3-Phase 4-Wire Rcbo

[Khonwan]

My 3-ph master breaker is situated 150m from my main house; it services my four houses plus other outbuildings on my farm. I am considering replacing this with a Safe-T-Cut 3-phase 4-wire RCBO. My shower and 2 other appliances at my house use 3-ph – is there a safety/speed issue with this 150m distance between RCD and appliance?

Since most of my appliances are obviously single phase, and since at any given time my system is obviously out of balance (not helped by the fact that my transformer is unbalanced in terms of voltage even at no load!), should this RCBO still function properly?

I am presuming that this 3-phase 4-wire RCBO should provided protection for my 3-ph and 1-ph appliances – am I correct?

[InterestedObserver]

In theory your main RCBO should be ok as long as all your wiring is in perfect condition and installed properly. Your farm is obviously spread out over a large outdoor area with lots of opportunity for earth leakage currents. Voltage/phase imbalance does not matter, just as long as you have no earth leakage current downstream of the RCBO. The only way to find out is to install the RCBO, but be prepared for nuisance trips. Both 1-phase and 3-phase appliances will be protected, as long as your wiring is intact. Code issues will be commented on by others.

Edited September 26, 2010 by InterestedObserver

[Khonwan]

Thanks for this confirmation. I already test for current leakage to earth on my overhead cables from time to time – so far so good, despite 8km of cable. Come to think of it, I have earthed neutrals after the main breaker (in addition to those between the breaker and my transformer) – will they affect the RCD?

[Crossy]

Come to think of it, I have earthed neutrals after the main breaker (in addition to those between the breaker and my transformer) – will they affect the RCD?

YES!!!

Any neutral-earth connection on the controlled side of an RCD will prevent it from operating correctly.

I would use individual 1 or 3 phase RCDs at each consumer unit, treating each building as an individual installation.

[InterestedObserver]

Thanks for this confirmation. I already test for current leakage to earth on my overhead cables from time to time – so far so good, despite 8km of cable. Come to think of it, I have earthed neutrals after the main breaker (in addition to those between the breaker and my transformer) – will they affect the RCD?

Your system configuration is not suitable for a main RCBO, you have neutral to earth connections downstream of the RCBO. Earth leakage current has a path to return to the RCBO and be summed by the current transformer inside.

Edited September 26, 2010 by InterestedObserver

[electau]

As Crossy has indicated, RCDs/RCBOs at each sub board. Neutrals must not be earthed on the load side of an RCD.

[Khonwan]

Thanks chaps. Glad I remembered that minor point!

[frenchfarangjomtien]

Hello,

Thanks to this board and Crossy I was using a RCBO in a new condo with completely new installation.

Suddenly after 1 year of using it it started to trip without any apparent reason, and then yesterday it was tripping in day time without any appliance switched on, and even with all the other switches turned off in the electric box (i mean that there was no electricity sent to any plug or light in the condo). All the small switches where off in the electric box and only the RCBO was on, but still it was tripping every 5 mns.

But last night i tried to switch it on again and it has been working until 6 morning will all lights, aircon, and appliances on, but then everything broke again at 6am.

Can you tell me if you think that this RCBO might have problems, or what else could be the cause ? When we installed it I had a problem once when the condo tried to connect the building TV antennae to our room, the RCBO was turning off everytime i was starting TV, then no more problem for 1 year.

How to test RCBO and be sure that it is the problem ?

We just changes to "normal" safecut to replace RCBO in the electric box and it is now working.

Thank you so much for your help.

[Crossy]

An RCBO that's tripping when everything else is off could be:-

A genuine leak L-E

A N-E short

A faulty RCBO

If you can replace the RCBO like for like do so, sadly this is not a cheap option.

I suspect damp somewhere, the best way to find it would be with an insulation tester and someone who knows how to use it.

In the absence of an insulation tester try disconnecting any circuits that go into damp areas (like your water pump), disconnect BOTH the L & N sides, leave alone and see if the problem goes away. Sadly without proper test gear you're in for a very slow process

You REALLY need to sort the problem as you have removed a vital safety device from your installation. That tripping RCBO could just be telling you you have a fault which may be lethal.

Have you tried disconnecting the TV since that was causing issues in the past and just 'went away'?

[Jdietz]

Any neighbors waking up at 6am?

[citizen33]

Another thing to exclude is rodents having knawed through insulation. I had a problem once with trips that was cured by making good some affected cables in the ceiling.

[frenchfarangjomtien]

Thank you, but i guess that there is no damp area in a condo ?

Now everything is working with the traditional breaker bought 700 thb that replace the RCBO bought 3000, and the RCBO has been sent to Schneider or Dsquare (company that sells it) to test it, so i will report later.

But i am still thinking that this RCBO is ok as it worked all night without any problem and just tripped in the morning at 6am.

You scared me again as you scared me before when i asked the electrician to install this RCBO following your messages here, but are you sure that anything could be wrong when everything is alright now ? Are you just working for Schneider Dsquare ? Please tell me the truth, i can accept it and will feel safer (just joking :-) ).

Really, i understand that this RCBO can be useful, but as i guess most of the people don't have one, it doesn't seem to be an obligation ?

Also, since there was the problem with TV antennae, we haven't connected the building TV antennae anymore, because we don't watch it, so it couldn't be the source of our problem now.

What should i do next if they tell me that the RCBO is not the problem ? Do you know ayone around Pattaya who can do the tests that you are talking about ?

Thank you so much again.

[electau]

There are several reasons why a RCD will trip.

The most likely is a faulty item of electrical equipment.

Isolate each circuit and the reset the RCD and see if it trips if it does not trip this is the where the fault will be found.

To check the RCD itself disconnect the load side and reset the RCD. If it still trips the RCD is faulty- replace the RCD.

Low insulation on the neutral conductor can cause tripping.Excessive earth leakage current can cause nuisance tripping.

An RCD must trip between 50% and 100% of its rated current in mA. Max leakage current should not exceed 30%. An RCD must not trip at 50% of rated current in mA.

[electau]

RCDs should be installed on the Main switchboard or sub board(s) within an electrical installation.

They should protect the final sub circuits only.

There must be no earth on the neutral on the load side of an RCD.

Consumers mains and submains do not require RCD protection.

[frenchfarangjomtien]

As RCBO trips even when all the others switches of the electric box are down and all appliances unplugged, the problem couldn't be any faulty electrical equipment right ?

I would like to know what exactly to tell to do to the building electrician who is not a scientist but always ok to try things and help.

Thanks again.

[Crossy]

Get him to do an insulation test on each circuit L+N joined together test to ground. Ensure that he removes both the L and N from the distribution box before testing.

Should be more than 10Megs although anything over a Meg would be ok as far as your RCD is concerned.

If he does not have an insulation tester then you have a problem

I suspect you have a N-E fault or a faulty RCD.

[bankruatsteve]

Any outside sockets with wasp nests in the holes? I've had that problem with the RCD.