I have seen this discussed many times. I don't know of any RNC manufacturer that makes primer and that is usually the key to putting it in their instructions. Personally I would use it but I have no documentation that requires it.
As Greg said, much discussed subject. Last discussion at a meeting and CEU class from Carlon mfg rep (real factory guy) was..." did any of you guys ever read the installation instructions??"
No mention of primer is made!
Shocker comment was that in order to do a Carlon PVC install to conform to UL listing that ALL components must be from Carlon including the glue!! That started a lively debate! (Substitute any mfg name for Carlon, the instructions should be the same.)
But, really how many of us read instructions?? Specially for PVC, conduit, NM?? LOL
There are quite a few things that don't make sense with plastic raceways. You can glue Smurf tube into a RNC connector but you can't glue Carflex (Flex nonmetallic) into one. That is strange to me because you can glue the white kind (spaflex) into an identical plumbing connector and it is rated the same as sch40. (well over 100PSI) I think that is simply because they sell the LFNC connectors for about 10x as much and a smurf connector is about the same.
I called them and they said they recommend using a chemical cleaner prior to using cement.
When you look at the installation instructions for the conduit there is no mention except for solvent...
I think the NEC should have a section regarding the installation of PVC etc and cleaning...we all know it will not hold if you just wipe it off or if it is wet/muddy...it will pull apart exposed or underground with freezing water inside...
The cleaner/primer makes a huge difference in how strong the joint is whether the pipe looks dirty or not. For most electrical uses it may not actually make that much difference but as AK Greg says, you don't want it pulling apart on you.
What are you worried about? That the electricity will leak out and make a puddle?
OK, so you want to be fussy. Could you show me a primer that's UL Listed? Did you know you're supposed to use listed cement?
As for the instructions ... UL has made clear, on many occasions, that they do NOT consider any statement along the lines of "use only our stuff" to be part of the listing instructions. This point was well developed in the "classified breaker' debacle.
As far as UL is concerned, you may use ANY product listed for it's purpose.
Look to the opening pages of any UL standard,and you will find many other standards referenced. This should tell you that products are tested while keeping in mind industry standards. For example, to ensure everyone uses the same threads on fittings. Or, that "schedule 80" means the same thing to everyone.