gserve
Senior Member
- Location
- New Hampshire
Does the PVC conduit have to be a certain length before an expansion joint is required in a horizontal run of 2" PVC under a mobile home?(Has to be ? feet before one is required)
expansion joints revisited
- Thread starter gserve
- Start date
- Status
- Location
- Massachusetts
Re: expansion joints revisited
It would depend on the temperature change you expect the raceway to be exposed to.
I see NH on your post so I would say a 100 F temperature change could be expected.
85 F Summer -15 F in the winter.
I come up with about 6' of PVC before you need an expansion fitting.
It would depend on the temperature change you expect the raceway to be exposed to.
I see NH on your post so I would say a 100 F temperature change could be expected.
85 F Summer -15 F in the winter.
I come up with about 6' of PVC before you need an expansion fitting.
gserve
Senior Member
- Location
- New Hampshire
Re: expansion joints revisited
Iwire, How do you come up with 6'?
Iwire, How do you come up with 6'?
pierre
Senior Member
- Location
- Westchester County, New York
Re: expansion joints revisited
As per table 352.44(A), assuming the mobile home is 30 feet long and the temperature change is 100 degrees per the year:
100 ft of PVC will expand or contract 4.06 inches.
divide that by approximately 1/3 and you have 1 inch of expansion. the code requires an expansion ffitting for 1/4 inch expansion or more.
As per table 352.44(A), assuming the mobile home is 30 feet long and the temperature change is 100 degrees per the year:
100 ft of PVC will expand or contract 4.06 inches.
divide that by approximately 1/3 and you have 1 inch of expansion. the code requires an expansion ffitting for 1/4 inch expansion or more.
Re: expansion joints revisited
If you are coming up out of the ground for an underground run that is all PVC conduit then an expansion joint is needed so that earth movement when the ground freezes and then thaws will not break the conduit. Same for the earth settling over time.
However, for an expansion joint to work under some circuitstances there needs to be slack wire somewhere. This could be a pull box or equivalent at the ends or in the middle.
On the last underground service that I did I used 2.5 inch schedule 80 PVC for most of the run. Had to use a pull box in the middle because of too may bends. Because the wire pulling force was easy for 4/o aluminum in this service, I arranged the pull box with 2 90 degree bends coming up inot the bottom. This avoide drilling holes in the synthetic concrete and allowed a U pull which gave me the slack that was needed by the expansion joint as the ground settled and so forth. There was no room at the meter location for a pull box or wireway that would give me slack there. You are probable wondering why I had to use this design and it was to avoid going over the fuel oil tank, digging up the driveway, blah blah blah.
If you are coming up out of the ground for an underground run that is all PVC conduit then an expansion joint is needed so that earth movement when the ground freezes and then thaws will not break the conduit. Same for the earth settling over time.
However, for an expansion joint to work under some circuitstances there needs to be slack wire somewhere. This could be a pull box or equivalent at the ends or in the middle.
On the last underground service that I did I used 2.5 inch schedule 80 PVC for most of the run. Had to use a pull box in the middle because of too may bends. Because the wire pulling force was easy for 4/o aluminum in this service, I arranged the pull box with 2 90 degree bends coming up inot the bottom. This avoide drilling holes in the synthetic concrete and allowed a U pull which gave me the slack that was needed by the expansion joint as the ground settled and so forth. There was no room at the meter location for a pull box or wireway that would give me slack there. You are probable wondering why I had to use this design and it was to avoid going over the fuel oil tank, digging up the driveway, blah blah blah.
- Status