Painting transformers and electrical equipment: method and safety

To paint a transformer or electrical equipment, work is done only on equipment that is de-energized and locked out, or outside the limits of approach set by the owner and the applicable regulations. The surface is degreased before any preparation, because oil prevents adhesion. Preparation is then mostly by power tools, bushings, insulators and gaskets are protected, and an ISO 12944 system suited to the site's corrosivity category is applied, usually a surface-tolerant epoxy followed by a polyurethane topcoat.

Transformer tanks, radiators, conservators, cable boxes, control cabinets, switchgear enclosures and steel supports age outdoors, often under de-icing salts, freeze-thaw cycles and UV exposure. Repainting extends their service life and makes leak inspection easier. It takes place, however, in an environment where electrical risk, the presence of oil and short outage windows change the method. This guide is for maintenance managers of industrial substations, plants and facilities in Quebec and Ontario.

Which electrical equipment can be repainted?

The metal surfaces that play no part in electrical insulation are repainted: tanks, covers, radiators, conservators, cable boxes, control cabinets, switchgear enclosures, frames and supports. Insulating and functional parts are protected and never painted.

Which safety rules apply near energized equipment?

Work is done on equipment that is de-energized, locked out and grounded under the owner's procedure, or outside the limits of approach set by the owner's rules and the applicable regulations. No distance is improvised on site: it comes from the owner, CSA Z462 and provincial regulations.

• De-energizing. The facility owner isolates, locks out and verifies the absence of voltage; lockout follows CSA Z460 and the site procedure.
• Work permit. Every intervention in a substation is done under permit, with a person in charge designated by the owner.
• Limits of approach. Neighbouring equipment that stays energized defines zones that workers, ladders, poles and lifts must not enter.
• Oil and flammability. No hot work; static control during spraying; cleaning products chosen accordingly.
• Environment. Containment of preparation debris and drips, response plan in case of an oil leak.

Our crews and qualified subcontractors work to site rules and under the supervision of the personnel designated by the owner.

How is an oil-contaminated tank prepared?

A tank is prepared by degreasing first, then removing rust and loose paint with power tools, and checking that no oil remains before application. Power tool cleaning on an oily surface only spreads the contamination.

• Degreasing. Solvent or detergent cleaning per SSPC-SP 1, rinsing, visual and touch check; active leaks are repaired before painting.
• Power tool cleaning. SSPC-SP 3, SP 11 or SP 15 depending on the required grade; our article on SSPC-SP 3, SP 11 and SP 15 power tool cleaning compares these grades.
• Abrasive blasting. Rarely possible on installed equipment: abrasive gets into radiators, gaskets and cabinets. When deeper preparation is needed, glass bead or dry ice blasting can be considered with suitable containment.
• Existing paint. An adhesion test and a compatibility test come before repainting; see our article on painting over old coatings. Old coatings may contain lead: sampling is required before any preparation, as explained in our article on lead paint overcoating vs removal.

Which ISO 12944 paint system should be chosen?

The system is chosen from the site's corrosivity category per ISO 12944-2, the target durability and the preparation actually achievable. For maintenance repainting of installed equipment, the most common combination is an epoxy tolerant of power tool preparation, followed by a UV-resistant aliphatic polyurethane topcoat.

• Urban site or ventilated interior. A C3 category system, often sufficient for sheltered cabinets.
• Outdoor substation exposed to de-icing salts or in an industrial area. C4 or C5 category depending on actual conditions.
• Seaside or very aggressive atmosphere. A C5 or CX system, with matching preparation.

Our article on ISO 12944 C3, C4 and C5 paint systems details these systems, and our overview of ISO 12944 explains the categories. The topcoat colour is set by the owner; a light colour limits solar heating.

How are radiators and control cabinets treated?

Radiators are treated with care, because their thin sheet and narrow gaps do not tolerate aggressive preparation or high thickness, which can reduce heat dissipation. Cabinets are treated mainly from the outside, with internal components protected.

• Radiators. Degreasing, gentle cleaning, localized touch-ups and low-thickness application per the equipment manufacturer's guidance; a badly corroded radiator is replaced or reconditioned in a shop.
• Galvanized radiators. A surface treatment suited to galvanized steel is needed for paint adhesion.
• Cabinets. Exterior preparation and painting, interior masked, door seals checked; internal condensation is handled by the ventilation or heating the owner provides, not by paint alone.

How is paint applied near insulators?

Brush and roller are used near bushings and insulators, and spraying is reserved for large, well-masked surfaces away from insulating parts. Paint mist settling on an insulator affects its properties and must be avoided.

• Masking. Bushings, insulators, nameplates, gauges, relief devices, breathers and sealing surfaces are protected before any preparation.
• Ambient conditions. Surface temperature, humidity and dew point per the data sheet; in an outdoor substation, weather often decides the schedule.
• Coats. Stripe coat on edges, welds and bolting, then full coats up to the prescribed dry film thickness.
• Cure. The time before re-energizing and before contact with oil is read from the data sheet and coordinated with the owner.

Which checks and records should be required?

Checks are required at each coat, with a record handed over before re-energizing. They serve as the reference for the next maintenance cycle.

• Before application. No oil, preparation grade, ambient conditions, complete masking.
• During and after. Dry film thickness per SSPC-PA 2, adhesion by the test set in the specification, visual inspection for runs, misses and contamination.
• End of job. Full removal of masking, cleaning of insulators, photo survey and report.

Our article on coating inspection for DFT, adhesion and holidays describes these tests, and our guide to maintenance painting of steel structures helps plan a programme.

How do you get a quote?

State the type and number of units, their location, current condition, exposure category and the length of possible outages. Pricing is on consultation: it depends on access, safety constraints, preparation, masking and the system. We work in particular in Montreal and Saguenay-Lac-Saint-Jean. For our industrial painting service, built on our protective coatings, send photos and equipment data sheets through the request a quote form: reply within 24 business hours.

Frequently asked questions

Can a transformer be painted while energized?

Not for parts within the limits of approach: the equipment has to be de-energized and locked out by the owner. Only surfaces outside those limits, under site rules, can be treated without an outage.

Does a transformer tank have to be blasted?

Rarely on site. Degreasing and power tool cleaning are usually enough for maintenance repainting. Full blasting is better done in a shop, with the unit drained and dismantled.

Does paint reduce radiator cooling?

Excessive thickness can reduce heat dissipation. The equipment manufacturer's guidance is therefore followed and coats are not built up on radiators.

What if the old paint contains lead?

The method is adapted: low-dust preparation, containment, worker protection and waste handling per regulations. Overcoating can be an option if the old coating is well bonded.