Where is the cad cell located?

The cadmium cell is simply a type of photo cell that is mounted in the oil burner tube, usually near the rear, where it can "see" the flame when the oil burner is operating properly.

A Cad (Cadmium Sulfide) Cell is a photo conductive flame detector that changes its electrical resistance depending on how much light is available at the sensor. This is a common flame detection device used on fuel oil fired burners. The Cad Cell is used in conjunction with an Oil Primary Control mounted to the oil burner.

When the Cad Cell is mounted inside the oil burner and the oil burner is off, the location is dark and therefore the resistance reading between the two yellow wires connected to the Cad Cell are very high. These two yellow wires are connected to the F and F terminals on the side of the oil primary control. Usually the resistance reading will be 1 M ohm (1 MegaOhm) or higher between the two yellow leads.

When the oil burner ignites the oil, the chamber in which the Cad Cell is located becomes brightly lit due to the flame. This light changes the electrical resistance in the Cad Cell. With a good flame and a good Cad Cell, the resistance reading should usually be between 300 to 1000 ohms. The oil primary control is usually looking for an electrical resistance below 1600 ohms in order to verify the flame is present.

Before the oil primary control will allow the oil burner to turn on, there must be a connection between the T and T terminals on the oil primary control to show a call for the heat to turn on. The oil primary control must also have a resistance reading higher than 1600 ohms between the F and F terminals where the cad cell is connected to. The readings from the Cad Cell at the F and F terminals verify that there is no flame present when the resistance reading is higher than 1600 ohms. Then after the oil primary control turns the burner on, sending power to the spark transformer, the blower and pump motor, and to the oil solenoid, the oil primary control looks for a lowering resistance reading on the F and F terminals indicating the flame is present.

If the resistance value does not lower below 1600 ohms after roughly the first 10 seconds of operation, the manual reset button will pop and the burner will shut off, signaling a problem.

In order to troubleshoot the Cad Cell, disconnect the Cad Cell wires from the oil primary control and connect a multimeter to the two yellow leads from the Cad Cell. One multimeter probe is connected to each wire and the meter is set to resistance to measure ohms. Turn the burner on by connecting the T and T terminals. Since the Cad cell wires are disconnected from the oil primary control, the resistance reading between the F and F terminals will be immeasurable which is an acceptable measurement for the oil primary control to turn on. Measure the resistance value on the cad cell while the flame is present.

OL= Bad Cad Cell

> 1600 ohms= Bad Cell or Weak Flame

<1600 ohms but >1000 ohms= Good Cell, Weak Flame

<1000 ohms= Good Cell, Good Flame

Also before turning the power to the oil burner on, check to make sure the Cad Cell sensor glass is clean so light can enter the glass of the Cad Cell Sensor.

> 1,000,000 ohms= Good Cell, No Flame, No Light

> 1600 ohms but < 1,000,000 ohms= Bad Cell, Accidental Light Entering

<1600 ohms= Bad Cell, Possible Flame Present, Chamber Open to Light

<0.5 ohms= Bad Cell, Shorted Wires

Looking for some hands on examples of troubleshooting a Cad Cell? Check out our

"Oil Burner Primary Control and CAD Cell Operation and Troubleshooting!" video below!

Check out our free Quizzes to test your knowledge here!

Check out our Free Calculators here!

If you want to learn about refrigerants and how they work in a system, check out our “Refrigerant Charging and Service Procedures for Air Conditioning” book . Test your knowledge with our 1,000 question workbook along with the answer key! We also have quick reference cards for use out in the field! Bundle Packs are a great way to save and get faster shipping! Check out www.acservicetech.com/store

Tools that we use: www.amazon.com/shop/acservicetech

Follow us on Facebook for Quick Tips and Updates here!

Published: 12/15/2021 Author: Craig Migliaccio

About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel

Are you uncertain about which CAD cells are which in New Bedford Harbor? The increased number of confined aquatic disposal cells has led to some confusion about which are where and what's in them. Here's the rundown as well as what will be going on with them in the next year.

