Ramona Greene found wiring wrapped in fabric in her late-1800s Georgetown rowhouse when the contractor went into the walls to gut and renovate her home.

Sparks flew out of the wall as Seth Feldman drilled a hole in his 1980s Chevy Chase, Md., house to hang up a picture.

This winter Bill Crandall had to “choose between heat, boiling water in the electric kettle and charging my electric car or risk blowing a fuse in my 1950s Takoma Park [Md.] house,” he said.

Electrical problems in your old house can be right there in plain sight or hidden behind the walls. It’s become particularly pronounced during the pandemic with parents and children Zooming and using electronics all day as they work remotely, overtaxing antiquated fuseboxes and frayed wiring.

So it’s important to upgrade, re-wire or otherwise fix the homes we either move into or already live in.

Electricians consider pre-1940 electric systems antiquated; 1940-1980 electric systems older and most likely to have problems today; and post-1980 systems the least likely to present major problems, said Daniel Blum, an inspector with Integrity Home Inspection Services in D.C.

“Bringing up to code” means upgrading the electrical system to install technology that reflects the latest research. For example, shock-protection receptacles can be added to an old bathroom to replace an existing wall outlet.

Recommendations for electrical system updates occur in phases, said Blum. Every three years the electric code is revised by the National Fire Protection Association to incorporate the research done in the preceding three years.

Costs for electrical services vary widely — from about $25 to $30 an hour (in addition to the service charge) to replace a receptacle; to about $200 to rewire an outlet; and to about $3,000 to rewire an electrical system.

Electricity is a complicated subject for most people. It’s much easier to understand water problems because you can see a leak or mold.

“You don’t see a fire before it comes,” said Catarina Bannier, an agent with the DC House Smarts team at Compass.

And it’s hard to imagine what’s behind the walls of your house.

Hiring a licensed professional inspector to check out internal house electrical systems is the usual route prospective buyers take to get a true sense of a property they’re considering purchasing. It’s also a vehicle for homeowners who want to upgrade their electrical systems but don’t know exactly what they need done.

A one-hour precontract inspection ranges from $195 to $275 depending on house size. A three-hour standard inspection ranges from $325 to $1,350 depending on price of the home, square footage, age and number of kitchens, electrical services, and heating and air-conditioning systems.

The inspector will identify problems that need to be taken care of. Traditionally, buyers may have asked the seller to make the electrical system repairs or lower the price. But that may not be possible in the current market.

“Today it’s not that simple,” Bannier said. “Buyers don’t have the luxury to reject an old house in this market. With lean inventory and multiple offers, buyers aren’t taking the chance of losing competitiveness by adding contingencies even as ordinary as an inspection clause. A few years ago I had a buyer who walked away because of an electric problem but I doubt I’d see that now.”

Rebecca Weiner, an agent with the Rebecca Weiner Group of Compass in D.C., suggests taking advantage of something called a pre-offer inspection. It’s a much shorter, less comprehensive inspection, that’s scheduled by the buyer with consent of the seller before an offer is made. The inspector spends about an hour instead of three.

“A pre-offer inspection lets you know what you’re buying, what fixes you’ll have to make and generally will make you feel more comfortable about the state of the house,” Weiner said. “If you’re out a few hundred dollars it’s a risk worth taking and the cost of doing the business of buying a house.”

“With covid some sellers are reluctant to allow pre-offer inspections, others limit it to an hour or two,” said Brian Sobotka, an agent with Long and Foster Real Estate in D.C. “I’m seeing more time limits.”

Blum, who has extensive electrical training, said his precontract inspections are one-hour walk-throughs, a “walk-and-talk” in agent-speak. He determines the age of the furnace, air conditioners and water heater, and the probable amp rating of the service.

During a full three-hour standard inspection, he said, “I verify that circuit breakers are properly matched to the corresponding electric wire sizes to prevent circuit overloading; and I sample random wall outlets in each room using a handheld plug-in tester to check polarity and grounding.”

After a standard inspection he’ll inform the buyer which sections of the electrical system have been updated and are okay and which parts are most in need of a redo.

Sobotka recommends an inspection even for new construction. “You can’t assume all’s well and perfect,” he warned, recalling a pre-drywall inspection for one home buyer.

“When you run electric wires they should be laid in straight lines and at right angles,” Sobotka said. “I noticed a lot of these wires weren’t straight. They were run diagonally across the studs because the developer wanted to save money. Not only is this not to code, it could pose a fire hazard if the wire were punctured. We had the builder rerun the wires. There was pushback but the issue was remedied.”

Most of the time you don’t discover these things until the inspection. Agents are typically more aware of electric issues than home buyers because they see so many houses “but we’re not electricians so we always should defer to professionals,” said Weiner.

“Even if I unscrew a socket and look inside I don’t understand what I’m looking at,” said Bannier. “I see a ton of wires in different colors going in many directions. You need an inspector to look at the invisible interior parts to see what kind of power is coming into the house and to ask basic questions.”

