ELECTRICAL LEVEL 3 MODULE 1 LOAD
CALCULATIONS AND BRANCH FEEDER
CIRCUITS EXAMINATION SCRIPT 2026
◉ size thhn recommended for a non-contiuous load with 130' of
single phase, 23a, 240v? Answer: vd = 2 x L x r x i / circular mils
vd = 2 x 130' x 12.9 x 23a / 10380 no.10 wire
vd = 7.43v / 240 = 0.031
0.031 x 100 =3.10%
need to size up to no.8 wire
◉ size thhn wire is recommended for a 240v, 3 wire circuit with 3
fixed 240v loads of 30a at 60', 30a at 80', and 20a at 100'? Answer:
determine load center length
60' x 30a = 1800
80' x 30a = 2400
100' x 20a = 2000
sum of loads = 80a
sum of products = a = 77.5 load center length
,310.15b16 no. 4 thhn wire for 80a is selected, now check for voltage
drop
vd = 2 x L x k x I / cm
vd = 2 x 77.5' x 12.9 x 80a / 41740
vd = 3.8v
240 x 3% = 7.2v so no.4 wire is permissible
◉ voltage drop of 208v, 3 phase, 32a load, 115' using no. 8 stranded
wire? Answer: vd = √3 x L x r x I / 1000
vd = 1.732 x 115' x 0.778 x 32a / 1000
vd = 4.96v
208 x 3% = 6.24v so no.8 stranded is permissible
◉ size thhn wire is recommended for a 208v, 3 phase, with 150' and
160a load? Answer: determine minimum ampacity required by
multiplying 160a x 125% to obtain 200a.
310.15b16 3 aught wire, no check voltage drop
vd = √3 x L x k x I / cm
vd = 1.732 x 150' x 12.9 x 160a / 167800
vd = 3.2
208 x 3% = 6.24v so 3 aught wire is permissible
, ◉ ampacity of 120v single phase, load rated at 1600va? Answer:
1600va / 120v = 13.33a
◉ ampacity of 3450va load at 277v, single phase? Answer: 3450va /
277 = 12.45a
◉ ampacity of 5200va load at 208v, 3 phase? Answer: I = va / v x √3
I = x 1.732
I = 14.34a
◉ ampacity of a 14000va 3 phase load at 480v? Answer: I = 14000va
/ 480v x 1.732
16.84a
◉ ampacity of a 5.5kw, 240v single phase? Answer: 5.5kw x 1000 =
5500va
5500va / 240v = 22.92a
◉ ampacity of a water heater with nameplate rating of 20kw, 208v?
Answer: 20kw x 1000 = 20000
20000 x(208v x 1.732) = 55.52a
CALCULATIONS AND BRANCH FEEDER
CIRCUITS EXAMINATION SCRIPT 2026
◉ size thhn recommended for a non-contiuous load with 130' of
single phase, 23a, 240v? Answer: vd = 2 x L x r x i / circular mils
vd = 2 x 130' x 12.9 x 23a / 10380 no.10 wire
vd = 7.43v / 240 = 0.031
0.031 x 100 =3.10%
need to size up to no.8 wire
◉ size thhn wire is recommended for a 240v, 3 wire circuit with 3
fixed 240v loads of 30a at 60', 30a at 80', and 20a at 100'? Answer:
determine load center length
60' x 30a = 1800
80' x 30a = 2400
100' x 20a = 2000
sum of loads = 80a
sum of products = a = 77.5 load center length
,310.15b16 no. 4 thhn wire for 80a is selected, now check for voltage
drop
vd = 2 x L x k x I / cm
vd = 2 x 77.5' x 12.9 x 80a / 41740
vd = 3.8v
240 x 3% = 7.2v so no.4 wire is permissible
◉ voltage drop of 208v, 3 phase, 32a load, 115' using no. 8 stranded
wire? Answer: vd = √3 x L x r x I / 1000
vd = 1.732 x 115' x 0.778 x 32a / 1000
vd = 4.96v
208 x 3% = 6.24v so no.8 stranded is permissible
◉ size thhn wire is recommended for a 208v, 3 phase, with 150' and
160a load? Answer: determine minimum ampacity required by
multiplying 160a x 125% to obtain 200a.
310.15b16 3 aught wire, no check voltage drop
vd = √3 x L x k x I / cm
vd = 1.732 x 150' x 12.9 x 160a / 167800
vd = 3.2
208 x 3% = 6.24v so 3 aught wire is permissible
, ◉ ampacity of 120v single phase, load rated at 1600va? Answer:
1600va / 120v = 13.33a
◉ ampacity of 3450va load at 277v, single phase? Answer: 3450va /
277 = 12.45a
◉ ampacity of 5200va load at 208v, 3 phase? Answer: I = va / v x √3
I = x 1.732
I = 14.34a
◉ ampacity of a 14000va 3 phase load at 480v? Answer: I = 14000va
/ 480v x 1.732
16.84a
◉ ampacity of a 5.5kw, 240v single phase? Answer: 5.5kw x 1000 =
5500va
5500va / 240v = 22.92a
◉ ampacity of a water heater with nameplate rating of 20kw, 208v?
Answer: 20kw x 1000 = 20000
20000 x(208v x 1.732) = 55.52a
