# what makes flexibility necessary

#### don_resqcapt19

##### Moderator
Staff member
Still have no idea of what you are trying to tell me. The "where necessary" applies to all of the permitted wiring methods in 501.10(B)(2).

#### romex jockey

##### Senior Member
Still have no idea of what you are trying to tell me. The "where necessary" applies to all of the permitted wiring methods in 501.10(B)(2).
because they changed the code to allow pvc in hazardous areas ,in recent times, means expansion considerations are not necessary for it, where we did not worry about that for GRC Don....~RJ~

#### romex jockey

##### Senior Member
because they changed the code to allow pvc in hazardous areas ,in recent times, means expansion considerations are now necessary for it, where we did not worry about that for GRC Don....~RJ~

#### don_resqcapt19

##### Moderator
Staff member
because they changed the code to allow pvc in hazardous areas ,in recent times, means expansion considerations are not necessary for it, where we did not worry about that for GRC Don....~RJ~
That has zero to do with 501.10(B)(2).

#### don_resqcapt19

##### Moderator
Staff member
how so Don?

~S~
Because rigid PVC conduit is not a flexible wiring method. 501.10(B)(2) is only about flexible wiring methods in a Class I, Division 2 location.

Liquid tight flexible non-metallic conduit (a PVC conduit, but not a rigid one) is one of the 7 flexible wiring methods permitted but my question is about the parent text that precedes those 7 permitted wiring methods.

#### __dan

##### Senior Member
In context, the use of words like necessary, sufficient, if, if and only if, are all describing an underlying Boolean logic form, formula, equation, or statement.

D = A and B and C ;. A B C D are Boolean data types, for D to be true, A, B, C are (all) necessary conditions (also must be true).

D = A or B or C ;, A, B, C are sufficient conditions. D is true if any sufficient condition is true.

meets_code = flexible and B and C. All are Boolean data types and the equation is evaluated by the rules for Logic. flexible (true or not) is a necessary but not sufficient condition for meets_code to be true.

The word necessary, in context, is used to describe a factor in a Boolean logic equation.

It is also called discrete math. That's where you will see necessary used, as it is used in your code reference.

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#### __dan

##### Senior Member
Something like this.

#### don_resqcapt19

##### Moderator
Staff member
In context, the use of words like necessary, sufficient, if, if and only if, are all describing an underlying Boolean logic form, formula, equation, or statement.

D = A and B and C ;. A B C D are Boolean data types, for D to be true, A, B, C are (all) necessary conditions (also must be true).

D = A or B or C ;, A, B, C are sufficient conditions. D is true if any sufficient condition is true.

meets_code = flexible and B and C. All are Boolean data types and the equation is evaluated by the rules for Logic. flexible (true or not) is a necessary but not sufficient condition for meets_code to be true.

The word necessary, in context, is used to describe a factor in a Boolean logic equation.

It is also called discrete math. That's where you will see necessary used, as it is used in your code reference.
The term necessary is a subjective term when you are trying to apply this rule. My only point is that there could easily be differences between the opinion of the installer and that of the inspection authority.

As I said in my first post, most of the flex installed in these locations is installed for convenience and cost reasons, and not because there is a physical condition that requires a flexible wiring method. An inspection authority, using the code language, could require the installer to hard pipe this equipment, because the inspection authority does not see a flexible wiring method as being necessary.

The code should remove that language and simply leave the choice of a flexible or non-flexible wiring method up to the installer, and only provide installation rules and permitted wiring methods for those two choices.

#### xptpcrewx

##### Power System Engineer
Those types of things are not very likely in a Class I, Division 2 location.
Not the best picture but how about something like this (Class I Div II) bottom entry with limited space? Note: There is nothing in 501.10(B)(2) that restricts the need for flexibility to movement/vibration...

#### romex jockey

##### Senior Member
Because rigid PVC conduit is not a flexible wiring method.
then why are we using expansion joints?

~RJ~

#### suemarkp

##### Senior Member
For the same reason the highway has expansion joints -- it isnt a flexible road. Flexible wiring methods should not need expansion fittings. Expansion/contraction flexing with means to accomodate it causes rigid things to break eventually.