Measuring 170v?

[kenai36]

Hello all.

Ive been called out to a fault on some electrical signage and lighting in a bus shelter. Everything is off which is normally simple to fix and have done this hundreds of times before. The problem I am getting is that I can only measure 170 from the cut out in the lamppost feeding the shelter. I've tried it with 3 different testers as I wasn't sure about the results but came back the same on all 3.

Might be be a stupid question and I've tried googling but can't find anything about it.

I'm probably being stupid but I just can't figure it out. I'm fairly new to all of this.

There has been some groundworks in the area but surely a damaged cable would result in less amps not volts.

Thanks in advance.

Rich

 

[telectrix]

could it be a lost neutral and you are reading a floating neutral voltage. test L-E to confirm.

 

[Guest111]

As Tel said could be a lost neutral,best policy in these situations is always to measure PE as well as PN.

 

[kenai36]

Hi mate thanks for the quick reply.

It's TNCS to the lamp post so I can only test between L + N.

Rich

 

[telectrix]

why.? you must have an earth terminal at the post.

 

[kenai36]

Yea but the earth and neutral are combined. The cable into the cut out in the lamp post is just 1 cable with 2 cores. The main aluminium core being the line and the outer core / sheathing is the N and Earth combined.

 

[kenai36]

I'm measuring from the live side of the cut out btw.

 

[telectrix]

so isolate the supply and perform continuity and IR tests. this should prove the cable.

 

[kenai36]

Sorry I don't think I'm making the point very well.

I've tested our SWA cable leading off to the shelter and that's all fine. When I measure the voltage at the suppliers side (where the street lighting guys have put the cable into the post) it reads at 170. There's nothing I can do as that cable is live spliced into the main service in the road so can't isolate it.

I just wanted to know why the supply to the whole installation was reading lower than 230. Would this be the case if someone has nicked the side of the cable for example? Meaning there isn't a direct route back to N so decreasing the voltage?

It'll to go back to the DNO just wanted to know out of curiosity.

Hope that explains it a bit better.

Rich

 

[Darkwood]

You can get volts drop due to damaged cable... their may be a high impedance fault in the supply cable this could drag the voltage down but not let enough current flow to operate the OCPD ...

As mentioned above you may have a N/E issue if its PME... i assume the armour is terminated in and out of each connection block on the street furniture... there maybe a poor connection causing overheating / high resistance again a possibility in your scenario.

 

[HandySparks]

A Ze or Z line (same thing in this case) test on the supply might indicate whether there's a proper low impedance supply or just some phantom voltage.

 

[VoltzElectrical]

I work on street lighting. With a voltage as you have specified, under the circumstances you have described, that would be bounced back to the DNO to sort out. Who knows what the cause is...it's their responsibility to provide you with a decent supply.

Voltz.