Heat tracing installation question

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jucesanc

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I'm installing 200 ft of heat tracing, to maintain a fuel gas line at 90 deg F. The temp will be controlled through an adjustable thermostat. The power comes from a 120 V panel that is 140 ft away. The thermostat switch ratings list 15 A.

I'm trying to determine what wire size to use for power from the 120 V panel to the thermostat. From an online calculator it looks like I need size 8AWG copper conductors, but that seems too large... Does this sound correct? The inputs were: 15 A, 120 V, 140 ft, single phase and 5% allowable voltage drop.
 
jucesanc said:
I'm installing 200 ft of heat tracing, to maintain a fuel gas line at 90 deg F. The temp will be controlled through an adjustable thermostat. The power comes from a 120 V panel that is 140 ft away. The thermostat switch ratings list 15 A.

I'm trying to determine what wire size to use for power from the 120 V panel to the thermostat. From an online calculator it looks like I need size 8AWG copper conductors, but that seems too large... Does this sound correct? The inputs were: 15 A, 120 V, 140 ft, single phase and 5% allowable voltage drop.
Click to expand...


Is this self-regulating heat tracing? How many watts per foot?
 
Something doesn't quite add up here.
If the cable is self regulating, a thermostat isn't needed.
I've never seen nor heard of self-regulating cable that operates at 90°F; the only self-regulating cable I'm aware of operates at ~35-40°F to protect against water freezing. Are you sure of the 90°F spec?
If it is a self-regulating cable that operates at ~35-40°F, it will never exceed that temperature, regardless of the thermostat setting.

That said, consider using 12 AWG:
200 feet at 8 watts per foot = 1600 watts. That's 13.3 amps at 120 volts, and 9Ω.
280 feet of 12 AWG Cu wire has a resistance of 0.45Ω. The two together would have a resistance of 9.45Ω, 12.7 amps will flow, and there will be 5.9 volts drop -- just about 5% -- in the Cu wire.
(this is neglecting the resistance of the heat-trace cable conductors, which is probably an unreasonable simplification)

Or using 14 AWG:
280 feet of 14 AWG Cu wire has a resistance of 0.7Ω. The two together would have a resistance of 9.7Ω, 12.4 amps will flow, and there will be 9.7 volts drop in the Cu wire.
Since resistance heaters are not harmed by low voltages, this would be adequate.
 
drcampbell said:
Something doesn't quite add up here.
If the cable is self regulating, a thermostat isn't needed.
I've never seen nor heard of self-regulating cable that operates at 90°F; the only self-regulating cable I'm aware of operates at ~35-40°F to protect against water freezing. Are you sure of the 90°F spec?
If it is a self-regulating cable that operates at ~35-40°F, it will never exceed that temperature, regardless of the thermostat setting.

That said, consider using 12 AWG:
200 feet at 8 watts per foot = 1600 watts. That's 13.3 amps at 120 volts, and 9Ω.
280 feet of 12 AWG Cu wire has a resistance of 0.45Ω. The two together would have a resistance of 9.45Ω, 12.7 amps will flow, and there will be 5.9 volts drop -- just about 5% -- in the Cu wire.
(this is neglecting the resistance of the heat-trace cable conductors, which is probably an unreasonable simplification)

Or using 14 AWG:
280 feet of 14 AWG Cu wire has a resistance of 0.7Ω. The two together would have a resistance of 9.7Ω, 12.4 amps will flow, and there will be 9.7 volts drop in the Cu wire.
Since resistance heaters are not harmed by low voltages, this would be adequate.
Click to expand...

I was quoted for a Thermon BSX Self regulating heating cable, with an adjustable control thermostat, and a terminator beacon. The cable is rated for 150 F max maintenance temp, the thermostat is rated for an adjustable range of 35-235 F. I'm 95% sure of the 90 deg F requirement for the line. If it's not 90 deg F then it's 90 deg C.

So how is a self regulating cable "set" for 90 F? The cutsheet shows max and min values. Would a self regulating cable work with a thermostat on a line that we want to keep at a constant 90 F, or would a different type of cable be required? I attached the cutsheets for the quoted: cable, thermostat, and terminator beacon LED.



View attachment BSX.pdfView attachment E4X-35235 & E4X-1 Datasheet.pdfView attachment End of Ckt Light-C1D1.pdf
 
jucesanc said:
I was quoted for a Thermon BSX Self regulating heating cable, with an adjustable control thermostat, and a terminator beacon. The cable is rated for 150 F max maintenance temp, the thermostat is rated for an adjustable range of 35-235 F. I'm 95% sure of the 90 deg F requirement for the line. If it's not 90 deg F then it's 90 deg C.

So how is a self regulating cable "set" for 90 F? The cutsheet shows max and min values. Would a self regulating cable work with a thermostat on a line that we want to keep at a constant 90 F, or would a different type of cable be required? I attached the cutsheets for the quoted: cable, thermostat, and terminator beacon LED.



View attachment 21511View attachment 21512View attachment 21513
Click to expand...
What your links do not show is exactly what type of self-regulating cable you are proposing to use, but looking up Thermon BSX does provide some useful information.

