I've been asked to upgrade a service from 800 to 1200 amps. It has (2) 3-1/2" conduits routed underground and under a parking lot from the utility transformer. The contractor suggested we try to pull the new 1200 amp conductors int he existing (2) conduits. I've tried but cant seem to find the magic combination including derating the neutral.
Any suggestions?
Thanks!
Sparky
Not that I am a big proponent of this type of install it is allowed...
230.90 Where Required. Each ungrounded service conductor
shall have overload protection.
(A) Ungrounded Conductor. Such protection shall be provided
by an overcurrent device in series with each ungrounded
service conductor that has a rating or setting not higher than
the allowable ampacity of the conductor. A set of fuses shall
be considered all the fuses required to protect all the ungrounded
conductors of a circuit. Single-pole circuit breakers,
grouped in accordance with 230.71(B), shall be considered as
one protective device.
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 conductors.
Using the code section above and also assuming you have multiple service disconnects you could size your service entrance conductors to the calculated load which may give you the wiggle room you need.
Pete