voltage drop

[spank]

i have been trying to find a fault on a 3 phase db! with all mcbs off red phase gives 236v, yellow 240v, blue 241v, when the lighting mcb is switched on and the lights switched on the red phase loses voltage to 212v and then when i turn more red phase circuits on it loses more voltage? yellow and blue phases are fine can any one help tell me what they think this is..?

 

[mfarrow]

Is the db fed directly from the DNO's supply? Sounds like there's a fault somewhere.

 

[RF Lighting]

What reference point are you measuring the voltage against?

Does the voltage rise at the same rate on the other two phases as it drops off L1?

 

[spank]

Is the db fed directly from the DNO's supply? Sounds like there's a fault somewhere.

the supply is a 70mm swa via bus bar to isolator then isolator to db

 

[spank]

What reference point are you measuring the voltage against?

Does the voltage rise at the same rate on the other two phases as it drops off L1?

measuring between L-E, L-N..
the other 2 phase dont change?

 

[plugwash]

i have been trying to find a fault on a 3 phase db! with all mcbs off red phase gives 236v, yellow 240v, blue 241v, when the lighting mcb is switched on and the lights switched on the red phase loses voltage to 212v and then when i turn more red phase circuits on it loses more voltage? yellow and blue phases are fine can any one help tell me what they think this is..?

Most likely a bad connection somewhere. Could also be a dodgy protective device or dodgy cable but these are less likely.

You need to work backwards through the system with your test equipment until you find the fault.

 

[spank]

i have been trying to find a fault on a 3 phase db! with all mcbs off red phase gives 236v, yellow 240v, blue 241v, when the lighting mcb is switched on and the lights switched on the red phase loses voltage to 212v and then when i turn more red phase circuits on it loses more voltage? yellow and blue phases are fine can any one help tell me what they think this is..?

Most likely a bad connection somewhere. Could also be a dodgy protective device or dodgy cable but these are less likely.

You need to work backwards through the system with your test equipment until you find the fault.

all connections checked and fine worked backwards only part not yet checked is tails from isolator to buss bar! unable to shut down at momemnt

 

[RF Lighting]

Is the db fed directly from the DNO's supply? Sounds like there's a fault somewhere.

the supply is a 70mm swa via bus bar to isolator then isolator to db

Does the voltage remain constant on the supply terminals of the isolator when you start to put some load onto the suspect phase?

Does anything else supplied by the busbar appear to be affected?

 

[spank]

Is the db fed directly from the DNO's supply? Sounds like there's a fault somewhere.

the supply is a 70mm swa via bus bar to isolator then isolator to db

Does the voltage remain constant on the supply terminals of the isolator when you start to put some load onto the suspect phase?

Does anything else supplied by the busbar appear to be affected?

the voltage drops to 212 with lightsand stays at that unless i turn more red phase mcbs on then it drops more...nothing else seems to be affected at all?

 

[RF Lighting]

I presume the lights actually come on?

It's sounding like a failed connection in the busbar chamber to me.

Have you had a look in there yet?

 

[333rocky333]

Did you measure phase to phase voltages.
I had a job where weird things were happening.
Found the cable blown apart and red and yellow welded together.
single phase voltages were all right but on testing had 2 red phase and 1 blue, the real yellow phase was blown away.

 

[spank]

Did you measure phase to phase voltages.
I had a job where weird things were happening.
Found the cable blown apart and red and yellow welded together.
single phase voltages were all right but on testing had 2 red phase and 1 blue, the real yellow phase was blown away.

no i didnt think in that? i will try that wheni get back there...strange fault