Verify voltage, clearance, and grounding rules from official sources before electrical work begins.
Key takeaways for electrical grounding and clearance checks for construction sites
- Verify that conductors that do not pass over more than 4 feet of roof overhang maintain at least 18 inches of clearance if the voltage is 300 volts or less and they terminate at a through-the-roof raceway or support, according to Washington State Legislature.
- Check equipment operated at over 150 volts to ground, except guarded motors or metal frames of electrically heated appliances that are permanently and effectively insulated from ground, according to Washington State Legislature.
- If a single grounding electrode has a resistance to ground greater than 25 ohms, install one additional electrode no closer than 6 feet to the first electrode, according to Washington State Legislature.
- Confirm that tools used in wet or conductive locations are supplied through an isolating transformer with an ungrounded secondary of not over 50 volts if they are not grounded, according to Washington State Legislature.
Verify electrical clearance and grounding before the shift
Federal regulations cover wiring design and protection.
Before your crew touches temporary power panels or energized equipment, you must confirm that the site meets specific regulatory standards. According to Legal Information Institute, 29 CFR § 1926.404 governs "Wiring design and protection."
However, federal rules are not the only layer of compliance. Depending on your location and specific site conditions, other jurisdictions may impose additional requirements. For instance, in New Zealand, the obligation extends to the operational state of the equipment itself. According to WorkSafe New Zealand, "You and other PCBUs on site (eg contractors) must ensure any electrical equipment you use or provide is operated safely and maintained so that it remains safe." This places a direct duty on the contractor to verify that tools and temporary power sources are not just installed correctly, but are also maintained in a safe operating condition.
Do not assume that a system that passed inspection last week is automatically safe today. Environmental factors, physical damage, and wear can compromise safety. The federal regulation provides the static design requirements, but the operational duty requires dynamic, daily checks. You are responsible for the condition of the equipment you provide or use. This means inspecting cords for damage, checking that enclosures are intact, and verifying that grounding connections are secure before the shift begins.
A filled reference table of electrical rules by publisher
The table below lists five specific electrical safety requirements drawn from official regulatory texts. Each row identifies the publisher, the rule topic, the specific value or requirement, and the source quote. Use this comparison to verify that your site’s temporary power setup meets the stated thresholds for clearance, grounding, and equipment placement.
| Publisher | Rule Topic | Requirement/Value | Source Quote |
|---|---|---|---|
| Washington State Legislature | Conductor spacing | 30 inches (762 mm) | "(A) Power conductors below communication conductors: 30 inches (762 mm)." |
| Washington State Legislature | Roof clearance | 18 inches (457 mm) | "(D) Where the voltage between conductors is 300 volts or less and the conductors do not pass over more than 4 feet (1.22 m) of the overhang portion of the roof and they are terminated at a through-the-roof raceway or support, the clearance from roofs must be at least 18 inches (457 mm)." |
| Washington State Legislature | High voltage | Services over 600 volts, nominal | "The following additional requirements apply to services over 600 volts, nominal." |
| Washington State Legislature | Grounding voltage | Over 150 volts to ground | "(B) If operated at over 150 volts to ground, except for guarded motors and metal frames of electrically heated appliances if the appliance frames are permanently and effectively insulated from ground." |
| Washington State Legislature | Electrode spacing | No closer than 6 feet (1.83 m) | "A single electrode consisting of a rod, pipe or plate which has a resistance to ground greater than 25 ohms must be augmented by one additional electrode installed no closer than 6 feet (1.83 m) to the first electrode." |
Clearance distances for conductors and roofs
Before energizing temporary power, verify the physical separation between power lines and communication cables. According to Washington State Legislature, power conductors installed below communication conductors must maintain a vertical clearance of 30 inches (762 mm). This specific spacing rule applies to the configuration where power lines are positioned underneath communication lines. Check this measurement on any overhead runs where both types of cables share the same support structure. If the power conductors are above the communication lines, this specific 30-inch rule does not apply in the same way, so confirm the arrangement before signing off on the installation. See Overhead line clearance above 50 kV in 6 steps.
Roof clearance rules depend heavily on voltage levels and the extent of the roof overhang. For low-voltage temporary power, the federal standard sets a minimum height above the roof surface. According to Legal Information Institute, where the voltage between conductors is 300 volts or less and the conductors do not pass over more than 4 feet (1.22 m) of the overhang portion of the roof and they are terminated at a through-the-roof raceway or support, the clearance from roofs shall be at least 18 inches (457 mm). This federal rule requires three conditions to be met simultaneously: the voltage must be 300 volts or less, the overhang coverage must not exceed 4 feet, and the conductors must terminate at a raceway or support through the roof.
State regulations mirror this federal requirement for similar scenarios. According to Washington State Legislature, where the voltage between conductors is 300 volts or less and the conductors do not pass over more than 4 feet (1.22 m) of the overhang portion of the roof and they are terminated at a through-the-roof raceway or support, the clearance from roofs must be at least 18 inches (457 mm). Note that this 18-inch minimum is strictly limited to voltages of 300 volts or less. Do not apply this 18-inch clearance to higher voltage services. If the temporary power panel supplies equipment operating above 300 volts, this specific roof clearance rule is not the applicable standard.
