Practice Test question I'm stumped on!

[jwnelson1]

Im preparing for my california exam and I have been running through some practice questions on code. I have come across a question I can not get the right answer for:

A store building measures 60 feet by 80 feet and is supplied by a 120/240 volt, three phase 4 wire delta system; the building has 60 linear feet of show window lighting. Which of the following is the minimum allowable number of 2 wire, 20 amp branch circuits required to supply the continuous general lighting and show window lighting in this building?
A) 7 B) 8 C) 11 D) 14

Per my calculations 16,800 volt amps(with the 125% demand factor included) % 2,400 Watts = 7 Branch Circuits

Am I missing something because the correct answer per the study guide is 14 Branch Circuits? :-?

 

[Dennis Alwon]

i get 7 branch cir also.

 

[jumper]

Here is what I came up with:
80*60=4800*3=14,400va , T220.12
60*200=12,000 va , 220.14(G)
26,400*1.25=33,000va , 210.19(A)
33,000va/120v=275 a , delta service=no three wire MWBC, no 1.732
275a/20a=13.75 cicuits

 

[Dennis Alwon]

Here is what I came up with:
80*60=4800*3=14,400va , T220.12
60*200=12,000 va , 220.14(G)
26,400*1.25=33,000va , 210.19(A)
33,000va/120v=275 a , delta service=no three wire MWBC, no 1.732
275a/20a=13.75 cicuits

very good I was figuring just the linear store lighting missed the point where it asked for both store and window lights.

 

[jumper]

Typical trick question on these practice exams.

 

[jwnelson1]

Thank you

Thank you

That helps out a lot guys.
Was racking my brain on that one. Couldn't figure out what I was missing.

 

[Smart $]

Typical trick question on these practice exams.

But it's even trickier than that... it does not specify the lighting voltage. What if all the lighting was 240V fixtures?

 

[scott thompson]

My take on the subject!

My take on the subject!

I came up with 13.75 Branch Circuits also (round up to 14 Branch Circuits).

60' x 80' = 4800 sq. ft.
4800 sq. ft. x 3.5 VA/sq. ft. = 16800 VA
16800 VA x 1.25 (LCL) = 21000 VA

60 feet Show Window x 200 VA / Linear foot = 12000 VA

12 KVA Show Window + 21 KVA General Lighting Loads = 33 KVA (33000 VA)

33 KVA ? 2400 VA (120V 20 Amp Circuit) = 13.75

Minimum of (14) 20 Amp Circuits.

Scott

 

[Smart $]

I came up with 13.75 Branch Circuits also (round up to 14 Branch Circuits).

60' x 80' = 4800 sq. ft.
4800 sq. ft. x 3.5 VA/sq. ft. = 16800 VA
16800 VA x 1.25 (LCL) = 21000 VA

60 feet Show Window x 200 VA / Linear foot = 12000 VA

12 KVA Show Window + 21 KVA General Lighting Loads = 33 KVA (33000 VA)

33 KVA ? 2400 VA (120V 20 Amp Circuit) = 13.75

Minimum of (14) 20 Amp Circuits.

Scott

Apparently the author of the question assumed the lighting to be 120V but he did not specify so. The lighting could be 240V, thus 7 could be the minimum number of 20A two-wire circuits. Last time I checked 7 is less than 14

 

[hurk27]

I came up with 13.75 Branch Circuits also (round up to 14 Branch Circuits).

60' x 80' = 4800 sq. ft.
4800 sq. ft. x 3.5 VA/sq. ft. = 16800 VA
16800 VA x 1.25 (LCL) = 21000 VA

60 feet Show Window x 200 VA / Linear foot = 12000 VA

12 KVA Show Window + 21 KVA General Lighting Loads = 33 KVA (33000 VA)

33 KVA ? 2400 VA (120V 20 Amp Circuit) = 13.75

Minimum of (14) 20 Amp Circuits.

Scott

Strange how you used 3.5 va for the lighting load, and didn't do the 1.25 for the show window for continuous load, but it still came out the same?

 

[jwnelson1]

Apparently the author of the question assumed the lighting to be 120V but he did not specify so. The lighting could be 240V, thus 7 could be the minimum number of 20A two-wire circuits. Last time I checked 7 is less than 14

The question did not specify 120 or 240 just a 120/240 circuit is used. You are correct, I would assume general lighting to be 120 for this type of question unless other wise specified. I am horrible with the math portions of load calculations and have been practicing to get better. All the comments and help that you and others provide greatly helps me out.:grin:

 

[scott thompson]

Smart $,

* Regarding the Voltage for Lighting:
Yes, you are correct. The OP does not indicate the Voltage of Lighting Fixtures; so in this scenario the Voltage may be 120V or 240V.
If there is an SDS, there are at least two more!

