Trace heating cable - testing issues

[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.