Download summary of requirements

June 7, 2006
SUMMARY OF REQUIREMENTS
The following is a brief summary of the new and revised paragraphs in the Standard for Standard For
Safety For Industrial Control Panels, UL 508A, which have a future Effective Date of March 1, 2007 and
the action that may be required to determine compliance.
Paragraphs
16.1, 16.2
16.3
17.4
29.2.1, 29.3.11
29.2.2, 29.6.2
General Subject and Comment
Grounding of power supply secondary circuits: The revisions may require
power supplies connected to a primary voltage greater than 150V to ground to
have their secondary circuit(s) grounded in accordance with 16.1 and 16.2.
Compliance with these requirements will be determined by UL inspection visits
following the effective date.
Slash rated components provided in secondary circuits: The new 16.3
requires the secondary circuit of a transformer or power supply to be grounded
consistent with the specific voltage requirements when components, such as
overcurrent protection devices, with slash voltage ratings are supplied in the
secondary circuit. This requirement applies whether or not the secondary
circuit is required to be grounded per 16.1. Compliance with these
requirements will be determined by UL inspection visits following the effective
date.
Color-coding of grounded circuit conductor: The revision causes
grounded circuit conductor(s) in the secondary of power supplies to be
identified by color in accordance the provisions in 17.4. Compliance with these
requirements will be determined by UL inspection visits following the effective
date.
Terminations for flexible internal conductors: Where flexible conductors,
including welding cable, flexible machine tool wires, and DLO cables, are
provided, terminals at both ends of the conductor must be suitable for use with
the conductor class. Manufacturers using flexible conductors after the effective
date must have terminals suitable for the purpose described in their follow-up
procedure. Compliance with these requirements will be determined by UL
inspection visits following the effective date.
Recognized component bus bars: The revisions permit use of previously
tested bus bar systems that may have increased ampacity and short circuit
current ratings as compared to the ratings allowed for bus bar assemblies that
meet the construction requirements in 29.2.2 and 29.6.2. Manufacturers
intending to use Recognized component bus bar assemblies must have all
parts, assembly requirements and electrical ratings described in their follow-up
procedure.
Subject No.
508A
Page 2 of 4
June 7, 2006
Paragraphs
General Subject and Comment
29.6.1, Table 29.1,
35.2.1.2, 36.2.4
Reduced ampacity for internal wiring of power circuits: The revisions
require Table 28.1 to be used for internal wiring ampacities; Table 29.1 has
been deleted. As a result, 16AWG and 18AWG conductors will no longer be
permitted in power circuits, 14AWG will be the minimum conductor size
allowed for power circuits. Manufacturers may need to modify existing
industrial control panel constructions so that power circuit conductors meet the
revised requirements following the effective date. Compliance with these
requirements will be determined by UL inspection visits following the effective
date.
38.2, 38.2.1, Table
38.1, 41.1, 42.1.2.2,
42.2.3.3, and 42.3.1
Ampacity of internal wiring of control circuits: The revisions require Table
28.1 to be used for internal wiring ampacities 14AWG and larger conductors.
The ampacities of conductors, 16AWG and smaller, in Table 38.1 are
unchanged. Manufacturers may need to modify existing industrial control panel
constructions so that 14AWG and larger control circuit conductors meet the
revised requirements following the effective date. Compliance with these
requirements will be determined by UL inspection visits following the effective
date.
31.4.1
31.4.3
31.4.4
Branch circuit protection for motor groups: The revised 31.4.1 may
require modification of the ampere rating of the motor group branch circuit
protection, or the ampacity of tap (power circuit) conductors, or both. Only
branch circuit type fuses and inverse- time circuit breakers are suitable as the
branch circuit protection for motor groups. Compliance with these
requirements will be determined by UL inspection visits following the effective
date.
Protection of tap conductors in motor groups: The new 31.4.3 will require
all motor tap conductors, i.e. conductors that carry current from a single motor,
to have an ampacity, per Table 28.1, that is coordinated with the overall size
(ampere rating) of the motor group. Manufacturers may need to modify existing
industrial control panel constructions by one or more of the following means: a)
increase the size of the tap conductors, b) reduce the number of loads in the
motor group, c) grouping loads having similar ampere ratings, or d) provide
additional protective devices. Compliance with these requirements will be
determined by UL inspection visits following the effective date.
Overcurrent protection for other (non-motor) loads included in motor
groups: The new 31.4.4 requires additional branch circuit protective devices
to be installed for non-motor loads in accordance with the requirements in 31.5
– 31.8 when the ampere rating of the branch circuit protection for the motor
group is too large to provide the required overcurrent protection. Compliance
with these requirements will be determined by UL inspection visits following
the effective date.
