Transitioning between conduit sizes and types using a threaded bushing

Question

US, Southern CA, NEC 2017

I need to transition from 1" PVC to 3/4" LFxC to connect to a weatherproof junction box with 3/4" NPT hubs.

My first thought was to glue on a socket x 1" NPT female fitting to the end of the PVC, and use a threaded adapter to connect to the 3/4" NPT male fitting on the end of the LFxC. I have seen plumbing versions of PVC bushings to go between 1" NPT to 3/4" NPT, but I assume using those is not allowed because they're not UL listed for conduit use.

Questions

• Does code allow use of a UL listed aluminum bushing like McMaster #7864T23 with non-aluminum fittings?
• If using LFMC instead of LFNC, the fittings I've found are steel - is there going to be a corrosion issue due to dissimilar metals?
• If I need to stay within the existing conduit types, is there a simple way to get from the 1" PVC to the 3/4" flex conduit fittings?

Answer 1

I'd get a weatherproof box with 1" hubs on it

Amazingly enough, weatherproof boxes with 1" hubs are a thing, although you may have to order one in through your nearest supply house (or online) instead of just stopping by the nearest big-box store. I would use one of those instead of trying to field-fabricate a swedged reducer down to 3/4", since you can use reducer bushings in the larger hubs much more easily than you can expand a smaller hub out to fit a larger conduit.

Answer 2

The fitting pictured above apparently is called by many different names: fabricated reducer, or swedge, or swage, and maybe others.. It is a common way of adapting a large conduit down to a smaller terminal or box. It's done routinely in my region where the power utility requires 3" conduit for everything, but sometimes one wants to install a meter base that can't accept conduit that large. They're nice, as compared to the square-ish plumbing adapter, because they give a nice taper which one presumes will help minimize the conductors catching on the edge when they're pulled through.

I hesitate a little in suggesting this because I haven't been able to find one in the 1"x3/4" size you need. However, 3/4" PVC conduit is relatively easy to heat form in the field. You could make your own part. Consider the bell end "coupler" on the end of a whole piece of 3/4" conduit. With a little heat you can soften that bell and then stretch it further until it either fits the inside of a 1" coupling, or even until it is large enough to slide directly onto the end of the 1" conduit. You could then put the 3/4" terminal adapter on the unmodified end of the 3/4" conduit and wind it into the hub.