Three phase tripping


Thread Starter


Hi All.

I have moved into a residential house that has a three phase supply. There is a large cu with most circuits on but there is also a 60a hot tub and a 63a kitchen/cooker circuit taken from L1 . both use a standard single phase cu.They work fine. There is also a seperate single phase consumer unit with power taken from L3. it has a 80amp rcd 30ml protection. it only has one 32amp circuit. My problem is this circuit It seems to power up fine with 240/245 volts on a meter, the earth is connected directly to the main bar below the cu. the neutral is taken from the only neutral that looks to be supplying L1 and L2. But as soon as i plug in any unit ie kettle or can opener the rcd trips. However the rcd test button is not working when pressed.

Any ideas greatly appreciated.


You absolutely need to call the utility company.

3-phase power is extraordinarily rare in a residential dwelling. You don't mention which country you are in, but if you are in the US, I cannot imagine the scenario where this would make sense AND meet residential codes.

Three phase power should require some type of load management, and while in theory any given leg can be used for single phase use, an imbalanced load can cause trouble. Typically 3-phase service is reserved for industrial clients who are penalized by the utility companies for failing to balance their loads.

In some rural areas home/shops were fitted with passive "pseudo" 3-phase provided from single phase by a special transformer configuration. I cannot imagine there are too many of those set ups still around, but perhaps this is what you have.

Regardless of the "How" you have 3-phase power in your home, you need to consult both the utility company and an electrician. There is absolutely NOTHING you should consider DIYing.
A little unusual, but not actually rare. Here it is simply a standard option when the power is originally connected. Since the power in the street here is 3 phase, each house normally gets one of the phases 1,2,3,1,2,3,1,2,3 up the street, so all three phases appear under the green mushroom thing in our front yard, and in our case, all are connected.