Help understanding PVC expansion fittings

prattz99

Member
Hi, I watched Mike's video on using pvc expansion fittings and I have some questions.
I don't understand how to set it!

Let's say I have a 40-50 1.5" run of PVC with a temperature range of 100F according to the chart I should see a expansion of up to 2" but when it comes to setting the joint for temperature it says to set it 3/4 in the barrel on a hot day. (which it is now 86F)


Is that 3/4 of the total 2" travel or just 3/4 of the way in the barrel regardless of the total PVC run?

https://carlonsales.com/techinfo/installationtraining/IT-NEMAEXJTA.pdf
 

SSDriver

Senior Member
Location
California
Occupation
Electrician
I would figure out where your temperature for that given day and time is percentage wise compared to the highest and lowest temperature for that area. Then set the barrel to that same percentage.
 

Carultch

Senior Member
Location
Massachusetts
If you are installing on a day where it is colder than the midpoint of the temperature range, your conduit is contracted more than average. You would therefore need to extend the joint so it is longer than half way through its range.

If you are installing on a day where it is hotter than the midpoint of the temperature range, your conduit is expanded more than average. You would therefore need to compress the joint so it is shorter than half way through its range.

Given an conduit temperature range of 0F to 100F, an installation temperature of 20F would mean you take it to its full expanded length, and then compress it 20%. Given an installation temperature of 80F, you would compress it to its shortest length, and expand it 20%.
 

kwired

Electron manager
Location
NE Nebraska
I would figure out where your temperature for that given day and time is percentage wise compared to the highest and lowest temperature for that area. Then set the barrel to that same percentage.
This.

You don't want the pipe to pull out when it is at maximum shrink length nor do you want it to bottom out when it is at max expansion length.

If you are at mid range of expected temp swings at time of install then install so pipe is midway of travel of the joint. If at 3/4 of the expected temp swings then you should install so there is only have 25% of travel left in the fitting.

If fitting doesn't have enough length for needed travel, you need more than one fitting in the run - this can happen on long runs and/or when wide temp range is expected.
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
I would figure out where your temperature for that given day and time is percentage wise compared to the highest and lowest temperature for that area. Then set the barrel to that same percentage.
I agree with this, but in reality I SWAG it. The ambient is less important than the actual temp of the PVC. A pipe in the shade in ambient 80F is different that a pipe in direct sun against a dark background with the same 80F ambient.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Not often mentioned (because normal slack in wire or cable will usually take care of it?) is that a large increase in length of a PVC run will require wires it contains to pull that much too. If the initial pull was done at low ambient temp and was "tight" there could be a problem.
 

retirede

Senior Member
Location
Illinois
Not often mentioned (because normal slack in wire or cable will usually take care of it?) is that a large increase in length of a PVC run will require wires it contains to pull that much too. If the initial pull was done at low ambient temp and was "tight" there could be a problem.
But the run doesn’t get longer - that’s what the expansion joint is for.
Picture a straight run between two fixed boxes. This distance between boxes never changes. As the conduit expands, the expansion joint “absorbs” the increase in pipe length!
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
That is absolutely right if you use an expansion joint, and thanks for pointing that out.
But the code also allows for the use of a freely moving elbow and a perpendicular run of pipe to take up the expansion. In those cases the box to box length actually increases by the expansion distance.
 

kwired

Electron manager
Location
NE Nebraska
But the run doesn’t get longer - that’s what the expansion joint is for.
Picture a straight run between two fixed boxes. This distance between boxes never changes. As the conduit expands, the expansion joint “absorbs” the increase in pipe length!
This has been my argument with expansion joints being required by some because of ground settlement or frost heave. Yes it may protect the raceway, but the contained conductors will not change length, they are going to push/pull from any slack available, if none then it may strain a termination. Might get away with it with small conductors but with ~200 amp conductors and larger they are likely going to strain terminations even if you have some excess conductor on the ends of the run in many cases.

Have seen conductors with strain on terminations before even with an expansion fitting.

Only solution IMO is to bury down to undisturbed soil depth or compact any fill as well as bury deep enough to be below frost line. Expansion fittings are for thermal expansion and not so much for other movement.
 

mikeames

Senior Member
Location
Germantown MD
Occupation
Teacher - Master Electrician - 2017 NEC
Next thing will be huge inline inductors to act as springs. When the conductors get stretched the inductors will stretch. I am kidding of course.
 

mikemac52

Member
Location
Long Island
Occupation
Entertainment Industry/Electrician
Slight change of direction. I have an inside 90 degree bend with the two legs needing expansion joints. Should the inside corner be anchored and allow the expansion to move away or let the corner float between the two legs.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Slight change of direction. I have an inside 90 degree bend with the two legs needing expansion joints. Should the inside corner be anchored and allow the expansion to move away or let the corner float between the two legs.
Welcome to the forum.

If the corner can float, you probably don't need expansion joints at all.
 

mikemac52

Member
Location
Long Island
Occupation
Entertainment Industry/Electrician
Welcome to the forum.

Thank you!

If the corner can float, you probably don't need expansion joints at all.
I'm expecting about 1 inch contraction on each leg. The ends of the legs will have anchored pull boxes. So it is okay to let the 90 degree elbow handle that movement?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
So it is okay to let the 90 degree elbow handle that movement?
In a word, yes. In the NEC:

Expansion joints (fittings) 250.98,
300.7(B), 352.44,
355.44, 366.44,
368.244, 424.44(C),
424.98(C),
424.99(C)(1), 426.20(E),
426.21(C), 426.22(D),
427.16
 

mikemac52

Member
Location
Long Island
Occupation
Entertainment Industry/Electrician
In a word, yes. In the NEC:

Expansion joints (fittings) 250.98,
300.7(B), 352.44,
355.44, 366.44,
368.244, 424.44(C),
424.98(C),
424.99(C)(1), 426.20(E),
426.21(C), 426.22(D),
427.16
... and then in the NEC, many words. :)
I like yes and that's what I went with. (didn't use)
Mike's video on the subject ended as they were discussing conflicting opinions over the necessity of expansion fittings with elbows.

Thanks again.
 

kwired

Electron manager
Location
NE Nebraska
I'm expecting about 1 inch contraction on each leg. The ends of the legs will have anchored pull boxes. So it is okay to let the 90 degree elbow handle that movement?
If it will expand to longer than distance to corner then you probably should have an expansion fitting, it is going to try to go somewhere if it hits at the corner and is still trying to expand.
 

mikemac52

Member
Location
Long Island
Occupation
Entertainment Industry/Electrician
If it will expand to longer than distance to corner then you probably should have an expansion fitting, it is going to try to go somewhere if it hits at the corner and is still trying to expand.
Thanks for the reply. Hopefully I'm okay on expansion. Its been warm here, the stuff is in the sun, my anchors give me 3/8? off the brick for a little extra direct radiation, but I umm... already did it.

Went with Larry's advice.
Thanks again.
 
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