Chapter Corner

Multi-Wire Branch Circuits

Posted in: Code Corner, January/February 2013

InsightsPicWireSpools.gifWhen the 2008 National Electrical Code (NEC) introduced 210.4(B) entitled "Disconnecting Means," this new requirement for multi-wire branch circuits drove many questions related to the application of handle ties in the industry. This requirement has also driven more use of field applied handle ties. The application of handle ties on two one-pole circuit breakers must be performed correctly as the lack of attention to details could cause you to apply the product outside of its rating. Two one-pole circuit breakers can be tied together with an approved handle tie but you must pay close attention to the markings and listing of the products to ensure that the breakers are not applied outside of their rating.

Shared Neutral Applications

The shared neutral application is familiar to many electrical contractors, especially in light of copper prices these days. Sharing the neutral on the home run circuit from the breaker to the first outlet can be one way of reducing material costs. Those applications where you would have pulled two two-conductor (+ ground) wires instead are pulled with a single three-conductor (+ ground) wire. Section 210.4 of the NEC addresses multi-wire branch circuits, noting that these circuits are those where all conductors originate from the same panelboard or similar distribution equipment.

An approved handle tie applied to two single-pole breakers for such applications as shared neutral installations ensures the installation meets the requirement of section 210.4(B), “Disconnecting Means,” of NEC 2011 which states:

(B) Disconnecting Means. Each multi-wire branch circuit shall be provided with a means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates.”

Section 210.4(B) does not require the breaker to disconnect all ungrounded conductors in the case of a trip. A breaker that operates such that only that pole which experienced the overcurrent trips, while the other doesn’t, is termed as an independent trip type of device. This section requires that when you turn the breaker to the off position, all poles are turned to the off position.

This is a safety requirement that ensures the first outlet box does not have energized conductors present. NEC 2008 introduced this new section as a result of Proposal 2-10 of the ROP document for NEC 2008. The submitter’s substantiation stated:

“Multi-wire branch circuits employing shared neutrals can offer unexpected shock hazards to electricians unless all ungrounded conductors from the multi-wire branch circuit are disconnected simultaneously. The safety concern associated with unintentional voltage being present on multi-wire branch circuits during maintenance is not always fully appreciated. An electrician may not know that a circuit is a multi-wire branch circuit when work begins. Even if aware of a multi-wire branch circuit, there is presently no requirement to identify and disconnect all ungrounded conductors of that multi-wire branch circuit. The present NEC correctly recognized this as a safety issue in 210.4(B) for the limited situation of ‘more than one device or component on the same yoke.’ While the use of multi-wire branch circuits is a valid use, it should be permitted only where a means is provided to disconnect simultaneously all ungrounded conductors of that circuit.”

Applying the Approved Handle Tie

InsightsPic_BreakrPnl.gifCare must be taken when applying an approved handle tie to two single-pole breakers in the field. As stated earlier, the practice of doing this was made easy due to the fact that most single-pole breakers you work with in residential systems are slash-rated. Sometimes the fact that most are slash rated can lead toward a violation due to not reading the labels. I guess this is a good example of the age old phrase, “familiarity breeds contempt.” Before you apply an approved handle tie, you must verify that the breaker carries the slash-rating for the application and ensure that the handle tie is approved for use on that breaker. The manufacture’s literature can be helpful and the label check is even easier.

There are single-pole breakers on the market that are not slash-rated. The Ground Fault Circuit Interrupter (GFCI) and Arc Fault Circuit Interrupter (AFCI) breakers are two examples. GFCI breakers provide a technical reason why the use of single-pole breakers in a shared neutral application with an approved handle tie is problematic. This is due to the fact that the breakers need all of the current that goes out on the hot to come back on the neutral. These devices act to trip the circuit if the current going out on the black wire (Hot) does not equal the current that comes back on the white wire (Neutral). Sharing the neutral with two GFCI breakers with this construction will result in instant tripping the moment a load on either breaker is energized.

Single-pole AFCI breakers on the market today, to the author’s knowledge, also carry a single voltage rating of 120Volts. Applying two 120V rated (NOT 120/240V) single-pole AFCI devices with an approved handle tie to serve shared neutral loads would be applying these devices outside of their rating. The bottom line for applying an approved handle tie to any pair of one-pole breakers is to check the label for the slash rating. Slash-rated breakers are available, even for GFCI and AFCI circuits.

Slash Ratings

The UL White Book, in the “Marking and Application Guide – Molded Case Circuit Breakers,” helps electricians understand the markings of circuit breakers. The “General” section, item 3 entitled “Voltage Rating” illustrates that all breakers are required to be marked with their voltage rating. This marking helps to ensure the proper application of these products - they must not be applied at a voltage outside of their rating. All UL 489 Molded Case Circuit Breakers are marked with a voltage rating chosen from the following:

DC Voltage Ratings: 60, 125, 125/250,160, 250, 500 and 600 volts.