CAD cells are specially designed holes dug in the harbor floor that are then filled with sediment contaminated by toxic polychlorinated biphenyls (PCBs). Once filled, the cell is left to sit for at least six months while the sediment inside it settles, then it is covered with 3 feet of clean sand.

There are currently three CAD cells in the harbor, all of which are located north of Popes Island. CAD cells 1 and 2 were dug as part of what is known as navigational dredging.

As part of that process to maintain the 30-foot deep shipping channels in the port, contaminated sediment that is dredged is placed in the two CAD cells, according to Paul Craffey of the state's Department of Environmental Protection.

CAD cell 1, dug in 2004 is just east of Sawyer Street and CAD cell 2, dug in 2008, is located just northeast of that one. Both are managed by the Harbor Development Commission and contain an average of 10 parts PCBs per million parts sediment.

CAD cell 3 is currently being dug north of CAD cell 2, near Fairhaven's Poverty Point. That cell will be filled with sediment dredged as part of the South Terminal construction project, according to Chet Myers, a consultant for the Harbor Development commission and the Massachusetts Clean Energy Center. He said CAD 3 will also contain sediment that is contaminated on average at 10 parts per million.

Also north of Route 6 and Popes Island is what is known as a Borrow Pit, which Craffey described as a CAD cell by another name. That hole was dug in the 1950s and 60s to create the bulkhead for the State Pier. Craffey said the state then took advantage of what was "already a very deep hole" to bury sediments from the first round of navigational dredging.

Together, the Borrow Pit, CAD cells 1 and 2 contain 250,000 cubic yards of contaminated sediment, the same amount of sediment that will be held by CAD cell 3 alone, Craffey said.

The Borrow Pit and CAD cell 1 have already been dug, filled and covered. CAD cell 2 will be covered with clean sediment that is dug from CAD cell 3 this summer.

By burying the sediment and then covering it with clean sand, Craffey said, the navigational CAD cells make the harbor cleaner than it would be if it was only being cleaned by the federal Environmental Protection Agency.

The EPA's cleanup of the harbor's Superfund Site would only clean the lower harbor to 50 parts per million, meaning there are "very few spots" on the Fairhaven side of the harbor or south of Route 6 that are contaminated enough to be cleaned by the EPA.

Because of this, Korrin Petersen, who works for the Buzzards Bay Coalition, called the navigational dredging CAD cells "a bonus."

Deputy Port Director Edward Anthes-Washburn said the navigational dredging has economic benefits because it allows the harbor to host larger vessels.

"Without navigational dredging, we'd basically have to shut down the port," he said.

As part of the EPA's cleanup of the harbor, the agency will dig a fifth hole above Popes Island to hold sediment with PCB levels between 50 and 175 parts per million.

That CAD cell, known as the Lower Harbor CAD Cell, will be filled with sediment the EPA was previously planning to dispose at an off-site facility, before it changed its harbor cleanup plan in 2010. The EPA is expected to put out to bid the digging of the CAD cell in the next week.

David Lerderer, of the EPA, said he believes CAD cells are a safe way to clean the harbor because "the contamination is being consolidated to a smaller area where it can be controlled."

Local environmental groups say they are not so sure about that, and argue that the Lower Harbor CAD cell's contamination levels will be too high to be safe.

"We think this is taking a short cut and increases risk in the harbor," Petersen said. But, she added, because the EPA is moving ahead with the plan, the coalition is working with the agency to evaluate its engineering "to make sure we are at least getting the best CAD cell possible."

Edwin Rivera, president of the Hands Across the River Coalition, said his group is "opposed to every CAD cell," because he believes the navigational dredging CAD cells set a precedent for more CAD cells in the future.

In December, The Standard-Times discovered plans by the EPA to develop an Upper Harbor CAD cell to be located above Coggeshall Street near Riverside Park. That CAD cell would contain sediment with contamination levels 68 times as toxic as the Lower Harbor CAD cell.

This week, Lederer said "there are no plans for more CAD cells beyond the lower harbor."