64
7X24 MAGAZINE FALL 2014
MDCs may be listed and labeled,
in which case, all factory-installed
equipment and wiring would be
certified under the listing
procedures. Listed MDCs are
only required to comply with
certain sections under Article
646; however, any field-installed
components would be subject to
full NEC compliance. The UL
2755
Outline of Investigation for
Modular Data Centers
is one way
to identify specific listing
requirements. MDCs that are not
listed must comply fully with
Article 646.
MDCs are permitted to use the
alternate, less stringent wiring
methods in Article 645 (646.3(L).
An approved disconnecting
means (i.e. EPO) is
required to
disconnect power
to all
electronic equipment and
dedicated HVAC systems
(646.3(N)). A nameplate is also
required on each MDC enclosure
that identifies the information
listed in 646.5 which includes the
full load current and short circuit
rating. The supply conductors
shall be sized at not less than
125% of the full load current
listed on the nameplate.
Flexible power cords and cables
that are listed for extra-hard
usage are permitted to be used
for interconnecting separate
MDC enclosures (646.9(A)).
However, they may not be used
for connecting an MDC to an
external power source, such as a
building electric service
(646.9(B)).
Workspace requirements for
MDCs must comply with 110.26,
which is the same for all
traditional data centers (646.18).
MDCs containing equipment
greater than six-feet-wide or
deep require one entrance to,
and egress from, the working
space (e.g. two doors),
regardless of the ampere rating
of the equipment (646.19).
Workspace requirements also
apply to low-voltage circuits
rated above 30 volts-rms, 42
volts-peak, or 60 volts-dc
(646.20).
summary
There are many new changes in
the 2014 NEC that will impact
data center designs and costs.
Standard designs will need to
change and the effect on costs
and equipment delivery times
will need to be determined.
The NEC is a consensus standard
that must be adopted at the state
level, often with amendments,
before it becomes enforceable.
More than half of the states have
adopted or are in the process of
adopting the 2014 NEC. The
following website tracks NEC
adoption
/state-adoptions.aspx.
Centercore Modular Data
Center in Omaha, NB
Centercore Modular Data
Center in Omaha, NB
Dennis R. Julian PE, ATD, DCEP is Principal A/E Design Services at Integrated Design Group Inc. He can be reached at
