3 phase meter

[dlt27]

The company I work for sent out some guys to connect up some temps through a 3 phase meter. Now the circuit was fed via an existing board with a 63A breaker and the existing board was backed up by a 160 amp mccb.(plus an rcd for the sub-main). The 3 phase meter so I have been told went up in smoke on 2 occasions and took out both breakers.
On the 3rd occasion I was sent to check it out. I found 2 phases reversed at db ie brown and grey connected wrong way around and I found brown phase to be carrying 96A and other 2 phases about 35A . I put everything right with phases and balanced loads so all were carrying about 50A. (Also existing meters were direct connect.) All I wanted to know is if anyone knew which of these faults would cause the meters to burn out?
I thought if phases were reversed it would just cause the wheel to clock backwards and also thought meters would carry 100A fine. Thanks for any info.

 

[Marvo]

I've never seen a metering unit that could be damaged by phase reversal. A make and model number for the meter would help so we can look for an on-line datasheet.

I assume this was direct on-line metering, not CT metering. Most likely terminations or possibly a highly inductive or capacitive load if it's an industrial installation.

 

[Knobhead]

I’ll go along with Mavo (but not if he’s wearing that outfit, I do have standards). Reverse phases won’t make any difference. It could only be load or poor terminations. As most meters are designed to withstand a reasonable amount of overload then I’d look at the terminations.

 

[dlt27]

No model no. Unfortunately. I think like you said it was overload.

 

[Jeffmo65]

Hi Gang , sorry to interject and change the subject slightly , however have been asked to fit a 3 phase meter in an industrial / commercial unit . The meter is going to be situated adjacent to the tennants DB so they know the landlord is not ripping them off . My question is , do i need to fuse the CT's if so i have read that the fuse must go before the CT , how is this possible if we are unable to remove the incomers from the dB due to their work load in unit . I know i can use split CT's but just wondering about the fuses

 

[Knobhead]

You should start a new thread not resurrect an old one. This was dead and buried.

You can get shell type CT’s (in two halves). BUT do not fit them with the board on load! (Unless you’ve got a death wish). Select your time, lunch break, shift changes or night time.

 

[Jeffmo65]

cheers Tony ,will start new in future , any info on the fusing of CT's

 

[Knobhead]

You never fuse CT’s or do anything to open circuit them. Open circuit them and the voltage on the secondary rises to dangerous levels.