Generator and Transformer Screening: Clearances to Hold

A generator screen or transformer fence hides backup power and utility equipment from the street, but it has to stand outside a set of clearances that other people control. The serving utility sets the space around its transformer. The National Electrical Code sets working space at the customer's electrical equipment. NFPA 37 and the generator manufacturer set setbacks and airflow. This guide puts those rules side by side so the screen can be drawn once and approved. The project's electrical engineer, the utility and the authority having jurisdiction (AHJ) make the final calls.

What clearances does a generator screen or transformer fence have to hold?

A generator screen or transformer fence has to hold every clearance around the equipment at the same time, and the largest one governs each side. Five sources usually apply:

• The serving utility. Its standards set the work zone in front of a pad-mounted transformer, the offsets on the other sides, and the gate rules.
• The National Electrical Code (NEC). Section 110.26 sets working space in front of the customer's electrical equipment, such as a generator breaker, control panel, transfer switch or switchgear.
• The generator manufacturer. Its installation instructions set service room and the airflow path.
• NFPA 37. It sets how far an outdoor engine-driven generator sits from building openings and combustible walls.
• Zoning. The local code usually says the equipment must be screened and how. See what zoning codes require for mechanical equipment screens.

This is about the site screen around the equipment pad, not a NEMA-rated transformer enclosure or the generator's own housing.

How far must a fence be from a pad-mounted transformer?

It depends on the utility, and the published numbers differ more than most site plans assume. Three published utility standards show the range:

Source	In front of the doors	Other sides	Gate and fence rules
One utility's landscape screen standard	8 ft minimum, measured from the edge of the pad	2 ft from the pad to walls and fences (1 ft for low planters)	Gates may sit close to the front if the 8 ft is clear with the gates open. Screens do not replace required barrier posts or fire walls.
One utility's fencing specification	At least 8 ft, widening 6 in for every 3 ft out	36 in from all fence components	Utility approval required. Gate at least 48 in wide, locked, with a shared hasp for the utility's lock. A center gate post must be easily removable.
One utility's enclosed-space guidance	10 ft clear work zone	Nonmetallic fence: 3 ft behind, 4 ft at the sides. Metallic fences are treated separately.	The gate must not block the work zone or the transformer's removal. The utility's lock goes on the gate.

These are examples, not a national rule, so check with your utility. Get the serving utility's current standard for the site and send it with the layout. Utilities often review a fence before it is built; one standard above can require an unapproved fence to be removed.

Why can a metal fence need more room?

Some utilities treat metal near energized equipment differently and set larger offsets for metallic fences and gates than for planting or nonmetallic screens. Check with your utility for its metallic-fence rule, and lay out a steel screen to that rule, not its landscaping rule. Whether the screen is bonded or grounded is a decision for the project's electrical engineer and the utility.

Where does the gate go?

The gate faces the transformer doors and swings clear of the work zone. Utilities need to operate the equipment with hot sticks and, one day, lift the transformer out and set a new one, so the opening has to be wide and unobstructed. One standard above sizes the gate from the transformer lid width plus 6 feet on each side for a metal enclosure. Wide openings like that may call for a 16 ft clear double gate or a custom 20 ft gate, or for leaving the front open where the code allows.

What clearance does a generator need inside a screen?

The generator manufacturer sets it, and service room and airflow both count. One manufacturer's installation guidelines for stationary industrial generators ask for a minimum of 5 feet of clearance around each side for repair, service and air circulation. The same guidelines tell installers to consider the proximity of walls and fences, keep air intakes unobstructed, and keep the exhaust discharge clear so hot air and exhaust do not circulate back to the intakes and overheat the unit. They also warn against facing the radiator discharge into the prevailing wind.

Other models publish their own numbers, so the engineer should confirm clearances for the scheduled unit before the screen is laid out.

Solid, spaced or perforated around a generator?

The choice trades opacity against airflow. A solid face screens best but sends the radiator discharge up and over the top, so the full clearances matter more. Spaced slats and perforated panels let air through the face. Some utilities also limit solid fences around their transformers, so check with your utility before choosing a solid face. The standard Alpine Citadel face is solid steel slats stacked tight, which is 100% opaque. Custom slat spacing and perforated metal panels are available where the equipment needs air through the screen. Ask the planner whether open infill meets the local screening rule before choosing it.

What does NEC 110.26 require in front of electrical equipment?

