Reducing Drain Lines Before P Trap

[AndrewK]

This may seem like a crazy question. Is it ok to reduce a drain line BEFORE the p-trap? for example, a shower has a 2" Drain that is reduced down to a 1.5" pipe and then goes into a 1.5" p-trap where it continues until the building drain.

I mean a shower or sink is almost like they're being reduced from the size of the basin to the drainpipe that leads to the p-trap already, why can't you reduce it further as long as you have an appropriately sized p-trap?

 

[Jeff H Young]

The quickest answer is code it dosent meet code to reduce a shower to 1 1/2. I could tell you this and that about why I think some old guy decided this is code. but bottom line is because thats what they thought right. will a shower work on 1 1/2? yes should you break code and go small? probebly not but ive seen it many times