Can anyone help me explain how heat trace works?

[hockeyoligist2]

I kinda know but I can't really explain it to the other electricians while troubleshooting problems.

Since we have been having record cold weather here in SC, we have been having to troubleshoot and repair a lot of heat trace in the last few weeks.

They don't understand how it heats since the wires don't actually connect to complete a circuit.

My limited understanding is that the material around the wires, inside of the insulation, is some sort of mineral that heats up due to voltage being present in the wires. Am I right?

Plus, most of them are on ground fault breakers. If I remember my codes correctly, in industrial applications a ground fault breaker isn't required. We are on 2012 code here.

 

[iceworm]

I kinda know but I can't really explain it to the other electricians while troubleshooting problems.

Since we have been having record cold weather here in SC, we have been having to troubleshoot and repair a lot of heat trace in the last few weeks.

They don't understand how it heats since the wires don't actually connect to complete a circuit.

My limited understanding is that the material around the wires, inside of the insulation, is some sort of mineral that heats up due to voltage being present in the wires. Am I right?

Plus, most of them are on ground fault breakers. If I remember my codes correctly, in industrial applications a ground fault breaker isn't required. We are on 2012 code here.

There are two that are most common:
Conductive plastic molded over the two conductors. The polymer acts as heating element
http://www.pentairthermal.com/Images/EN-RaychemBTVpipefreezeprotection-DS-H51086_tcm432-26253.pdf


http://www.pentairthermal.com/Images/EN-RaychemVPL-DS-H56825_tcm432-26414.pdf
This one has a heating wire wrapped around the two conductors. Each wrap conducts, xx watts/foot.

Some use PTC heating element (wire or plastic) and is self regulating. As ambient goes up, the cable temp goes up, the heating wire resistance increases, drawing less current.

ice

 

[iceworm]

... Plus, most of them are on ground fault breakers. If I remember my codes correctly, in industrial applications a ground fault breaker isn't required. We are on 2012 code here.

Paraphrased from NEC 2011
426 Outdoor deicing and snow melting: requires GFP for equipment

427 Fixed heating for pipelines and vessels: requires GFPE - exemption for industrial requires alarm, qualified personnel, continuous operation necessary for safety

Both require a braid over the elements.

T-shoot (personal experience)
Issues are:
mechanical damage, shorting the two main conductors
water infiltration at the ends, End termination not sealed. Feed end not sealed.

Look at the connection boxes first.

If it is tripping the GFPE, look for mechanical damage

The polymer can start burning at end back toward the feed end, inside of the outer sheath, not trip the GFPE. I've seen that twice - freaky

Disclaimer: I've seen the inexpensive, blue, round, smaller than a pencil, residential - I don't know what is in that for conductors. I suspect it is a poorly mechanically protected two conductor with a polymer heat element. But i don't know that.

ice

 

[hockeyoligist2]

All of ours have a braid over the elements. So, I think that it's OK to take it off of a ground fault?

I put one on a regular breaker this morning and it held. A temp fix in an emergency, since the pipes were frozen and it is supposed to be colder tonight.

"mechanical damage, shorting the two main conductors
water infiltration at the ends, End termination not sealed. Feed end not sealed."

I ran in to water infiltration this morning, when I opened the termination box it was full of ice. I thawed it out with my heat gun and dried it out and it was OK. It had a cross threaded cover.

The ones that I couldn't get to the ends, because of insulation probably have water at the end. They have enough insulation and other heat trace to survive tonight. Fingers crossed!

After all I work for a sewer company, lots of water!

 

[iceworm]

All of ours have a braid over the elements. So, I think that it's OK to take it off of a ground fault?

I put one on a regular breaker this morning and it held. A temp fix in an emergency, since the pipes were frozen and it is supposed to be colder tonight. ...

All have to have a braid. Unless you meet 427.22 - Industrial, GF alarm, and (1) and (2) all have to have a GFPE.

Yes, I understand a temporary fix in the winter. But you know it is leaking (electrons). Take care of yourself and don't let the dog pee on the pipes.

ice

 

[hockeyoligist2]

Thanks Ice.

I had an almost new ground fault breaker from a panel that I salvaged from another plant.

I installed it yesterday and it held all night and was still holding an hour ago!

I'm hoping it was just weak or damaged from so many trips.

 

[Little Bill]

We are on 2012 code here.

Man, we only have new codes every 3 years! 2005,2008,2011... We must have missed the 2012 one!

 

[iceworm]

Thanks Ice.

I had an almost new ground fault breaker from a panel that I salvaged from another plant.

I installed it yesterday and it held all night and was still holding an hour ago!

I'm hoping it was just weak or damaged from so many trips.

Uhhhh.... How come so many trips? Leakage? Are you using GFCI or GFPE CBs?

There are milliamp clamp-on CT meters available. The techs have one and they really like it for t-shooting trace. I think it is a fluke 360, ~$700 - $800 If the boss squawks about the money, remind her of the cost of freezing up one line.

ice

 

[iceworm]

Man, we only have new codes every 3 years! 2005,2008,2011... We must have missed the 2012 one!

You did. Most do. Sometimes us special sorts require special codes :blink:

ice

 

[hockeyoligist2]

Man, we only have new codes every 3 years! 2005,2008,2011... We must have missed the 2012 one!

A typo!

 

[hockeyoligist2]

Uhhhh.... How come so many trips? Leakage? Are you using GFCI or GFPE CBs?

There are milliamp clamp-on CT meters available. The techs have one and they really like it for t-shooting trace. I think it is a fluke 360, ~$700 - $800 If the boss squawks about the money, remind her of the cost of freezing up one line.

The operators kept resetting the breaker instead of calling us. I checked with them this morning and it is still holding. The boss squawking about money is another issue, our coffee budget is higher than our tool budget!

 

[kwired]

Uhhhh.... How come so many trips? Leakage? Are you using GFCI or GFPE CBs?

There are milliamp clamp-on CT meters available. The techs have one and they really like it for t-shooting trace. I think it is a fluke 360, ~$700 - $800 If the boss squawks about the money, remind her of the cost of freezing up one line.

The operators kept resetting the breaker instead of calling us. I checked with them this morning and it is still holding. The boss squawking about money is another issue, our coffee budget is higher than our tool budget!

Iceworm asked if you are using GFCI which is class A with 4-6 mA trip and is for people protection or GFPE which is class B and is generally preferred for such installations and has a trip point of 30-100 mA and is for equipment protection.

 

[tom baker]

I use blank face GFCIs for my short runs of heat trace.
The material between the wires has a negative temperature cofficent, IE when its colder, it looses resistance, becomes conductive, and hotter. Back in the 80's with regular heat trace, there was a lot of fires from overheated heat trace, particulary under mobile homes.
In Bremerton there is a concrete pier "boardwalk" with 277V heat trace. It caught on fire and the fire dept had no way to get underneath and put out the fire. Got everyone all excited! Turned off the circuit. Two weeks later another run caught on fire. There was no GFPE installed.

 

[Sierrasparky]

I use blank face GFCIs for my short runs of heat trace.
The material between the wires has a negative temperature cofficent, IE when its colder, it looses resistance, becomes conductive, and hotter. Back in the 80's with regular heat trace, there was a lot of fires from overheated heat trace, particulary under mobile homes.
In Bremerton there is a concrete pier "boardwalk" with 277V heat trace. It caught on fire and the fire dept had no way to get underneath and put out the fire. Got everyone all excited! Turned off the circuit. Two weeks later another run caught on fire. There was no GFPE installed.

regular GFCI can cause false tripping. 5ma not 30ma of a epd type