Maximum allowed

[nickelec]

This maybe a stupid question and after a while in the industry I still fully don't understand something maybe someone can give me some clarification in laymen's terms, let's say I have an 800 amp MDP being ved via 2 sets of 500mcm with 4 200a switches . And I installed 4 200a 3 phase 40ckt MLO panels .Assuming there's no additional loads . In my eyes each set is capable of carrying 800 amps not 800a equally devided between the 3 phases. how many 2 pole 30s could I put my math says 80.

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[Smart $]

In general, OCPD ratings and conductor ampacities are based on the Article 220 calculated load. That calculation commonly permits the application of demand factors which reduce the result. That is, the sum of all connected loads is typically greater than the calculated load. Code requires the OCPD ratings equal or exceed its connected load. So when you sum up all the OCPD ratings, branch and feeder, at any particular level of distribution, the sum can easily exceed the connected load.

 

[Ingenieur]

Each 200 can carry 200 x 480 x sqrt3 = 166.3 kva
a 30/1 is 14.4 kva
panel can handle 166.3/14.4 = 11.5
assume 11
ab 4 30/1 cb's
bc 4
ca 3
a leg gets 210 A ((4+3) x 30)
b 240
c 210
too much

200 A per lug / (30 A per leg x 2 legs) = 3.33, rnd to 3
ab 3 30/1 cb's
bc 3
ca 3
a leg 180
b 180
c 180

9 per panel 130 kva 80% loaded
36 total

 

[Smart $]

Each 200 can carry 200 x 480 x sqrt3 = 166.3 kva
a 30/1 is 14.4 kva
panel can handle 166.3/14.4 = 11.5
assume 11
ab 4 30/1 cb's
bc 4
ca 3
a leg gets 210 A ((4+3) x 30)
b 240
c 210
too much

200 A per lug / (30 A per leg x 2 legs) = 3.33, rnd to 3
ab 3 30/1 cb's
bc 3
ca 3
a leg 180
b 180
c 180

9 per panel 130 kva 80% loaded
36 total

200A × 480V × sqrt(3) ÷ ((30A × 80%) × 480V) = 14.4 circuits max, best balance 12 per 200A panel

200A × 480V × sqrt(3) ÷ ((30A × 75%) × 480V) = 15.4 circuits max, best balance 15 per 200A panel


Of course, we are making a major assumption of 75 or 80% loading. Code requires using the actual load.

 

[Ingenieur]

15 30/1 per 200 lug panel loaded to 75% or 22.5 A or 10.8 kva per ckt
162 kva / 166 kva = 97% loaded
what i does each lug carry?

 

[Smart $]

15 30/1 per 200 lug panel loaded to 75% or 22.5 A or 10.8 kva per ckt
162 kva / 166 kva = 97% loaded
what i does each lug carry?

162kVA ÷ 480V ÷ sqrt(3) = 195A

Compliant if the load is noncontinuous.

 

[jumper]

You guys realize those pairs of 500s are only good for 760A.

 

[Smart $]

You guys realize those pairs of 500s are only good for 760A.

I do, and I thought about it prior to my first reply in this thread. Got sidetracked. Glad you brought it up because the total load cannot exceed 760A.