AC Voltage Ratings: 120, 127, 120/240,240, 277, 347, 480Y/277, 480, 600Y/347 and 600 volts

This reference identifies the existence of breakers that can be designated with a single voltage rating or a slant (or slash) voltage rating. A circuit breaker that carries a single voltage rating is intended for use in circuits where the circuit voltage and the voltage to ground do not exceed the voltage rating of the breaker. A slash-rated breaker, such as 120/240V, is intended to be used in circuits where the circuit voltage does not exceed the higher of the two voltages and the voltage to ground does not exceed the lower of the two voltages.

This reference notes the following when it comes to a slash-rated breaker:

“Two-pole independent-trip breakers and single-pole breakers with handle ties that are rated 120/240 V ac have been investigated for use in line-to-line single-phase circuits or line-to-line branch circuits connected to three-phase, four-wire systems, provided the systems have a grounded neutral and the voltage to ground does not exceed 120V.”

A peek into UL 489 provides an understanding of what extra testing and requirements a slash-rated breaker must endure to qualify for this slash rating. Section 6.1.5 entitled “Operating Mechanism” includes Section stating the following:

“ Single-pole circuit breakers rated at 120/240 V ac or 125/250 V dc shall have provision for the use of handle ties. Handle ties, when installed, shall:

a) Operate both circuit breakers when either circuit breaker handle is manually operated;
b) Not be readily removable; and
c) Not obscure the ampere marking on either circuit breaker.”

These physical requirements/qualities of an approved handle tie illustrate what an approved handle tie means physically for a circuit breaker. Section 7 of this same UL standard covers the performance based testing for breakers with the handle tie in place. Section is specific for single-pole breakers rated 120/240V. I’ll note here that most single-pole breakers that we encounter on residential systems are slash-rated in this manner.

This permits the use of approved handle ties in the field in cases where a contractor decides to “share the neutral,” a practice some electrical contractors employ to reduce the amount of wire required for home run circuits. Section identifies the testing that must be performed on these single-pole, slash-rated breakers as follows:

“ If a pole circuit breaker is rated at 120/240 V AC or 125/250V DC, see, two such circuit breakers shall be tested together in the intended manner as a two-pole independent-trip circuit breaker in the overload, endurance, interrupting, and dielectric voltage-withstand test described below. Two such ‘pairs’ of circuit breakers constitute a set.”

When two one-pole breakers are combined via an approved handle tie, they must both be slash-rated breakers. This ensures that proper testing has been performed on the “pair” of breakers for their application. Even if applied on only single phase circuits, as is the case of shared neutral applications, this “pair” of breakers may be called upon to interrupt a line-to-line fault, a condition for which they have not been tested if they are rated 120V only. The above introduces the term “Independent-trip,” which operates such that any single breaker in the pair of combined breakers may trip without causing the trip of the other breaker(s). This can be the result of applying an approved handle tie to two, one-pole breakers. Handle ties have become more popular these days due to recent NEC changes.

National Electrical Code Requirements

The NEC is not silent when it comes to handle ties and their application as discussed above. The various sections in the NEC that address this topic can stand for a little improvement but the requirements that align with the UL standards are there.

The key sections in NEC 2011 pertinent to this discussion include the following:

  • Article 210 Branch Circuits
    • 210.4 Multi-wire Branch Circuits
      • 210.4(B) Disconnecting Means
  • Article 240 Overcurrent Protection
    • 240.15 Ungrounded Conductors
      • 240.15(B)(1) Multi-wire branch circuits
    • 240.85 Application

Our first stop is going to be in Section 240.85, “Application.” This section is within chapter VII of article 240, which focuses on circuit breaker over-current protection. The language in this section mirrors that which is in the “Marking and Application Guide for Molded Case Circuit Breakers” found in the 2012 version of the UL White Book that was previously referenced in this article. Section 240.85 states the following:

A circuit breaker with a straight voltage rating, such as 240V or 480V, shall be permitted to be applied in a circuit in which the nominal voltage between any two conductors does not exceed the circuit breaker’s voltage rating. A two-pole circuit breaker shall not be used for protecting a three-phase, corner-grounded delta circuit unless the circuit breaker is marked 1φ–3φ to indicate such suitability.

A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed the lower of the two values of the circuit breaker’s voltage rating and the nominal voltage between any two conductors does not exceed the higher value of the circuit breaker’s voltage rating.

