When reading Manuf. Specs. in your opinion, does the word SHOULD be as mandatory as Shall per NEC 90.5A. The reason I ask this its because I had a contractor tell me that since the word shall is not used, it is a recommendation. I don't agree.

Would like your perspective on this...

Thanks

If you look up should in a dictionary.
Shall is the past tense of should.It is not a permissive term.
I think we as electricians are to focused on the word shall. Because it was beat in our heads for so many years.So we always think that if the sentence does not contain shall it s not a requirement.
So I agree with you.
Unless the install document has a glossary to explain the verbiage.

I'm not so sure. What you SHOULD do is not the same as what you MUST do. Right?

From an Inspector's view point should is not required to be done. From a Contractors view point if I don't do the should and something goes wrong the manufacturer will probably tell the Contractor "you should have done what we suggested so no warranty"

That's my point Bryan.
We believe that SHALL and MAY rule in the NEC.
But then we must refer to other documents published by others than the NEC. Which include UL and other NRTL'S and the manufactures.
Then the abuse we put on the english language.
BTW I don't recall Must in NFPA 70.
Which is not any part of shall or may.

This really is a problem we have all the time. ICC language doesn't match NFPA language. UL language doesn't match ICC or NFPA language. Each manufacturer uses their own language.

It's a real difficult call sometimes...

The NEC (NFPA 70) is written as Code to be legally adopted by jurisdiction. The wording is enforced as electric code and referenced and adopted by a jurisdiction...such as the state of Florida.
Mfg's Installation instructions are reference material and can be evaluated by the inspector or official. I wouldn't expect reference material to contain mandatory wording...(e.g..increasing the size of condenser supply conductors due to distance of the circuit.) although it may void the warranty...

But, Section 110.3(B) clearly indicates manufacturer's listing and labeling instructions shall be complied with and UL has clearly indicated installation instructions are a component of the listing instructions.

I just poked "must" into the search engine in the 2008 handbook. I saw it a lot in the commentary but only a few times in the actual code and the examples I saw, seemed to use "must" in the sense that it was physically required more than just being legally required. (example 110.9 " ...Equipment intended to interrupt current at other than fault levels shall have an interrupting rating at nominal circuit voltage sufficient for the current that MUST be interrupted."

This is an easy one. 110.3(b) requires the installation be done to manufacturer's specs. If the manufacturer's specifications say that the contractor SHOULD cut his toe nails before leaving the jobsite, then the contractor MUST cut his toenails before leaving the jobsite. Simple.