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FAQ on UL Grounding Lugs and
Grounding Wire Pressure Connectors
UL Listed Lugs with Grounding Capabilities are labeled with the IEC grounding symbol.
Q. When building to NEC codes what kind of grounding lug or wire connector can I use?
A. NEC NFPA70 Article 250.8 connection of Grounding and Bonding equipment, states:
(A) Permitted Methods. Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one or more of the following means:
(1) Listed pressure connectors
(2) Terminal Bars
(3) Pressure connectors listed as grounding and bonding equipment
(4) Exothermic welding process
(5) Machine screw type fastener that engage not less than 2 threads or are secured with a
(6) Thread forming machine screws that that engage not less than two threads in the
(7) Connections that are part of listed assembly
(8) Other listed means
Author Comment (1) UL486A-B ZMVV (2) UL1059 Listed Terminal Blocks (XCFR2) (3) UL467 KDER
Q. What is a “Listed Pressure Connector”
A. Most commonly, a “Listed pressure connector” is a wire connector that is UL Listed to Standard UL486A-B category guide ZMVV Listed for General Use
Typically, Dual Rated for both copper or aluminum wires.
Q. Can I use a ZMVV2 UL Recognized (not ZMVV Listed) wire connector for grounding?
A. Only after further UL investigation for the mounting means and probably other “Conditions of Acceptability” that are defined in the ZMVV2 Recognized file and with more delay and added evaluation cost. That is not normally considered worth the trouble if a Listed ZMVV wire pressure connector is available.
Q. So if I use UL486A-B Listed ZMVV connectors I avoid all that extra review and cost?
A. Yes, UL486A-B LISTED ZMVV wire pressure connectors are treated as having been fully evaluated for grounding use (in dry locations like electrical cabinets) when mounted in the manner they were clearly intended (typically bolted).
Q. I see some grounding bars that are UL listed under UL467 category KDER, what is that all about?
A. Yes there are two standards that are used to List wire grounding and bonding equipment UL486A-B (ZMVV) and UL467 (KDER)
UL486A-B is a very exhaustive standard of testing since connectors are tested for full continuous and cycling power use including a 500 cycle over current test and a default 10,000 SCCR rating.
UL467 testing is subjects the device to a one-time current rush test mimicking a single short term shorting to ground situation.
Both are considered to be adequately tested for the purpose of grounding wires under UL and NEC.
Q. UL467 is a standard for “grounding and bonding” whereas UL486 is for “wire connectors”, what does UL say about the use of UL486 wire connectors for grounding?
A. This is the UL sensible rationale for the UL486 Listed ZMVV being the most common grounding lug used for grounding applications and being “grandfathered in” as a natural extension of proven wire connector technology for grounding, as well as power use.
From: Osborne, Robert D.
Sent: Friday, June 26, 2015 2:54 PM
Subject: RE: ZMVV Ground lugs versus KDER ground lugs
The ZMVV connectors do undergo additional heating tests, since they are current carrying. On the other hand, the KDER product undergo short-time current tests – so the test programs have differences. For the Code, the idea is that a KDER product is tested to carry the fault current, not operational (“normal”) current. It shouldn’t see current flow, except under a fault condition, so no need for it to pass a Heating or Heat Cycling test. The ZMVV product is not subjected to the short-time current test, but is subjected to the Heating Tests, as it is the connector used in the circuit that is carrying operations current. Since it is in the circuit, it also carries the fault current during a short circuit event. So if it has to carry the fault current in the ungrounded circuit, it can also conduct this fault current if it’s installed in the ground-reference circuit.
Hopefully this makes sense. Feel free to direct the customer to me if they have additional questions.
Robert D. Osborne
Distinguished Member of Technical Staff
Energy & Power Technologies
12 Laboratory Drive
RTP, NC 27709-3995 USA
Q. Can I use a KDER, UL467 wire connectors for power use like a current carrying neutral bar or power distribution bar?
A. No. The more limited testing (short term current spike) with no long term power testing means that power use is not permitted since there is no testing for current carrying longer than a single spike.
Q. So if I want to buy and stock one part to use both in the power side of my electrical cabinet and the grounding requirements, the UL486A-B ZMVV Listed wire connectors is the way to go?
