Failing a cable then switching circuit off?

[sharpy1983]

Hi Guys,

recently passed my 2391 and testing power cables on the motorways and A Roads. Came across this scenario last week.

3 core SWA cable has had Cpc cut and only line and neutral terminated, but cable is glanded and connected to the MET at both ends and I am getting a r1 r2 continuity reading when I drop the cable. Zs reading is within spec for protective device also but cable fails line-earth and neutral - earth on insulation resistance (0.5MOhm and 0.75MOhm). I isolated and locked off the circuit as the regs state that IR is a minimum of 1 meg.

Just been informed that I should have left the circuit on as the Zs is ok.

Just trying to clear things up as I am new to testing and want to do the right thing.

cheers!

 

[telectrix]

sod the Zs. a IR reading that low needs investigating. you did the right thing.

 

[sharpy1983]

Thanks mate

 

[Clive P]

Hi,
I'm with Tel on that one, sounds like the cable has been damaged and the earth has been chopped out as it's probably in contact with L-N, can only get worse; good call stick by your guns.

Regards.

 

[sharpy1983]

Cheers Clive I was thinking that's why the CPC had been chopped.

 

[Marvo]

I agree with the comments above. Possible the cable has been damaged somewhere along its length. Completely isolate the cable and disconnect the armour from the galnds. Mega between the armour and a known good earth. If the ins reading is low then the cable is a write-off. Also if the cable is damaged the armour will be corroding which means your Zs won't be reliable.

 

[Guest55]

so you've killed the power to lighting on a motorway / dual carrigeway cos of a I.R reading in excess of 500,000 ohms and a Zs value that complies ??
how much of the highway is unlit ?
how long will it remain out ?
did you get approval from your superiors to shut down lighting ?

so when theres a multi car pile up in the dark and the highways agency launch an investigaton do you think your actions will stand up to technical scrutiny ?
i dont , best get it switched back on sharpish , if you've still got a job.

 

[sharpy1983]

Biff, it's not a lighting circuit, it's a single 5 lane gantry and a message sign. The cable has an IR reading lower than what the regs state as a pass and my name and signature goes on the condition report so I'm making sure I cover my arse.

My actions will stand up to BS7671 and that's the important thing.

Guessing that's why your name is biff?

 

[Guest55]

where does it say in bs7671 that circuits below 1 meg IR should be isolated ?

anyways , if you think you did right then thats all that matters , what do i know lol.

 

[Marvo]

Lol, you didn't say exactly what the cable supplied but gantry signage and even street lighting is just a 'nice to have' we do just fine without them where I am

Maybe just report it for further investigation or replacement.

 

[MDJ]

Lol, you didn't say exactly what the cable supplied but gantry signage and even street lighting is just a 'nice to have' we do just fine without them where I am

Maybe just report it for further investigation or replacement.

You have guns there don't you fella so street lights are not a requirement haha, okay sorry Just kidding.

 

[sharpy1983]

Doesn't say it has to be isolated but it does say that minimum IR for a LV circuit is 1MOhm. Plus this cable was PIRd 5 years ago and the observations stated the cpc had been cut, for what reason other than a short between line and cpc?

Nackered Cables direct buried on sides of wet motorways won't last long and I'm not being the go to guy when a contractor or joe public gets a belt.

you might be a bit of mr know it all I'm just being safe.

 

[sharpy1983]

What does it matter what's on the end of the cable? It's street furniture, it's in the regs, it's failed!!!

 

[Des 56]

I am not commenting on the justification of your actions with regard Bs 7671 because that's your opinion and you are the guy on the job

What I would like to know
You are testing the installation and will be signing the report that goes along with that testing.what authority do you have for deciding to isolate this circuit?
I would have thought,permission to do so would have to be sought before this action is taken
I can well understand something that is an immediate danger not being re energised by yourself,but this is a system degradation that needs attention rather than something needing immediately isolation

 

[SparkyJoe]

so you've killed the power to lighting on a motorway / dual carrigeway cos of a I.R reading in excess of 500,000 ohms and a Zs value that complies ??
how much of the highway is unlit ?
how long will it remain out ?
did you get approval from your superiors to shut down lighting ?

so when theres a multi car pile up in the dark and the highways agency launch an investigaton do you think your actions will stand up to technical scrutiny ?
i dont , best get it switched back on sharpish , if you've still got a job.

Dunno about yours, but my car has lights.