what makes flexibility necessary

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don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
From the first revision report:
501.10(B)(2) Flexible Connections.
Where flexibility is necessary, one or more of the following shall be permitted: ...
Who determines if flexibility is necessary? What does that even mean? Very little of the LFMC that I have installed in Class I, Division 2 areas was necessary. The equipment could have been hard piped. The flex is installed for convenience and cost savings, not because movement and/or vibration made the use of LFMC necessary.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
From the first revision report:

Who determines if flexibility is necessary? What does that even mean? Very little of the LFMC that I have installed in Class I, Division 2 areas was necessary. The equipment could have been hard piped. The flex is installed for convenience and cost savings, not because movement and/or vibration made the use of LFMC necessary.
Well, this is the one place where they honor the claim that the NEC is not a design guide. If you or the customer deem it necessary, and the AHJ goes along, then it's necessary.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Well, this is the one place where they honor the claim that the NEC is not a design guide. If you or the customer deem it necessary, and the AHJ goes along, then it's necessary.
That is my problem, this is a subjective rule and leaves the decision up to the inspecting authority and not the designer or installer.
 

Josh111

Senior Member
Location
USA
From the first revision report:

Who determines if flexibility is necessary? What does that even mean? Very little of the LFMC that I have installed in Class I, Division 2 areas was necessary. The equipment could have been hard piped. The flex is installed for convenience and cost savings, not because movement and/or vibration made the use of LFMC necessary.
The flexibility was necessary to reduce the risk of worker injury due to over exertion while connecting to equipment. No, probably examples would be equipment that vibrates.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
The flexibility was necessary to reduce the risk of worker injury due to over exertion while connecting to equipment. No, probably examples would be equipment that vibrates.
But my point is that for most of my installations, there is no physical reason that requires flexibility. The LFMC is just for cost reasons and convenience.
 

__dan

Senior Member
The phrase "suitable for the purpose" comes to mind, maybe 110.3 A (1), examined for suitability, or something like that. It's kind of a boilerplate grey area language, but probably can be found many times in the code with similar wording. In Ct interpretations come from the State and enforcement from the Town, so they do have a say about it, along with the owner (the guy paying the bill along with his agents and reps).

EMT has a lot of flex to it within a range, but vibration transmission is also a factor (or something that can be considered, when 'examining for suitability'). I like to think about it the way I think about thermal insulation. Not all R values are the same. So as you layer different types insulation, each peforms in a different way and the combination can perform much better than the same type all the way through.

Vibration and frequency transmission would work the same way. Different materials will filter or transmit differently, and a layered combination will have much better performance filtering over a wider range.

So factors to consider for suitability, equipment that has vibration, carried vibration from elsewhere that you want to stop, allowances for expansion / contraction, settling, ...

I always see flex at transformers and usually think all EMT and LB's would have been fine. The trannys have thin flex pads and bolts that you are supposed to loosen at the flex pads. But then if there's no flex and the conduit runs over someone's office, and he / she can hear it humming ... (is it suitable ...).
 

DrSparks

The Everlasting Know-it-all!
Location
Madison, WI, USA
Occupation
Master Electrician and General Contractor
What they mean is hardwired equipment that may need to be moved for cleaning or maintenance. E.g. commercial cooking equipment, fixtures in a ceiling grid, etc

Sent from my SM-A326U using Tapatalk
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
From the first revision report:

Who determines if flexibility is necessary? What does that even mean? Very little of the LFMC that I have installed in Class I, Division 2 areas was necessary. The equipment could have been hard piped. The flex is installed for convenience and cost savings, not because movement and/or vibration made the use of LFMC necessary.
Unfortunately, the code does not define what necessary means. Just like it stubbornly refuses to define other terms that are ambiguous.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
What they mean is hardwired equipment that may need to be moved for cleaning or maintenance. E.g. commercial cooking equipment, fixtures in a ceiling grid, etc

Sent from my SM-A326U using Tapatalk
Those types of things are not very likely in a Class I, Division 2 location.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Unfortunately, the code does not define what necessary means. Just like it stubbornly refuses to define other terms that are ambiguous.
My point is that the use of flex should be pretty much at the discretion of the installer and after the installer has determined that flexibility is needed then the code should tell us what types of flexible connections are permitted and how they can be installed.

The use of the "where necessary" makes it subjective and could leave it up to the inspection authority and not the installer.
I have submitted a PC on this.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
My point is that the use of flex should be pretty much at the discretion of the installer and after the installer has determined that flexibility is needed then the code should tell us what types of flexible connections are permitted and how they can be installed.

The use of the "where necessary" makes it subjective and could leave it up to the inspection authority and not the installer.
I have submitted a PC on this.
Won't get any argument from me on this. It makes little sense to me to say you can do something if it is necessary but not define what constitutes necessary. An install is either safe enough or it is not. If it is safe enough, it should be an option available to the designer regardless of the necessity.
 
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