Expension joints for EMT

[lile001]

There are expansion joint fittings available for EMT. I can find reference to expansion joints in 300.7 (B), which requires them "where necessary", a rather vague requirement.

1. Would an expansion fitting always be required at a building expansion joint, considering that some "give" would be expected with a normal EMT installation? Especially if the run is short?

2. Here is a calculation of expansion in 10 feet of EMT over a typical temperature range in my state:

Expansion coefficient of steel 6.50E-06 in/in/?F per NEC 300.7 (B) FPN


for 10 feet of conduit: 120 inches
6 F design temperature winter
99 F design temp summer
not subject to direct sunlight

93 delta T, ?F
0.072" expansion in 10 feet of conduit due to temperature change.

I would argue that .07" of expansion is negligible, and expansion joints are not needed in runs of EMT under 10 feet.

Any opinions?

 

[tonyi]

Concrete and steel have pretty close coefficients of expansion. Not identical, but within about 10% of each other...

If there's any concern, just put a superfluous Z-bend in the run somewhere.

 

[benaround]

lile001,

If that 10' length of EMT was leaving one 'concrete' type building and was

directly entering another 'concrete' type building,I would use expansion

fitting.

 

[iwire]

For us it is generally in the specs to use expansion joints when crossing a building expansion joint, beyond that it seems like common sense.

 

[Jim W in Tampa]

Even at .07 inches i do think it would effect the connection over years.

 

[tom baker]

I've seen EMT to 4 S boxes with flex loops across the building expansion joint

 

[paul]

I've only encountered this in the type of situation Iwire mentions. We just put a flex to emt coupling in the run and about a foot of flex, then back to emt and continue on our merry way. One particular job we had to put pipe bonding clamps and a bondwire so that the flex wasn't carrying the fault.

But to answer you question, I don't know of any expansion fitting for emt.