Before you add a 240-volt appliance, you need to make sure you've got what it takes.
Testing a Circuit Breaker Panel for 240-Volt Electrical Service
Updated on Dec. 27, 2024
A 240-volt service powers heavy-duty appliances like ovens, air conditioners, water heaters and electric dryers. If something goes wrong in that panel, it may cause those systems to fail, damage the appliances, or even lead to electrical hazards.
“This is why you should test the panel to confirm that each 240-volt breaker is supplying the proper voltage,” says Daniel Vasilevski, director of Bright Force Electrical. “Breakers will weaken or fail over time, and when they do, they may not deliver the full 240 volts consistently.”
Testing your 240V circuit breaker panels is also important to ensure all of the wiring going into the individual breakers has not become loose or broken. “It’s also good to look at it and just make sure there are no loose wires that could arc or spark in the panel,” says Todd Tripp, a home improvement expert with JustAnswer.
Here’s what to know about testing your 240V circuit breaker panel.
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What to Look for in the Breaker Box
Unless your home is very old and has never had its electrical service updated, it has 240-volt service from the street and into the main electrical panel as well. While you’re at it, take this opportunity to learn about vampire energy for standby power that can make many of your appliances run 24 hours a day.(Also, explore what modern home buyers need in new home appliances.)
Nearly every main electrical panel has two 120-volt wires and one neutral wire running to it from the utility company. Each wire powers one “bus” (copper vertical leg) inside the main service panel. That’s why you usually see two columns of circuit breakers (or fuses) when you open your service panel door.
The common 120-volt circuits that power everything from your lava lamp to your vacuum cleaner are powered by one of those two buses. The standard 15- or 20-amp circuit breakers work by clipping onto one of the buses. Then, the circuit’s hot (red or black) feed wire is clamped to the circuit breaker, while the neutral (white) wire and bare copper ground wire are clamped to the common neutral bar.
The way you get a 240-volt circuit is simple. A “double-pole” circuit breaker is clipped into both 120 buses at the same time, so the voltage to the circuit is doubled. That’s why these circuits have two hot wires, a neutral, and a ground at their 240-volt outlet to carry electricity to the appliance.
Do you have enough amperage capacity in the service panel for a new 240-volt appliance?
Service panels are rated for the maximum amps they can provide. A 60-amp panel found in an older home, for example, can handle up to 60 amps of current to the house. The panel has to be large enough to handle the existing electrical demand of the house plus the new appliance without exceeding the panel’s amperage rating. (A standard, no-frills electric range needs 40 amps.) Figuring this out is more complicated than simply calculating the electrical load of the circuit breakers already in the panel.
The electrician you hire to install the new circuit will help you decide if the panel is up to the task. Most home electrical panels have plenty of power for extra appliances, but if you have to increase the capacity, there are solutions. Most likely, if you have enough circuit space, you’ll have no problem adding the range circuit, especially if you don’t have any 240-volt power-hungry appliances like air conditioners, electric water heaters or dryers. Here are a few ideas for covering an electrical panel.
Is there physical space in the service panel for another double-pole 240-volt breaker?
Last, there have to be two spaces left in the panel for two additional circuit breakers. If the available spaces aren’t stacked directly above each other, existing breakers can be pulled and reinserted in new positions to provide that arrangement.
If you have an older panel that has fuses instead of breakers, or if the circuit breaker panel is already full, an electrician can add a subpanel to handle the extra 240-volt circuit. A subpanel is a mini electrical panel that is fed from the main panel to create spaces for more circuits. Adding a subpanel is relatively inexpensive, depending on how much work needs to be done and the condition of your service panel.
A subpanel probably isn’t worth the investment if you have a fused panel. It would be better to have the main home electrical panel upgraded to a modern circuit breaker panel–based one with plenty of room for extra circuits. Putting in a larger panel with higher amperage capacity may be several times the cost of a sub panel. It also might entail improving the home’s electrical system to bring it in line with local or national electric code requirements, a substantial additional expense.
FAQ
What tools are required to test a 240-volt breaker panel?
The most important tool is a digital multimeter (DMM), which can measure voltage, current and resistance.
“In a 240-volt panel, the multimeter determines whether a breaker or circuit is receiving the correct voltage,” says Vasilevski. “It works by measuring the electrical potential between two points and gives you a precise reading.”
Vasilevski also recommends using a non-contact voltage tester, which detects the presence of live voltage by sensing the electrical field around a conductor. “It is quick and easy to use and is an important first step when working near a breaker panel to confirm whether the system is live,” he says.
Beyond those tools, you’ll also need an insulated screwdriver, insulated gloves, safety glasses and a flashlight. A thermal scanner, aka FLIR, can also be a big help.
“Great care and caution need to be exercised when taking the cover off of your circuit breaker panel and testing the voltage to the double pole, breakers and the supply,” says Tripp.
What are the signs of a bad 240-volt breaker?
One of the most obvious signs is when the breaker trips repeatedly. Others include inconsistent voltage, no voltage, tripping without a load, being difficult to switch on and off, feeling spongy, flickering or surging appliances and lighting and visible damage.
“If you see discoloration, a melted appearance or even a burning smell near the panel, this is a red flag,” says Vasilevski. “These signs suggest the breaker has overheated or is arcing, posing a serious fire hazard.”
When a breaker won’t reset once tripped or immediately trips or refuses to reset, that could also indicate a bad breaker,” says Docia Boylen, owner of Handyman Connection of Golden. “Using your digital multimeter (DMM) you can check to see if the breaker is outputting electricity,” she says.
About the Experts
- Daniel Vasilevski is director and owner of Bright Force Electrical and has worked as an electrician for more than a decade.
- Todd Tripp is a general contractor and founder of Trip Mills Builders in upstate South Carolina, and a home improvement expert with JustAnswer.
- Docia Boylen is owner of Handyman Connection of Golden, Colorado, and was honored with several awards at the 2024 Handyman Connection Annual Conference.
Next: Check out homeowner’s guide to an AC fuse box.
