Nec 230.42 & 240.4(c)

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rickjus

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Is the following a violation to the referenced articles?

- 1,600 AMP, 3-Phase, 4-Wire, 277/480 V service.

- Feed from transformer to main disconnect: (4) parallel runs of 4 # 500 KCMIL ? 4? C.

- Computed load is less than 1,520AMPS.
 
Does your service have a 1600 amp single disconnect or does it have multiple mains (up to six)?

Pete
 
LarryFine said:
Is that because you have to add areas and not ampacities?
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4 times 380 equals 1520
A 1600 amp main

240.4(C) Devices Rated Over 800 Amperes. Where the overcurrent device is rated over 800 amperes, the ampacity of the conductors it protects shall be equal to or greater than the rating of the overcurrent device defined in 240.6

240.6 240.6 Standard Ampere Ratings.
(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600.

These conductors would need to be protected with not more than 1200 amp Overcurrent device
 
Mike,
I agree with you however I was told that 240.4(C) does not apply to services as the wire is on the line side of the overcurrent protection device.

So I quoted 230.42(B) of which I was told it refers to 230.79(A) through (D) which references residential installations and not commercial installations.

IMO those conductors need to be 600KCMIL as the 4" C is in the ground already. Just having a hard time justifying it.
 
If the (4) sets of 500KCM are owned by the POCO, then there is nothing forcing them to follow the NEC. They have their own rules (probably the NESC) to follow.

On the other hand, say the transformer and the (4) sets of 500KCM are owned by a industrial plant. Then the the conductors are then feeders, and the tap rules would apply. Probably 240.21(C)(4). No matter which tap rule you use, I think you will find you have to terminate the feeders with OCP that limits the current to the ampacity of the conductors. In other words, you need the full 1600 amps of wire. In fact, even if this were under 800A, you couldn't use the next size larger breaker. A single set of 500KCM wire could only be protected at 380 amps or less, not 400 amps.

Steve
 
Steve,
Good point, however in this situation the conductors are not owned by the POCO.

However, you lost me with the part about still not being able to use 500KCMIL if we are 800A or lower? This transformer is a utility transformer and not a dry-type.
 
Looking at 230.42(b)

(B) Specific Installations In addition to the requirements of 230.42(A), the minimum ampacity for ungrounded conductors for specific installations shall not be less than the rating of the service disconnecting means specified in 230.79(A) through (D).

The basic rule in 230.42(B) requires ungrounded service conductors to be sized large enough to carry the calculated load and to have an ampacity not less than the minimum rating of the service disconnecting means required by 230.79(A) through 230.79(D).



230.79 Rating of Service Disconnecting Means
The service disconnecting means shall have a rating not less than the load to be carried, determined in accordance with Article 220. In no case shall the rating be lower than specified in 230.79(A), (B), (C), or (D).

(D) All Others For all other installations, the service disconnecting means shall have a rating of not less than 60 amperes.


230.79(d) as I see it, applies to this 1600 amp disconnect. I agree that 230.79(c) applies to a residential application, but the rest of 230.79 applies to all other installations whether residential or commercial.

I also believe that 240 would apply to the service conductors even though the OCPD will not provide overcurrent protection, It will provide overload protection for the conductors.

Pete
 
rickjus said:
Mike,
I agree with you however I was told that 240.4(C) does not apply to services as the wire is on the line side of the overcurrent protection device.
IMO those conductors need to be 600KCMIL as the 4" C is in the ground already. Just having a hard time justifying it.
Click to expand...

If you read 240.11 Scope there is nothing there that exempts you installation from complying with 240.4(C). I think you can stuff 600 kcm in 4" C.
 
bob said:
I think you can stuff 600 kcm in 4" C.
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Not a problem at all.

I just did four 500s and a 250 in 3" EMT.

I am all but certain four 600s of any 600 Volt insulation type will fit in any 4" raceway.
 
A single set of 500KCM wire could only be protected at 380 amps or less, not 400 amps.

Steve
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Why? If it's 800 amp or less and the connected load does not exceed the ampacity of the conductors then rounding up to the next standard size is permitted. This would apply to one set of 500kcmil with a 400 amp OCPD or two sets with an 800 amp OCPD.
 
steve66 said:
In other words, you need the full 1600 amps of wire. In fact, even if this were under 800A, you couldn't use the next size larger breaker. A single set of 500KCM wire could only be protected at 380 amps or less, not 400 amps.
Steve
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Steve you need to clear this up. 500 kcm terminating in a 400 amp breaker is done all the time. Of course the load could not exceed 380 amps.
 
rickjus said:
Ron, this is what I'm looking for, thanks. Would this also apply to SERVICES 800AMP and lower?
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I'm having a problem applying 230.90 to a single 1600 A Main.
are you trying to use exception 3 ( it applies when two or more ocpd are used)

Exception No. 3: Two to six circuit breakers or sets of
fuses shall be permitted as the overcurrent device to provide
the overload protection. The sum of the ratings of the
circuit breakers or fuses shall be permitted to exceed the
ampacity of the service conductors, provided the calculated
load does not exceed the ampacity of the service

Charlie
 
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