The low temperature BSX heat trace is capable of maintaining temperatures up to 150F. For lower temperatures a thermostatic control is required.
There are two general classes of self-regulating heat trace:
1. Anti-freezing heat trace, where the maximum trace temperature will probably be lower than 90F. The semiconductor parallel resistance element between the two leads will increase in resistance with temperature and, as long as a minimum heat load is present, can regulate to some temperature not too far above freezing. At higher temperatures the heat output is reduced to the point that constant-on losses may be acceptable. The self-regulation also insures that places where the heat trace is installed at too close a pitch or crosses itself will not overheat dangerously.
2. Process heat trace, where the average temperature of the pipe is regulated by a thermostat and the self-regulation serves primarily to keep parts of the controlled run from overheating, again where the insulation is particularly good, the trace is installed too densely or the trace crosses itself.
The latter seems to be what the OP is describing.
If the design temperature is really 90C instead of 90F, then the BSX tape will not work, as its maximum maintenance temperature is 150F (65C).

From the point of view of temperature maintenance rather than energy efficiency, the voltage drop in the supply cable can be 20% or more without causing heat regulation problems.
 
GoldDigger said:
What your links do not show is exactly what type of self-regulating cable you are proposing to use, but looking up Thermon BSX does provide some useful information.

The low temperature BSX heat trace is capable of maintaining temperatures up to 150F. For lower temperatures a thermostatic control is required.
There are two general classes of self-regulating heat trace:
1. Anti-freezing heat trace, where the maximum trace temperature will probably be lower than 90F. The semiconductor parallel resistance element between the two leads will increase in resistance with temperature and, as long as a minimum heat load is present, can regulate to some temperature not too far above freezing. At higher temperatures the heat output is reduced to the point that constant-on losses may be acceptable. The self-regulation also insures that places where the heat trace is installed at too close a pitch or crosses itself will not overheat dangerously.
2. Process heat trace, where the average temperature of the pipe is regulated by a thermostat and the self-regulation serves primarily to keep parts of the controlled run from overheating, again where the insulation is particularly good, the trace is installed too densely or the trace crosses itself.
The latter seems to be what the OP is describing.
If the design temperature is really 90C instead of 90F, then the BSX tape will not work, as its maximum maintenance temperature is 150F (65C).

From the point of view of temperature maintenance rather than energy efficiency, the voltage drop in the supply cable can be 20% or more without causing heat regulation problems.
Click to expand...

This heat trace will be installed on a 200 ft section of process line that moves fuel gas from a fuel filter to a boiler. We mainly want to prevent condensation from forming inside this 4" line. Also verified that it is 90 deg F that we are aiming for. An operator used a thermal? gun and verified that the current temperature of the line is 85 F - 89 F depending on which section he measured.
 
jucesanc said:
This heat trace will be installed on a 200 ft section of process line that moves fuel gas from a fuel filter to a boiler. We mainly want to prevent condensation from forming inside this 4" line. Also verified that it is 90 deg F that we are aiming for. An operator used a thermal? gun and verified that the current temperature of the line is 85 F - 89 F depending on which section he measured.
Click to expand...
Sounds like a fairly low wattage heat tape (but somebody needs to do the calculation) plus the sort of thermostat you linked to will do the job. Overdesigning the heat tape (higher wattage than actually needed) will be taken care of by the thermostatic controller, but it may cause undesirable temperature cycling.
One caution is that if there is much fuel gas flow it may cool the line significantly compared to heat losses to ambient, so that needs to factor into the calculation too.
 
drcampbell said:
Something doesn't quite add up here.
If the cable is self regulating, a thermostat isn't needed.
I've never seen nor heard of self-regulating cable that operates at 90°F; the only self-regulating cable I'm aware of operates at ~35-40°F to protect against water freezing. Are you sure of the 90°F spec?
If it is a self-regulating cable that operates at ~35-40°F, it will never exceed that temperature, regardless of the thermostat setting.

That said, consider using 12 AWG:
200 feet at 8 watts per foot = 1600 watts. That's 13.3 amps at 120 volts, and 9Ω.
280 feet of 12 AWG Cu wire has a resistance of 0.45Ω. The two together would have a resistance of 9.45Ω, 12.7 amps will flow, and there will be 5.9 volts drop -- just about 5% -- in the Cu wire.
(this is neglecting the resistance of the heat-trace cable conductors, which is probably an unreasonable simplification)

Or using 14 AWG:
280 feet of 14 AWG Cu wire has a resistance of 0.7Ω. The two together would have a resistance of 9.7Ω, 12.4 amps will flow, and there will be 9.7 volts drop in the Cu wire.
Since resistance heaters are not harmed by low voltages, this would be adequate.
Click to expand...

I wouldn’t advise using #14 since protection for this circuit is probably a 20A CB, which would require #12 minimum. Also 5% VD is borderline maximum - I would go with #10’s to err on the safe side.


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AKElectrician said:
I have never installed heat trace with out a t stat, why run heat trace when it’s not cold? And why make it so someone forgets to turn it on/off?
Click to expand...

Agreed. I’m used to seeing RTD’s installed along the piping to be traced


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