three phase low voltage leg

[llaht]

was attempting use of my coffing electric hoist, only got chattering of relays...

240volt three phase, delta with hi-leg supplied by POCO from apparently phase converter on the exterior pole.

I checked voltage, as it has been known in the past to drop a leg completely, but all my regular single phase lighting is working.

Go to disconnect for hoist and check on incoming
A-B = 247v
B-C = 247v
A-C = 60 v !!

A-to ground lug = 123v
B-to ground lug = 123v
C to ground lug = 137v !!

I traced back to main disconnect for three phase, which is fed from meter...
Got the same voltage as noted above.

I think it is POCO side... have called them, but stressed it was not an emergency ... probably first mistake.

thoughts out there??
and i have searched but not found anything conclusive.

 

[Bretny]

Sounds like the power companys issue if your measured at your mains.
My father had a issue with one of the 3 phase legs beging switched from them. It happens.

 

[wyliesdiesels]

was attempting use of my coffing electric hoist, only got chattering of relays...

240volt three phase, delta with hi-leg supplied by POCO from apparently phase converter on the exterior pole.

I checked voltage, as it has been known in the past to drop a leg completely, but all my regular single phase lighting is working.

Go to disconnect for hoist and check on incoming
A-B = 247v
B-C = 247v
A-C = 60 v !!

A-to ground lug = 123v
B-to ground lug = 123v
C to ground lug = 137v !!

I traced back to main disconnect for three phase, which is fed from meter...
Got the same voltage as noted above.

I think it is POCO side... have called them, but stressed it was not an emergency ... probably first mistake.

thoughts out there??
and i have searched but not found anything conclusive.

Ive never heard of a PoCo using a phase converter. That just isnt practical.

Where did you hear that theyre using a phase converter?

How many transformers are on the pole feeding your place?

And im gonna assume C phase is the hi-leg, which should be ~208v to ground...

 

[mm08822]

Based upon voltage readings provided, I'm assuming 3 xfrmers.
If A-C is 60 volts and C-grd is 137 volts, seems like 1 xformer is bad. Vectorially, these voltages are possibly.

It's for the POCO to fix.

 

[llaht]

two transformers on the pole...

a-c and C-grd readings are both correct... not a HF meter, but a fluke.

on the incoming switch before the 3ph breaker panel, wire has orange tape, so assumption that is hi leg.

Meter feeds this switch which feeds 3ph breaker.... i went to this wire set to check incoming.

I called in to POCO... and my mistake was telling them 'no hurry' to my knowledge no show yet.

 

[alfredeneuman]

The 2 transformers are powering your building with no phase converter involved.
It's called open delta to open delta connection.

 

[wyliesdiesels]

two transformers on the pole...

a-c and C-grd readings are both correct... not a HF meter, but a fluke.

on the incoming switch before the 3ph breaker panel, wire has orange tape, so assumption that is hi leg.

Meter feeds this switch which feeds 3ph breaker.... i went to this wire set to check incoming.

I called in to POCO... and my mistake was telling them 'no hurry' to my knowledge no show yet.

if you have 2 transformers then that is open delta. Where did you come up with there being a phase converter?

Which leg, going off your a-b-c readings list, has the orange tape and/or what was its reading to ground?

Not sure why you would tell them no hurry either? Obviously you have a major service issue that should be corrected quickly. Most likely a bad transformer which will take the PoCo some time to assemble a crew to get out there and replace.

The 2 transformers are powering your building with no phase converter involved.
It's called open delta to open delta connection.

How do we know its open delta on the high/primary side without looking at it?

The only way i know of determining open delta on the primary side is to see if there is a connection to ground on the 3rd bushing instead of connecting to a 3rd high voltage phase leg on top.

 

[alfredeneuman]

Agreed.
We wouldn't know for sure without checking the primary connections.

 

[llaht]

Re: three phase low voltage leg--- solved

SOLVED... it was incoming power at pole

thank you all for the responses...

POCO came today, replaced bad fuse before pole transformers (one leg)

I've had this occur before as a result of squirrels, etc, but apparently the previous issues were on a separate leg that resulted in the 120v lighting not working...

Lights were working this time, it was only when i attempted to run 3ph devices did the issue show itself.

coffing hoist now works, mill now works, and now the results are....
A-B= 247v
B-C= 247v
A-C= 247v

to ground
A- 123v
B- 123v
C- 212v

Again, thanks for the responses and education....

 

[wyliesdiesels]

Looks like it was the fuse feeding the second transformer with the hi leg.

The primary transformer(the center tapped one feeding the 120v circuits) wouldve been the one to loose power last time when the squirrel messed around.