Testing live installation

[skatingsparks]

Ok how to upset everyone.

A client wants a COC on an installation that cannot be switched off. Discuss....

I said to the client it can't be tested effectively. Yes, you can do earth test (fly lead method) when live. Insulation resistance... No chance. Polarity, yes. Make and break check, nope. Earth leakage (I don't there are any). Voltage off load, not possible.

I accept there are things that cannot be turned off. What do you guys think....

I do a lot of shop work in malls and, no the mall will not let you shut down the entire mall so you can do a no load voltage test.

This job isn't a shopping centre and i understand it can't be turned off. The consequences would be quite dire. What can you do in these situations.

Just curious. I know most will say "won't touch with a barge pole"

[bergie]

wont touch with a barge pole

[Dave A]

I always ask - what do you do when there's a power failure? That tends to take the wind out of their sails most times. Even where there are backup generators, there's still a point where the power goes down before the standby power kicks in.

You just have to stand firm. The power needs to go off at some point. At least this will be a planned outage.

We've had to work around some pretty crazy hours for the outages at some instances, but haven't had one yet where they actually, genuinely, and absolutely could not make a plan.

And yes, that does include some shopping centres - with backup generators to boot. And high end IT installs on UPS. And 24/7 manufacturing plants.

You want a COC - the power will be going off at some point. Make a plan.

I do a lot of shop work in malls and, no the mall will not let you shut down the entire mall so you can do a no load voltage test.

Probably worth pointing out that if the mall is the only point of consumption on the transformer, you can't shut down absolutely everything on the load side of a transformer anyway. On some of the heavier supplies, some of your readings are going to have to be calculated anyway.

[AndyD]

The IR of the installation at 220v can be calculated by measuring global installation leakage whilst live.

We've actually issued two CoC's in the past decade on critical installations in conjunction with the area electrical inspector. You could try liase with him but if it's just a corporate convenience thing I doubt he'll entertain the required test exemptions.

You say you don't think there's any RCD's, I'm interested to know what the installation is...

[skatingsparks]

Its the power to control panels of a baggage handling system at an international airport. Everything is interlinked so if one part goes down the whole system shuts down (ie the whole airport baggage handling system gets weird from check in to baggage collection). I'm seeing the baggage handling system as a (very big) appliance. I mean everything that runs on the system is from one of about 36 panels (that I know of not all of which are required to be tested) which are interlinked by profibus signal cables so they can talk to each other. I think anything connected to the control panel is part of the fixed appliance.

Shutting a mall down, inconvenient, shutting an international airport baggage handling system down... er no.

I worked on the system during the install when it was being upgraded for the world cup in 2010 but I was working for a company then. Another company put the power to the panels and I was doing the power from the panels to the motors and control cables for the e-stops etc.

What do you think?

[AndyD]

Yeah, as you say anything fed from a control panel isn't part of the electrical installation for CoC purposes, only the main power distribution DB's and sub DB's plus the final circuits to the point of isolation.

Is there a back-up power solution ie generator/UPS etc connected to the baggage handling system? If there is it makes your life fairly easy. Back-up power would also be a double-edged sword because if there isn't any then it's going to be kinda difficult to motivate it as a critical system and get it considered for any special treatment or exemptions.

TBH if the rest of the installation is compliant plus there's no socket circuits then I would seriously consider just issuing the CoC with a calculated IR result and leave out any off-load voltage results you can't obtain and include your reasons in the notes section.

[skatingsparks]

Thanks Andy. I'm going to do a site visit just have look, see if its feasible to pretty much what you suggested. I'll make clear to client, they who won't allow us to switch off, the limitations of what we are doing and I figure if I cover all those limitations in the notes section I think it will be OK. Going to have proper look first before deciding. Its just ones of those kind of jobs that could lead to the big jobs which would take the business to the next level but I'm not going to sign off something that will give sleepless nights. I'm a bit OCD when it comes to COC's

[ians]

Testing live installation

A fluke 1653b, 435, mA meter and a ti 25 problem solved. You can collect all the readings and some and have recordings so that you can join the CYA club 😉 no need to be OCD. I believe the most import part of an COC or any electrical installation for that matter is the earth. Hence the reason i own and use a mA clamp meter, it tells you all sorts of info and with a basic understanding of ohms law many readings can be calculated from other tests. Something to think about.

[skatingsparks]

So the panels had UPS inside just to keep the PLC's powered up in the event of a power failure giving time for the generator to kick in. The whole system is just one big lump of earthed metal. The conveyers are metal standing on metal mesh floor all interlinked with steel work. The panels often stood in groups running different lines. Each panel was individually fed with its own SWA and separate earth wire. The earth reading were pretty much always 0.01 ohms using a fly lead from a local main panel (fed from a substation). The local main switch had its kA rating on it so that was noted as the kA rating (from supplier). The MCB's inside the panels were rated at 35kA(!). The supply cables were mostly massively over sized for the expected load. We did ins res from the local mains to the panels where it was possible to isolate and stated a limitation on what we were not permitted to turn off. The testing was done less that 5 years ago. For voltage on load and off load we measured when the machine conveyors were not running and again when they were running (meaning the load was the power to the PLC and the cabinet light and fan which is barely 1 amp when not running and worst case scenario when it is running).
All reading were good. The only things we could find were no glands on the earth cables coming into some panels, the earth cable were coloured black (which are now been marked with green and yellow earth tape or heat shrink inside the panel and where it enter the panels), one over size breaker on a 2.5 surfix cable (40 amp) and one real mess where a panel was drawing 180 amps through a 160 amp isolator when the machine was running. Taking the new thermal imaging camera down there tomorrow see if that picks up anything else.

That's the best I can do in the circumstances.

[Dave A]

The local main switch had its kA rating on it so that was noted as the kA rating (from supplier). The MCB's inside the panels were rated at 35kA(!). The supply cables were mostly massively over sized for the expected load.

I handed out my copy of the SANS code to a new employee the other day, and I've still got to replace it. So I can't reference the specific section. But look up the section on PSC, particularly on how to calculate PSC.

Yeah - the kA rating might seem high, but don't assume what's in there now is enough. We've had installations that have needed 200kA ratings at the main switch where there was "only" a 50kA rated switch in place.
One might expect that someone did it right with the original installation, but CYA and do the calculation anyway. (If you haven't already).

You'll need the transformer's internal resistance rating from the plate on the transformer, + the size and length of the main supply cable.

[AndyD]

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

[Dave A]

I prefer to measure the PSCC.

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

[skatingsparks]

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]

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]

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?