Combustion Catalog | Fives North American

Industrial Spark Igniter Construction Terminology

Full Insertion Length

Straight mounting thread with shoulder and crushable metal gasket

Electrode mounting thread


Insulator (ceramic)

Insulator Nose

Secondary Insulator

Electrode crimp

Terminal nut

NPT (tapered pipe) mounting thread

Metal Shell

Electrode or spark gap

Part number (sometimes)

Full Insertion Length Electrode Length Ground electrode or "side wire"



Igniter insulators are normally made from high quality glazed Alumina. Their length projects out well past both ends of the metal igniter shell to prevent high voltage power from arcing to the metal shell. The length that the insulator sticks out can vary depending on the manufacturer of the igniter. It is especially important to consider the length of the insulator nose as it relates to the electrode insertion length. MOUNTING THREAD Most industrial igniters have mounting threads to attach to a pilot or burner. The two most popular styles of threads are: Straight machine threads, normally one of the standard metric spark plug threads (10 mm X 1.0), (14 mm X 1.25) or (18 mm X 1.5). These igniters typically are made with a shoulder where the igniter seats (usually with a crushable metal gasket). One advan- tage of these igniters is the mounting shoulder guarantees the electrode insertion into the burner is always at the same length. Tapered pipe thread (NPT) is also very popular, with ½”-14 NPT thread being the most common. The advantage of pipe thread is many burners have NPT threaded lighting ports, and pipe adapt- ers are common and inexpensive. The disadvantage is the inser- tion length can vary dependent on the amount of pipe taper. Bulletin 4055 Page 8

Most industrial igniters are made with a metal shell (usually steel) that has mounting thread and supports an insulator that keeps the igniters electrode isolated. In most designs one end of the metal shell has been formed around the insulator with an indus- trial press which permanently locks the insulator into the shell. ELECTRODE Unlike most automotive spark plugs, most industrial igniters do not have a built-in resistor. The center electrode is usually a solid rod all the way through the igniter. Most electrodes are made from materials that have a high resistance to thermal stress and oxidation, like Kanthal or high Nickel alloys. For proper igniter operation there must be a small gap between the electrode and an electrically grounded area where a spark can form when power is supplied by an ignition transformer. Some igniters have an additional ground electrode (sometimes called a side wire) to provide this place for the ignition spark to form. Igniters without a ground electrode must have a ground path provided by an additional adapter or by a surface inside the burner stabilizer. A spark gap, close to 1⁄8 ” (3 mm) +/- 1 mm is most common.

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