Power wall socket question

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#1006740 16-Mar-2014 15:19

Bung:
gregmcc:
Bung: The only thing typically 10A is the cheap breaker built into plug strips. The fuse or breaker rating is determined by the .cable and its surroundings. Short term current higher than nominal probably wouldn't trip either. In an office if you ever manage to trip the breaker it's surprising sometimes how many other computers are affected.

I think you need to re-read what you said here, the fuse or breaker rating IS NOT determined by the cable and it's surrroundings, you need to go and take a look at a circuit breaker and read the number on it, a 10A circuit breaker has a rating of 10 amps.

Step back a bit. How does the rating of the protection get chosen? Do you see 1 socket and put in a 10 amp breaker or do you look at the appropriate breaker for the size of cable and how surrounded in insulation it will be?

]

Strictly speaking the circuit breaker is chosen to protect the cable, so a 2.5mm cable could have a 20-25A breaker on it even though the socket outlets are rated for 10A.

You should never try and draw more than 10A from a 10A rated plug/socket, doing this over an extended period can cause overheating and a fire.

richms

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#1006870 16-Mar-2014 20:52

2.5mm should be 16A if the cable is surrounded by insulation, 20 if it is in free air. Then there is the earth loop impedance which may require derating the cable - same thing that causes derating due to length.

Not uncommon for large houses to have to have 4mm power circuits just to get a 20 amp breaker on it, havent seen anyone have to go to 6mm ever.

Old houses are likly to have a 1.5mm or whatever the inch equivilant was, so that should be on a 10A if it is surrounded by insulation or 15/16 if not.

More to the point is the condition of the wall socket - old ones stretch and get hot from poor connections.

Richard rich.ms

sir1963

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#1006943 16-Mar-2014 22:01

richms: 2.5mm should be 16A if the cable is surrounded by insulation, 20 if it is in free air. Then there is the earth loop impedance which may require derating the cable - same thing that causes derating due to length.

Not uncommon for large houses to have to have 4mm power circuits just to get a 20 amp breaker on it, havent seen anyone have to go to 6mm ever.

Old houses are likly to have a 1.5mm or whatever the inch equivilant was, so that should be on a 10A if it is surrounded by insulation or 15/16 if not.

More to the point is the condition of the wall socket - old ones stretch and get hot from poor connections.

Old imperial size was called "Three-oh-two-nine", three strands of 0.029inch

floydie

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#1010913 22-Mar-2014 00:18

as a sparky i can tell you now that 90% of power circuits are fed by a 20A breaker. each breaker usually has 5-6 outlets on it.
in the scheme of things the 10A socket outlet is the weakest link in the chain. you could theoretically pull 20A through one socket outlet and the breaker wont trip...but your wall may catch on fire.

two PC's arent going to pull huge amps unless both are 750W monsters running at 100% capacity which i doubt.

you could always get a sparky around to change your single outlet for a double (or even quad) outlet.

Bung

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#1010922 22-Mar-2014 05:05

floydie: you could always get a sparky around to change your single outlet for a double (or even quad) outlet.

Check the rating of the fitting, it will probably still be 10A total rather than per outlet. ]

floydie

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#1011113 22-Mar-2014 19:23

no. sockets outlets are rated at 10A per socket. thats the law.
so a normal double PP has 2X10A outlets on one faceplate.

richms

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#1011115 22-Mar-2014 19:26

I'd love to see what 40A would do to one of the quad outlets then ;)

Richard rich.ms

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gzt

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#1011181 22-Mar-2014 22:31

Bung's not making much sense there.

The Brits solve this problem with fused plugs.

I do wonder about this situation. It does seem like random hopes in some way. NZ mandated RCD's long back which is better than nothing, but again it's a luck thing that might get an earth fault in the scenario.

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Bung

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#1011190 22-Mar-2014 23:17

gzt: Bung's not making much sense there.

The Brits solve this problem with fused plugs.

I do wonder about this situation. It does seem like random hopes in some way. NZ mandated RCD's long back which is better than nothing, but again it's a luck thing that might get an earth fault in the scenario.

I'm just repeating what Energy Safety feed the public.

Electrical Code of Practice for
Homeowner/Occupier’s Electrical Wiring Work in Domestic
Installations 2004 (NZECP 51:2004)

"B2 SOCKET-OUTLETS
B2.1 Never overload socket-outlets. Socket-outlets are designed
to take one or two electrical appliances, (the total current
rating of a double socket-outlet is 10 A). "

I've seen AS/NZS 3112 quoted as the source of this rating but I can't find it online. I know that the temperature rise test only uses 1 outlet. If the fitting has a rating that is the sum of the socket ratings you'd expect all sockets to be loaded during testing.

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#1011200 22-Mar-2014 23:56

Thanks for that, I completely missed the point first time round. Cheers. ; )

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webwat

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#1011433 23-Mar-2014 17:02

Lizard1977: Thanks. I figured the socket would be 10A, but I wasn't sure whether that 10A would be shared across all the sockets in the room. Our fuse board is on the old-ish side (that's a whole other story) and it looks like the fuse/circuit breaker is either 16A or 6A (i'm guessing the former).

The PCs wouldn't be at full load all the time, but I figured the PSU wattage would indicate maximum usage. I reckon the total maximum wattage would be no higher than 1700W, which at 240V gives about 7A and 34ohms. So I think the single socket approach should be fine...

In full use by a user is different from full capacity power draw, so you are still unlikely to ever use more than half of maximum except possibly during startup if you have 4 hard drives in each PC etc etc.

The usual problem is that the PC and router etc are on the same circuit that you later want to plug a heater or vacuum into, which do use all their power rating (close to the 10A circuit capacity) when running at full speed. If it doesnt trip the breaker you could still be running the circuit at close to capacity a bit too frequently.

Time to find a new industry!

floydie

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#1011471 23-Mar-2014 19:38

the regs count a double outlet the same as a single for the purposes of calculating maximum demand and the number of outlets on a RCBO. that doesnt mean that the physical outlet is only capable of carrying 10A. as i said...each socket can carry 10Amps. if the "shared 10A theory" was true, your house would burn down every time you plugged a portable heater in to one of the sockets a double outlet.

I certainly would not consider any fitting that couldnt internally handle the 20A combined of both sockets to be electrically safe.

( i think from memory the quad outlets are counted as a 16A total rated for MD calculations but would have to check on that..)

Bung

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#1011498 23-Mar-2014 20:55

A test would be two heaters. The duty cycle on most other combinations wouldn't do much. If you recall the old PDL double. That was two singles on one faceplate that had to be strapped together. The modern double has the contacts arranged more like cheap plug strips.

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#1011516 23-Mar-2014 22:03

That is a not a great idea. Edit: Due to potential risk it is a bit silly in a domestic context.

BTR

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#1011595 24-Mar-2014 09:20

sbiddle: A standard power socket is rated at 10A and the fuse or circuit breaker will typically be 10A, but could be 15A. Basic ohms law will let you work out the load.

You might actually find that in most domestic cases that the MCB (circuit breaker) is actually 20 amp for power sockets, 10 amp for lights and usually 16amp for hot water cylinder.

If OP is worried why not upgrade the single socket to a dual and get a sparky to install a second dual next to the existing socket. Would cost less than $150 to do this.

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