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#134006 10/20/02 09:30 AM
Joined: Dec 2001
Posts: 2,498
T
Member
Here in Austria B types are used for residential and C types are used for workshop ect equipment with motors, causing a high startup surge. I was told at Baumax (like Home Depot) that they're the equivalent to quick and slow diazed fuses.

#134007 10/20/02 03:21 PM
Joined: Aug 2001
Posts: 7,520
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pauluk Offline OP
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Quote
You are forgetting that those breakers also have a thermal protection and therefore at 40A consumption on a 20A breaker type C will also trip after 25 seconds

The thermal characteristics of the C/B with a moderate overload, rather than a drastic short circuit, could certainly make all the difference. While thinking of this, keep in mind also my comments above about some appliances in the U.K. having 0.5 sq mm. cords as well.

As David has pointed out, there is nothing to stop us using type-C breakers in residential applications, so long as the appropriate disconnect times can be achieved. Back when I was a kid in the early 1970s, my father rewired a 1930's house using the Crabtree C50 range C/Bs (I'll leave it your imagination to work out just how he happened to be using commercial-spec breakers! [Linked Image]).

That was on an old urban TN-S supply with a solid ground path on the armor of the cable, and thus a very low loop impedance. (It was also before the 5 sec. & 0.4 sec. disconnect times were part of the Regs., but I'm sure it would have satisfied those requirements anyway.)

I wouldn't mind betting that at the time, it was probably the only house in the street to have any sort of breakers rather than the rewireable fuses which were the most common form of protection in the early 70s.



[This message has been edited by pauluk (edited 10-20-2002).]

#134008 10/20/02 03:35 PM
Joined: Aug 2001
Posts: 7,520
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pauluk Offline OP
Member
Looking back through this thread, I'd like to pull out one of David's point for the ring circuit:
Quote
Providing it is correctly designed, it allows a lot of sockets to be installed on a circuit with little chance of over-loading.(Kitchens excepted.)

The correctly designed aspect is something which I feel is often overlooked, and as noted, this certainly applies to kitchen areas.

Many people latch on the "one ring for 100 sq. meters" part of the Regs., and then just blindly follow that without allowing for the anticipated load which should also figure into the design.

U.K. members will bear me out on this: How many times do you see a two-ring house with one ring for each floor? The upper-floor ring is seldom loaded to more than a very small fraction of its capacity, especially now that central heating is widespread and thus the need even for portable heaters in bedrooms has diminished.

Then you look at the ground-floor ring and find it feeding a washing machine, a clothes dryer, and a dishwasher, as well as all the kitchen outlets.

The washing machine and dishwasher heating elements are usually 3kW, although admittedly they wouldn't be considered a continuous load. But the dryer element could easily be running for two hours at a stretch.

The countertop receptacles will likely be used for toasters, microwave ovens, and all the other high-power kitchen gadgets, including in most British homes the ubiquitous electric kettle (another 2 to 3kW).

These days, people do expect to be able to run everything at once. The one-ring-per-floor arrangement was fine years ago when the average British home didn't have the high power consumption found in a modern kitchen. But I think it's time the Regs. were amended to make allowance for increased kitchen loads and that designers make a better job of distributing the load between circuits.

I concede that there is a tendency now to specify a separate kitchen ring circuit, but to my way of thinking, that achieves very little. If somebody installs a separate ring for the kitchen area, we still have all the major appliances on the one ring while the other two rings are feeding a TV and an electric blanket.

Better yet, I'd like to see separate circuits specified (NEC-style) for washers, dishwashers and, especially, tumble dryers.

P.S. I'm using the terms ground floor and upper floor here to avoid the possible confusion over what constitutes the first, second floors, etc.

For those international members who aren't aware of the differences, allow me a slight detour to explain:

In the U.S.A. first floor means the ground floor. The level directly above it is the second floor.

In Britain, first floor means the first level ABOVE the ground floor, i.e. U.K. 1st floor = U.S. 2nd floor.

So much for English being a universal language! [Linked Image]


[This message has been edited by pauluk (edited 10-20-2002).]

#134009 10/21/02 07:30 AM
Joined: Sep 2002
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C
C-H Offline
Member
Quote

You are forgetting that those breakers also have a thermal protection and therefore at 40A consumption on a 20A breaker type C will also trip after 25 seconds. A type B breaker 32A will never trip at 40A consumption.

Quite right! This is why the 2.5 mm2 cables in ring mains run risk of overheat and fire. With radial circuits, this risk is neglible.

But, to an appliance cord, the thermal part of the breaker means little. If you put a 0.75 mm2 cord at 40A for 25 seconds, it will get very, very hot. (BTW. From the graphs you submitted, I get the "Must break" curve to be 200 seconds at 2 times the rating.)

You have pointed out that the thermal part is the same for both type B and C. Hence, there is no difference in current carrying capacity between the breaker, unless the current is 3 times the breakers rating. What is the purpose of using type C in a residential environment? You won't get more power out, except in a short-circuit situation.

#134010 10/21/02 04:29 PM
Joined: Oct 2002
Posts: 177
B
Member
>What is the purpose of using type C in a residential environment? You won't get more power out, except in a short-circuit situation.

Maybe because that with type C, bigger motors can start without making it trip or maybe because it's cheaper.

The way that we look at it, is that we use type B only in TN systems (here it's only in industrial installations) to protect for ground-fault problems.

#134011 10/22/02 02:15 PM
Joined: Sep 2002
Posts: 1,498
Likes: 1
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C-H Offline
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>Maybe because that with type C, bigger
>motors can start without making it trip

Yep. For this reason 10A type B are quite useless as the inrush current of some vaccum cleaners can trip it. Also, for those big blue and red (IEC 309) sockets, type C is an obvious choice, as you can expect them to be used with large motors.

But here large single-phase motors are rarely used in places like living rooms and kitchens. If you need something like a five horse power motor, you'll probably put it in the garage connected to a big red 3-phase socket.

#134012 10/22/02 05:40 PM
Joined: Oct 2002
Posts: 177
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Member
> Also, for those big blue and red (IEC 309) sockets, type C is an obvious choice, as you can expect them to be used with large motors.

What do you mean by big blue and red (IEC 309) sockets?

#134013 10/23/02 08:30 AM
Joined: Dec 2001
Posts: 2,498
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Member
He's referring to the blue-grey (single phase) and red-grey connectors (the large ones for 3ph)
Don't you use them in Belgium? I've seen them all across Europe.

#134014 10/23/02 12:38 PM
Joined: Sep 2002
Posts: 1,498
Likes: 1
C
C-H Offline
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Also known as CEE 17

[Linked Image from i.kth.se]

#134015 10/23/02 01:29 PM
Joined: Oct 2002
Posts: 177
B
Member
Thank for your clear information. Yes, we have them in belgium, too. http://www.gepowercontrols.com/47/72/78/10037/index.html#23240


[This message has been edited by Belgian (edited 10-23-2002).]

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