In a couple of instances here in NZ I have had Inspectors who require extra plastic shrouding over metering CT busbars, even when the busbars are in a completely sealed chamber with metal fixed covers which require two tools to remove, engraved warning labels and are sealed with the power authority seal which only authorised persons are allowed to break. Add to this the fact that the Main Switchboard should be in a locked room and this requirement for additional plastic shrouding just seems frivolous.
The 1% of inspectors who raise this requirement always cite Reg 94, which states "all practicable steps must be taken to prevent accidental contact with live parts through the use of barriers and screens etc". It seems that the whole matter hinges on the interpretation of the word "practicable".
In all cases the Inspector will require that an extra plastic cover-plate be fitted under the metal fixed cover. This plastic cover-plate will take 15 seconds to remove for anyone with the same tools used to remove the metal fixed cover.
The only reason anyone needs to access a CT chamber is for CT maintenance when the meter stops running and in this case the main switch has to be switched off.
I am not ragging individual inspectors here, and in no way do I think my opinion is final. I would like to hear other members thoughts on this matter, especially from Australasia and the UK.
I don't think either the inspectors or installers are at fault here, it's that the code is too vague. It should simply state that all parts needed for type approval must be fitted. Given the number of photographs on this forum of installations left without their covers on, and of other cables routed through cabinets, double insulating busbars has its merits.
kiwi, That's a rather good point. I've heard of this sort of thing being asked for before, not locally, but there was an Inspector making all sorts of noise about it at a recent Refresher course I attended. CT busbar chambers by thier nature, as you have mentioned are sealed equipment and would normally be only accessed by Authorised personnel, the ones we use down here use a security screw system. For those outside of NZ:
Reg. 94. Protection against direct and indirect electrical contact- (1)A person having control of any works, electrical installation, electrical appliance or associated equipment must take all practicable steps to minimise the risk of direct or indirect contact with the works, electrical installation, appliance or associated equipment. (2)Compliance with any of the following criteria is deemed to be compliance with subclause (1): (a)Prevention of the passing of an electric current through the body of a person or limiting that current so that shock currents and thier duration cannot exceed the IEC shock currents standard: (b)Automatic disconnection of the power supply to the works, electrical installation, appliance, or associated equipment, as the case may be, on the occurence of a fault: (c)Use of screens, barriers, or fittings which prevent direct or indirect accidental contact with the live fittings or exposed conductive parts.
Oddly enough, we are told at work that all CT equipment is to be shut down before accessing the transformers, it's in our Health and Safety policy.
[This message has been edited by Trumpy (edited 05-07-2005).]
Kiwi, One thought just struck me. As I understand things, (I could be wrong here too) the 1997 Electricity Regulations are no longer in force. Instead guidance should be sought from AS/NZS 3000:2000, as far as I'm aware these superseded the old Regs. Section 1.7: Protection for Safety applies to this sort of thing. In particular, sub-sections 1.7.1- 184.108.40.206. Hope this helps.
I was under the exact same impression as you Trumpy. I thought the Regs had been superceded. Apparently not ! Someone from the Energy Safety Service told me last week that the old Regs HAD NOT been superceded but INTEGRATED.
We are now in a situation where we must reference the Regs, the AS3000, the companion standards to AS3000 and some of the old codes of practise, the Act, and any Bulletins the ESS publishes on specific issues. Joe Sparky is going to have to tow a mobile library behind his van to keep up.
Once again there are government officials drawing enormous salaries here and producing zero results. They won't accept responsibility for, and are too lazy to produce a single standardized document with clear rules and guidelines, a document where the buck stops and where the government takes responsibility for its regulations it forces us to uphold.
This situation is another example of government bludgers getting between Joe Sparky and his hard earned dollars and not really helping him.
Sorry Guys I was off on a rant there. Thanks for your input Gideonr and Trumpy. It does seem like a good idea to double insulate CT bars. I guess what I was looking for was a constructional requirement or specification which would put this matter to rest, and not be left up to Inspectors and Installers to argue about at crucial commissioning times.
Re: C.T. chamber covers#143103 05/08/0507:05 AM05/08/0507:05 AM
kiwi, Before we start getting too ridiculous here, I've shot an e-mail away to a friend of mine that I did my time with as an Electrician. He's now 2IC to the Chief Electrical Engineer (or there is bound to be a new title for everyone, with it being a Government Dept). (Didn't I just draw the short straw!!) But I will post the results of that e-mail here. Now kiwi, one thing you must make clear, is this requirement from a design point of view, or from an installation point of view?. I've unloaded some big switchboard units before and the person has asked me to inspect them and make sure that they comply before they are signed off as delivered. Luckily they have complied (for my skins sake). Just let me say this though, all local switch-board manufacturers do know the Regulations and Codes of Practice here, to sell non-compliant gear here in a small market like NZ, will shut you down in no time flat. I also believe that you have to be a Registered Electrician to even assemble Switch-boards here. Could kiwi, confirm that?.
[This message has been edited by Trumpy (edited 05-08-2005).]
Just my opinion, as I'm not generally involved with this sort of equipment, but I would have thought that the single cover does indeed constitute a "practicable" solution which is quite adequate in preventing contact with energized busbars.
Maybe extra insulation would be of added benefit if work needed to be done inside the chamber with power on, but that's not quite the same thing.
Re: C.T. chamber covers#143105 05/09/0504:13 AM05/09/0504:13 AM
Could I throw in a ha'penny worth here, done from a rather practical problem I keep facing when having to do (pukka) power quality investigations.
My beef is you either have nowhere to clamp on the CTs and/or voltage croc clips, or you have wide open busbar.
I would so love to see a set of (preferably double) insulated busbars where the CTs can go, and then studs for the voltage take-off (maybe the voltage can have an 'inverted-L' shape cover to stop direct contact). It appears the switchpanel designers don't see 'testing' ever being needed.
Re: C.T. chamber covers#143106 05/09/0505:37 AM05/09/0505:37 AM
Thanks again for the help guys. Trumpy, I think this is a design issue because switchboards must be designed to comply with Regs, Codes, Standards and OSH requirements. AS 3439 definitely implies that the extra plastic shrouding is unnecessary if a tool is needed to open the CT cabinet and "Authorised Persons Only" seals and labels are used. And if creepage and clearance distances are compliant.
Paul says the extra shrouding is a good idea and I agree. There are Meter Potential fuses on the CT busbars and I guess you should be able to change those fuses with a plastic shroud still over the CT bars.
According to the Act Trumpy, switchboard builders who do the prescribed wiring and the testing have to be licensed. Bolting cabinets together etc can be done by anyone.
Its uneconomical but our guys insist on building their own boards, metalwork and all. They're too fussy to let a labourer do their metalwork. In Australia its common for electrical mechanics and labourers to assemble cabinets and even do busbar work.