Heat Trace - Mixed wattage cables in a circuit

Status
Not open for further replies.
csc_wyo

csc_wyo

Member
Location
Denver
Occupation
EI&C Engineer - Oil & Gas/Heavy Industry
I have a proposed installation that combines 5w/ft, 8w/ft and 10w/ft self-regulating heat trace cable on single branch circuits. I've argued that this doesn't meet the installation guidelines, but the process engineers tell me they do this all the time. Even if they have, I don't believe this will work based on my understanding of how the cable works.

Cable specified is Nelson LT210-J, LT25-J and LT28-J.

Can someone tell me otherwise? Code/mfgr references?
 
I don't see any real issue as long as you don't overload the "bus" wires. That heat trace has multiple parallel paths between the bus wires. Those conductors are just conductors that run on the outside edges of the trace. The core between the bus wires is where the heat is produced.
 
LarryFine said:
Should be no different than mixed loads on any circuit.
Click to expand...

Agreed. I wasn't concerned about the branch feeder feeding the heat trace cable, that's sized appropriately. I wasn't sure if having an 8w segment downstream of a 5w segment would overload the 5w segment.
 
csc_wyo said:
Agreed. I wasn't concerned about the branch feeder feeding the heat trace cable, that's sized appropriately. I wasn't sure if having an 8w segment downstream of a 5w segment would overload the 5w segment.
Click to expand...
Oh, you mean in series, not parallel. That I'm not sure about.

If Don is correct, it should work. The manufacturer is the one to ask.
 
If you think about it, it's not actually a series connection like light bulbs strung end to end, because the resistance is in the cable itself.

I may be wrong, but to me, it would not affect the wattage of each individual tape, it would only make it to where if you lost the return connection at any point, the complete line would go down.

Course I may be all wet on this one, just thinking out loud.

JAP>
 
csc_wyo said:
...which is why I'm concerned that I could overload/overheat a lesser rated segment from a larger rated segment downstream of it.
Click to expand...
So if the 5 watt/ft is first, use the maximum permitted length for that trace and convert it to maximum watts. If the wattage total of all three lengths is less than that, I don't see an issue.
 
don_resqcapt19 said:
So if the 5 watt/ft is first, use the maximum permitted length for that trace and convert it to maximum watts. If the wattage total of all three lengths is less than that, I don't see an issue.
Click to expand...

I think the OP is thinking the wattages of the lower wattage tapes would be "Overpowered" If hooked in series with a higher wattage cable.

I don't see where hooking the cables in series would affect the wattages at all since the resistance is between the (2) conductors of the tape itself, not any resistance between the different wattage tapes.

I don't see how you could loose any wattage when hooking the tapes in series since your simply hooking conductors together without the resistance.

JAP>
 
don_resqcapt19 said:
So if the 5 watt/ft is first, use the maximum permitted length for that trace and convert it to maximum watts. If the wattage total of all three lengths is less than that, I don't see an issue.
Click to expand...

This was going to be my fail safe calc, and appreciate the confirmation.

JAP - Thanks for the input as well!

I do have a call in to the Mfgr, but we'll see about that return call. I won't hold my breathe. I think I'm set on what I needed. Thanks again for everyone's input!
 
If Don's assessment is correct, this method would be like plugging X-mas light strings together end-to-end.

It's just that I wasn't aware you could connect heat tapes together that way.
 
LarryFine said:
If Don's assessment is correct, this method would be like plugging X-mas light strings together end-to-end.

It's just that I wasn't aware you could connect heat tapes together that way.
Click to expand...
I have never done it with different wattage tapes, but have have installed "Tee" connections a number of times. I don't see any functional difference between a tee connection or an end to end connection. The brand I typically use, has both tee and splice connections that are designed to be under the insulation.
 
Status
Not open for further replies.
Top