[Question] Complicated electrical wiring question/issues

[BeInControl]

Hi All,

This is my first post. I have a Home Automation company specialising in high-end residential projects. I've been in the industry for more than 15 years, but it is the first time I've encountered this particular issue. I'm not a qualified electrician, thus the contracted electricians will do the lighting wiring into our DB's that contain our circuit breakers and dimmer/relay modules.

At this particular site we had 10 DBs in various locations, but the main DB and our main lighting DB were in the basement plant room. The wiring was done as follow:
* Council mains into wall box with large main input breaker and 4 copper bars (3 phase and neutral)
* Wall box to about 10 x 3-phase breakers, each supplying the various other DB's throughout the house, but one set of cables go straight from the copper bars onto the breakers at the top of our lighting DB next to this main DB.
* Our breakers in our DB are then linked with a 3-phase bus bar - 12 x 10A breakers
* We have a Earth connection bar at the top of our DB and a Neutral bar at the bottom. Inbetween is our 8 channel dimmer and relay modules.
* The Twin-and-earth cables get split at the top of our DB so the earth gets connected at the top earth connection block, the live gets connected to the dimmer output and the neutral at the bottom connection block

No for the issues...

With so many twin-and-earth cables at the top and people looking for cables and pulling cables, ext. Somehow one of the earth cables snapped and touched the top of the 3-phase bar. This caused all sorts of weird things, but wouldn't it have been saver if we had our own 3-phase input breaker instead of the supply coming straight from the mains box copper bars?
Also, some pumps have now blown at was connected to other DB's, but shouldn't these have been connected to earth leakage?

How can a short between earth and live not trip any breakers? We had to run and switch DB's off.

Thanks for any advice.

[GCE]

Without seeing photo's of the installation it would be difficult to comment and be correct
I am also assuming that the house is in the process of being wired , tested and commissioned.

Off the top and the way I visualize your description the lighting panel has been attached to the main DB as a compartment and the main switch is the main incoming.I would expect your Lighting panel when built to have its own isolation point /circuit breaker before coming to site with a certificate for the panel that was wired by suitable qualified people.

Not all Pumps do not need to be on earth leakage and that is dependent on the usage

It sounds as if the earth in the twin and earth became live , the live traveled down the twin and earth looking for a point to earth itself and tried to earth through a light or pump that it was controlling - If the installation was still being commissioned it is possible that it tried to earth in a couple of different places that were not quiet ready to accept an earth fault.

It also could be coincidence , and I have seen where there was a welder busy and his welding earth clamp came loose - While welding the pipes the welding rod tried earthing through the electrical installation and burnt all the earth wires throughout causing untold damage

Very difficult to comment without seeing the state of the installation and the amount of work being carried out

[SeanM]

Morning

Did you get a COC for the electrical installation?

If there was an earth wire touching live this should of been pick up with your insulation resistance test.

[SeanM]

And yes any live to earth should cause a breaker to trip further back at least.

[AndyD]

Can you post some photos?

With busbars in a distribution enclosure or MCC panel, if certain criteria is met, certain areas within the panel can be designated as 'fault free zones' and as such can be left inadequately protected against overload ie without an appropriately rated OCPD because the degree of mechanical protection means a fault in this area is highly unlikely. Usually within such zones the area around the busbars would be totally enclosed to prevent any accidental contact so a stray CPC should never cause a problem. It's possible however that an unsuspecting installer might remove the panels enclosing such a zone in order to allow the entry of numerous cables which could have a bad ending....Without pictures it's all guesswork.

It sounds to me that the fault caused one of the phases to trip which would cause damage to any 3-phase motors (pumps) that weren't adequately protected. When a 3-phase motor is run on only 2 phases it's always a race between the thermal overload disconnecting the power to the motor and the two windings in the motor that still have power failing due to overheating.

**edit** I just reread your first post and realised this is a domestic installation. Panels with fault free zones are almost never found in domestic installastions so my ramblings above are probably completely irrelevant.

[sytcee]

While waiting for pictures, I notice the following as an amateur technician;

1. That your DB is supplied directly from the Main DB Busbars. It's bad practice not to protect outgoing circuits.

2. Your DB has Earth Connections at the top of the DB. In close proximity to live top connections of the your protective devices. Any chance of an earth fault would have to trip the Utility's Main CB. At times you actually find the Utility used an Isolator instead of a CB. So nothing trips!

3. Had note1 above been followed, note 2 would not have mattered much although it would still be condemnable practice.

Sent from my SM-G955F using Tapatalk

[ians]

I love reading stuff like this...and we wonder why the industy s so f%^&* up...let me go turn the kettle on and order a muffin

[skatingsparks]

How can a short between earth and live not trip any breakers? We had to run and switch DB's off.

Never assume there is an incoming earth - first thing I check these days - Half the time, there isn't one.

If your earth reading is high on your loop test (maybe picking up an earth from the mains box being in the wall, from metal conduits being buried in the structure or bonded water pipes) the breaker won't trip. Recently found an earth fault loop impedance so high the fault current was 15 amps on a 20 amp breaker. Why would it trip?

[Darking]

With copper theft so high its a wonder anyone has an earth conductor anymore.