Portable Grounding Sets: Why Each Phase May Need Its Own Grounding Cable

The short answer is: each phase that could become energized must be connected into the temporary protective grounding arrangement, but that does not automatically mean each phase needs a completely separate cable running to an independent ground point.

A portable grounding set for three-phase work is often built with three phase-end leads connected to the conductors and a common grounding lead connected to an approved grounding point. In other configurations, each phase may use an individual phase-to-ground cable. The correct arrangement depends on the available fault-current path, the grounding point, conductor geometry, induced-voltage exposure, work location, and the employer’s approved procedure.

The important distinction is between grounding every phase and using one independent grounding cable for every phase. All phases need to be effectively bonded into the protective grounding system. Whether that is achieved through a common grounding cluster or through separate phase grounding cables is a system-design and work-method question, not a matter of visual symmetry.

Why all phases must be included in the grounding arrangement

Temporary protective grounds are installed after the circuit has been de-energized, isolated, locked or tagged as required, and tested for absence of voltage. Their purpose is not simply to connect metal to earth. They are intended to protect workers if the line or equipment becomes energized unexpectedly.

Possible sources of unintended voltage include:

• Accidental closing of a switching device;
• Backfeed from generators, transformers, customer-owned generation, or another source;
• Induced voltage from adjacent energized circuits;
• Incorrect identification or isolation of conductors;
• Stored electrical energy or capacitive coupling;
• Equipment failure or an operating error elsewhere on the system.

If a conductor becomes energized while properly installed temporary grounds are in place, the grounding set is expected to carry fault current long enough for upstream protective devices to operate. It also helps hold the conductors, grounding point, and worker-accessible bonded components at substantially the same potential within the protected work zone.

Leaving one phase ungrounded can create a serious exposure. That phase may remain at an induced or backfeed voltage even when the other two phases are grounded. A worker contacting the ungrounded phase while also contacting grounded equipment, another phase, or a structure could become the path between different electrical potentials.

A common grounding lead is not the same as “one cable for three phases”

Confusion often arises because portable grounding equipment can look simple from a distance. A three-phase grounding set may include a grounding cluster with three line-end clamps and one ground-end clamp. The three phase leads join at a common junction, and the grounding lead runs from that junction to the grounding source.

That arrangement does not leave two phases unprotected. Each phase has its own connection from the conductor to the common cluster. The common grounding lead must be capable of carrying the fault duty associated with the installation. The phase leads, clamps, ferrules, junctions, and grounding connection must also be rated and maintained for the intended duty.

In practical terms, a three-phase cluster ground usually provides:

• A direct bonding connection for each phase conductor;
• Phase-to-phase bonding through the cluster;
• A common path to the grounding source;
• A lower likelihood that phases inside the protected zone will rise to significantly different voltages during a fault.

However, a common-grounding-lead arrangement is only acceptable when it is designed, rated, and installed for that application. It is not acceptable to improvise a multi-phase grounding system by attaching undersized jumpers, mixing incompatible clamps, or assuming that a structure ground is adequate without verifying the fault-current path.

When separate grounding cables for each phase may be appropriate

Separate phase grounding cables can be required or preferred when a common cluster arrangement does not provide the required protective performance at the actual work location. This may occur in several conditions.

The conductors are widely spaced. On overhead lines, bus structures, or substation equipment, phase spacing may make a standard cluster set impractical. Leads must reach the conductor without strain, sharp bends, excessive sag, or an arrangement that interferes with safe work. Individual cables may provide a more controlled installation.

The work area needs grounds on both sides. A work location can be exposed from more than one direction. For example, a section of line may have possible energization sources at either end. Grounding may be required on both sides of the worksite, with the exact configuration determined by the isolation points, system design, and approved work procedure. A single set at one location does not necessarily establish an equipotential zone where personnel are working.

There are multiple grounding points or bus sections. Switchgear, substations, and industrial distribution systems may have compartmentalized bus sections, tie breakers, transformer connections, and alternate feeds. Separate grounds may be used to ensure each isolated section is effectively bonded and protected against the specific paths by which it could become energized.

The grounding source is not common to all conductors. A grounding set must connect to a known, suitable grounding point. If the available grounding locations differ by phase, equipment section, or physical location, individual grounding leads may be necessary. The key issue is not whether the cables look separate; it is whether each conductor has an effective low-impedance fault-current path to the system grounding arrangement.

Induction conditions are significant. Parallel energized lines, adjacent buswork, and transmission corridors can induce voltage and current onto an isolated circuit. In these situations, the grounding arrangement must account for both electric-field and magnetic-field coupling, as well as the possibility of circulating currents. More grounding points are not automatically safer: an improperly planned arrangement can create hazardous differences in potential or expose workers during installation and removal.

The protective objective is an equipotential work zone

The most useful way to evaluate portable grounding configuration is to focus on the worker’s electrical environment. The objective is to create an equipotential zone: a work area in which the worker, the conductor being handled, and bonded conductive parts are kept at nearly the same electrical potential if accidental energization occurs.

