Panelboard Defects, Subpanels and Problem Panels

Multiple conductors in one lug

A lug is a terminal that clamps a conductor to a bus, a circuit breaker, or a terminal bar. A lug is usually listed for a single conductor. More conductors in a lug than the device allows is a common enclosure defect. On a circuit breaker, it is sometimes called a double tap.

The device manufacturer's instructions set how many conductors a lug may hold. The general rules are:

• Energized and neutral conductors: one conductor per lug.
• Equipment grounding conductors (EGCs): two per lug, if both are the same size.

Instructions on the panelboard label override the general rules. A lug not designed for more than one conductor may let a conductor slip out.

The most common exception is a group of Square D circuit breakers rated 15, 20, and 30 amps, some sold under the Homeline brand. A double saddle on these breakers sits beneath the lug screw and holds two conductors if they are the same size.

An overcurrent protection device (OPD) may fail to protect multiple conductors in one lug, or the conductors may be overfused. Multiple conductors in one lug can be especially dangerous.

The same rules apply at terminal bars. Doubled neutral conductors in one lug are not allowed. Two EGCs in one lug are allowed if they are the same gauge.

Copper and aluminum conductors in the same lug can corrode. A lug with anti-oxidant paste can look good. A deteriorated lug is a defect.

Other typical defects inside enclosures

1. Rust: rust indicates that water may be leaking into the enclosure. It could raise resistance and start an electrical fire. Moderate rust is reportable, and so is significant rust, including rust on a dead front cover.
2. Bus bar deterioration: a deteriorated bus bar is a typical defect inside an enclosure.
3. Contaminants in the enclosure, such as paint and drywall joint compound: these could also raise resistance and start an electrical fire.
4. Damaged conductors and insulation: the conductor and its insulation should be undamaged. Nicks in a conductor or its insulation, and missing strands on a multi-strand conductor, should be trimmed back to undamaged material or replaced. All strands of a multi-strand conductor should be inside the lug.
5. Melted insulation and charred conductors: these indicate a loose lug connection, or an overcurrent the OPD did not interrupt.
6. Excess uninsulated conductor at the lug of a circuit breaker: bare conductor should not extend beyond the circuit breaker case. Exposed conductor past the case creates a possible electric shock hazard.
7. Conductors not inserted straight into lugs: a conductor should be substantially straight where it enters a lug. A substantially skewed conductor may not be securely fastened. A sharp bend at the lug can also make the conductor appear reduced in size.
8. Pointed screws used to secure enclosure covers: the point could pierce the insulation on a conductor and energize the enclosure. Tape is not an acceptable repair for the damaged conductor.
9. Branch circuits not labeled: each branch circuit should have a permanent label with enough detail to tell it apart from the other circuits. A label based on how the current occupant uses a room is not acceptable.
10. Neutral conductors that are energized but not marked as such: a neutral conductor may serve as an energized conductor. It must carry a permanent mark at every accessible point and inside the enclosure, usually black marker or electrical tape.
11. Circuit breaker manufacturer different from panelboard manufacturer: panelboards and breakers are designed to work together. A breaker made by another manufacturer may not be installed, even where it appears to fit. Certain models may be interchanged between manufacturers. Determining which ones is outside the scope of a home inspection. The home inspector should recommend evaluation by an electrician.
12. Handle ties absent or improper on 240 volt or multiwire branch circuit breakers: these circuits must disconnect both conductors at the same time, using an approved handle tie between the breaker handles. Wire, nails, and other improvised ties are not permitted.
13. Absent tabs and knockouts: a knockout is a removable disc in the enclosure wall for a cable or conduit entry. A tab is a removable piece in the dead front cover at a breaker space. An open tab or knockout is an electrical shock hazard. Tape, cardboard, and other makeshift fillers are not permitted. Replacement material must be similar to the original.
14. Low voltage components inside the enclosure and conduit: door bell transformers, telephone cable, coaxial cable, and other low voltage components may not share an enclosure or conduit with high voltage components, unless non-conductive guards physically separate the two.
15. Too many circuit breakers on panelboard, or half-height circuit breakers in wrong slots: both limits appear on the panelboard label, which gives the maximum number of branch circuits and which slots, if any, accept half-height breakers.
16. Panelboard ampacity greater than the ampacity of the service entrance or feeder conductors: a minimum ampacity for the supply conductors is printed on the panelboard label. Supply conductors may exceed this minimum, but may not fall below it.
17. Cables and conduit that are not secured to the enclosure: a cable should enter the enclosure inside conduit or through a cable clamp. Metal conduit should be joined to the enclosure by a metal fitting. Without one, the installer should add a bonding jumper.
18. Fused neutral: an OPD should not be connected to a neutral conductor. In the rare case that the OPD opens the neutral, current stops but the circuit remains energized. The defect is usually limited to very old electrical systems.
19. Damaged enclosure: an enclosure should be intact, free from physical damage, and have all manufacturer approved parts installed. Covers and doors should open at least 90 degrees without binding, for safe access inside. A cover that a wall prevents from opening does not open at least 90 degrees.

Standards: IRC 2018 sections cover NM cable ampacity (E3705.4.4), branch circuit conductor ampacity (Table E3705.1), panelboard ampacity rating, circuit identification, and one neutral per lug (E3706), AFCI and GFCI locations (E3902), and general cabinet and panelboard installation (E3907).

