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Re: Questioning the electrical norms [Re: LongRunner] #215741 07/12/15 01:51 AM
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gfretwell Online Content
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I don't have a problem with toaster wire heaters but heat is a very occasional thing here. We run the central heat once or twice a year for a day. Other than that we have a 1400w heat strip in the electric fireplace that my wife might run an hour or so on a few cold mornings. For such occasional use, we really do not need the cost and complexity of the other systems


Greg Fretwell
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Re: Questioning the electrical norms [Re: gfretwell] #215913 08/14/15 09:53 AM
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Meadow Offline
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Originally Posted by gfretwell
Toasters in the US are the metaphor for a potentially deadly appliance but they sell for $10 US (less than a 12 pack of beer).
I suppose we just trust the GFCI and get on with our lives. The actual death toll from kitchen appliances is lost in the margin of error in the statistics.


The lack of ground pins on small appliances are actually what got GFCIs into homes. Had their been a mandate GFCI could have been delayed if not eliminated in some areas of the home.


This goes into the history:
http://www.necconnect.org/resources/gfcis/

Last edited by Meadow; 08/14/15 09:54 AM.
Switches on Australian sockets [Re: LongRunner] #220839 06/16/20 10:42 PM
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LongRunner Offline OP
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As noted in aussie240's history of the Australian plug, they made sense for safety with the flimsy flexes we had to tolerate early on. With modern (much more reliable) cords, however, I'm not so sure; given that switches are subject to wear (quality switches should last 10,000+ cycles at their rated load, but still by no means forever), and even breakage if stressed enough (including at the pivots; although a good design should avoid exposing live parts even then, replacement will still be necessary and predictably inconvenient).

In general I prefer to switch on/off primarily with the appliance's own switch (especially for shop vacuum cleaners and the like with substantial inrush current, whose own switches are often higher-rated as well), using the outlet switch sometimes as an additional safety (for items that can be dangerous if accidentally switched on).

Clipsal (our main Australian brand of electrical fittings) already have quite a few 'auto-switched' (the active contact disconnects from mains when the plug is removed) single outlets (and even a twin in their older "Standard" series); although observing their outrageous list prices, I can understand why hardly anyone bothers with them. crazy

Otherwise the only real problems I can see might be with appliances designed on the expectation of switched outlets.

The '80% rule' (America) [Re: LongRunner] #220867 06/30/20 03:06 AM
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LongRunner Offline OP
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I suppose it made a certain amount of sense (at least early on) as far as fuse ratings are concerned (reducing thermal stress on the fusible element by staying comfortably below its limit most of the time, with an occasional excursion to full capacity allowed for momentary or infrequently-used loads).

But is it the optimal strategy for overall resource use? I'm not so sure. In Europe (as has been mentioned before) their fuses (and naturally circuit breakers too) are specified so they can bear their rated Amperes continuously (albeit this did accordingly require somewhat more generous cable sizing with earlier fuse types); and since the bulk of Australian electrical practices (apart from the plug) originate from Europe (including Britain) albeit with local amendments here-and-there, this is naturally the case here too.
(So with our traditional 240V, the normal 10A outlet indeed supports heaters up to and including 2400W, including this one on full power as I type; and the British with the same 240V but 13A outlets can draw up to 3120W each.)

Certainly on circuits dedicated to a single (or 2 or 3) high-power load (air conditioners, hot water tanks, tankless water heaters, and your goliath 5kW+ tumble-dryers wink ; and probably silliest of all, those oversized central fan heaters a.k.a. "electric furnaces" grin), I fail to see any practical benefit whatsoever to keeping this old rule.
(The cables themselves are the least-stressed part of the system, and also contain the most copper when they're run for a decent length; so surely the European way of building the supporting hardware for continuous full load is more resourceful here.)

Granted, the rule itself will continue existing in America for a long while to come (at least on portable appliances, so long as old equipment is still in use); but for new installations, I think continuous-rated circuit protection is clearly the way to go (where available).

Last edited by LongRunner; 06/30/20 03:20 AM.
Re: The '80% rule' (America) [Re: LongRunner] #220871 06/30/20 08:49 PM
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gfretwell Online Content
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I suspect most breakers will run pretty close to 100% forever but the convention is any continuous load needs to be on a circuit with ampacity of 125% of that load (enforced a couple of places in the code). The trip curves published usually show an overcurrent will be sustained for some period of time based on the type of breaker.


