Torque Recommendations NFPA 70b conflict with manufacture?

[mikeames]

I was reading Mikes Pool safety publication https://www.mikeholt.com/files/PDF/Swimming_Pool_Safety_by_Mike_Holt_rev.pdf

In there he states to torque to 90% of manufactures recommendations according to NFPA 70b.

"Torque all terminals to 90% of the manufacturer’s recommendations in accordance with NFPA 70B. "


Why would manufactures recommend one spec and then NFPA70-b recommend otherwise? If that is the case wouldn't the manufacture overrule anyone else?

 

[zbang]

And why would the NFPA recommend less that the mfg?

 

[jusme123]

When installing equipment, follow the manufactures listed torque values.

NFPA 70B is a book for the maintenance of electrical equipment

 

[mikeames]

That's my question. Why would Mike write this in his documentation several times. What am I missing? I am guessing since it is in the scope of MAINTENANCE that you would only re torque to 90% because you don't want to disturb the connection and possibly over torque. So going to 90% check the connection to make sure it not too loose yet does not break it free over the specified value? That's my guess. I hate guessing.

 

[zbang]

You can't actually (re)torque a bolt without turning it, all you can do is see if it's really loose ('cuz of "sticktion"). Lots of discussion on these fora about that.

I have no idea about the 90%, either.

 

[Jraef]

I find no evidence of anything relating to 90% of manufacturer's recommended torque in my copy* of 70B, in fact just the opposite; there are multiple references to using the manufacturer's recommended torque values.

I think the context of Mikes web page is regarding INSPECTING equipment that is already installed. So my speculation on his reasoning is that in the process of CHECKING torque, you check it at 90% because you don't want to snap a bolt off by accidentally going over 100% and having to try to prove that you didn't. Using 90% ensures that you knew it was not loose without running the risk.

*My copy is 2006... so take that for what it's worth.

 

[FionaZuppa]

I might venture a guess MH is on the 90% # because most field work probably overshoots that setting (while doing the deed) by ~10%, or the cheap tools being used overshoot the setting by ~10%.
Maybe, maybe not, just guessing.

 

[FionaZuppa]

The MH doc clearly states

Step 1. Electrical Service – Inspect service equipment to ensure it’s in compliance with the National Electrical Code:

Seems that doc is a "inspection" doc, and 90% is a re-torque "check" value, so perhaps if you get movement at 90% then the item was loose and you should get it back to 100%? Perhaps 90% so that if it's at 100% already the 90% will not disturb the "seating". If you go in at 100% then the err in the tool could likely disturb good set fittings and you will think it was all loose. Again, just guessing, but this does seem in alignment with the MH 90%.

Read 70B too.

ref: https://www.nfpa.org/Assets/files/AboutTheCodes/70B/70B_F2015_EEM-AAA_FR_Statements.pdf