Installing A Circuit Breaker

Circuit Breakers

A breaker is designed to protect your wires from carrying too much current, and to trip off on an overload or a short circuit.  That is why proper sizing of breakers is so important (i.e. #14AWG wire on a 15 Amp breaker, #12AWG on a 20 Amp breaker, etc.).  This is all spelled out in the CEC and NEC.  Never oversize a breaker to solve a tripping breaker problem!

The first question to ask yourself is – Why am I replacing this breaker?

If you are adding a circuit, and now need to install the breaker, then this of course is necessary.  The situation that I run into a lot is people wanting to replace a breaker because they think that it is faulty, or has failed, or trips off too often.  Not that breakers don't sometimes fail, but more often than not, the breaker is just doing what it's supposed to do, and the problem causing the breaker to trip needs to be rectified first.   

To Test for a Faulty Breaker

Unplug any devices that are on this affected circuit, shut off all lights, and then see if the breaker will reset.  If it resets with all known loads disconnected, then you can start re-connecting devices one by one, and/or turn on lights to determine where the problem is.

Turn off the breaker before plugging the item back in, and then reset, because if you have a short circuit in a device you can get a high inrush of current that can arc severely, possibly burning you or worse.  When a short circuit has occurred, an extremely high amount of current can flow before the breaker trips.  

Use a Voltage Tester!

If the breaker won't reset, and doesn't put out voltage on the load terminal (use a reliable voltage tester or a volt meter to check), even when all known loads are disconnected, then you probably have a faulty breaker, and it needs to be replaced. 

You will need to get all the information that you can (brand name, part numbers, breaker size, breaker type, etc.) so that you can get the proper replacement from your supplier of choice.  

Panels

Most homes will have a combination panel, with a main breaker, and then all the branch circuit breakers below.

Figure 1:  Combination Panel

Take note that even after taking off the panel cover, you don't have access to the main breaker compartment without removing the main compartment cover as well.  Don't open this cover.  If you have a problem with the main breaker, you will need to call in a qualified electrician for this. 

Figure 2:  Panel Cover Removed

Older Homes In older homes you may have a fused disconnect switch to disconnect power from the distribution panel that will isolate the breaker box to allow safe replacement of the branch circuit breakers.

In any case, arrange for some back up lighting beforehand, either with a reliable battery operated flashlight or lantern, or a portable generator with a trouble light, or lamp, etc.

In our example, let's assume that you have an ordinary combination panel, with a 100 Amp 2-pole main breaker, and then a branch circuit compartment.  We'll use a Cutler Hammer, CPM 120 Panel.  

Step One

Before shutting off the main breaker, shut off all branch circuit breakers first.

It is always best to remove the load from a breaker before shutting it off.  With the main breaker off, the buss bars that the branch circuit breakers connect to are isolated from the incoming voltage and will be safe to work on.  

Never just assume that the breaker has shut off properly - check for voltage on any adjacent two breakers to assure that the panel is dead.  

Figure 3:  Testing Power to Panel

Most homes will have 'push in' or 'stab in' type of breakers.  In some cases, usually in commercial applications, the breakers bolt into place on the buss bars.

 

Figure 4:  Square D Bolt-In Style Breakers

Figure 5:  Federal Pioneer Stab-In Style Breakers

Figure 6:  Cutler Hammer Stab-In Style Breakers

Step Two

Start by disconnecting the wire from the load terminal of the breaker and pull the wire out of the way to facilitate removal of the breaker.  

Step Three

Carefully pry the defective breaker out of its position as shown here.

Figures 7 and 8:  Carefully Pry Out Breaker

Take note as to how the breaker locks into position in the panel.  In the case of Cutler Hammer (formerly Westinghouse, Nova Line, etc.) the back of the breaker pushes back into a mounting strip first, and then pushes onto the buss bar.  

Re-insert the new breaker and push firmly into position.  Then re-attach the wire to the load terminal.  

Figure 9:  Re-Insert New Breaker

Figure 10:  Push Breaker Firmly Into Place

Figure 11:  Re-Connect Wires to New Breaker

Figure 12:  Check Breaker Connections

While you have the branch circuit compartment open, inspect for any other potential problems, like loose terminals, and it is a good idea to re-tighten all connections while you're in there.

Step Four

Now you put the panel cover back on, and if you have installed a breaker for a new circuit in a new position, you will have to remove the appropriate breaker knock-out from the panel cover.

Figure 13:  Turn On Main Breaker

After the cover is back on, it's a good idea to shut off all of the branch circuit breakers, then turn on the main breaker, and then one-by-one turn on all of the individual breakers.  Then check and test everything to see that all systems are normal.

Figure 14:  Turn On Individual Breakers

Figure 15:  Replace Panel Cover

Start:
First: Turn Off The Power.

Installing a basic single-pole circuit breaker involves 4 steps:

1. Feed the cable into the breaker panel.

2. Connect the ground wire.

3. Connect the neutral wire.

4. Connect the hot wire to the breaker and snap it in place.

Step 1:

	In this case, the power was controlled by a 100 amp breaker on the main breaker panel. I turned off the breaker.
	Then I removed the cover from the breaker panel.

This situation is a little different from most houses. This house has a 200 amp main breaker panel, which feeds 3 subsidiary breaker panels. This is a good technique for house wiring, although it does cost a little more.

This method allowed me to shut off the power at the main panel, so the 100 amp sub-panel had no live wires anywhere.  But there was still power to some parts of the house.