For a "Simple" reply, I figured L-N Loads for the General Lighting + Show Window Lighting, with the L-N Voltage being 120V.

Also neglected to verify the L-N Loads will be applied across ?A to N, & ?C to N; as the Voltage to Ground on ?B will be >200 VAC.

So, if the Lighting was connected L-L, the 2 Pole (240V) Circuits could be connected "A-B", "B-C", and "A-C", and as mentioned, (7) Single Pole Circuits would be result. This will be (4) 2 Pole Breakers minimum.

We might even go as far as connecting Lighting to 3 Pole Circuitry, using a given Line as a Common.
That scenario adds another choice to the topic!


Hurk27,

Article 220.14(G), and 220.43(A) does not indicate LCL for Show Window Lighting, although I would figure it as LCL on any Project with Show Window Outlets!

To achieve an answer relevant to the one favored on the exam, I applied LCL to the General Lighting Loads only, and figured Show Window Lighting at 100%.

Scott

 

[Smart $]

...

So, if the Lighting was connected L-L, the 2 Pole (240V) Circuits could be connected "A-B", "B-C", and "A-C", and as mentioned, (7) Single Pole Circuits would be result. This will be (4) 2 Pole Breakers minimum.

The OP stipulates two-wire 20A branch circuits. It would be (7) two-pole breakers, minimum. You cannot get (7) 20A 240V branch circuits from (4) 20A two-pole breakers (and be compliant).

We might even go as far as connecting Lighting to 3 Pole Circuitry, using a given Line as a Common.
That scenario adds another choice to the topic!

Afraid not. Again, the OP stipulates two-wire 20A branch circuits. What you propose would be a three-wire circuit.

That aside, 3? wiring of lighting banks typically do not use a common line. The loads are connected in balanced fashion: A-B, B-C, and C-A. As such, the minimum number of circuits would be: 33000VA ? 240V ? 1.732 ? 20A = 4 circuits (3-pole breakers)

Hurk27,

Article 220.14(G), and 220.43(A) does not indicate LCL for Show Window Lighting, although I would figure it as LCL on any Project with Show Window Outlets!

To achieve an answer relevant to the one favored on the exam, I applied LCL to the General Lighting Loads only, and figured Show Window Lighting at 100%.

Scott

I think hurk's main point is that you used 3.5VA/ft? instead of 3VA/ft? listed for Stores in Table 220.12. Had you used 3VA/ft? and not factored in the show window as continuous as you did, you would have totaled at only 12.5 circuits.

Hindsight is generally not available during testing

 

[RB1]

According to my calculation 15 circuits are required.

14,400 * 125% = 18,000/2400 = 7.5 for Gen Illumination
12,000 * 125% = 15,000/2400 = 6.25 for show windows

Because the question asked about numbers of branch circuits and not feeder load, wouldn't you need to round up to the next whole number for each category?

 

[drbond24]

According to my calculation 15 circuits are required.

14,400 * 125% = 18,000/2400 = 7.5 for Gen Illumination
12,000 * 125% = 15,000/2400 = 6.25 for show windows

Because the question asked about numbers of branch circuits and not feeder load, wouldn't you need to round up to the next whole number for each category?

7.5 + 6.25 = 13.75

Rounds up to 14.

 

[RB1]

7.5 for general illumination rounds up to 8. 6.25 for show window rounds up to 7. Therefore 8 + 7 = 15. You're not combining the circuits are you?

 

[Smart $]

7.5 for general illumination rounds up to 8. 6.25 for show window rounds up to 7. Therefore 8 + 7 = 15. You're not combining the circuits are you?

There is no requirement to keep circuits dedicated to the type of load.

 

[RB1]

I didn't know that you could combine the calculation methods listed in 220.10 and apply it to a single branch-circuit. Very interesting.

 

[RB1]

In order for the load to be evenly distributed among the general illumination circuits as required by 210.11(B), which general illumination circuit(s) would supply the show window?

 

[Smart $]

I didn't know that you could combine the calculation methods listed in 220.10 and apply it to a single branch-circuit. Very interesting.

Article 220 is regarding calculations. Application of the calculations is handled in other articles. For example, the minimum number of branch circuits required falls under 210.11.