Foam insulation

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coulter

Senior Member
Dennis Alwon said:
...UF cable encapsulates the conductors and does not seem to be a problem so why would the foam. ...
I'm not sure this applies. I'd expect wire coverings to be designed with as high a thermal transfer coefficient as available. Heat insulation with as low as available.

carl
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
For those interested, a single NMB cable only increased in temperature about 1.5 - 2 degree in the approximate 1hr I kept track. Doubling the the cable back thru resulted in a temp rise of 20 deg in about 20 minutes. I used a portable 1500 watt heater. 2" db conduit filled with foam and split in half.

My days of being a test a lab are limited. To many variables.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Tom --- I am assuming you used foam insulation and had not much affect until you doubled back. What do you mean by double back---The same wire thru the foam twice (looped thru). Were the wires separated?
 

coulter

Senior Member
Tom -
Your experiment was great.

Couple of questions:

How long was the foam section?

Was this sprayed foam or a molded foam sleeve?

carl
 

coulter

Senior Member
Tom -
Your experiment was great. I'm working to data that is 25 years old. Materials have changed. You taking time to do this give us information that isn't in the NEC - and may not be in an IEEE paper.

Couple of questions (If we understand your model, we understand the limitations):

How long was the foam section?

Was this sprayed foam or a molded foam sleeve?

carl
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
We used foam from a can that is used to seal up around windows etc. The 2" DB conduit was about 3' long.

It took several tries and several hours to get the foam to expand and dry sufficiently. Long story in itself. I was not prepared for the substantial temp increase due to the bundling but was suprised the single cable did not get warmer. We did not let it reach a max operating temperature nor did we leave it unattended. Rented shop and wood work bench.
 
Spray Foam Insulation In Residences

Spray Foam Insulation In Residences

NEMA Bulleting No. 95 - Thermal Effects of Type NM-B Cable Encased in Spray Foan Insulation Used in Residences addresses this issue.

However, I am dealing with an issue regarding XHHW service entrance cable.
Approximately 2 feet at each end of the cable in encased in the spray foam - where the cable leaves the meter base and where it enters the remote panel. The rest of the cable runs through a fire-rated floor ceilng assembly. The spray foam insulation is BioBased 501. In tests, it will begin to char at temperatures exceeding 400 degrees Faranheit and has an ignition point of 700 degrees Faranheit. The Alcan Stabiloy cable is suitable for operation at 600 volts or less at a maximum operating temperature of 90 degrees Celsius which equals 194 degrees Faranheit. I am a Builder and not an electrician but I would think that the circuit breaker would trip before the temperature would ever reach 400 degrees.

The inspector wants me to produce a report from an acceptable testing agency showing that the this installation has been tested. He will not accept a letter from the insulation manufacturer.

Any suggestions.
 
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