crankshaft
Member
no one said anything about a mast. weather head with pvc to meter pan secured to the structure. where did you get the word mast in any of these posts
Unistrut Clamps
- Thread starter frank_n
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marinesgt0411
Senior Member
- Location
- Naples,FL 34110-9285
I always thought the reason to strap conduit was to keep it from moving.
secured and supported, if it can move it is not secured
if you are worried about expansion put in a expansion coupling
unistrut straps come in differant sizes some you use on EMT will not work for flex and some you use for other conduit will not hold EMT I have three differant sizes of half inch unistrut straps three differant sizes of three quarter, and two differant sizes of one inch
next you will be telling me you can not use mini's to strap conduit.
PVC can be made to look as good as EMT or RIGID flexable conduit can also be made to look as good the way it looks is all in workmanship
secured and supported, if it can move it is not secured
if you are worried about expansion put in a expansion coupling
unistrut straps come in differant sizes some you use on EMT will not work for flex and some you use for other conduit will not hold EMT I have three differant sizes of half inch unistrut straps three differant sizes of three quarter, and two differant sizes of one inch
next you will be telling me you can not use mini's to strap conduit.
PVC can be made to look as good as EMT or RIGID flexable conduit can also be made to look as good the way it looks is all in workmanship
- Location
- Massachusetts
marinesgt0411 said:
OK than can you explain what they mean here.
We not making it up.
If you strap it tight with strut clips it is not fastened so that movement from thermal expansion or contraction is permitted
You won't find those words in any of the metal raceway sections.
Where I am we can't use EMT minnis on PVC we have to use plastic ones.
marinesgt0411
Senior Member
- Location
- Naples,FL 34110-9285
So what we are saying is that the only acceptable way of secureing RNC is with PVC straps that will expand at the same rate as the conduit.
one hole and two hole metal straps, mini's and unistrut straps all keep the conduit from moveing
and what do we do about PVC in concrete
If we are worried about expantion we put in an expantion coupling, but that is normally if the conduit run is both inside and outside subject to differant tempuratures
one hole and two hole metal straps, mini's and unistrut straps all keep the conduit from moveing
and what do we do about PVC in concrete
If we are worried about expantion we put in an expantion coupling, but that is normally if the conduit run is both inside and outside subject to differant tempuratures
- Location
- Illinois
- Occupation
- retired electrician
crankshaft
Member
expansion and contraction becomes a problem when a weather change of 100 degrees is expected. a 100 ft run will move 4 inches in length if the temp changes 100 degrees. for shorter runs and less temp varies do the math, it will be marginal. pvc shall be SECURELY fastened within 3 ft of conduit termination. if you look at a expansion characteristic chart of pvc you will see that for most runs in average weather the expansion is fractions of an inch per 100 ft of conduit. hardly a severe problem.underground or underground encased in concrete is even less of a problem b/c underground temp stay more constant than the air. if air swings 60 degrees, underground may swing 30 or 40 degrees. the last thing is the load support tests for expansion and contraction of pvc and fittings and straps are for horizontal loads only.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Click-It makes a slick nylon PVC strap, with a strut adapter. You install the clic it first and then snap the PVC into it. Its now sold by Arlington, but not the strut adapter. I have them down to size 8 (mm) and use for coax, tubing and other small lines. The clic it will allow the PVC to move its a snug fit.
- Location
- Massachusetts
crankshaft said:
Crank you might want to read the NEC, as soon as the 'math' shows more than 1/4" movement you must provide expansion fittings.
In my area figuring a 100 F temp change is quite reasonable for outdoor runs.
That means even a 10' stick that is secured at both ends needs an expansion fitting.
If you happen to live in an area that has only a 50 F change it is less of a problem.
Again I point out I am not making this stuff up, the doubters should read the RNC Article.
crankshaft
Member
the expansion fitting is for 1/4" or greater only in a straight run between securely mounted items such as boxes, cabinets, elbows or other terminations. if you have a 100' run but its broken up by one of these items thats the footage you use to determine the amount of movement. in 50 degree change if you have 20' then an elbow its going to be 3/8" expansion. yes this is 1/8" over the 1/4" limit but hardly cause for concern. where are you that 100 degree change is quite reasonable. i dont think there is anywhere in this country that 100 degree changes is quite reasonable. look on a temp chart of the nation. oh i know now everyone is gonna jump on saying around here 5 yrs ago it was 0 in the winter and a 100 in the summer.
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- Location
- Massachusetts
Crank it's up to you if you want to ignore the NEC.
A 50 F change in 20' of PVC between two fixed points requires an expansion fitting.
In my area it is quite common to see PVC fittings pulled apart from contraction and PVC bowed from expansion.
For us 95 F in the summer and 0 F in the winter is usually reached at least once a year.
A 50 F change in 20' of PVC between two fixed points requires an expansion fitting.
In my area it is quite common to see PVC fittings pulled apart from contraction and PVC bowed from expansion.
For us 95 F in the summer and 0 F in the winter is usually reached at least once a year.
crankshaft
Member
your right if the change is 3/8 between secured points than that requires a ex. fitting b/c the code says 1/4". you want to call it ignoring the nec thats fine. i am fine with 3/8" movement as this is 1/8 more for the once a year the temp swing is substantial. so i have 10' of 2" from weather head to pan w/o an ex. fitting and gal ridgid 1 hole straps and have passed all over the area. whats the ex. expected on this run. i get about 3/8"-1/2". is there an inspector out there that would red flag and require an ex. fitting on 10' 2" from head to pan w/2 1 hole straps. i am gonna answer its a good install b/c a weather head is not a securely mounted termination
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fracas666
Member
- Location
- Northern New Jersey
Everybody here seems to be assuming that PVC straps and clamps allow movement from thermal expansion and contraction. Is this true? It's been a while since I installed RNC above ground. Don't PVC straps and clamps grip the RNC just as much as a metal strap or clamp would?
Ron
Ron
- Location
- Massachusetts
fracas666
Member
- Location
- Northern New Jersey
Carlon doesn't make the same statement for their two hole strap. Does that imply that the two hole strap doesn't allow for expansion and contraction?
Ron
Ron
- Location
- Massachusetts
fracas666 said:
Sure but we still have to comply with the NEC which requires the supports to allow movement.
With the two hole strap that is easily accomplished by leaving it a little loose.
There is nothing vague or optional about this requirement, I am very surprised that many responses to this thread do not seem aware of this or feel it is optional.
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fracas666
Member
- Location
- Northern New Jersey
iwire said:
What is vague about this reguirement is whether the strap can be metallic or not. A metallic strap can meet the requirement also, "that is easily accomplished by leaving it a little loose."
The only place that I see where the code might require the supports to be nonmetallic is article 352.100.
352.100 Construction. RNC and fittings shall be composed of suitable nonmetallic material that is resistant to moisture and chemical atmospheres.
If you consider supports to be fittings then they must be nonmetallic.
Article 100-Definitions
Fitting. An accessory such as a locknut, bushing, or other part of a wiring system that is intended primarily to perform a mechanical rather than an electrical function.
Ron
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