Testing live installation

**AndyD** · 24-Jul-14, 05:26 PM

I prefer to measure the PSCC, calculations can give very different figures to actual measurements.

**Dave A** · 24-Jul-14, 08:33 PM

Originally Posted by AndyD

I prefer to measure the PSCC.

When you aren't allowed to switch off the main switch?

**skatingsparks** · 24-Jul-14, 09:54 PM

I measure at each control panel with 2 different loop testers and reading well within limits. The earth readings were very very low (the panels are side by side with SWA cables and separate earths and the whole structure is metal). I checked the bonding by the main panels, plenty of it but the with the size of the structure its hard to trace the bonding. I did a fly lead test to many metal parts of the machines and the structure and my Fluke 1653b and it alway read 0.01 ohms from local sumains. Its one big lump of earth metal. The only thing keeping the earth fault currents and PSCC down is the length of run of the conductors (100+ meter runs) but the cables are very oversized for there designed load so volt drop was minamal.
The baggage handling company is only responsible for the protective device from the sub main to there panels which is the only part they are concerned about.

Took the new Flir E4 for a spin whilst the panels were on full load. The only sign of any heat was from the contacter coils. Nothing to worry about

How ever at a very good customer house my guys were doing a favour job at, just moving a pool pump housing, we had an incident. When dinner time came round and the oven was on, washing machine spinning, geyser was on we noticed that hot cable smell. Pointed the Flir at the DB to find the main cable was running at 180 degrees. Went to tell the client we urgently needed to switch off the power. Just as i got back to the board BoooooM!!! cable had melted through and touched down to earth. The customer confessed to trying to temporarily connect a generator to the board. He hadn't put the cable back in the right side of the terminal, feels tight with a screw driver but its not tight on the cable. I like the new thermal camera and the MSX feature is pretty nifty.

**AndyD** · 26-Jul-14, 03:23 AM

Originally Posted by Dave A

When you aren't allowed to switch off the main switch?

Yes, I have a tester that performs PSC (L-E) + (L-N), ZE (Zdb), ZN, ZL etc as a live tests. A good investment for a couple of grand.

**Dave A** · 27-Jul-14, 08:45 AM

Originally Posted by AndyD

Yes, I have a tester that performs PSC (L-E) + (L-N), ZE (Zdb), ZN, ZL etc as a live tests. A good investment for a couple of grand.

Perhaps we're missing each other.

If the installation is live and running behind the main switch, and you're testing the PSC at the main supply point, doesn't the running installation affect the accuracy of the PSC test reading at the main switch?

**AndyD** · 28-Jul-14, 10:16 PM

No, the load the installation is under at the time of test shouldn't have any noticable effect on the live PSC or PEFC result taken at the point of supply.