1500A 3 Phase 4 Wire + Integral Housing Grounding Aluminium Busduct

Chase-out the location of the neutral/earth cross-over point, and eliminate the fault.

Thanks..

If there were no trips before the tenants moved in and now you're getting trips, I'd be looking at what equipment your tenants are using, maybe it'll be obvious which piece of equipment (old, dirty, no maintenance done, frayed wiring, etc.) might be "leaky".

If not you'll need a recording power analyzer that will allow you to capture the time, residual/neutral/harmonic currents, relay operations and whose equipment is starting and causing the trip. Good old observation will help too, like wiggling cord sets, sequential unplugging of equipment until the problem stops, etc.

There may be someone who has a particularly "noisy" or harmonic generating piece of equipment; sheathed resistance heating elements can also get leaky as the element insulation starts failing at a bend and leaking to the sheath. Let us know what you find.

Thank you...

20 tenants trip an 80A fault relay, so each tenant theoretically faults 4A. Isolate the returns if you can, and find out what faults you are getting on which supply, or protect each tenant separately. Other than that, I go with PWSLACK for the GA. You should be able to use a current clamp meter to read the fault currents without disturbing any tenant suppy. You will need to measure each and every supply branch to determine the most likely tenant. Some are probably quite small and others are probably much worse. Can you inspect tenants to set down guidelines for maximum fault currents ? I once knew of a computer system that faulted almost every friday at 13:00 and it took personal monitoring to discover that friday was the staff tea day and the water kettle tripped the breaker. Do your tenants need your appoval before installing equipment ?

I hardly think a E/L trip set at 80A is going to be operated multiple faults in 20 flats.

Shut the supply off and do IR tests on the bus-duct.

Remember to isolate each tap off point including the neutral from the bus otherwise you'll be paying for a lot of TV's and other household items you've blown up.

You have not specified where the earth fault relay is provided. Is it in the incomer of the main panel or in the 1500 Amps busduct feeder. The location of the CT for Earthfault relay is important. In Indian context, the CT is placed in the neutral bus and this is fobbed of as earthfault protection. In your case I suspect this, as you have indicated that the problem started after the 7th floor got occupied. As the loads will mostly be single phase, the unbalance current in the neutral would have setoff the relay. If this is the case (most probably is, as the installation is tripping intermittently) you just need to increase the relay setting at the cost of sensitivity.

However if your REF protection of main incomer is operating (provided the system is properly designed), then you will need to investigate the problem more seriously and Insulation resistance test of the complete installation and/or physically verifying the system for any insulation failure should be undertaken. Again you have not mentioned which feeder, Main incomer or the 1500 Amps bus duct feeder, is tripping.

Please revert to the forum with your findings.

Its the earth fault relay protecting the 1500A busduct...the incomer earth fault relay is set a 120A 0.5s

The earth fault relay is insufficient to prevent electrocution of users. All it is doing is showing-up that there is a neutral-to-earth connection somewhere in the building.

It needs detection and correction before someone gets hurt/killed. Do it now/this morning/within the hour.

Please let the forum know what and where the fault was, as it will be a learning exercise for its readers.

The shut down is arrange on coming sunday...I will post the finding after the shut down.

Then like I said earlier, the relay and CT are most probably wired to measure the neutral current. If you can reproduce the wiring schematic, we should be in a position to confirm.

If in doubt, consult a qualified Electrician.

If the installation has been installed and tested correctly, then the cause is two-fold:

1. There is a connection between neutral and earth somewhere in the building
2. There is too much reliance placed on a building-wide trip device whereas there needs to be a lower-rated one at each tenant's distribution board, so that a fault on one branch doesn't take out the whole building, thereby narking off the other tenants.

...so the installation cannot have been wired and tested to the latest edition of British Standard 7671. If it had been, then the fault would appear at an individual user's dis-board, making the cause easier to detect and rectify.

Hi Sir,

I believe the connection between the netural and earth happens along the busduct, reason is that the busduct conductor format as such (E, N, L3, L2, L1)...as such I believe is connected somewhere there.

we are arranging a shut down this coming sunday..will keep you posted on the findings.Thanks

In standard, commercially available busducts as described by you in header, it is not possible to tie the neutral and earth conductors even accidentally along the length of the busduct. If at all it can happen, it will only be near or after the tap off point at each floor level. I can only wish you "Happy Hunting".

Check each taping at the floors to make sure there was no mistake by taping the 'E' as neutral for any of the floors or within the floor area. If the load is small, it might not trip, but as more faulty connections are activated, the accumulated current will trip the unit . This might be the reason it does not trip all the time.