90.9(D): Compliance - Hard Conversion?

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DavJ09

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I don't quite understand Hard Conversion. If something is subjected to change how may it be interchangeable with the original measurements?

Is this code in reference to say receptacles and their approved leveling/volt or is it specific to changes such as dimesions of boxes and such?


-- J. Davis (tapatalk!)
 
I believe hard conversion is specific & precise where soft conversion is an acceptable estimate -- PI = 3.14141414141414141414141414141411414141414___hard or just 3.14 soft ---- condiut sizes in inches = metric sizes non dimensional but in sequence.
I could be wrong so I'll wait for the wolves & see if I survive my thought pattern
 
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I agree, soft conversions are 'abouts' while hard conversion are 'exacts'.

Technically the 208Y/120 and 480Y/277 are soft conversions.
208 divided by 120 = 1.733333 while 480 divided by 277 = 1.732852 neither of which is 'equal to' 1.732051 the square root of 3.
The hard conversions would be 207.4861Y/120 or 480Y/277.12813
 
DavJ09 said:
So, its to do with measurements/calculations rather than parts or equipment?

-- J. Davis (tapatalk!)
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Yes and no.
A hard conversion is a conversion in which we fudge the final result to get a useful number in the other system.
So a tap may "less than 3 m (10 ft)" even though 3 meters is actually just a bit less than 10 feet. This is an example of hard conversion.

In other circumstances, such as safety clearances, where the standard is originally defined in the first set of units, you have to use a mathematically correct conversion (or round up) to preserve safety when enforcing the rule using the second set of units. This, for some odd reason, is called soft conversion. :(
In this case, a 30 inch required clearance becomes a 762mm clearance, and "rounding down" to 760mm or even 750mm is not allowed.

At least that is how I interpret it. This is one case where the examples in the Handbook [2011 page 8 ff] is very helpful in understanding what the very unclear language means. The Handbook gives examples!
 
From the Handbook commentary:
Soft conversions do not change the physical dimension. Hard conversions are rounded or approximate values of the original dimension. Soft conversions are required when an approximation would negatively impact safety. ...
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Well, now, I'm confused again! Thanks, Don! =b (I'm joking)

So, soft conversions are based on equipment not being changed but the measures contained in wiring can be? And, hard conversions are based on approximation (in respect to 90.1(A), of course).

I do not have the handbook. I'm in a hardship for finances at the moment.

-- J. Davis (tapatalk!)
 
I would instead characterize it as:
Hard conversions go from a "standard" measurement in one system to a acceptably close standard measurement in the other system.
E.g. from a standard SAE bolt to the closest standard metric bolt.
Or from a 4" square box to a 10cm square box (assuming that the latter are made, of course.)
The soft conversion goes to the relatively exact equal in the other system even if it means abandoning standard sizes and custom fabricating something.

Tapatalk!
 
Ahhh, so hard conversion is basically adjustments to make it fit (safety provided) and soft conversion is "do not stray too far" from what is outlined.

I think I've got! Do I?

-- J. Davis (tapatalk!)
 
When you put it that way, I think you have it exactly backwards.
It confuses me the the hard conversion is inexact while the soft conversion is rigorous, but that is what the Handbook examples indicate. :(

Tapatalk!
 
A quick google search is showing me that soft conversions are exact, while hard conversions are approximate, but based on either closest easy-to-use measurement, or nominal equivalents in accepted international standards. An example of a hard conversion to an easy-to-use measurement would be 3 m/10 ft. An example of a hard conversion to an international standard would be from a 1/2" bolt to a M12 or M14 bolt or 3/4" PVC to 20 mm or 22 mm PVC (these are actual trade sizes available in EU, whereas Carlon gives 21 mm as their "equivalent").
 
PetrosA said:
A quick google search is showing me that soft conversions are exact, while hard conversions are approximate, but based on either closest easy-to-use measurement, or nominal equivalents in accepted international standards.
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Old dog learns new concepts - Thanks.:dunce:

This link (towards bottom, under terminology) has a good explanation.
http://lamar.colostate.edu/~hillger/faq.html#hard-soft
 
mwm1752 said:
I believe hard conversion is specific & precise where soft conversion is an acceptable estimate -- PI = 3.14141414141414141414141414141411414141414___hard or just 3.14 soft ---- condiut sizes in inches = metric sizes non dimensional but in sequence.
I could be wrong so I'll wait for the wolves & see if I survive my thought pattern[/

I appear to be bass ackwards & wolf fodder to boot -- Thanks for the web link Jim very helpful
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