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 IAEI News>Focus on the Code >CMP-9
Question
1. The practice of using switch disconnect enclosures
as wiring gutters or splice boxes could be circumvented
if the wording of 110.59 [NEC 2002] could be
inserted for installation of equipment of less than 600
volts. I will have to use convoluted reasoning to arrive
at the result, unless the Code has a forthright
statement, such as 110.59, to ease the task. — W.H. Answer 1. If I
understand the question, the reader is asking that the words “unless
special designs are used to provide adequate space” should be added for
switch enclosures under 600 volts. Switch disconnect enclosures are covered
by Article 404. Section 404.3(B) states, “Enclosures shall not be used as
junction boxes, auxiliary gutters, or raceways for conductors … unless the
enclosure complies with 312.8.” Section 312.8 allows enclosures to be used in this
manner when the conductors do not fill the wiring space at any
cross-sectional area to more than 40 percent of its cross-sectional area of
the space and 75 percent if splices and taps are present. Enclosures are
generally intended to accommodate only those conductors that will be
connected to the switches and overcurrent devices; but additional conductors
passing through the enclosure can meet the present Code. If the
suggested language were added to 312.8, this would limit the use of the
disconnect switch enclosures. A testing laboratory would need to list
special design enclosures to the size of the conductors and the location
where the space is adequate for the conductors to be installed. Keep in mind
that the language in 110.59 is very limited. It covers only switch
enclosures over 600 volts in tunnels. The present language allows the
installer more options in designing the installation. One needs to have the
knowledge to calculate the cross-sectional area and fill to assure the rules
of this article are complied with. I
believe the Code is very clear and workable to the installers at
present. — Don Offerdahl, CMP-9 | Return
to top | Question
2. I have a question about box fill. For example,
if you used a wirenut on metal boxes to join the grounded
conductor, all grounds would be counted as one based on the
largest conductor. What would happen if you were to use a
green screw in the back of the box (do not forget it is a
metal box) or one of those green clamps that slide over the
side of the box? Is this considered a clamp and an additional
amount must be added? — A. K. Answer 2. Section
314.16(B) covers box fill and subdivision 5 covers the
equipment grounding conductors. In the question you refer to
grounding clamps that slide over the side of the box. These
are grounding clips and not clamps, so would not be covered in
paragraph 2 where it refers to cable clamps. These clips,
along with the grounding screw, do not take up a lot of space
as do the other items that are covered by this section, so I
do not think it was the intent of the Code to count
this item in the calculation for box fill. — Don Offerdahl,
CMP-9 | Return
to top | Question
3. Article 314.23 states that enclosures
shall be supported in accordance with one or more of the
provisions in 314.23(A) through (H). There is language within
the section that refers to "rigidly
supported." The question is, does the installation
of a 4-inch metal outlet box on a single metal stud
meet the intent of being rigidly mounted? Or, is there a
requirement for additional bracing? For discussion
purposes, the specific box I reference is a 4-inch square
metal outlet box manufactured by RACO (Hubbell) with an
integral FM bracket. — C. P. Answer 3. Your
specific box reference of a 4-inch square metal outlet box
manufactured by RACO with an integral FM bracket, for the
readers who aren’t familiar with FM bracket, is a box that
has a side bracket that secures the box to the side of a
2" x 4" wood or metal stud. When this box with bracket is used on the
2" x 4" wood stud, it provides a rigid support
method. When it is used on a metal stud, the box does not
become rigid until after the sheetrock is applied. Care is
needed by the sheetrock installer to properly cut the
sheetrock to accommodate the box. If the sheetrock installer’s
cut is off, the metal stud and box will move and leave the box
not as secure as it could be. I believe the Code has
left this up to the authority having jurisdiction to determine
if the boxes are securely fastened in place. If the authority having jurisdiction feels
that the boxes are not securely fastened in place, they could
ask for additional support as pointed out in 314.23(A). —
Don Offerdahl, CMP-9 | Return
to top | Question
4. Is a mini breaker (a single 20–15 amp
breaker) counted as one or two devices per 384-15? I have seen
many of them used and perhaps exceeding the allowable number
of overcurrent devices if counted as two. It is a single-pole
breaker, but since it has two means of disconnects perhaps it
should be counted as two. — C. R. Answer 4. Let
me start out by pointing out that Article 384 in the NEC 1999
was changed to Article 408 in the 2002 Code. Article
408 covers all switchboards, panelboards, and distribution
boards installed for the control of light and power circuits.
There are two definitions of panelboards. They are a
power panelboard, which is one having 10 percent or fewer of
its overcurrent devices protecting lighting and appliance
branch circuits. A lighting and appliance branch-circuit
panelboard is one having more than 10 percent of its
overcurrent devices protecting lighting and appliance branch
circuits, which you are referencing in your
question. In 408.15, it states a two-pole circuit
breaker shall be considered two overcurrent devices.
With that statement it points out that overcurrent devices are
counted rather than pole spaces. It is important when
installing breakers in panelboards to check the panelboard
instructions and to select the manufacturer’s breakers that
are approved for that particular panelboard but in no case is
it permissible to use more than 42 overcurrent devices in a
panelboard other than those provided for the main overcurrent
device. — Don Offerdahl, CMP-9 | Return
to top | Question
5. This question relates to the allowable number
of overcurrent devices in a lighting and appliance panelboard.
UL 67 restricts the number of overcurrent devices to one per
pole per 10 amperes for the service. Given this, a 100-ampere,
120/240-volt, single-phase, three-wire residential panel would
be limited to 20 overcurrent devices. If a contractor
installed twin (piggyback) breakers, it would be possible to
have up to 40 breakers (although only 20 devices) in the
panel. If this were done, would this be Code-compliant?