A. Yes. One part does it all and these typically Dual Rated parts (see connector UL label) are able to take both copper and aluminum wire.
Q. UL486A-B covers mechanical (screw type) wire connectors and crimp tool tube type connectors, but not twist on wire splicers which are UL486C. Are all these permitted for ground use if they are ZMVV Listed wire pressure connectors?
A. Yes, if you check carefully for the ZMVV Listing under UL486A-B (not just “Listed” and not ZMVV2 Recognized) and use according to the product labeling and other codes.
Q. What does UL508A (Industrial Control Panels) say about Grounding wire connectors?
A. This broad umbrella standard chooses the gold standard wire connector standard UL486A-486B for wire pressure connector lugs.
14.2 An Industrial control panel shall be provided with a field wiring terminal for the connection of an equipment grounding conductor. The terminal shall comply with:
a) The component requirements of a field wiring terminal in accordance with Section 28, Field Wiring: or
b) The requirements in the Standard for Grounding and Bonding Equipment, UL 467.
28.2.2 A pressure wire connector of a component other than a terminal block shall:
a) Comply with the requirements in the Standard for Wire Connectors, UL 486A-486B or the Standard for Equipment Wiring Terminals for Use with Aluminum and/or Copper Conductors, UL 486E; and single and multi-pole terminal blocks in plastic use UL1059 (XCFR2) to evaluate the assembly and UL486 to evaluate the metal wire connector lug within.
The Standard UL508A provides a list of standard panel “building blocks” for components that may be used in UL rated electrical panels. The UL Category control number is very useful in determining which “off the shelf” Listed components qualify because it avoid unneeded “follow up” evaluation costs for the panel builder. There is much confusion about UL486A-B wire pressure connectors since they may be UL Listed ZMVV “UL” or UL Recognized ZMVV2 “UR”. You can see that the UL508A paragraph 28.22 SA1 table specifically states category code ZMVV for the “Listed Pressure Wire Connectors”. This use of ZMVV “Listed” UL486A-B Wire Connectors builds on the notion that they are intended for “General Use” and do not have the extra follow up services needed for only ZMVV2 UL Recognized wire connectors.
Q. What does UL508 (Industrial Control Equipment) say about the UL standards for Pressure Wire Connectors?
A. Again you see the “gold standard” UL486A-B standards for wire connections.
25.5.16 Relocated as 25.5D.2 December 12, 2002
25.5A Evaluation of pressure wire connectors
25.5A.1 A field-wiring pressure wire connector provided with or specified for use with industrial control equipment shall comply with one of the following, as applicable:
a) The performance requirements in the Standard for Wire Connectors, UL 486A-486B; or
b) The performance requirements in the Standard for Equipment Wiring Terminals for Use With Aluminum and/or Copper Conductors, UL 486E.
Q. Why does UL508 and UL508A allow use of UL486E as well as the “gold standard” UL486A-486B?
A. UL486E has a concession in that permits much lower wire pull out and secureness standards than UL486A-B has, in exchange for a verified wire strain relief built into the panel or casing to avoid wire strain being felt by the wire connector inside.
Q. Do grounding wire pressure connectors have to be green?
A. No, typically a grounding wire pressure connector may be clearly identified using nearby labels or markings with the grounding sign or words or abbreviations, in lieu of being green.
UL508 and UL508A permit if “plainly identified” with the marking “GROUND”, GROUNDING”, “G”, “GR”, “GRD”, “GND”, GRND” or the like, or IEC publication 417 symbol 5019 or Green/ Yellow bicolor labeling or plastic color.
Green/Yellow Bicolor Labeling or Plastic Color
IEC publication symbol 5019
Note that if a connector IS green or otherwise marked in any way to indicate “grounding” use it MUST be used for grounding and not any other use such as power.
References: UL LLC, NEC CODE, NFPA.
Please find more information at ULStandards.com and NFPA.org
This general information is provided as an introduction only. There are many requirements, national, local, and other codes and AHJ’s (Authority Having Jurisdiction) which might impact on the final approvals.
This information is provided for educational use only and no claims are made for its completeness, accuracy, and may not be updated.
IHI thanks Robert Osbourne and George Davis for help in compiling this information
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