Subpanel grounding and bonding

Why subpanel grounding is different

IRC 2018 Section E3607.2 (NEC 2017 Article 250.24(A)(1)) prohibits connecting a grounded (neutral) conductor to ground anywhere downstream of the service disconnecting means. Section E3607.3.2 provides the exception. Past the service equipment, neutral conductors must stay isolated from EGCs and from all other bonded metal.

This rule exists because the neutral conductor carries current. Under normal conditions it is at zero voltage and is not a shock risk. Reversed polarity, at a receptacle or inside a lamp or similar device, could energize the neutral. A ground fault in improperly bonded metal is a similar risk. Either way, metal bonded to the EGCs could become energized and shock anyone who touches it.

A neutral grounded at a distribution panelboard creates parallel return paths for current. The condition of those paths is unknown.

Subpanels

For grounding and bonding, a subpanel is any panelboard downstream of the service equipment. This includes a main panelboard of the main lug type. Appliances, appliance disconnects, junction boxes, and outlets are included too.

Terminal bars in a subpanel

• Neutral conductors should land on their own neutral terminal bar or lugs, isolated from both the EGCs and the enclosure.
• EGCs should not connect to the neutral terminal bar. The neutral terminal bar should not connect to the enclosure.
• EGCs should connect to a separate grounding terminal bar, which should be bonded to the subpanel enclosure.

The two most common bonding methods are mounting the grounding bar directly on the enclosure and connecting it with a bar or strap.

Detached buildings

A detached building includes a barn, a storage shed, a work shed, or a guest house supplied with electricity from the main house.

A single branch circuit of 15 or 20 amps serves many detached buildings. That arrangement needs no special grounding or bonding connections if the circuit has an EGC, which it should.

Two or more branch circuits, or a feeder to a subpanel, require a grounding electrode system at the detached building.

New work. New branch circuits and feeders to a detached building should include an EGC, connected to the grounding electrode. Neutral conductors should remain isolated from both the EGC and the subpanel enclosure. The feeder to the detached building is a four wire feeder: two ungrounded (hot) wires, one grounded (neutral) wire, and one equipment grounding (bonding) wire.

Existing work without an EGC. An existing circuit or feeder to a detached building that has no EGC may remain. If no grounding electrode is present, one should be installed. The subpanel there should be set up as a main breaker panel. EGCs and neutral conductors may then share terminal bars. Both should be bonded to the enclosure and connected to the grounding electrode.

Typical defects, subpanels

Home inspectors should report these subpanel defects:

1. EGCs and neutral conductors on the same terminal bar: this includes an EGC and a neutral joined in a wire nut inside the enclosure.
2. EGCs or EGC terminal bar not bonded to enclosure: this includes an absent bonding jumper between the grounding bar and the enclosure.
3. Other typical defects inside enclosures: every item on that list also applies to subpanels.

Standards: IRC 2018 sections cover the GEC connection location (E3607.2) and grounding in detached buildings (E3607.3).

Potential problem panelboards

A few older panelboards have known or suspected problems. Home inspectors should look for them and make recommendations when one is found. Online sources describe them, and some home inspectors direct clients to those sources. Some electricians do not know of these alleged problems.

Most of these panelboards have reached or exceeded their expected service life. This end of life condition should be reported in addition to any brand specific defects.

Three potential problems are alleged across these brands:

• circuit breakers that do not trip when they should
• circuit breakers that are energized while showing deenergized
• arcing at the circuit breaker to busbar connection, not visible unless the breaker is removed

Federal Pacific Stab-Lok

Federal Pacific Stab-Lok panelboards sometimes carry the FPE logo on the enclosure. Other names for them are Federal Electric and Challenger. They appear most often in houses built from the mid-1950s to the early 1980s. The alleged design defects involve the circuit breakers, the panelboard, and the enclosure. All three potential problems are alleged.

On these panelboards, removing the dead front can be difficult, and breakers may fall out as it comes off. Some home inspectors do not remove these covers.

A substantial majority of experienced home inspectors report the panelboard, describe its potential risks, and recommend that a qualified electrician evaluate it. Because some electricians do not know of the alleged problems, some home inspectors recommend replacement.

Only Stab-Lok panelboards are involved. The alleged defects do not apply to other Federal Pacific panelboards.

Zinsco and Zinsco-Sylvania

Zinsco panelboards, also sold as Zinsco-Sylvania, appear most often in houses built from the 1940s to the 1970s. The alleged design defects involve the circuit breakers and the panelboard. All three potential problems are alleged. A majority of experienced home inspectors report the panelboard, describe its potential risks, and recommend that a qualified electrician evaluate it.

Bulldog Pushmatic

Bulldog Pushmatic panelboards are found mostly in houses from the 1950s and 1960s, and may be found in houses built up to the 1990s. The alleged design defects involve the circuit breakers, especially those from the 1950s and 1960s. Two problems are alleged: breakers that do not trip when they should, and breakers energized while showing deenergized.

Experienced home inspectors are split on these panelboards. Some believe the evidence is insufficient to warrant reporting these panelboards. Others report 1950s and 1960s panelboards for two reasons: advanced age, and listed replacement parts that may be hard to find and may be costly. These home inspectors report the panelboard, describe its potential risks, and recommend that a qualified electrician evaluate it.

Numbers and Rules to Memorize