It requires a clear working space in front of electrical equipment that may be serviced while energized, and an outdoor screen may not sit in it. In the 2020 NEC text of Section 110.26:

• Depth is 3 ft for 0–150 volts to ground. For 151–600 volts it is 3 ft, 3 ft 6 in or 4 ft for Conditions 1, 2 and 3.
• Condition 2 applies when grounded parts face the live parts across the space. The code counts concrete, brick and tile walls as grounded.
• Width is the equipment width or 30 inches, whichever is greater, and doors must open at least 90 degrees.
• Height is 6 1/2 ft or the equipment height, whichever is greater.
• Outdoors, no architectural appurtenance may be located in the working space, and the space from grade to 6 ft above the equipment is dedicated to the electrical installation.

Utility-owned transformers follow the utility's standards. Confirm the NEC edition the jurisdiction has adopted, and let the electrical engineer decide which condition applies when a screen faces the equipment.

How far must a generator be from the building under NFPA 37?

NFPA 37 sets the core rule at 5 feet. An engine-driven generator installed outdoors, with its weatherproof housing, sits at least 5 feet from openings in the walls of structures and at least 5 feet from structures with combustible walls. The standard allows less in some cases, such as walls with a 1-hour fire-resistance rating or a housing shown by testing not to ignite nearby combustibles. Those exceptions vary by edition, so confirm them with the fire marshal.

The setback is measured to the building, not to the screen. Alpine Citadel is noncombustible steel construction, but it is not a fire-rated assembly and is not a fire barrier. Where a code calls for fire separation, that requirement is met separately.

Will a screen reduce generator noise?

No, do not count on it. A slatted steel screen is a visual screen, not a noise barrier. If a property-line noise limit applies, that is a separate design for an acoustical consultant and may change the generator's housing or location.

How do you lay out a generator and transformer screen?

Draw the clearances first, then the screen around them. A layout that clears review usually shows:

1. The serving utility's clearance standard, with its document number and date.
2. The transformer front work zone, side offsets, and any metallic-fence offset, confirmed with your utility.
3. The generator manufacturer's service and airflow clearances, and the radiator discharge direction.
4. NEC working space in front of each panel, breaker, transfer switch and switchgear.
5. NFPA 37 setbacks from building openings and combustible walls.
6. Gate locations, swing and clear width, and the lock arrangement the utility wants.
7. Truck access for fuel delivery and equipment replacement.
8. Infill type and opacity, keyed to the zoning rule.
9. Screen height against the tallest unit and the local fence-height limit.
10. Wind design criteria and who provides sealed calculations.

The screen is a freestanding structure, and a solid face takes the most wind. Alpine Citadel is engineered to ASCE 7-22 for each site's wind speed, exposure and risk category; see how Alpine engineers each site.

How do multi-site programs standardize this screen?

Make the detail parametric. A prototype built across many service territories meets a different utility on almost every site, so a fixed footprint fails somewhere. A program detail that travels well sets the screen height from the tallest scheduled unit, makes the transformer offsets and gate width variables filled in from each utility's standard, defaults to the larger metallic-fence offset, and places the gate on the door side every time. The finish and infill stay the same everywhere. Alpine supports programs with per-site layouts and kits packed by site and release; see Alpine's national programs.

Alpine Citadel is structural steel throughout, ASTM A36 or equivalent, with no aluminum components. It comes in standard heights of 6, 7 and 8 feet, custom heights from 5 to 10 feet, standard 12 ft and 16 ft clear gates, and any RAL color. Product details are on the generator and transformer screen wall page. To check a layout, send the site plan, the equipment schedule and the utility's clearance standard through the Alpine quote request, and Alpine will lay the screen out around those clearances.

Sources

• Pacific Gas and Electric Company. Greenbook Document 063422, Landscape Screen for Pad-Mounted Transformers, Rev. 04. 2017.
• Citizens' Electric Company. Underground Specification CR-UG-04, Fencing/Screening Around Transformers. 2022.
• Pacific Power and Rocky Mountain Power. Electric Service Requirements White Paper: Gated Areas and Enclosed Spaces. 2021.
• National Fire Protection Association, reprinted by the International Code Council. NFPA 70 National Electrical Code 2020, Section 110.26, Spaces About Electrical Equipment (in the 2021 International Solar Energy Provisions). 2021.
• National Fire Protection Association. NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines. 2024 edition.
• Generac Power Systems. Installation Guidelines for Stationary Industrial Generators, Part No. 046622 Rev. E. 2015.