Is This A Differential Switch?

[kriswillems]

Hi,

First of all. Sorry for my English. I don't know the technical terms for an electrical installation.

The people that installed the electricity in our house (friends of my father in law) did a terrible job. I've never seen electricity that is done so unsafe like this. Everything just hangs together with tape. They didn't use any cable connection box nor did they put those little hats on top of connected cables. They just put some tape around connected cables and left every lying open under the roof with a lot of dust on it.

But this in not what is worrying me the most. I am worried there is no differential switch in our home. We have a small baby in this house and we have those Thai plugs on the wall, which have no child protection at all.

When I asked my father in law, he said the following thing contains a differential switch, but it just looks like a circuit breaker to me.

Does this thing contain a differential switch? If so, at how many mA will it switch off? I can't find any information on the device.

Edited March 19, 2008 by kriswillems

[Crossy]

Possibly

Are there three or four wires going in and out?

Does the white rectangle to the left and below the switch say 'test' on it? Does pressing it turn off the breaker?

There seems to be an adjustment (the min-max knob). Although the brand is Safe T Cut (well known for their ELCB trips) I would expect there to be an indication of min and max trip current available.

Edited March 19, 2008 by Crossy

[kriswillems]

Possibly

Are there three or four wires going in and out?

Does the white rectangle to the left and below the switch say 'test' on it? Does pressing it turn off the breaker?

There seems to be an adjustment (the min-max knob). Although the brand is Safe T Cut (well known for their ELCB trips) I would expect there to be an indication of min and max trip current available.

We have loadcenter LO12A on this web-site.

http://www.safe-t-cut.com/Thai/product/Loa...ter-Europe.html

If you open the English version of the safe-t-cut web site, these load centers are not there.

The description doesn't say anything about differential current.

The white button says test.

There are 3 wires going in and 3 wires going out (which are L1, L2 and L3)

The NULL doesn't pass anything (no fuses, no circuit breakers, no differential switches) and is straight connected to the plugs on the wall.

Edited March 19, 2008 by kriswillems

[kriswillems]

This is the wiring diagram.

Edited March 19, 2008 by kriswillems

[Crossy]

OK, I'm sure you have an ELCB (differential switch), the 'test' button is a giveaway

BUT

I'm not sure of the wiring, particularly the fact that the neutral is not sensed, the breaker cannot tell the difference between a load between Lx and N (ok) and Lx and E (someone being zapped).

I am not an expert on 3-phase installations, hopefully someone more versed in these things will pop up. I would have thought a 3-phase 4 wire unit would be the correct device.

[kriswillems]

Crossy. I would have thought the same.

This makes me believe this is not a differential switch although there is a test button.

Maybe the test button is part of an advanced circuit breaker...?

Suppose there is no load on L2 and L3.

If I touch L1 and there is going 1A through my body to the ground

Or

I connect a resistor between L1 and NULL and there is 1A going to the NULL

This should be exactly the same for this device: L1 has 1A going in and out, L2 and L3 = 0 A going in and out.

[Crossy]

Crossy. I would have thought the same.

If I touch L1 and there is going 1A through my body to the ground

Or

I connect a resistor between L1 and NULL and there is 1A going to the NULL

This should be exactly the same for this device: L1 has 1A going in and out, L2 and L3 = 0 A going in and out.

Exactly ^^^

Pretty sure you have a unit intended for 3-phase 3-wire (no neutral), in Thailand we are 3-phase 4-wire.

I agree that it provides no protection from shock in its current configuration.

Where are all the industrial electricans that usually pop up on these subjects?

Edited March 19, 2008 by Crossy

[kriswillems]

Yes, but what is very strange is that the wiring diagram shows 380V on Lx (I suppose they mean between Lx and Ly).

In a house without NULL you would have 220V on Lx (i.e. between the lines).

[Rimmer]

If it was a Residual current device and the installation is as bad as you say then you would most likely likely get nuisance tripping. Looks like an ordinary 63a breaker to me, Anyone know about IEC 942-2 that should give a clue.

I believe the standard for RCDs is IEC1008, VDE0664, CEE27

As a matter of interest we were always taught that in a domestic installation in order to protect a childs life you need a 30mA device but given the nature of the beast in Thailand this level of sensitivity would never stay in so I dunno what to say.

