Combustion Catalog | Fives North American

Industrial Spark Igniter Construction Terminology


ignition timer must be used to keep the spark igniter on through the trial for ignition interval to give the main flame time to light.

It’s common for industrial burner manufactures to attach a sec- ondary insulator to long electrodes to support the electrode tip in the burner stabilizer. These insulators are often held in position by “crimping” the electrode on both sides of the insulator which widens the electrode slightly. Specialized tooling is generally required to reliably crimp the electrode, and the insulator is often specially designed and may only be available at a reasonable cost to the original manufacturer. TERMINAL NUT The “standard” electrical connection on most spark plugs is the SÆ terminal nut. This connection is ¼” Ø with a reduced diameter in the center to allow a wiring clip in the ignition cable boot to lock the ignition cable onto the terminal. Most igniters made in the USA have an 8-32 threaded stud that the terminal nut threads onto. Most igniters made everywhere else have a 4M (4 mm) threaded stud. While the major diameter of both these threads are nearly the same, neither terminal will fit on the others con- nection. In Europe it’s common for the ignition cable boot to connect di- rectly to the 4M stud instead of a terminal nut. Most igniters have a removable terminal nut but on a few designs the terminal is not removable. PART NUMBERS Many industrial igniters have an identifying part number on the insulator (often sealed under the ceramic glaze). These numbers are the manufacture’s part number, but in many cases, burner manufactures modify “standard” igniter products to make spe- cialized designs. When buying a replacement igniter, it is impor- tant to know the burner manufactures part number and not just the part number on the igniter. Using the incorrect igniter can cause unreliable burner operation.

The igniter body must be connected to the system ground for the spark to form reliably and to prevent a hazardous electrical shock condition for personnel. When picking a 4085-ignition cable, the "N" style standard 90° boot is a good fit for most 4055 electrodes. The ceramic insu- lator is too large in diameter for a type "W" boot. See bulletin 4085 for more details. The 4055 can be used as an alternative to the standard 10 mm spark plug in the 4442 burner by installing it in the OBS port. See the table on page 2 for the correct size. To provide replace- ment flame observation, install a pipe tee in the gas inlet with an in-line gas tight observation port. Many North American igniters are made with common elec- trodes. Use the bulletin to find the replacement electrode part numbers, and not just the number on the electrode. It’s a good idea to keep extra spark igniters and ignition cables as spare parts. When setting the insertion length of an adjustable igniter like the 4055-M, use the least insertion length as possible to achieve reli- able ignition. In most cases the further an igniter is set into the burner the greater the thermal stress on the igniter electrode. REPLACING DISCONTINUED IGNITERS If you need to find a new igniter for an obsolete or discontinued burner there are many factors to consider. Read the "industrial spark igniter construction terminology" section in this bulletin to learn the industrial igniter lingo. If the igniter you need has a simple design, check for a direct replace- ment in this bulletin. If the igniter has a ground wire attached directly to the shell, it’s probably a common igniter. If the igniter has a secondary insulator it will be much harder to find a direct replacement. Spark igniters can be very expensive to build if they have custom ceramic parts and may not be cost effective to build if the volumes are not very high. Because igni- tion is critical to safe burner operation and the cost of developing new parts for discontinued burners is so high, it may be better to replace old burners with new ones that are supported and have a reliable source for spare parts. You can ask your Fives North American representative for help finding an igniter or a complete replacement burner. Provide pictures, descriptions, every igniter dimension you can measure, and how many you need.

Terminal Nut

Part number (sometimes)


The spark should be maintained through the trial for ignition interval and then de-energized by the Burner Management System. Leaving a spark on constantly will reduce the life of the igniter and could cause several dangerous conditions.

Since sparks produce ultraviolet (UV) light, they can often be detected by UV flame supervision equipment, in these cases, an

Bulletin 4055 Page 9

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