Here are some common electrical issues and how to address them:

● Overloading means more amperage is induced to flow through the electric wire than it has the capacity to carry.

“Overlamping light fixtures is a common thing that everybody does. You ignore the wattage limit and toss in a 100-watt bulb when the fixture is designed for 50 watts,” said Allen Gallant, a three-decade master electrician and owner of Gallant Electric in Lexington, Mass. He was the electrician-contractor for “This Old House,” the PBS home-improvement TV series, for 15 seasons.

“The bulb’s intense heat can scorch or melt the socket and insulation on the fixture’s wires, which increases the risk of sparks and a possible fire,” he said. Today LEDs are replacing incandescent bulbs. They emit much less heat while offering the same brightness.

“When the pandemic started we got many calls because of overloading,” said Chuck Niglio Sr., a 35-year master electrician and owner of Chuck Niglio and Son Electrical Contractors in Silver Spring, Md.

“Circuits were overloaded because the whole family was home,” he added. “Parents were on Zoom calls, kids were on Zoom classes. The coffee pot was on all day. Cellphones, printers, scanners were being used on top of all the usual appliances. It was too much for the various circuits to handle. If you have an accumulative load more than the circuit breaker can handle, the circuit breaker in the panel box will trip off.”

Niglio surmised that many callers didn’t know that they simply had to go to their circuit breaker panel box and flip a breaker switch back to the “on” position. If he sent a technician to the house he’d have to charge them a minimum-hour fee of $130.

Instead, he walked people through the steps themselves while talking on the phone. The handle of the breaker switch that’s “tripped” typically has some play in it, meaning it moves slightly back-and-forth to the touch. You must turn it all the way off and then back to the “on” position.

“When any circuit trips, it’s a good idea to inventory the outlets, lights and other equipment running on that circuit, to allow you to balance the circuit more efficiently,” Niglio said. That means walking around the house, looking at the collective number of devices that are plugged in and trying to distribute them more evenly in different locations.

● Grounding refers to the third wire or prong in an outlet. It’s safer to have three-prong outlets but some older homes don’t in some of the house wiring. This means there’s a heightened risk of shock or fire in the event of a malfunction; but electricians are able to replace two-prong receptacles with properly grounded three-pong ones without rewiring the whole house at a modest cost.

● A short circuit is an instantaneous massive overload of an electrical circuit caused by the live metal of a wire or device directly touching any kind of grounded metal object. What happens is a “modest explosion of the metal parts or if the circuit breaker doesn’t shut off in time, the wires — and the house — can catch on fire,” Blum said. “You should always call a licensed electrician because this is too hazardous a situation for any homeowner to deal with this.”

● Knob and tube wiring is an antiquated wiring method that was used when the average home had few appliances or electric devices and needed much less electricity than we do today. The wires were covered with fabric; white ceramic knobs secured them to the house frame; and white ceramic tubes were installed where the wires penetrated the frame.

Household insulation was often laid over the wiring, which created a dangerous situation. When an electric current flows through the wires, heat builds up and the insulation prevents it from dissipating — so a fire-inducing condition is created. It’s generally understood that this type of wiring isn’t safe and should be replaced.

● Cover plates of receptacles and switches can be painted but not the sockets and switches themselves.

● Aluminum wiring is a safety hazard. It was installed in the 1960s and ’70s because it was cheaper than copper. Aluminum isn’t as good as copper because it’s a softer metal and expands more when heated.

Continual expansion and contraction can lead to movement of the wires inside the wall, loose wires and overheating. The wiring itself isn’t actually the problem because aluminum conducts electricity safely; the problem is at the connections of the wire to the switches, outlets and other electric devices.

Those connections can deteriorate and become a fire hazard. If you’re not sure your home has aluminum wiring, hire an inspector to investigate and recommend what safety measures, connector replacements or rewiring you need.

● Some circuit breaker panels, especially those without a single main shut-off valve and installed before 1980, should be replaced, said Blum.

“During an inspection I observe the condition of the circuit breaker panel/main panel, describe the upgrades an electrician is likely to propose,” he said. “If I see that the main electric wire attached to the side of the house is degraded or perforated I’ll recommend a complete service upgrade — called a ‘heavy-up.’ ”

● Homeowners should watch over their electrical systems as judiciously as they do their heating, cooling and plumbing systems, with regular professional maintenance checks, and get anomalies taken care of.

● Not enough outlets is a common complaint. “People always want more light even in the garage and closets and finished basements,” said Jerry Alice Lineback, who lives in a 20-year-old house in Paradise, Calif.

Her bathroom had one outlet that she used for a water flosser appliance, radio, electric toothbrush and blow dryer with a three-outlet plug-in. But that wasn’t sufficient. So she installed a new outlet herself.

“I have lots of electric experience from years of living in older homes and especially helping my father rewire our 19th-century farmhouse in Garnett, Kansas, where I grew up,” she said.

● Not everyone can or should do their own electrical work. Some electric fixes may seem easy but Blum counsels people against amateur renovation. “Particularly in the oldest homes, Harry Homeowner should resist the temptation to get involved,” he said.