This section provides guidance to help with the proper application of the product within its rating. It offers a simple check to ensure you don’t exceed the rating of the device - measure the voltage between any two conductors.

Section 240.15(B) is another area of the NEC that provides guidance for the application of handle ties. 240.15(B)(1) language is not specific on the voltage rating requirements of the two one-pole breakers being handle tied. This section simply permits an approved handle tie to be applied in the field. 240.15(B)(2) does specify the voltage rating of the breakers handle tied for line-to-line connected loads. It is possible for one to mistakenly assume that two one-pole breakers rated 120V may be handle tied as long as they are supplying single-phase line-to-neutral loads based on the words in these two sections. This would be in error though as other sections of the code and UL requirements mentioned above help us understand the proper application of these devices.

Section 240.15 has seen considerable changes over the years. Previous editions of the NEC, going at least back to the 1987 version of the Code, saw this “Ungrounded Conductors” section as 240-20. 240-20(B) in NEC 1987 read as follows:

 “(B) Circuit Breaker as Overcurrent Device. Circuit breakers shall open all ungrounded conductors of the circuit.”

This had one exception: “Individual single-pole circuit breakers shall be acceptable as the protection for each ungrounded conductor of three-wire, direct-current or single-phase circuits, or for each ungrounded conductor of lighting or appliance branch circuits connected to four-wire, three-phase systems, or five-wire, two-phase systems, provided such lighting or appliance circuits are supplied from a system having a grounded neutral and no conductor in such circuits operates at a voltage greater than permitted in Section 210-6.”

This verbiage was in place, for the most part, at least as far back as NEC 1962. This section saw considerable changes in NEC 1993, NEC 1996, NEC 2005, and NEC 2011. It was in NEC 2008 that the section went from 240.20 to 240.15.

NEC 1990 introduced section 240.83(e), “Voltage Marking.” This section stated the following: “Circuit breakers shall be marked with a voltage rating no less than the nominal system voltage that is indicative of their capability to interrupt fault currents between phases or phase to ground.” This section also included a Fine Print Note (FPN) as follows:

“A circuit breaker with a straight voltage marking, e.g., 480V, may be applied in neutral grounded systems or grounded wye or grounded and ungrounded delta systems. Circuit breakers with slash voltage markings, e.g., 480Y/277V, 120/240, may be applied only in grounded neutral systems.”

This section ultimately ended up being split between 240.83(e) and a new 240.85 “Application” section, which was added in NEC 1996. This section has seen some changes to better clarify the proper application of a circuit breaker.

This review illustrates that in some cases, many different sections of the code work together to ensure a safe installation. When you think you found the answer to your question quite easily, look a little harder, you just may learn something more.

Summary for Safety

We’ve talked a lot so far about ratings, UL requirements for single-pole and two-pole devices, and the NEC. Let’s provide a quick overview via the following bulleted items:

  • A circuit breaker that carries a single voltage (120V) rating is intended for use in circuits where the circuit voltage and the voltage to ground do not exceed the voltage rating of the breaker. You cannot apply an approved handle tie to these breakers.
  • A slash-rated breaker, such as 120/240, is intended to be used in circuits where the circuit voltage does not exceed the higher of the two voltages and the voltage to ground does not exceed the lower of the two voltages. Single-pole breakers with slash ratings can have approved handle ties applied for shared neutral applications.
  • GFCI single-pole devices only rated 120V cannot have an approved handle tie applied. This not only is a UL violation but also results in instant tripping of the device. For those shared neutral applications, two-pole 120/240V rated GFCI breakers are available.

  • AFCI single-pole devices rated 120V cannot have an approved handle tie applied. This is a violation of the UL listing and for those shared neutral applications, two-pole 120/240V rated AFCI breakers are available. Should a one-pole AFCI carry a 120/240V rating, an approved handle tie may be applied for shared neutral situations.

The bottom line in the application of an approved handle tie is to read the labels and the manufacturer’s instructions to ensure you are not applying the product outside of its rating.

As always, keep safety at the top of your list and ensure you and those around you live to see another day.

Thomas Domitrovich, P.E. is a National Application Engineer with Eaton Corporation in Pittsburgh, Pennsylvania. He has more than 20 years of experience as an Electrical Engineer and is a LEED Accredited Professional. Thomas is active in various trade organizations on various levels with the Independent Electrical Contractors (IEC), International Association of Electrical Inspectors (IAEI), Institute of Electrical and Electronic Engineers (IEEE), National Electrical Manufacturer’s Association (NEMA) and the National Fire Protection Association (NFPA). Thomas is involved with and chairs various committees for NEMA and IEEE and is an Alternate member on NFPA 73. He is very active in the state by state adoption process of NFPA 70 working closely with review committees and other key organizations in this effort.