Greg Fretwell
Re: The '80% rule' (America) [Re: LongRunner] #220872 07/01/20 08:14 AM
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Texas_Ranger Offline
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The only rule I'm aware of is "Ib<=In<=Iz", which means that the load current must be smaller or equal to the overcurrent protection device's nominal current and the latter must be smaller or equal to the wiring's maximum rated current (depending on cross-section but also factors such as ambient temperature and grouping as well as length, i.e. voltage drop). An additional design guideline states that appliances larger than 1.5 kW should be supplied by a dedicated circuit but this applies to the design of new installations, not to plug-in appliances in existing installations. There's nothing in the electrical regs to keep a homeowner from plugging a 3.5 kW electric oven into the place's only 16-amp circuit. Or into an ancient 10-amp circuit that also supplies all the kitchen sockets, as I saw in an older place a few months ago. The ceramic Diazed fuse holder showed considerably signs of heat damage! I only looked at the place as it was cleared out after the tenant had passed away so I'm fairly certain it'll all get rewired or may already have been.

Austria does have a rather arbitrary rule that is somewhat similar to the US 80% rule. In any other country that I'm aware of, the rated current of an RCD (e.g. 40 or 80 or 100 amps) equals the required overcurrent protection (to protect the RCD from thermal damage). In Austria, unless the manufacturer explicitly specifies the maximum overcurrent protection, the rated current is taken to be the "thermal limit current", i.e. tied to the OCPD's trip curve! Example: a class gG/gL fuse must blow within one hour at 1.6x its rated current. Therefore, according to the regs, an RCD must be able to withstand that overcurrent for one hour and a 40-amp RCD must be protected by a 25-amp fuse. Most manufacturers have two ranges of RCDs for the Austrian market, one regular, affordable, and one much more expensive "nameplate rated" series (we're talking almost three times the price!). Eaton calls this the X-series and that's become a synonym for RCDs that don't need de-rated OCPDs. A 40/4/0.03XG would be a time-delayed 40-amp four-pole RCD that can be connected to a 40-amp main fuse according to their nomenclature. Otherwise you could also fit a 63-amp regular G-type RCD but that's as expensive as the 40-amp XG. In domestic properties in Vienna that's rarely an issue because the standard supply is only 25 amps per phase but in the surrounding areas it's a considerable problem because the standard supply is 35 amps there. In some areas of Germany it's 63 amps (three-phase) even for the smalles studio apartment, which I find slightly ridiculous.

Re: The '80% rule' (America) [Re: LongRunner] #220877 07/05/20 12:03 AM
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Compared to the Germans we are close, they have a minimum of about 25KVA for a service and it is 24KVA here. That might even be for a little cable box on a pole if it is metered. We needed a 100a service for a picnic shelter with a single 2 tube T12F40 light. When we get around to changing that to LED it gets even sillier. I admit they do go nuts at Christmas and string a few hundred watts of Christmas lights around it. We are ready tho. There are seven 20a circuits available if we want to bring in a Carnival. wink


Greg Fretwell
Re: The '80% rule' (America) [Re: LongRunner] #220882 07/08/20 09:14 AM
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Yeah, I think the US, Canada and Germany are the only countries in the world with such substantial connections. On the other end of the spectrum you've got places like Spain and Italy, where the minimum supply was, until very recently, 3.5 kVA! I believe Italy increased that to 5.5 and Spain to 7.2 kVA. Smaller apartments in Italy didn't even bother with a fuse board, they just had the DNO-supplied 15-amp RCBO built into the meter base. In older houses even larger apartments didn't have one - I distinctly remember a 3br place in Torino with that exact setup. Electric oven and water heater too. One night the combination of these two plunged the whole place into darkness. Watching the owner take a picture off the wall in the hallway to get to the meter was quite funny!

Re: The '80% rule' (America) [Re: LongRunner] #220884 07/09/20 04:35 PM
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The scary thing here is in a time when we are supposed to be conserving, there are more people getting 320 and 400 amp services. (96kva) That used to be a computer room, back when computers took up a big room and pumped water to cool them


Greg Fretwell
Re: The '80% rule' (America) [Re: LongRunner] #220891 07/13/20 12:40 PM
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HotLine1 Offline
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Or on the commercial side,,,,
2X26 KV, and 1x13.2 KV primary services...….1.5M SF distribution center!


John
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