Heat trace.

[Marks58]

Hello all, searched thru posts and couldn't find an answer to my heat trace question(s). If 240V is applied to a 120V heat trace over a period of time, would it be ruined? It didn't catch on fire. Yet.:happyno: (Somebody hooked it up wrong or....)

I megged it and got a low reading (15Megaohms) but haven't been able to access the outside area yet so there could be some braid touching one of the bus wires or a bad splice or....
Also I read where I should meg btwn the braid and the pipe. But aren't they touching here and there?
This is a job at work that got dumped on me because it's not a fun one. I have only worked there a year so don't know the history of this heat-trace installation.

 

[charlie b]

The voltage rating of any electrical component is based on the ability of its insulation system to prevent leakage of current from the internal current-carrying metal parts (e.g., wire, windings, bus bars, etc.) to the outside world. If you hit something with twice its rated voltage, the insulation system will eventually break down. That will result in an arc, a short circuit, a fire, or some other not good thing. How long this will take is an unknown and unknowable thing. Symptoms of the breakdown may include low meggar readings or evidence of overheated insulation (discoloration, brittleness, etc.). The component might never be destroyed by an overvoltage, or it might fail in a very short time.

Welcome to the forum.

 

[infinity]

Self regulating heat trace cable works on the principle of lower temperature equals lower resistance and more heating. If you leave 240 volts applied to the cable and substantially lower it's ambient air temperature it will probably fail or open the OCPD.

 

[kwired]

Many heat trace cables are "self regulating". As temperature increases the resistance increases and they put out less heat.

I suppose it is possible if you applied the wrong voltage it will regulate itself to some extent, but if left with double the rated voltage applied for extended period of time I would still expect a failure to eventually happen.

 

[Marks58]

Thanks for the information. Based on that, I'm going to recommend that they replace the complete heat trace from the j-box out rather than just splice a chunk on the end of it. It'll be a pain (it's covered with insulation and and aluminum) but it'll be less than the pain felt if the pipes freeze and break come February!
And what do you think about the 2nd part of my question....how they recommend megging btwn the braid and the heat-traced pipe? They are in contact a lot plus the braid is grounded at the j-box. Well, it would be disconnected from equipment ground for megging but the only barrier to direct contact btwn the two would be paint or the eventual rusting of the pipe. We're talking about outside braided heat-trace. Maybe (have I answered my own question?) they are referring to hazardous location heat trace as it has an outer layer of insulation on it....
I love your site! Never knew it was here. What a wealth of information. Thank you!

 

[kwired]

Thanks for the information. Based on that, I'm going to recommend that they replace the complete heat trace from the j-box out rather than just splice a chunk on the end of it. It'll be a pain (it's covered with insulation and and aluminum) but it'll be less than the pain felt if the pipes freeze and break come February!
And what do you think about the 2nd part of my question....how they recommend megging btwn the braid and the heat-traced pipe? They are in contact a lot plus the braid is grounded at the j-box. Well, it would be disconnected from equipment ground for megging but the only barrier to direct contact btwn the two would be paint or the eventual rusting of the pipe. We're talking about outside braided heat-trace. Maybe (have I answered my own question?) they are referring to hazardous location heat trace as it has an outer layer of insulation on it....
I love your site! Never knew it was here. What a wealth of information. Thank you!

I would think it is pointless to meg between the braided shield and the metallic pipeline, you likely will get a low resistance without use of a megger as you said they are in contact with one another it should be expected that they will have low resistance between them, and neither is intended to be a current carrying component of the heat trace any way.

 

[Marks58]

Well, I went out last night and checked the ends of the heat trace to make sure there wasn't any shorts or indicator lights installed. After that I went inside to the j-box and megged it. Came out to 2.2 Gigaohms which is the maximum reading on the megger so based on that, our plan is to attach new 120V heat trace to the existing 120V h.t. Would you do the same? I would like to just replace it but that would involve removing a bunch of insulation with a metal outer cover. Will let you know how it turns out.