There has been some discussion about whether push-to-connect type plumbing fittings (Shark-Bites are a common brand name) maintain electrical continuity when using them on metal piping.
As near as I can tell, the unsatisfactory answer is that they are not tested or listed for continuity through them. One thing is certain, any bonding achieved through the connectors is purely “coincidental” as there is certainly no “positive” connection between the brass fitting and the metal pipe.
Coincidental contact between the fitting and the pipe happens when the pipe makes accidental contact with the fitting (intentional contact for this purpose was not designed into the fitting). Whether the pipe is inserted all the way or not, there may be no continuity through the fitting—functional or otherwise.
So what is the definition of electrical continuity–or better yet “functional continuity?” By lining up 3 pennies in a row touching each other, you will have continuity across the pennies, but how would that continuity function under a live load? Would it create an effective ground fault path to trip a breaker if necessary?
Not likely, and likely a bonding jumper would be necessary around such plumbing fittings.
In fact there is actual documentation from the manufacturer of Shark-Bite, push-to-connect fittings that recommends jumping around the fittings when used with metal piping.
I set up a little experiment with an assembly of 4 push-to-connect fittings to see how much voltage drop there would be. The voltage drop of the circuit through the soldered pipe assembly on the left (without any push-in-connectors) was 4.6%.
The voltage drop through the push-in-connector assembly without any load was up-and-down but generally around 25%. By merely wiggling the assembly a bit the voltage drop varied up and down. Under the load of a 1500 watt space heater, the fluctuation varied widely from 45% to 75%.
It was interesting to note that when I initially started the test, the assembly was plugged into an AFCI protected circuit. As soon as I turned on the 1500 watt space heater, the AFCI breaker tripped. I could actually hear the arcing at the connections. Seems like the AFCI functioned as intended.
The experiment and test results pictured above were completed on a circuit that was not AFCI protected. I found the results to be pretty dramatic.
This is a side view of the assembly, painted black for thermal uniformity.
Here is the thermal image of the assembly prior to turning on the heater.
Here is an image of the temperature within the assembly after 60 seconds.
Here is the temperatures within the assembly after 2 minutes: >356 degrees F. My decision that it probably was not a good idea to continue the experiment game next, as it appeared I now had two heaters in the room instead of one.
So while this little experiment may lack in some controls that would be present if the same testing was done in a professional laboratory, or by Myth Busters, it is likely good enough to conclude that push-in-connectors cannot be relied upon as a ground fault path and could even be a fire hazard if the piping they were in were to become energized.
The bottom line is that proper bonding is necessary around push-in-connectors installed in metal piping systems—or better yet, perhaps other types of fittings should be used.
By Charles Buell, Real Estate Inspections in Seattle
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