[kriswillems]

I pressed the test button. The electricity goes off. However, the handle of the switch on this devices doesn't flip down when doing this. I've to manually pull it down and push it up again to put the electricity on again.

Edited March 19, 2008 by kriswillems

[Crossy]

Looks like an ordinary 63a breaker to me.

The adjuster and 'test' button are causing me confusion

Kris, I suggest that you are seeing normal operation (pull down and up to reset).

IMHO you should replace this device with a 4-wire unit to provide protection for your loved ones.

Rimmer has a good point, if you load up one phase the breaker would see a massive imbalance and ought to trip.

Edited March 19, 2008 by Crossy

[kriswillems]

I think the adjuster is used to set the overload current between 44 and 63A.

The test button probably heats some resistor inside the device for testing if the thermal circuit breaker really switches off.

I feel like safeTcut intentionally sells these useless boxes at low prices, knowing that most Thai people would think it contains a differential switch.

Tomorrow I will connect a device using 1A between the ground wire (I hope that one is connected) and the L1. If the switch doesn't switch off I know it's useless. I will add a differential switch of 100mA (if there's enough space in the box). I think 30 mA will never hold here.

In Europe I've already touched line wires with a differential switch of 100mA. It didn't feel nice, but the switch went off and I didn't die. So I guess it's better than no protection at all.

Edited March 19, 2008 by kriswillems

[Rimmer]

A couple more things that might be relevant.

It's only wired for single phase.

It says BREAKER on the case, it does not say earth leakage circuit breaker or residual current device or ground fault interupter.

IEC 947-2 is not a standard for RCDs

[kriswillems]

Feel bad about this. I am living on a tight (Thai) budget, but have to think about my kid first.

We've 2 of these boxes in our house.

If I add a differential switch I can put it in front of this breaker, right?

Behind is a bit hard because of the thick copper bars that leave the device.

I should make the NULL also pass through the differential switch before it goes to the distribution rail, right?

Thanks Rimmer and Crossy for your help!

Edited March 19, 2008 by kriswillems

[kriswillems]

Another thing. I am going to test with a milk bottle warmer (280W) between L1 and the ground wire (at a plug in the house). Is this test dangerous?

[kriswillems]

I just did the test.

The plug of milk bottle warner had round pins. So, I could actually force it into the plug in the wall the wrong way, between the ground and the line. The bottle warmer worked as usual! It's a 280W device. So more than 1A went to the ground. When I put the bottle warmer between the other pin (NULL) and the ground the bottle warmer didn't work (as expected).

If that would have been me instead of the bottle warmer, I would be dead!

[lopburi3]

Safe-T-Cut is a very old and experienced manufacture of RCD (my unit was made in 1977). The photo unit I suspect is made for industrial use and would be set for the trip that they wanted - have no idea what set from factory. Normal home units have adjustable stops of about 5-30ma.

[kriswillems]

Safe-T-Cut is a very old and experienced manufacture of RCD (my unit was made in 1977). The photo unit I suspect is made for industrial use and would be set for the trip that they wanted - have no idea what set from factory. Normal home units have adjustable stops of about 5-30ma.

http://www.safe-t-cut.com/Thai/product.html

My product is a very standard thing (in on the second row on the right).

And even if it would be an industrial unit you would at least expect it to switch off at 1A, which it doesn't do (see test with bottle warmer).

There are 2 possibilities:

1. Safe-t-cut just sells load centers without RCD.

2 This thing is made for a 3x220V net without NULL

I don't understand why they sell this.

If it contains an RCD, it will only work on a 3x220V net (without NULL). I don't know if such a net exists in Thailand.

If it doesn't contain an RCD, they really try very hard to confuse the customer.

Personally I believe it doesn't have an RCD, because for the units that contain an RCD it's explicitly mentioned on the WEB-site.

For those who can read Thai: last 2 units on the first row and third unit on the second row have an RCD.

Edited March 19, 2008 by kriswillems

[elkangorito]

What you have is a "trip free" 3 pole 63 Amp Moulded Case Circuit Breaker (in a 160 Amp frame). The tripping current is adjustable between 44 & 63 Amps. It has a Short Circuit capacity of 50 000 Amps at 400/415 volts. The "test" button simply tests the trippng mechanism. IT IS NOT AN EARTH LEAKAGE PROTECTION DEVICE.