Most houses have just one panel, which contains the main breaker (typically 100 to 200 amps) and a large collection of single pole (120 volt) and double-pole (240 volt) breakers. In these cases, installing a breaker can be done safely, BUT...

There are still live wires present.  The big wires that enter the panel and feed the main breaker.  Avoiding contact with these wires is very important. (Worse would be accidentally shorting the service entrance wires with a metal tool, because they have a huge current capacity, and short-circuiting these wires would create a massive arc, like a big industrial welder, which would continue until something in the circuit was melted.  I know of no circuit breaker (other than the main breaker) that protects your service entrance wires from shorting.  I have seen 240 volt service entrance wires short together (during a windstorm) and the sparks are spectacular. I was surprised to learn that most step-down transformers that supply houses do not have short-circuit protection.

Breaker Panel Anatomy: 1, 2. Incoming Hot wires. There is 240 volts between these wires, or 120 volts between either wire and the neutral line. 3. Neutral wire. This is at the same electrical potential as the ground. At the main breaker only, the neutral is connected to ground. 4. Ground Bus Bar. This strip of metal has a row of screws for connecting the ground wires of the various circuits. 5, 6, 7. Neutral Bus Bars. This panel has 3 short bus bars for neutral wire connections. Some panels have only one long bar. 8. Circuit Breakers. Each single-pole breaker connects to one of the two hot bus bars. Each double-pole breaker connects to both of the bus bars (thus providing 240 volts between hot wires). 9. The last available space in this panel. Our new breaker will go here.

Note in the above photo that there is no main circuit breaker. This is a main lug type of panel, used as a subsidiary panel (sub-panel).  The breaker that feeds this panel is upstream, at the main panel. 

	I touched the probes of my electrical tester to the incoming hot wires...
	...No voltage, just as planned.

 

This is the volt-meter reading with the power turned on. That could really hurt.

 

	After I installed a 3/8" cable clamp, I ran the cable into the panel. See Installing A Cable Clamp for more info.
	I tightened the clamp with a cordless drill-driver on a low torque setting.

 

	I used a sharp knife to CAREFULLY slit the cable jacket.
	And then I cut away the jacket, all the way back to the cable clamp.

 

Step 2: Connect The Ground Wire

	A closer view of the ground bus bar.
	The new ground wire was snaked through the maze of wires. I made some bends so the wire would lay in an orderly fashion.

 

	I loosened a screw and inserted the ground wire...
	...and I tightened the screw firmly.

Notes On Screw Tightness:

Most circuit breaker panels have instructions that dictate the proper amount of torque (twisting force) to apply to the screw when tightening.  This panel specified 20 inch-pounds for #12 and #14 wire.  I have never seen an electrician use any type of torque measuring device when installing electrical equipment.  But be warned, there is a correct amount of tightening, and it's quite firm. Certain things can happen when the conductors are under full current load, such as heating, thermal expansion and distortion of the round copper wire. If a screw is not tight enough, a wire may begin it's career being secure but eventually become loose after repeated heating/cooling cycles.

Of course, if a screw is tightened too much, the threads will strip or the drive slot will strip. Anybody with doubts about tightness should purchase a good quality torque wrench and screwdriver attachments and become familiar with just how tight 20 inch-pounds feels like.

 

Step 3: Connecting The Neutral Wire

	The neutral line feeding the panel is supposed to be marked white (this one was covered with white electrical tape, which is OK).
	I routed the wire neatly and made some bends.

 

	I stripped the insulation from the end of the wire and inserted the bare end into a connection terminal.
	The screw was tightened.

 

Step 4: The Hot Wire

	There was one empty spot in this panel.
	A Square-D brand of single-pole breaker, 15 amps.

 

	A view of the connection terminal on the breaker. Two wires can be attached.
	A view of the bottom. The metal U-clips on the right hold the unit to a plastic bar in the panel. The U-clips on the left (hard to see in this shot) are part of the circuit, and connect to the hot bus bar.

 

	The hot wire was stripped and secured under the screw.
	Note the metal bus bar. The circuit breaker grabs on here.

 

	The installation sequence. First the hold-on clip is pushed onto the plastic bar. (I angled the breaker so a photo could be taken. In practice the breaker is parallel to its neighbor.)
	With my thumb I pushed firmly until the breaker was seated. The left end was still not connected.

 

The business end was pushed in firmly until it was seated. There are no screws that attach this type of breaker to the panel, it is held in only by spring clips.

 

Wrapping Up:

	The last knock-out was removed from the panel cover.
	I will leave this breaker turned off until the rest of the circuit is finished.

 

A Few Thoughts On Fear And Electricity

A relative showed me how to replace a circuit breaker, and pointed out the dangers.  When the main breaker is turned off (in a typical one-panel house) there is still voltage in the panel, at the two big hot wires that feed the main breaker.

Touching these wires would require a lot of carelessness. Or stupidity. My only fear is accidentally touching the live metal parts with the wire I'm working on, possibly causing a short and a big nasty arc. Whenever I have shorted something, I've always jumped or jerked my hand away, and it's that involuntary reaction that I figure might pose the biggest risk of injury.

I have become a firm believer in organizing the house's electrical system by using subsidiary panels. My preference is too locate a sub-panel near the kitchen, in the garage, on the second floor, etc. I prefer to have all basic 120 volt circuits connected to one of several sub-panels, leaving the main panel to supply only the sub-panels and the larger 240 volt appliances (range, dryer, water heater, well pump)