What will be the effect if the threaded portion of conduit is not fully fitted to the coupling?

Answer 1

In the United States, the NEC requires that runs of conduit be continuous and connections be made wrench tight. If done properly this provides added grounding protection to your circuits. If a connection is left loose, that added grounding protection does not exist.

There are times when threaded connections simply won't thread completely. This may require that the conduit threads be "run" with a threader to remove whatever is preventing this from happening. With experience you learn what is acceptable or not acceptable. Generally, if the connection is "wrench tight" and is otherwise secure, that is sufficient.

Answer 2

When threading rigid conduit to a coupling you will seldom get full thread coverage Three to four thread penetration will suffice to keep the conduits together and maintain the metallic system intact.

With explosion proof systems code requires full five thread coverage. With explosion proof fittings, this can be accomplished because of the finer machining of the threads in the fittings that the conduit screws into.

Answer 3

You would not have a full metallic conduit system. A complete system is needed to make an electrical bond for the whole electrical system. In older conduit systems before a code change the metallic system was used to carry any fault currents back to the distribution to trip the breaker.

Any break in the conduit system would prevent this from happening and hence the electrical code change.

Answer 4

The cable inside the conduit will be exposed.

Answer 5

And you will loose the integrity of your ground if you are using the conduit as your equipment grounding conductor.