Trace heating cable - testing issues

[JNJLAG]

Hi , Wondered if anyone can help , i currently install and test Trace Heating Cable on Mechanical Pipework for Frost protection . Recently our Clients are asking for a recordable test that states cable lengh of the circuit and a test to determine if there is a fault in the cable.
Currently using the Fluke 1503 to perform the resistance / continuity test for the client but have now requested this as an addition.

Any help would be greatly appreciated

 

[DPG]

Is it not sufficient to give the end-to-end resistance of the cable? As long as you know how many Ohms per metre the cable is then you will know what figure to expect.

 

[James]

Insulation resistance between live (heating cable) and the pipe or heating cable braid would be a good additional test.

 

[JNJLAG]

Is it not sufficient to give the end-to-end resistance of the cable? As long as you know how many Ohms per metre the cable is then you will know what figure to expect.

Ah , i cannot perform end to end as the cable is installed on the pipe to a Max of about 130mts. i can do this on the drum , which i do but the request is for installed

 

[DPG]

Could use an R2 lead. Admittedly it would need to be a long one!

 

[JNJLAG]

Is it not sufficient to give the end-to-end resistance of the cable? As long as you know how many Ohms per metre the cable is then you will know what figure to expect.

Could use an R2 lead. Admittedly it would need to be a long one!

Thanks , i have had someone mention a Megga tester performs such test , also a Time Domain Reflectometer

 

[DPG]

Thanks , i have had someone mention a Megga tester performs such test , also a Time Domain Reflectometer

A time domain reflectometer seems excessive unless there is a known fat which needs finding.

 

[JNJLAG]

A time domain reflectometer seems excessive unless there is a known fat which needs finding.

Problem being , as soon as the cale is installed and tested the Laggers insulate the pipe , so if we cannot determine where the fault is ,we would have to strip all the insulation off too

 

[DPG]

But assuming the end to end resistance and IR tests are OK then all is good right? On the rare occasion you get a fault then wouldn't you replace the cable, bearing in mind its a new install. Or would the customer accept a repair on a newly installed cable?

 

[JNJLAG]

But assuming the end to end resistance and IR tests are OK then all is good right? On the rare occasion you get a fault then wouldn't you replace the cable, bearing in mind its a new install. Or would the customer accept a repair on a newly installed cable?

Agreed , but no they would not accept the repair unfortunately

 

[DPG]

Agreed , but no they would not accept the repair unfortunately

That's what I mean, so you wouldn't need a TDR to find it! Because it would be getting ripped out anyway.

 

[timhoward]

How does the heater wire work, is it a single high resistance wire that is connected both ends, or does it have two conductors and you have to install a bridge at the far end?

 

[DPG]

How does the heater wire work, is it a single high resistance wire that is connected both ends, or does it have two conductors and you have to install a bridge at the far end?

Good point.

 

[Rockingit]

How does the heater wire work, is it a single high resistance wire that is connected both ends, or does it have two conductors and you have to install a bridge at the far end?

I was also wondering if there might be an option to use the actual pipework (assuming it's copper/brass throughout..) as a return. You'll get some very high r1r2 readings but it will at least prove continuity.

 

[James]

2 types of heating wire

type 1 is a single wire , you buy it in pre made lengths and has the right resistance for the watts per m required at that length.

the other type can be cut to any length and has 2 wires joined by lots of parallel resistors or a single resistive strip between the cores for its entire length.

 

[Lucien Nunes]

Is it not sufficient to give the end-to-end resistance of the cable?

Ah , i cannot perform end to end as the cable is installed on the pipe to a Max of about 130mts.

I think what was meant by 'end-to-end' was across the heating cable circuit from line to neutral, not physically from one end of the pipe run to the other. Each length of cable must surely be terminated in a way that brings the line and neutral connections together into the same box where they connect to the supply. That is where you would take the resistance measurement.

Is the cable printed with length markers that could be logged during install, and used to corroborate the measured resistance and resistance per unit length with the installed length? If those three parameters check out, and the insulation resistance is tested and proves good, then I think you have all reasonable data to claim it's intact short of a full visual inspection.

 

[timhoward]

The Fluke 1503 that is currently being used can also do the insulation resistance testing.
However, I think it doesn't have a 250v setting, only 500v and 1000v

It would be safe to join L and N together and test to the pipe at 500v but to play safe I wouldn't test L to N at 500v without the cable manufacturer's advice.
The equivalent Megger tester which also has a 250v (and 100v) range is probably the BM80, which regularly come up on ebay as the fashion is for all-in-one multi function testers these days.

 

[Lucien Nunes]

I wouldn't test L to N at 500v without the cable manufacturer's advice

It's a permanently-connected resistive load, so testing L-N with an insulation tester wouldn't yield any useful information anyway.