Subject No.
508A
Paragraphs
65.1
Page 3 of 4
June 7, 2006
General Subject and Comment
Revised requirements for industrial control panels marked for use with
industrial machinery:
1. Revised reference to 2002 edition of NFPA79.
66.1.1, 66.1.2, 66.1.4
2. Specific enclosure metal thickness and door width requirements have
been deleted. Enclosures that meet the requirements in section 18.3
of UL508A are acceptable.
66.1.3
3. Revision eliminates requirement for all enclosures to have a door.
Enclosures with covers may be used in accordance with the exception
to18.4 of UL508A. Revision adds specific travel requirement for
accessibility of components on or behind swing out panels.
66.1.5
4. Revision to 66.1.5 describes the conditions that require the enclosure
doors to be interlocked with the disconnecting means and that all
doors must be prevented from opening.
66.1.5.1
5. New 66.1.5.1 describes the requirements for operation of the interlock
defeat mechanism that were extracted from 66.1.5 and does not
change the current requirement.
66.1.6, 66.1.8
6. Requirements for lighting circuits have been combined into 66.1.8.
Panels containing internal maintenance lighting circuits or that supply
external work light circuits will be required to be protected by means
of 15A branch circuit protective device.
66.1.9
7. New requirement for mounting components to facilitate their
replacement. This requirement will prohibit components from being
mounted to a fixed sub-plate or sub-panel by means of a machine
screw and nut.
66.2.1
8. Revision will require physical arrangement of all control circuit
components, regardless of voltage, to be grouped or mounted
separately from all power circuit components.
66.2.2
9. New 66.2.2 will require grouping, separation or color coding of field
wiring terminals of power circuits, control circuits, and externally
supplied control circuits (yellow wire).
66.1.7, 66.3.1
10. Requirements for grounding internal maintenance lighting circuits and
external work light circuits have been combined into 66.3.1.
66.3.2
11. Revised 66.3.2 requires control transformer secondary circuits that
are not grounded to be provided with ground detection means.
66.3.4
12. New 66.3.4 requires a bonding conductor to be factory supplied
between the control panel enclosure and a door containing electrical
components operating at more than 30Vrms.
66.5.3
13. Revised 66.5.3 allows for additional color options for grounded circuit
conductors in power circuits.
Subject No.
508A
Paragraphs
66.5.4, Table 66.1A
Page 4 of 4
June 7, 2006
General Subject and Comment
Revisions for control panels for industrial machinery (continued)
14. Revision to 66.5.4 allows for 16AWG and 18AWG conductors to be
provided in power circuits when sized and protected in accordance
with Table 66.1A.
66.5.7
15. Revision to 66.5.7 requires power circuit conductors, 14AWG and
larger, to be sized based on ampacities from Table 28.1.
66.6.1
16. Revised 66.6.1 allows only terminals to be provided on the line side of
the disconnecting means. Other components cannot be installed on
the line side of the disconnecting means.
66.6.3
17. New 66.6.3 requires the disconnecting means to be readily operable,
and lockable in the “off” position independent of the position of the
enclosure door.
66.7.1
18. Revised 66.7.1 allows Class T fuses to be optionally used as branch
circuit fuse.
66.8.1
19. Revised 66.8.1 extends the application of the mechanical and
electrical interlock requirement to contactors of wye-delta controllers.
66.8.3, 67.3.2
20. New 66.8.3 requires the use of Listed robot controllers and marking
referring to the designated manipulator arm to be installed in the field.
66.9.1
21. Revised 66.9.1 allows orange as an alternate color-coding to yellow to
identify control circuit conductors that remain energized when the
main disconnecting means is opened.
66.11.1, 66.11.2,
Tables 66.5 and 66.6
22. Deleted Section 6.11 requirements for control transformer protection.
Control transformer overcurrent protection shall comply with Section
42.1.
66.12.3
23. Revised 66.12.3 requires emergency stop switches to be self-latching
or maintained position switch.
67.1.1
24. Revised 67.1.1 adds the ampere rating of the largest heater load to
the panel nameplate electrical ratings.
67.1.2, 67.1.3
67.4.1
25. Revised 67.1.2 and new 67.1.3 provides clarification of the location of
the existing marking requirements.
26. Revised 67.4.1 allows alternate cautionary markings to identify a
control panel enclosure containing electrical equipment.
The revisions and additions described in items 3, 4, 6 – 9, 11, 12, 15 – 17,
19,20, 23, and 24 above may require modifications of existing industrial control
panel designs that are marked for use with industrial machinery in order to
comply with the requirements on the effective date. Compliance with these
requirements will be determined by UL inspection visits following the effective
date.