Grounding requirements for equipment and electrodes
Washington rules address equipment that operates at over 150 volts to ground, according to Washington State Legislature. The quoted wording excepts guarded motors or metal frames of electrically heated appliances where the appliance frames are permanently and effectively insulated from ground, as stated in the same source. Verify the voltage rating of any temporary equipment before energizing it to determine if this threshold applies.
Supports and enclosures for conductors must be grounded, according to Legal Information Institute. This federal rule identifies specific categories of equipment that require grounding connections. Check the specific subsections referenced in the regulation to confirm if your equipment falls into one of the listed types, according to Legal Information Institute.
For grounding electrodes, a single electrode consisting of a rod, pipe or plate which has a resistance to ground greater than 25 ohms must be augmented by one additional electrode installed no closer than 6 feet (1.83 m) to the first electrode, according to Washington State Legislature. This spacing rule applies when the measured resistance exceeds the specified limit. Measure the resistance of your existing electrode before installing additional rods. If the resistance is high, install the second electrode at the required distance.
Record the voltage of each piece of equipment and the resistance of your grounding electrodes in the daily log.
Special rules for wet locations and high voltage
When your site power exceeds standard thresholds, specific exemptions and additional protections apply. Review these conditions before energizing circuits in challenging environments.
Tools likely to be used in wet and/or conductive locations need not be grounded if supplied through an isolating transformer with an ungrounded secondary of not over 50 volts, according to Washington State Legislature. This provision in WAC 296-155-447: allows for a specific exception to standard grounding requirements. The exemption applies only when the power source is an isolating transformer. The secondary side of that transformer must remain ungrounded. The voltage on that secondary side cannot exceed 50 volts. If your setup uses a different transformer configuration or higher voltage, this exemption does not apply. Verify the transformer specifications and voltage output before relying on this rule for wet location tools.
For services operating at higher voltages, additional requirements are triggered. The following additional requirements apply to services over 600 volts, nominal, according to Washington State Legislature. If your site receives power above 600 volts, you must consult the specific additional requirements listed in this regulation. Do not assume that lower-voltage clearance or grounding rules are adequate for these high-voltage services.
Federal regulations also structure protections around voltage levels. The heading in 29 CFR § 1926.404 is "(e) Overcurrent protection—(1) 600 volts, nominal, or less," according to Legal Information Institute.
Measure the voltage of your incoming service and the output of any isolation transformers. Record these values in your daily electrical log to confirm which rules apply to your current setup.
Illustrative example
A run at 300 volts crosses 4 feet of roof overhang, ends on a through-the-roof support, and needs 18 inches of roof clearance. Power conductors below communication conductors need 30 inches of separation. One rod at 25 ohms gets a second electrode 6 feet away.
Contact distance and pole-mounted apparatus
Washington State rules require attention to equipment within 8 feet (2.44 m) vertically or 5 feet (1.52 m) horizontally of ground or grounded metal objects and subject to employee contact, according to Washington State Legislature. The same state regulation applies to distribution apparatus such as transformers and capacitors mounted on wooden poles at a height exceeding 8 feet (2.44 m) above ground or grade level, according to Washington State Legislature. Federal regulations also address distribution apparatus such as transformers and capacitors mounted on wooden poles at a height exceeding 8 feet (2.44 m) above ground or grade level, according to Legal Information Institute.
Do this today
Write roof clearance, conductor spacing, and electrode resistance in the daily log today. Before repair, use Lock out the circuit: 5 checks before repair starts and Record 8 lockout tagout fields in a site log.
FAQ: Electrical grounding and clearance checks for construction sites
What is the minimum clearance from roofs for 300-volt conductors?
It is at least 18 inches (457 mm) only when voltage is 300 volts or less, the conductors do not pass over more than 4 feet of overhang, and they terminate at a through-the-roof raceway or support, according to Washington State Legislature.
How far apart must additional grounding electrodes be installed?
According to Washington State Legislature, a single electrode consisting of a rod, pipe or plate which has a resistance to ground greater than 25 ohms must be augmented by one additional electrode installed no closer than 6 feet (1.83 m) to the first electrode. You must install the second electrode at a distance of at least 6 feet from the initial one if the resistance measurement exceeds the 25-ohm threshold.
When are tools in wet locations exempt from grounding?
According to Washington State Legislature, tools likely to be used in wet and/or conductive locations need not be grounded if supplied through an isolating transformer with an ungrounded secondary of not over 50 volts. The exemption applies only when the tool is powered by an isolating transformer that features an ungrounded secondary circuit operating at 50 volts or less.
What height threshold applies to distribution apparatus on poles?
Washington State Legislature names cases of distribution apparatus such as transformers and capacitors mounted on wooden poles at a height exceeding 8 feet (2.44 m) above ground or grade level.