1

The service entrance will use 2.5" RNC, about 100' run underground, with 2 90 degree sweeps, with the second sweep coming up to a meter/panel mounted on the outside of the house. The conduit will be about 3' underground, and will rise 3-4' above ground to reach the panel. So the total vertical rise will be about 6'-7'.

The climate is zone 4 in the northern part of Georgia. Temperature fluctuation might be as much as 90 degrees F throughout the year.

Do I need (code requirement) or should I have (good practice) an expansion joint on the vertical rise? If it was cheap I'd just do it it, but it looks like a $55 part. Is it required or worth it?

  • 1
    Where I'm from, the utility requires an expansion joint on every new meter. – Tyson Dec 20 '17 at 13:47
1

My utility requires them. Climate zone 4, the ground freezes, so frost heaves/movement from frost are likely. That's what these deal with on short risers from the ground. Whether or not code required, if the conduit breaks from movement after installation, it will cost a lot more than $55 to fix.

1

In this situation it is not because of temperature fluctuations that I believe in expansion joints it is because of the ground settling. After a couple of years that PVC conduit will pull right out of the meter base. I have seen it break the knock-out's out of the container. And please don't tell me about bedding it in sand. I don't see any need for one on the pole. Upon installation, I would leave the expansion joint at 15%.

0

In general expansion joints are used on long runs where the conduit is attached to material that may expand and contract under certain weather conditions. What I can also tell you is in the state I work in, I really haven't seen expansion joints on vertical risers. That may or may not apply in Georgia, but you can always resort to just driving around and see what everyone else is doing with similar installations.

  • I don't use expansion joints on short verticle runs either. Under ground not needed. – Ed Beal Dec 20 '17 at 13:20
0

The National Electrical Code states as follow:

(B) Expansion, Expansion-Deflection, and Deflection Fittings. Raceways shall be provided with expansion, expansion-deflection, or deflection fittings where necessary to compensate for thermal expansion, deflection, and contraction.

Informational Note: Table 352.44 and Table 355.44 provide the expansion information for polyvinyl chloride (PVC) and for reinforced thermosetting resin conduit (RTRC), respectively. A nominal number for steel conduit can be determined by multiplying the expansion length in Table 352.44 by 0.20. The coeffi‐ cient of expansion for steel electrical metallic tubing, intermediate metal conduit, and rigid metal conduit is 1.170 × 10-5 (0.0000117 mm per mm of conduit for each °C in temperature change) [0.650 × 10-5 (0.0000065 in. per inch of conduit for each °F in temperature change)]. A nominal number for aluminum conduit and aluminum electrical metallic tubing can be determined by multiplying the expansion length in Table 352.44 by 0.40. The coefficient of expansion for aluminum electrical metallic tubing and aluminum rigid metal conduit is 2.34 × 10-5 (0.0000234 mm per mm of conduit for each °C in temperature change) [1.30 × 10-5(0.000013 in. per inch of conduit for each °F in temperature change)].

The key words here are "where necessary".

In Michigan we have even greater temperature swings and I have never seen an expansion joint on an underground lateral.

Not a bad idea necessarily, but unless required, I wouldn't spend the money unless you are really worried about frost heave.

Good luck!

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.