Expansion Fittings

[dclinspects]

Hello,

Question on the use of expansion fittings for underground services supplying
load and line side at the meter box. Do they need expansion fittings..?
300.7 states they do, to provide for expansion and contraction.. Looking at
the other article 352.44 states only if the PVC moves
0.25 inches or more..in 100 degree C increments... The handbook states only
on long runs...
What is defined as a long run?

Can you provide some guidance/clarification?

Thanks...

 

[augie47]

Re: Expansion Fittings

If I may....
Given: if the temp changes the conduit will expand or contract accordingly
1st thing to look for would be if the conduit is
installed between fixed points. If not, such as a riser to a weatherhead, it can expand/contract freely provided the support allows (352.30).
If the conduit is installed between fixed points, expansion joints may be needed. Determination is made by the temperature change to which the conduit is subjected. 352.44 says exp joint needed for >1/4" .At 100o temp change, conduit would expand 4.06". Applying the math that would be 1/4" in a little over 6'. Here, we allow 8' or so.
You mentioned underground. Make note that the temperature change 24" underground would be minimal, and debatable if an expansion joint would be needed at all. You might also note, on some jobs an expansion joint is added on the "riser" from and underground conduit run to allow for ground settling.
Hope this helps.

[ September 12, 2005, 02:26 PM: Message edited by: augie47 ]

 

[iwire]

Re: Expansion Fittings

If you live in an area that has frost heaves you will need a expansion fitting between the earth and the first support.

This is not the same issue as thermal expansion and contraction of the PVC itself.

The frost usually raises the grade and of course in the spring it sinks back down, the expansion fitting stops (or tries) the PVC from being ripped out of the meter socket.

 

[augie47]

Re: Expansion Fittings

dclinspects:
all kinds of free advice today and worth every penny you pay
If you already are aware of this, I apologive, but it's often overlooked.....
On outdoor vertical installation, be sure to install the joint with the barrell down so that rain won't enter the opening and result in a burst upon freezing.

 

[pierre]

Re: Expansion Fittings

See 300.5(J) for ground movement, and 300.7(B) for expansion fittings. Also read the FPNs after 300.5(J) &.7(B)