I need to relocate the outlet for the fridge and found that I had to turn off two circuit breakers on the distribution board to isolate the outlet.
I opened up the distribution board and all looked normal - with the wires from each of the circuit breakers heading off into the roof space along with the rest of them.
I opened up a wall outlet and found that of the three red wires - One went off to the next wall outlet, the second was livened when one CB only was turned on, and the third was livened only when the second CB was turned on. But as originally wired - the separate live wires from each of the circuit breakers were connected together at that wall outlet.
Tracing back further I found that there is another outlet that is directly connected to the second CB, and the two outlets are interconnected by the third wire.
My query - is that sort of interconnection of two circuits good practice ? If a fault in an appliance were to occur then the CB's would not trip until twice the rated current was exceeded. ( 2 x 20 = 40A )
Remember that there will be sections of single conductor between some outlets where a fault could occur and points where the two circuits are interconnected.
Thanks
rich1969,
Mar 24, 3:19am
Definitely not good practice, wired by someone who does not have a clue
tintop,
Mar 24, 3:37am
I agree - but cant find any reference in the house to the electrician that did the original work.
I have opened up all the affected outlets now and used a test lamp and a 6V battery to find the ends of each cable run. Just sorting out the best 'reconnect' to distribute the various appliances to best even the load on each circuit. Heat pump, microwave, toaster, elec jug, dishwasher, clothes washer, dryer. and my air compressor. Grrrr.
johotech,
Mar 24, 3:38am
Definitely a mistake. It should never be wired like that.
Both circuit breakers would trip on a short circuit type fault. But they would not be protecting the cable from overload as they are required to do.
Possibly some DIY wiring in the past?
johotech,
Mar 24, 3:41am
That type of work is not covered by the "homeowners exemption" ECP51. Particularly excludes any work on a switchboard or even opening a switchboard to access or run cables.
tintop,
Mar 24, 3:49am
Thanks johotech,
I realise that - but needs must at times. I am not running any cables as such, just changing the way they are connected :)
I am confident in what am doing, but was a bit taken aback by the problem that I found.
mm12345,
Mar 24, 3:58am
Doesn't strike me as a "mistake", but something done deliberately by some moron who was convinced that he could hear the voltage drop through the single line on a hifi system - or something like that.
rotormotor7,
Mar 24, 4:02am
Could gave been a ring circuit back in the day, switchboard has been upgraded and one of feeds put into its own breaker.
More likely that a wall been removed and was originally 2 circuits and all wiring was located to the one power point. I had that with lighting in a kitchen once, trying to isolate and only when 2 fuses were out as this senario.had to split at lightswitch with connectors.door had been deleted and filled by the looks of the framing behind gib. Also a fellow spark was redoing a 3 phase switchboard and one breaker tripped as soon as turned on.he couldnt figurd it until i told him to check voltage across breaker. 400v. was a ring circuit back in the day.
tintop,
Mar 24, 4:14am
Possibly - but more probably a a cock up during construction. A lot of the cable runs are in conduit buried in a poured slab suspended concrete floor or inside grout filled concrete block walls.
The house s about 12 years old.
russ18,
Mar 24, 5:13am
Have seen this several times, always appeared to be poor quality work during alterations and needs to be fixed.
easygoer,
Mar 24, 7:21am
I doubt that an Electrician did it and it is unlikely that it was an error during the original construction, it would have been picked up during the original testing, the most likely will be additions by a DIY person who was confident that they knew what they were doing
tintop,
Mar 24, 7:46am
Well - I have worked out a scheme using the existing cable runs between the outlets to spread the load between the 2 circuits. It will involve making some wire to wire connections in behind the outlets to achieve this, but doable.
I guess I best check all the rest of the circuits n the house now as well. Grrrr
timbo69,
Mar 24, 7:51am
Don't the English do it that way? perhaps some pom's first job over here. ?
tintop,
Mar 24, 8:02am
It could be - all the wire to wire connections were twisted anticlockwise before they were inserted into the outlet terminals and the screw tightened up.
So I look for a left handed pom ?
ryanm2,
Mar 24, 5:51pm
They do a ring main system - 2 feeds at the switchboard, not 2 feeds randomly behind a power point.
t_naki,
Mar 24, 6:09pm
A few times I have found what used to be a ring main separated at the switchboard with the two legs in two different circuit breakers, usually after a switchboard upgrade.
rotormotor7,
Mar 24, 6:42pm
Ditto.
tintop,
Mar 24, 9:08pm
Well - I have sorted out a way to separate the two circuits and a temporary 'fix', but the layout is not very logical.
Dist Board -> lounge wall outlet ( heat pump) -> Laundry wall outlet - via conduit in a concrete wall ( washing machine, dryer) -> Kitchen wall outlet, return via the same conduit ( electric jug, microwave) end.
My only concern is heat buildup in the conduit if the washing machine ( self heating), dryer, elect jug, and the microwave are all in use at the same time. But the concurrent use of these can be managed.
Ms Tin now tells me that she wants a new benchtop, and one of the cupboards has to go Haha! This will give access to most of the stuff up and enable a proper fix at a later date. Once the kitchen is in bits, the 'there and back' to the laundry will be able to be eliminated.
The second circuit that was cross connected to the first will now only have the fridge, dishwasher ( self heating) , toaster, and garbage grinder connected to it.
Oh - and I will be unearthing the building records to track down the electrician. ( if he has managed to avoid electrocution in the last 10 years) :)
t_naki,
Mar 24, 11:32pm
There is no problem with overheating in the conduit as the cooling effect of the concrete and conduit will be large. Also TPS cable can safely operate at pretty high temperatures with no problems. At least much higher than two circuits running at 20A and even then I doubt that they would be at that level for long.
biggles45,
Mar 25, 12:10am
I'm a left handed pom but it wasn't me!
tintop,
Mar 25, 12:19am
Cheers.
Looking forward to having it sorted out properly though when the kitchen bits get taken out.
tintop,
Mar 25, 12:21am
lol :)
tintop,
Mar 25, 12:42am
Might have been a left handed Scot.
The slack at the outlets is pretty miserable!
tintop,
Mar 25, 12:43am
1:45. At least the TV is going! Live on Prime - a game of some sort. :)
tintop,
Mar 25, 4:48am
The two circuits separated and everything reconnected and working.
Thanks for the advice guys :)
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