new 3phase supply but only 2 working?

traineelectrician · 23 Jun 2011

on a new build theres a 3 phase supply coming into the house... at the board and at the meter it reads:

L1 244V
L2 10V
L3 244V

theres also a 3 phase socket coming off the board, which has a transformer ran from it. but the reAdings from the terminals on the switch to the transformer read:

L1 241v
L2 119v
L3 241v

can anybody make any sense of that??

ricicle · 23 Jun 2011

What are you testing between phases and neutral ?

Sounds like a missing L2, or a very bad contact/connection. Either way it needs investigating.

flameport · 23 Jun 2011

As above, some fault with the supply.
The 119v is probably not 119v at all, but induced from the adjacent wiring.

The readings would probably be more consistent if the voltage was taken with a load such as an electric heater connected between L2 and neutral.

ericmark · 23 Jun 2011

If transformer is delta then that's about right with one missing phase.

Lectrician · 24 Jun 2011

ericmark said:
If transformer is delta then that's about right with one missing phase.

With the transformer switched on, yea.

Don't try putting a mototr in it's place though!

sparkticus · 24 Jun 2011

Most likely the main service fuse for L2 is blown or not even installed. If its sealed leave it to the DNO.

You say "house" is this a new private dwelling? If so is the 3 phase socket a temporary arrangement for on site equipment? Is it connected via the CU?

Anything tripped on the CU? I recognise that you say no L2 output at the meter which indicates the main service fuse but something on the board would most likely have tripped also.

Keep in mind the transformer or its cables may have taken out L2. Best to isolate that thing for now.

Lectrician · 24 Jun 2011

I assume this is either a new service or a new installation to an existing service? (I guess it has to one - lol!).

I am putting it out there....

You have not simply assumed that a three phase head has three phases present?

With SPLIT PHASE, it is more often than not presented to a triple pole head, with one fuse not doing anything. The metering will also be TP, often with the 'missing' phase connected, but with no cable from the meter.

Only a vague chance, but worth asking. Measure the voltage from phase to phase and see if it is higher than expected. Split Phase would give you 460 - 480 volts.

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new 3phase supply but only 2 working?

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