Raintight fittings
- Thread starter pierre
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Re: Raintight fittings
A taper tap cuts a conical thread, unless it is run through the complete coupling.
A pipe die is conical and will cut a tapered thread.
Only the pipe or conduit needs to be tapered for a wrench tight fit that will hold pressure. A lubricant or conductive sealant insures a good low impedance connection.
A taper tap cuts a conical thread, unless it is run through the complete coupling.
A pipe die is conical and will cut a tapered thread.
Only the pipe or conduit needs to be tapered for a wrench tight fit that will hold pressure. A lubricant or conductive sealant insures a good low impedance connection.
russellroberts
Senior Member
- Location
- Georgia
Re: Raintight fittings
I'm not much of an authority on anything,but I have done a lot of work with galvanized water lines.
There are 2 common pipe threads,the tapered National Pipe Thread,and the straight National Standard Free-Fitting Straight Mechanical Pipe Thread. They will both tread on conduit or water pipe,but only the NPT will seal without a sealant of some type. And then it won't hold water pressure.
Years ago I was attempting to repair a water leak for a customer,and tried to use a 1/2" rigid coupling to keep from making a trip to the plumbing supplier,it didn't work and I got wet.
Russell
I'm not much of an authority on anything,but I have done a lot of work with galvanized water lines.
There are 2 common pipe threads,the tapered National Pipe Thread,and the straight National Standard Free-Fitting Straight Mechanical Pipe Thread. They will both tread on conduit or water pipe,but only the NPT will seal without a sealant of some type. And then it won't hold water pressure.
Years ago I was attempting to repair a water leak for a customer,and tried to use a 1/2" rigid coupling to keep from making a trip to the plumbing supplier,it didn't work and I got wet.
Russell
- Location
- Illinois
- Occupation
- retired electrician
Re: Raintight fittings
Bennie,
Sure it can. The diameter of the threads at the open end of the fitting is larger then that at the inside end. For NPT the taper is 1:16 or 3/4" per foot. Straight threaded pipe couplings do exist, but they are not "NPT" and I'm not sure of what they are used for. Every plumbing coupling that I have ever seen used has a tapered thread. I have seen straight treads on hydraulic fittings but those fittings use "O" rings between the two part to make the seal. The common NPT thread requires the use of "pipe dope" or teflon tape to make a complete seal. There is also a NPTF which has some differences in the treads to permit a complete seal without the use of "pipe dope".
Don
Bennie,
Sure it can. The diameter of the threads at the open end of the fitting is larger then that at the inside end. For NPT the taper is 1:16 or 3/4" per foot. Straight threaded pipe couplings do exist, but they are not "NPT" and I'm not sure of what they are used for. Every plumbing coupling that I have ever seen used has a tapered thread. I have seen straight treads on hydraulic fittings but those fittings use "O" rings between the two part to make the seal. The common NPT thread requires the use of "pipe dope" or teflon tape to make a complete seal. There is also a NPTF which has some differences in the treads to permit a complete seal without the use of "pipe dope".
Don
russellroberts
Senior Member
- Location
- Georgia
Re: Raintight fittings
The NPTF threads and the NPT threads appear visually the same but when tightened,the NPTF threads will "crush" slightly to allow a seal w/o sealant. The NPT threads will generally keep water out,but won't hold internal pressure w/o a thread sealant.
I'm holding a 3/4 rigid coupling,and a 3/4 galv. coupling. The rigid coupling has threads that go completely through the fitting,the galv.threads don't. I also have a galv. pipe nipple that has threads on one end about 4" long,the rigid coupling will thread all the way up like a nut, the water coupling won't.
Russell
The NPTF threads and the NPT threads appear visually the same but when tightened,the NPTF threads will "crush" slightly to allow a seal w/o sealant. The NPT threads will generally keep water out,but won't hold internal pressure w/o a thread sealant.
I'm holding a 3/4 rigid coupling,and a 3/4 galv. coupling. The rigid coupling has threads that go completely through the fitting,the galv.threads don't. I also have a galv. pipe nipple that has threads on one end about 4" long,the rigid coupling will thread all the way up like a nut, the water coupling won't.
Russell
websparky
Senior Member
- Location
- Cleveland, Ohio
Re: Raintight fittings
RMC installed with listed raintight couplings and connectors is then considered a "raintight" installation. However, your point of when RMC and threaded couplings are installed as being not as raintight as the EMT style is correct. The idea that is often promoted is that "raintight" is the same as "liquidtight or watertight" and therefore no moisture will enter the system. As we both know, there is a major difference in these two listings. Consequently, many times RMC is thought of as "liquidtight or watertight" when in fact it has no such listing. When RMC or any conduit system (exclucing liquidtight)is used outdoors, it needs to be installed "arranged to drain" which is an indicator that it will let moisture enter the system.
Is this then a code violation when we use RMC on a service entrance with threaded couplings? No. Service entrances are not required to be "liguidtight or watertight" only "raintight" just as the meter enclosure is only "raintight" or "rainproof".
Hi Don,
RMC installed with listed raintight couplings and connectors is then considered a "raintight" installation. However, your point of when RMC and threaded couplings are installed as being not as raintight as the EMT style is correct. The idea that is often promoted is that "raintight" is the same as "liquidtight or watertight" and therefore no moisture will enter the system. As we both know, there is a major difference in these two listings. Consequently, many times RMC is thought of as "liquidtight or watertight" when in fact it has no such listing. When RMC or any conduit system (exclucing liquidtight)is used outdoors, it needs to be installed "arranged to drain" which is an indicator that it will let moisture enter the system.
Is this then a code violation when we use RMC on a service entrance with threaded couplings? No. Service entrances are not required to be "liguidtight or watertight" only "raintight" just as the meter enclosure is only "raintight" or "rainproof".
Re: Raintight fittings
Couplings that will permit water to flow into the pipe will also let water flow out. This is desired in the event of water from condensation. This is necessary for underground conduit.
Unless the job specs require draining methods, the underground conduit is a submerged location not a wet location. A submerged location requires marine cable.
Couplings that will permit water to flow into the pipe will also let water flow out. This is desired in the event of water from condensation. This is necessary for underground conduit.
Unless the job specs require draining methods, the underground conduit is a submerged location not a wet location. A submerged location requires marine cable.
- Location
- Illinois
- Occupation
- retired electrician
Re: Raintight fittings
Dave,
Don
Dave,
I don't beleive that rigid conduit couplings are required to pass the "raintight test" that EMT couplings are required to pass.
Don
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