Low voltage present at yellow phase??

[newtrade]

Was doing a Ze at a 3 phase db. At yellow phase theres only a low voltage present from indication by test lamps. Back at the Isolator from the mains incoming getting full voltage. any help on whats causing the low voltage at db?

 

[telectrix]

you need to measure what the voltage is and then check connections, fuses, etc.

 

[vernam616]

Test the load side of breaker

Better still call someone who knows, you shouldnt be messing around with three phase if your not competant with measuring voltage

 

[newtrade]

Mains comes in and its fine. but from isolator to pass through isolator to db. Its like lower than 12v.

 

[telectrix]

are you saying that you have a correct voltage into an isolator, and a much lower voltage out? if so , could be a knackered isolator on 1 pole.

 

[ashrow]

Newtrade

Is is a fused isolator or just a switched isolator ? (give us a make and model number if in doubt)

 

[newtrade]

it goes from a fused mem isolator to a switched pass through then to Db

 

[ashrow]

so thew fuse on the MEM isolator is ok for that phase ?

 

[newtrade]

From the mains to the incoming of the fused isolator is the correct voltage. When i test the pass through isolator coming from the mains this is producing the lower voltage. Then the Voltage at the DB is the same as the Incoming side of the pass through isolator.

 

[vernam616]

I reckon this is a wind up

 

[ashrow]

newtrade

i got to go eat with my family, but please answer the following

Why was you testing the Ze
Are you an Electrician
Was there a fault that made you look into finding the issue(s)?

(Be back in about 20 mins)

 

[martinh287]

Sounds like the yellow phase fuse has gone and you have a small voltage on your earth making your voltage indicators light up 12v

 

[newtrade]

ashrow

I'm doing a periodic test on the install. So Ze on each phase at DB.
Just newly qualified - first time came across this. More experienced guy wasn't sure either.
Reason looked into was - When i went to test the first phase i got a indication it was safe to test. but on yellow phase nothing came up on meter. But test lamps showing less than 12V on indicator lights.

 

[plugsandsparks]

Are there any loads on the yellow phase in the DB and are they working ?

 

[UNG]

ashrow

I'm doing a periodic test on the install. So Ze on each phase at DB.
Just newly qualified - first time came across this. More experienced guy wasn't sure either.
Reason looked into was - When i went to test the first phase i got a indication it was safe to test. but on yellow phase nothing came up on meter. But test lamps showing less than 12V on indicator lights.

I think a good start would be selecting the correct test equipment to verify the voltage as it sounds like the test lamp you are using is either faulty or unsuitable for what you are doing
Secondly I would suggest you and the "more experienced guy" with you seek the assistance of someone who is familiar with and experienced working on three phase installations

 

[ashrow]

Back

If you were doing a "real" periodic i am sure the client would of noticed that any circuits on the said yellow phase were not working and also any 3phase equipment would of failed by now
Also its a ECIR now
Good luck anyway, i am out of this thread

 

[SYKRAPS]

What does the yellow line run in the DB this could give you a clue

 

[Spudnik]

OP,

As others have said, you need to provide explicit detail of all associated test equipment and switch gear being tested.

Pics would be even better.

 

[High Tower]

Back

If you were doing a "real" periodic i am sure the client would of noticed that any circuits on the said yellow phase were not working and also any 3phase equipment would of failed by now
Also its a ECIR now
Good luck anyway, i am out of this thread

You have a excellent point......but I have seen numerous largish 3ph installs with no 3ph loads. The one I'm doing at the moment has 5x 3ph DB's and only 2x 3ph loads

 

[ashrow]

Agreed High Tower (i also have come across this, only once in my time though and that was in a pub/carvery)
But from my point of view i have never come across where anyone would do a Ze on a periodic inspection where any kind of fault would not of been noticed prior to that inspection (unless the yellow phase did not supply any circuits (very rare in my opinion)

I do hope the original poster posts again so we know the out come and anyone that reads this thread learns a bit more

 

[SYKRAPS]

Not saying that it was great in any way as I would definately do it different but I once came across a 3p board that had one of the supply cores split by a contactor to control the supply to storage heaters so very unbalanced but this could be what is going on here maybe.

 

[newtrade]

checked that. sorted mate cheers

 

[newtrade]

martinh287'

 

[Knobhead]

checked that. sorted mate cheers

And the fault was.........

 

[ipf]

And the fault was.........

Mysteriously lost....?

 

[ackbarthestar]

Agreed High Tower (i also have come across this, only once in my time though and that was in a pub/carvery)
But from my point of view i have never come across where anyone would do a Ze on a periodic inspection where any kind of fault would not of been noticed prior to that inspection (unless the yellow phase did not supply any circuits (very rare in my opinion)

I do hope the original poster posts again so we know the out come and anyone that reads this thread learns a bit more

That's a coincidence. Just done one yesterday. 3-phase intake. One phase out, nothing connected to it. so hasn't been noticed.
Strangely enough, it does appear to happen, although it was only the second time I've come across it.