ptonsparky
Tom
- Occupation
- EC - retired
Can someone tell me why expansion joints are used below a meter socket when it changes to direct bury cable 18" into the ground? Money maker?
expansion joints
- Thread starter ptonsparky
- Start date
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mgookin
Senior Member
- Location
- Fort Myers, FL
From a geotechnical perspective all the soils of the earth are in constant motion. It is presumed the building is not (although it is but in relation to the building it moves differently).
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
Some people act like sheep that can't think for themselves. I have a feeling someone's boss told the help they will use an expansion fitting for all UG laterals into meterbases and someone took that a little to far without thinking WHY it was needed. But, that's just a guess...
In northern territories, building foundations are required to be at or below the frost line. Around my parts it is roughly 3' deep. This construction approach assumes the building will maintain relatively the same elevation year round.
The earth above the frost line is subject to heave from freezing and expanding upward in the winter, then thawing in the spring and recompacting through summer and fall. The change in elevation isn't a lot, but solid risers can make a mess of meter cans if there is no relief.
- Location
- Massachusetts
Some people act like sheep that can't think for themselves. I have a feeling someone's boss told the help they will use an expansion fitting for all UG laterals into meterbases and someone took that a little to far without thinking WHY it was needed. But, that's just a guess...
In my area you there is a good chance you won't pass without one. Smart$ explained why.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Doesn't that section permit S loops with a short straight piece of conduit without the expansion fitting?
- Location
- Massachusetts
Still have to keep the section of conduit from being pulled out of the bottom of the meter socket.
ptonsparky
Tom
- Occupation
- EC - retired
OK. In my area I do not see the problem as described unless the raceway 90s and continues on. That and if they pour concrete sidewalks that encases the raceway.
- Location
- Massachusetts
The building sits on a footing below the frost line, the sidewalk does not. The sidewalks can and sometimes do move relative to the building.
One of the stores I work at had to remove one of their outer doors during cold spell becuse the sidewalk came up and stopped the door from opening.
I ran into the same issue at a Lowes garden center emergency exit gate I was their to work on the security system door contact and found the gate would not open due to frost lifting the sidewalk. In that one I fixed it by sawzaling the bottom of the gate a bit.
mwm1752
Senior Member
- Location
- Aspen, Colo
POCO is the requirement here
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
frostline? i think its more about relative movement and less about frostline. the meter is attached to building thus will not move relative to building, but the building itself (with attachments) will move relative to earth (regardless of frostline). bldg/item above frostline just means more relative movement, and, the riser will pass through that frostline zone, etc.
300.5(J) doesnt call out expansive soils? this type of soil can be as bad as frost lifting, the big diff though, frost lift is like a solid, expansive soils usually swell only when wet, but they both can do damage. poco by me does not use expansion joint of relief method in expansive soil.
300.5(J) doesnt call out expansive soils? this type of soil can be as bad as frost lifting, the big diff though, frost lift is like a solid, expansive soils usually swell only when wet, but they both can do damage. poco by me does not use expansion joint of relief method in expansive soil.
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- Location
- Massachusetts
It's all about the fact the building is supported below the frost line and is pretty much stationary. Everything above the frost line is subject to movement from freezing and thawing.
If you want to dispute this knock yourself out. I have seen it happen again and again so I am not likely to change my view and neither are the words in the NECs FPN that tell us frost heaves are one of the reasons for the requirement.
Yeah, frost line. What does someone from AZ know about frost line and remedial expansion joints? :blink: (rhetorical)
300.5(J) doesn't call for expansion joints specifically as a remedy, or frost heave as a cause. Just one possible scenario...
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
It's all about the fact the building is supported below the frost line and is pretty much stationary. Everything above the frost line is subject to movement from freezing and thawing.
If you want to dispute this knock yourself out. I have seen it happen again and again so I am not likely to change my view and neither are the words in the NECs FPN that tell us frost heaves are one of the reasons for the requirement.
i not disputing. what i am saying is, even if the foundation is below that frostline you still get relative movement between bldg and earth (a fact). surely things above/in the frostline zone are subject to way more relative movement.
Frost Line – 30 inches into undisturbed soil for exterior footings in all areas of Coconino County
do i need to list them all ??
- Location
- Massachusetts
Perhaps a little movement between the Earths core and the building but no movement between the building and utilities when both are below the frost line
FionaZuppa
Senior Member
- Location
- AZ
- Occupation
- Part Time Electrician (semi retired, old) - EE retired.
not 100% true. there will always be relative movement even when frostline is at zero inches. the amount of movement will likely be non-impacting to anything running in-ground up to the structure. you jumping inside the dwelling will cause relative movement
maybe the Q is more about a hard riser conduit that is smooth (like pvc) and is vertical between meter and reaches ~20" below frostline, why would you need an expansion joint as we would not think the earth would be able to lift on a smooth conduit, but in fact frozen earth can dig into objects to create lift points to exert force on.
Should have known you'd be a northern AZ'n (or familiar therewith). :lol:
Do you mean list areas with frost line below 0" in AZ or scenarios which require earth movement relief? Actually, the answer to your question is no on both parts, but I was curious as to the object of your question.
- Location
- Massachusetts
not 100% true. there will always be relative movement even when frostline is at zero inches. the amount of movement will likely be non-impacting to anything running in-ground up to the structure. you jumping inside the dwelling will cause relative movement
So why we bring up movements so subtle that they are not damaging to the utilities when we are discussing a code section about protection from damage? :huh:
Well we could break out the slide rules and spend a lot if time working this all out or we would go the commonsense approach.
In some areas frost heaves where damaging conduits, conductors and cables. Someone put in a proposal asking for this to be addressed and it was accepted. As smart mentioned an expansion joint is a choice made to deal with this problem but other solutions could be employed if the AHJ was agreeable.
Johnnybob
Senior Member
- Location
- Colville, WA
not 100% true. there will always be relative movement even when frostline is at zero inches. the amount of movement will likely be non-impacting to anything running in-ground up to the structure. you jumping inside the dwelling will cause relative movement
maybe the Q is more about a hard riser conduit that is smooth (like pvc) and is vertical between meter and reaches ~20" below frostline, why would you need an expansion joint as we would not think the earth would be able to lift on a smooth conduit, but in fact frozen earth can dig into objects to create lift points to exert force on.
I'm a few degrees north of you, and I can tell ya, a flat, smooth stretch of county road can turn into a roller coaster, in the dead of winter. And while the frost line's only about 30" most of the winter, for 2-3 weeks every winter, it drops below -20F, and when it does, the ground heaves alot. It's worse where theres more moisture in the ground!
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