For the purposes of counting the number of allowable
overcurrent devices, are these twin (piggyback) breakers
counted as one or as two breakers? If we see such a panel with
20 piggyback breakers, is this installation Code-compliant? — K.C. Answer 5. Article
408 covers switchboards and panelboards. Section 408.15 tells
us that not more than 42 overcurrent devices can be installed
in lighting appliance panelboards. As we look further,
the last paragraph indicates that "a 2-pole circuit
breaker shall be considered two overcurrent devices; 3-pole...
considered three overcurrent devices," which
would indicate that a twin piggyback breaker has two
overcurrent devices. As for the 10 amps per pole, I
checked with UL and they indicated the sections of UL 67
that you are referencing were removed five years ago during a
revision of the standards. That section was more or less
a rule of thumb when split-buss panelboards were frequently
used. The panelboard instructions indicate the type and number
of overcurrent devices. Some panelboards have restriction
features built into them that limit the half size breakers
that may be installed. The twin breakers have rejection
features that will not permit them to be installed in the
panelboard except in the non-restricted portion of the
panelboard. If the installer has followed the instructions on
the listed panelboard, the installation should be Code-compliant.
— Don Offerdahl, CMP-9 | Return
to top | Question
6. My question is about a lighted switch and what the Code says about current flow through the switch in the
lighted position. Is there any concern about the amount of
current that may flow around an open switch as that current is
the amount that would flow through the light bulb that is
lighting the switch? In a specific case, an amount of 15–20
mA may flow through an external light to illuminate the switch
when it is in the off position (but not enough to energize
major lighting). — M. F. Answer 6. In
reference to a lighted switch, please check out Article 100,
Switching Devices, Section 404.15, and UL 20 for snap
switches. Using this information and after talking to UL, I
see no violation if the switch is not marked off and on. My concern is with 15–20 ma current flow;
this is high, too high. 1.5–2.0 mA is more in range and
would not cause a hazard. Hope this helps. — Joseph
Bolesina, CMP-9 | Return
to top | Question
7. What is the maximum hole diameter tolerance
allowed in 480-volt and greater switchgear or cabinets for
safe operation? This would be for both OEM level and
retrofit. — C.O. Answer 7. In
review, the National Electrical Code addresses the
maximum hole diameter allowed in a 480-volt and greater
switchgear. Section 110.12(A) states that unused openings of
cable or raceway shall be effectively closed. Section
110.13(A) covers mounting of the electrical equipment and (B)
covers cooling of electrical equipment. UL 891 dead-front
switchboard is the category in which this equipment is listed.
UL 891, 8.5.3 states that an enclosure, when completely
assembled, shall have no opening other than ventilation
opening that will permit the entrance of a .125 inch diameter
rod. If the distance between an opening and the nearest live
part is more than 4 inches, the opening shall not permit the
entrance of a rod having a diameter greater than 0.5 inch. If
the voltage is over 600 volts, 110.31(B) and (D) state
ventilating or similar openings shall be designed so that
foreign objects inserted through these openings are deflected
from energized parts. If this equipment is listed using UL
891, the manufacturer will have to adhere to these opening
requirements. — Don Offerdahl, CMP-9 | Return
to top | Question
8. Is there a minimum height at which a 220-volt
subpanel can be placed? I have reviewed the NEC and could not find a reference to the minimum height, but
the building inspector says that it is implied in the Code that the panel should be installed at shoulder
height. Our panel was installed at about 3 feet above the
ground and the contractor says that it is safe and according
to Code. Please let me know who is correct. —
S. H. Answer 8. Your
question is asking for the minimum height of subpanels.
Switchboards and panelboards are covered in NEC-2002 in
Article 408. This article does not cover any requirements for
the minimum height of the installation of a switchboard or a
panelboard. Sections 408.6 and 408.17 refer to 312.2(A) if the
switch or panelboard are installed in damp or wet locations.
Section 312.2(A) states that the enclosures need to be
designed for the environment in which they are going to be
installed. If installed in a damp location, the enclosure
shall be placed or equipped so as to prevent moisture or water
from entering or any accumulating within the enclosure. If the
enclosure is installed in a wet location, it needs to be
weatherproof. If the panel is a disconnecting means for a
mobile or manufactured home or recreational vehicle (RV), the
requirements are found in 550.32(F) and 551.77. The
requirement states that the bottom of the mobile home or RV
enclosure containing the disconnecting means is not less than
2 feet above the finished grade, so keep in mind that the Code is not a design manual but requires minimum standards for
hazards to life or property. — Don Offerdahl, CMP-9 | Return
to top | Question
9. My question is about a lighted switch and what
the Code says about current through a switch in the
lighted position. Is there any concern about the amount of
current that may flow around an open switch, as that current
is the amount that would flow through the light bulb that is
lighting the switch? In a specific case, an amount of 15–20
mA may be present through an external light to illuminate the
switch when it is in the off position, which is not
enough to energize major lighting. — M. F. Answer 9. Your
question on the amount of current that would flow on a lighted
switch is not covered specifically in NEC-2002. This is
why Section 110.3(B) is so important. Enforcing the Code without the testing and listing of an electrical product’s
use leaves a big gap in supply. General use snap switches are
attested under UL-20. That standard will accept a current flow
of 0.5 mA which can be used to illuminate the switch handle.
As always, install and use the device in accordance with how
it was listed.—Don Offerdahl, CMP-9 | Return
to top | The views of the authors of Focus on
the Code and the editor are provided solely as a public service. |
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