ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades C.T. chamber covers

Hi Marcspages. Insulated bars & testing tap-offs with removable covers are a great idea but unfortunately would triple the cost of a CT chamber, and Electrical Engineering Consultants always have one eye on the money and don't consider making safe provisions for power analysis testing without a shut-down later on.

I guess the Metering CT chamber is an obvious choice for live power analysis meaurement when a shut-down is inconvenient

I can imagine how putting clamps & croc clips on bare bars could be very nerve-racking. I would wear a welding helmet and a thick pair of rubber gloves.

The OSH rules in NZ forbid persons working on or in the vicinity of live parts. Unless there is an approved procedure in place to minimise risk of injury etc.

So unless their is a CT chamber with properly shielded testing points, the main switch should be off while you connect your test leads. This may mean that you have to get up in the middle of the night to do the shut-down, but its still preferable to attaching leads to bare live bars. Fault currents are very high at CT busbars and one tiny mistake can cause a big bang.
Also you can charge more for "after-hours work".

Kiwi,

"Sir, I need to throw the big switch on your bank's data centre while I connect my PQ recorder". Yeah, right!

In actual fact, I have only had one client (oh yes, it was a bank too!) to date who would not let me connect live - to their detriment! Before I could connect up the kit at the next scheduled shutdown, they lost their data centre because of a set of loosening busbar bolts (something the PQ survey would have picked up).

Strangely, I don't get the shivers with open busbars. It's more for the cowboys I've seen in action. I'm more than happy to work live to 690VAC (or thereabouts - I get vertigo at 1kV).

But I ramble, the whole purpose was merely a ha'penny thought should it influence someone to put in reasonably costed testing facilities for our modern power-hungry world!

Marc.

It's a sad fact that people who are not electrically qualified can say 'no you can't shut that down'

My answer would probably be seen as confrontational, but it does make a point. That would be "It can't be shut down? Oh good, that means you have it on a UPS right?" *CLUNK*...

Good one! It does make you wonder how many of these "can't be interrupted" supplies do have a UPS backup though, doesn't it?



[This message has been edited by pauluk (edited 05-11-2005).]

There are occasions where this wouldn't apply.
Namely: In a hospital or place where there was other medical equipment, in any place where the other guy's bigger than me, and if the breaker/switch was on the output side of a large UPS, that just ends up making you look like a doofus

That's a rather good point Paul.
For those people that have installations that "Can't be shut off", it is up to them to have a back-up power supply system.
I've heard just about all of the various excuses as to why the power must stay on and I haven't heard any that are convincing enough yet.
kiwi,
Just a little note about "Inspectors".
I was talking to a Power Company Inspector at work the other day and he said that the term "Electrical Inspector" doesn't have the same meaning as what it did before 1992.
He said that to even get an Inspectors Licence, is so simple it's not funny these days, considering that you only have to have 3 years qualifying experience and sit an exam to get there.
When he did his, you had to have 15 years qualifying experience as a Registered Electrician, hold Advanced Trade Certificate
and sit a 4 hour written exam.
He also said that a lot of the newer Inspectors these days gave inconsistant rulings on various work, often picking up little things, but leaving out serious safety issues.

Excellent point Chipmunk ! Often, an unplanned shutdown is the best way of testing the health of auxillary and emergency electrical services in a large building. Managers who get twitchy over unplanned shutdowns always change their opinion when they find that the emergency lights in the stairwell did'nt start or that the airconditioning did'nt restart.

I believe that working on live equipment is to be avoided or at least undertaken in controlled situations where the risks are minimised to ridiculously low levels. We have all been obliged to work in live situations at one time or another to make the corporate budget, and we have all seen the results of the accidents.

I think the safe testing tap-offs for main switches that Marcspages longs for are the answer. Now someone just needs to convince the bean-counters and they can start specifying this in their designs.


Trumpy I had no idea that it was three years experience required for Inspectors. Jeez that means that you could spend three years drilling holes as an apprentice then another three after your registration wiring cottages then the next day your an Inspector certifying a 2400A central supply for a shopping mall. An extreme example I know, but I think it highlights the pitfalls of NZs electricity deregulation.

Finally an answer, from Bill:

Hope that this helps.

Thanks for that reply Trumpy. It confirms that the way CT chambers are constructed in the industry right now is compliant. No drastic (expensive) changes are required.

I see the EWRB has issued an email today announcing that they have struck a deal with Standards New Zealand to make standards documents, referenced in the Regs, available online.

Guess I'll have to take back my comments on "government officials not helping Joe Sparky" now!

Shucks !

Thanks for the info kiwi!
So does that mean that we won't have to fork out huge amounts of our hard-earned money to get the standards we need?.
Did the e-mail state which standards would be offered?.

Cheers mate.