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mgtrp, I'm not quite following the downstream DB comment. Is this including an outbuilding arrangement? My understanding is that if it's single installation (with no outbuilding) there should only be a single MEN otherwise we'll have parallel return paths. In terms of higher fault level, if...

In Aus, minimum LV depth to top of cable/conduit is: * 500 mm * 300 mm if covered with 75 mm concrete. * 50 mm if chased in rock.

I mostly agree, but often have a case in my designs where a smallish gen (500 kvA say) will be connected to a sub-board that might be a 50 m run from the MSB containing the MEN. With typical X0 values, the additional impedance in the fault loop along the earth conductor to the MEN and then back...

Most commonly in this part of the world, 3p/3p is used for switching at the board containing the MEN and 3p/4p used at DBs with a remote MEN. 4p/4p configuration remains acceptable under AS/NZS 3000:2007 but is not encouraged to the extent that it was in AS/NZS 3010:2005. It is true that a...

To help with your first question, how valuable it is depends on how critical your loads are and how important it is to understand the details of any supply issues. If you decide that it's important to have some idea of what's going on, your next step is to decide how much info you need. Basic...

Earth leakage through the SMPSs on the office PCs and data centre rack equipment might be a big part of the problem. Along with increaingly leading pf comes the leakage through all these capacitors. If you have small UPS throughout the building these add up to 5 mA each also. In a large...

Edison - yes, our NEC equivalent (AS3000) deliberately avoids nominating a resistance value. Although it's geared towards ensuring fault clearance under fully metallic return conditions I would prefer it nominate a value and then for the periodic verfication standard (AS3019) to enforce the...

To summarise my local (Aus) requirements, you need the following for USTs at least: -Double walled tank w/ interstitial monitoring. -Double walled pipework (incl. vent, fill, etc) w/ interstitial monitoring on wet legs. -Monitored transition pits where joining with single walled pipe. -All...

junmal, Fluke publish a testing guide that includes a section on what a "good" ground resistance value should be. It makes reference to NEC and IEEE recommendations (though I'm unsure if these remain current). http://support.fluke.com/find-sales/Download/Asset/2633834_6115_ENG_A_W.PDF For the...

I'm an end user so aside from the varying volts it appears like any other two wire system. I would have suspected that it would be less than 10 Ohms though. 2000 A on a single return would be interesting - these must be the SWER isolation poles I see with the fencing around the base to stop...

Yes, efficiency loss is a problem although running at HV helps. As davidbeach noted, on a network level, these losses aren't enough to justify the additional 1000's (10s of 1000's in my part of the world) of kms of conductor. Ultimately, the customer bears most of the technical drawback...

Isolation is fairly straight forward as long as you know where the sources (rectifier, bypass, battery, output if paralleling) are switched. ScottyUK mentioned a critical point though, large UPS can carry significant energy in filter caps once isolated so best to isolate then wait a while before...

SteveFehr is correct in that there's no substitute for primary and secondary protection in your boards. Best practice these days is for diverters at your MSB and multistage filters at your DBs. I look after a lot of mountaintop sites in high GFD areas so my critical controls items are all 24 V...

In Aus, the main issue is seperation of different voltage levels. If your control voltage 24 V ac or dc, the LV in the same "wiring system" can cause an EMC issue.

It's not so much that you'll overload your prime mover, but for (especially for leading loads) you might need to limit the demand to stay within the safe range of the P/Q curve. If we compare supplying 1MVA at unity to 1MVA at 0.9 (leading or lagging), you're actually reducing the load on the...

I agree with ESOXmaniac. I have loads of rackmount UPS on site and am forever telling the field crews not to discharge test them by pulling the IEC input connector for exactly those reasons. If you check the equipment manuals, there should be a note along these lines buried somewhere. Further...

Also, if you're referring specifically to switchgear ratings, there might be more than one "fault" rating. Typically, large LV CBs may offer kA figures for things like Icu (ultimate breaking capacity), Ics (service level rating - usually some derate multiple of Icu) and Icw (withstand rating -...