Earth itself is not always a zero-voltage reference during a fault. When fault current flows into a grounding system, voltage gradients can develop. A person standing on the ground and touching an energized or faulted object can be exposed to touch potential. A person walking through an area with different ground voltage levels can be exposed to step potential.

For this reason, temporary protective grounding should not be judged only by the question, “Is there a cable connected to ground?” The better questions are:

• Is every conductor that can energize the worksite bonded into the grounding arrangement?
• Would the installed set carry the available fault current until protective clearing occurs?
• Are the worker and the object being handled within the same equipotential zone?
• Could an alternate feed, induced source, or switching error energize a section outside the installed grounds?
• Are the grounding connections located close enough to the work position to provide the intended protection?

A grounding configuration that is electrically acceptable at a remote point may not provide the same protection at the employee’s exact work location. This is why line work and substation grounding plans often distinguish between system grounding, protective grounding, and personal protective grounding practices.

Fault-current rating is often the deciding technical limit

Portable grounding cables are safety devices, not general-purpose bonding leads. Their conductor size, strand construction, ferrules, clamps, and connections must be suitable for the maximum available fault current and the expected clearing time. A cable that survives low-level induced current may fail catastrophically if it must carry a high fault current from an accidental energization event.

Using separate cables for each phase does not remove this duty. Each individual cable must have a suitable rating for the current it may carry, and a shared grounding lead must be rated for the combined duty it could see. The ground connection itself is equally important. A correctly rated cable attached to a poor, contaminated, painted, corroded, or mechanically insecure grounding point is not a dependable protective ground.

ASTM F855 covers specifications for temporary protective grounds used on de-energized electric power lines and equipment. Utilities and industrial facilities may also apply internal grounding tables and engineering calculations based on available short-circuit current and protective-device clearing time. The applicable procedure should define the approved cable size, clamp type, installation method, and inspection requirements for the voltage class and system location.

Do not confuse phase bonding with a substitute for grounding

Bonding all three phases together is valuable because it reduces voltage differences between phases. But phase-to-phase bonding alone is not necessarily the same as connecting the circuit to an effective grounding source.

A three-phase conductor group that is bonded together but not connected to an approved ground may still float at an induced voltage relative to earth and nearby grounded equipment. Conversely, grounding only one phase while leaving the other phases unbonded can leave dangerous phase-to-phase voltage differences within the work area.

A proper temporary grounding arrangement commonly needs both functions:

• Bonding: connecting conductors and relevant conductive parts so they remain at similar potential;
• Grounding: connecting that bonded system to a suitable point that provides a fault-current path and reference to the electrical system ground.

The exact hardware arrangement differs among overhead distribution lines, transmission structures, metal-clad switchgear, substations, cable systems, and industrial plants. The electrical purpose does not change.

Installation sequence matters as much as cable quantity

A correctly selected grounding set can still be hazardous if installed in the wrong order. Standard safe-work practice generally requires connecting the ground end first, then applying line-end clamps with an approved live-line tool or other specified method. Removal is performed in reverse order: line-end clamps are removed first, and the ground-end connection is removed last.

This sequence reduces the chance that a worker handles an ungrounded cable that could become energized through accidental contact or induction. It also ensures that, once a phase clamp is applied, the cable already has a path to the grounding point.

Before installation, operators should verify that the circuit is de-energized using approved test methods and equipment appropriate to the system voltage. A visual open point, an open disconnect, or a control-room indication is not by itself proof that a conductor is dead. Isolation and absence-of-voltage verification are separate safeguards; portable grounds are added after those safeguards are established.

Common errors when deciding how many cables are needed

Assuming a grounded neutral makes phase grounds unnecessary. A neutral conductor may be grounded at multiple points in a system, but it is not automatically a substitute for temporary protective grounding of de-energized phase conductors at a worksite.

Using one phase ground as protection for the other phases. Unless the phases are intentionally bonded through a rated grounding cluster or another approved arrangement, grounding one conductor does not reliably protect the others.

Choosing by cable length alone. Longer leads may reach more easily, but unnecessary length adds impedance, creates handling difficulties, and can complicate placement. Cable routing must support both electrical performance and safe physical access.

Mixing components from different sets without approval. Cables, clamps, ferrules, and cluster bars are part of an assembly. Combining parts with different ratings or connection designs can reduce the assembly’s fault-current capability.

Installing grounds where they are convenient rather than where they protect the work. A remote ground may satisfy a visual expectation while failing to establish a protected zone around the worker.

The practical answer before work begins

Each phase should have a deliberate, verified connection into the temporary protective grounding system. That connection may be through separate phase grounding cables or through a properly rated three-phase grounding set with individual phase leads and a common grounding lead.

The decision should not be made from the number of cables visible in a kit. It should be based on the approved grounding plan for the specific circuit: isolation points, possible sources of energization, available fault current, clearing time, conductor spacing, grounding locations, induced-voltage conditions, and the position where work will occur.

If the grounding arrangement cannot clearly show how every exposed phase is bonded and grounded, how fault current will be carried, and how the worker remains inside an equipotential zone, the configuration needs engineering or supervisory review before work proceeds.