Expansion Fittings for 1.5" EMT on Roof?

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roblsmith3

Member
Location
Cary, NC USA
I know I know, that this has been posted before but to be honest it was never answered, merely tiptoed around! I'll give more specifics......we have a 300' run of AC conductors in a 1.5" EMT on a flat roof mounted about 3.5" off the roof with rubber roof blocks. The project is located near Charlotte, NC and we are on the 2014 NEC.....so the temp difference in extremes is ~135 degrees Fahrenheit. According to chart 352.44, the change would be 5.48 in/100 ft x EMT multiplier of .2 equals 1.1" per 100 ft. Since this is a 300' run, that would be a movement of 3.3" total. Now, considering it is a PITA to bend 1.5" conduit to avoid using expansion joints and the cost of each expansion joint is about $150/piece. Are they really necessary? What is another way to go about this without bending or using the joints? I had heard using LFMC would also work but I do not know if that is code compliant. Thanks and look forward to the wise elders of the forum to bring me some clarity!:?
 

Smart $

Esteemed Member
Location
Ohio
Can you make the last few feet a 90° bend or an offset of LFMC/LFNMC?

You are only required to have one expansion joint if you run straight the entire length.

I never really liked this requirement. The structure to which the conduit is mounted also expands and contracts. The requirement for an expansion joint should be based on the difference of conduit CoE and structure CoE.
 

Carultch

Senior Member
Location
Massachusetts
Can you make the last few feet a 90° bend or an offset of LFMC/LFNMC?

You are only required to have one expansion joint if you run straight the entire length.

I never really liked this requirement. The structure to which the conduit is mounted also expands and contracts. The requirement for an expansion joint should be based on the difference of conduit CoE and structure CoE.

I agree that it should be based on relative expansion, instead of absolute expansion.

The other issue I have with this requirement is that only the PVC article specifies how to know objectively "where necessary to compensate for thermal expansion and contraction", with a 1/4" change in length being the defining limit per 352.44. Metal non-flexible raceways do not specify an equivalent number. And it is often needed for PVC, because in a 0F to 100F temperature swing, that is less than an individual 10 ft stick for PVC. There is no XXX.44 for RMC, EMT, or IMC.

So by omission, there is no way to know when it is required for EMT. Other than the crossing of a building expansion joint, which is when it is required for all raceways.
 
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Smart $

Esteemed Member
Location
Ohio
I agree that it should be based on relative expansion, instead of absolute expansion.

The other issue I have with this requirement is that only the PVC article specifies how to know objectively "where necessary to compensate for thermal expansion and contraction", with a 1/4" change in length being the defining limit per 352.44. Metal non-flexible raceways do not specify an equivalent number. And it is often needed for PVC, because in a 0F to 100F temperature swing, that is less than an individual 10 ft stick for PVC. There is no XXX.44 for RMC, EMT, or IMC.

So by omission, there is no way to know when it is required for EMT. Other than the crossing of a building expansion joint, which is when it is required for all raceways.
I think the CMP believes the Informational Note infers a 1/4" change for other types too. :blink:
 

Smart $

Esteemed Member
Location
Ohio
The CMP believes that the note implies 1/4", and so code users can infer that from it.
Correct.

Let me restate it the way I meant it...

I think the CMP believes one can infer from the Informational Note that a 1/4" change is also required for other types.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Correct.

Let me restate it the way I meant it...

I think the CMP believes one can infer from the Informational Note that a 1/4" change is also required for other types.
They can believe anything they want, but nothing in Article 352 applies to EMT as an enforceable rule.
 

roblsmith3

Member
Location
Cary, NC USA
We are coming out of a jbox on the roof and running 300' to an LB and then penetrating into the building. There are no expansion joints on the building on the roof. If you go inside the building there are expansion joints approximately every 8 feet. Sounds like just 1 expansion fitting and then straps that allow the conduit to slide according to Smart $?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Aye... but 300.7(B) is enforceable and can be implemented at the AHJ's discretion.
True, but a subjective rule as it does not specify where it would be necessary to compensate for thermal expansion and contraction. In contrast with the rule for PVC that specifies such compensation is necessary where the thermal expansion/contraction will exceed 1/4".
 

Smart $

Esteemed Member
Location
Ohio
True, but a subjective rule as it does not specify where it would be necessary to compensate for thermal expansion and contraction. In contrast with the rule for PVC that specifies such compensation is necessary where the thermal expansion/contraction will exceed 1/4".
I agree, but at least it is set in stone so to speak for PVC. But with 300.7(B) being subjective, the AHJ could require an expansion joint where expansion/contraction is less than 1/4" relative.
 

roblsmith3

Member
Location
Cary, NC USA
Thank you all for the help. Instead of using an LB to penetrate the building after the long straight run, we are going to use LFMC and form an arc and penetrate the building.
 
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