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#52 - FDC Plugs: What they are and how to install one

Posted by Jason Hugo & Cameron Sharp on 6/30/2016 to Fire Sprinkler System Components
FDC plugs prevent foreign material from entering a building’s fire department connection (FDC). What’s an FDC? Well, it is the brass access point that supplies additional water to a building’s fire sprinkler or standpipe system during an emergency. They’re usually outfitted with two, 2 ½” swivel inlets; FDC plugs fasten to these inlets to ensure smooth distribution. 

FDC plugs come in aluminum or brass. Not to be confused with breakable caps, which connect to the swivel using eye bolts, plugs are threaded and fasten into the swivel. They require a wrench to both fasten and remove. A thorough comparison of plugs and caps is available here. Plugs purchased from sites like QRFS and other reputable companies are universally accepted as the standard for every fire department connection.

Unfortunately, we have found theft to be the number one reason our customers replace FDC plugs. Brass is often stolen for its scrap value, and both FDC plugs and the fire department connection are made from brass. 

As building owners and facilities professionals, it is very important to keep FDCs protected – an ounce of prevention is worth a pound of cure! Keeping the inlets protected can help avoid expensive, mandated system flushes. As an alternative, aluminum FDC plugs can be substituted to reduce theft. 

Unless you’re from San Francisco or New York, which use 3” FDCs, it is likely your building’s FDC requires 2.5” plugs. This measurement represents the inner-diameter of the inlet where the threads of the plugs fasten. Identifying threads is important for coupling selection. The most common thread used for fire equipment is National Hose Thread (NH), also known as National Standard Thread (NST). Municipalities determine whether or not to follow NH thread sizing.  

Some of our readers may be looking for residential fire protection. With you in mind,      1 ½” FDC plugs were created. Made with solid brass, this plug withstands up to 300 PSI and is used on single outlets. Special threads are available upon request.  

Provided below are 3 highly useful steps for replacing a FDC plug:
*If installing plug into empty FDC skip to step 2

1. If your FDC contains an obsolete breakable cap, remove by unfastening eye bolts and clear away remaining debris.
2. Fasten FDC plug into swivel by turning wrench clockwise until snug.
3. Attach chain to fire department connection for easy retrieval when removed

Buying FDC Plugs

FDC plugs are the most durable way to protect your building’s fire department connection. While browsing for your next set, keep in mind a couple things. First, is to choose between brass and aluminum. Both options work equally efficient, but aluminum has been found to be less affected by theft. The second thing is to determine the correct thread size. You want to ensure it is compatible with the FDC – they are heavy, so you only want to ship them once. 

QRFS proudly carries brass and aluminum plugs for both 2.5" FDCs, and cast iron for 3" FDCs. We got your back San Francisco and New York. Our plugs come standard with NH threads, however, special threads are available upon request. 

FDC plugs protect your building and occupants; they save you money, by eradicating the need for repetitive system flushing; and they provide quick access for firefighters. Visit the link below to browse all available FDC plugs. 


This blog originally posted by Jason Hugo and Cameron Sharp at QRFS.com/blog on June 30, 2016. If you like what you've read, check us out at Facebook.com/QuickResponseFireSupply or at Twitter @QuickRsponseFS.

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