exceeding 6000 W.

Question 7

Which loads of a single dwelling are taken at 100% demand?

Answer 7

• Air conditioning
• Electric tankless water heaters
• Electric water heaters for steaming
• Swimming pools
• Hot tubs
• Spas.

Question 8

If a single dwelling has an 85 m² main floor and a calculated load of 89 Amperes, what will be the minimum ampacity of it’s service conductors?

Answer 8

100 Amperes, because of 8-200(1(b))

Question 9

How are loads 1500 W and under accounted for in service calculations?

Answer 9

With the basic load.

Question 10

Bus bar ampacity should always be “_____” the ampacity of the service conductors.

Answer 10

Equal or greater than.

Question 11

What is the minimum number of branch circuit positions required in a single dwelling? And a dwelling unit?

Answer 11

16, where at least half could be double pole breakers and with at least two left open for future use.

8.

Question 12

Generally, could a dryer always be fed with #10 conductors and protected by a 30A breaker.

Answer 12

Yes, unless specified as hardwired.

Question 13

What is the first thing to ask yourself, when performing an apartment service calculation?

Answer 13

What wire am I sizing?

This is because there are multiple different subrules, which size:

Dwelling unit feeders, Main service feeders and house panel feeders, respectively.

Question 14

When dealing with automobile heater recepticles, which rule must be referenced?

Answer 14

8-400.

Question 15

When calculating a demand for an apartmain main service feeder, what is the demand factor for which to take additional resistive loads?

Answer 15

They are taken at 75%.

Question 16

When calculating a demand for an apartmain main service feeder, why must one separate the heating/ AC loads out of the dwelling unit calculations?

Answer 16

This is beacuse not all residents will use all of their appliances at once, which allows us to put a significant demand factor on the smaller suite’s contribution to the total demand. However, since the building must be heated and cooled as a unit, we can only apply the specific demands associated to the total of all Heat/AC wattage.

Question 17

What is the minimum ampacity of an apartment panel feeder?

Answer 17

60A.

Question 18

When sizing an electric space heating branch circuit, what must be done to find the wire and overcurrent size?

Answer 18

Simply divide wattage, by nominal voltage and go buy your wire. Now take the ampacity of the wire you bought and divide that by 0.8; this will give you the ampacity to protect with your overcurrent device. For example, if the ampacity after upsizing was 27A, you go with a 30A breaker.

Question 19

What are the main uses for Table 39?

Answer 19

To size feeders and overcurrent devices for apartment dwelling units and single dwellings.

Question 20

Would you want to always use table 6 to size an apartment main feeder raceway?

Answer 20

No, often the neutral wire can be “de-rated” at 70% of the excess of 200A, so we will not always have three wires of the same size. In these cases we must use tables 8, 9 and 10.

Question 21

Which branch circuit loads are generally considered continuous?

Answer 21

Air conditioner.

Electric water heater.

Pool heater.

Electric vehicle charging.

Unknown loads.