This is a rather expensive item to have since it is not entirely necessary.

I believe that it was made in Malaysia.

Edited March 19, 2008 by elkangorito

[Crossy]

What you have is a "trip free" 3 pole 63 Amp Moulded Case Circuit Breaker (in a 160 Amp frame). The tripping current is adjustable between 44 & 63 Amps. It has a Short Circuit capacity of 50 000 Amps at 400/415 volts. The "test" button simply tests the trippng mechanism. IT IS NOT AN EARTH LEAKAGE PROTECTION DEVICE.

Thanks for the insight Elk, not seen a regular breaker with a 'test' button before

So as noted, it should be replaced by a proper 3-phase 4-wire combined MCB/ELCB (RCD, GFI or whatever we are calling it today). If it's an expensive unit maybe our OP can get some credit against the correct device.

Alternatively, he could replace the MCB's that supply his outlets with individual ELCB's assuming there is space, if there are not too many needed probably a cheaper option.

It's always a pain trying to fix something that's been done incorrectly, unfortunately the concept of 'right first time' seems alien here

Edited March 20, 2008 by Crossy

[Rimmer]

What you have is a "trip free" 3 pole 63 Amp Moulded Case Circuit Breaker (in a 160 Amp frame). The tripping current is adjustable between 44 & 63 Amps. It has a Short Circuit capacity of 50 000 Amps at 400/415 volts. The "test" button simply tests the trippng mechanism. IT IS NOT AN EARTH LEAKAGE PROTECTION DEVICE.

This is a rather expensive item to have since it is not entirely necessary.

I believe that it was made in Malaysia.

Wow! Well there ya go Believe you are 100% right.

Just as as a side diversion, Back in the days when I owned a suit I was responsible for sales and marketing of MCBs MCCBs and RCDs into South East Asia and the Middle East manufactured by our factory in Malaysia.

I'm way out of touch now but back then the leading brand of RCD was manufactured in Germany by F&G.

Our factories tested Thai made RCDs and came to the conclusion that they would never pass British Standards and were in fact quite dangerous. No doubt they have now progressed to a level where they will perform as advertised.

[kriswillems]

thanks that confirms what I was suspecting.

individual earth leakages devices for all the outlets are to expensive.

I'll need to add one EARTH LEAKAGE PROTECTION DEVICE, 63A, 30 mA or 100mA (will check what they have) or replace the 63A breaker with a combined unit ( EARTH LEAKAGE PROTECTION DEVICE and breaker).

If I add an EARTH LEAKAGE PROTECTION DEVICE, may I put it in front of 63A circuit breaker?

Or should it really be put behind?

In Europe we always put the main circuit breaker first and after that the EARTH LEAKAGE PROTECTION DEVICE.

Is there a problem with turning that around? I guess not?

Edited March 20, 2008 by kriswillems

[lopburi3]

You want 30ma or better (lower) for personal protection.

[lopburi3]

Safe-T-Cut is a very old and experienced manufacture of RCD (my unit was made in 1977). The photo unit I suspect is made for industrial use and would be set for the trip that they wanted - have no idea what set from factory. Normal home units have adjustable stops of about 5-30ma.

http://www.safe-t-cut.com/Thai/product.html

My product is a very standard thing (in on the second row on the right).

And even if it would be an industrial unit you would at least expect it to switch off at 1A, which it doesn't do (see test with bottle warmer).

There are 2 possibilities:

1. Safe-t-cut just sells load centers without RCD.

2 This thing is made for a 3x220V net without NULL

I don't understand why they sell this.

If it contains an RCD, it will only work on a 3x220V net (without NULL). I don't know if such a net exists in Thailand.

If it doesn't contain an RCD, they really try very hard to confuse the customer.

Personally I believe it doesn't have an RCD, because for the units that contain an RCD it's explicitly mentioned on the WEB-site.

For those who can read Thai: last 2 units on the first row and third unit on the second row have an RCD.

Was not looking for a load center as the photo seemed to be stand-alone. I see on there English language page they have stand alone three phase RCD units available but the load centers do not seem to offer built in option (in my brief look).

[elkangorito]

You want 30ma or better (lower) for personal protection.

Lop is 1000% correct. In addition, here are the types of RCD's available (in Thailand?). Look for the symbols on each RCD. If you wish to adequately protect people from earth leakage resulting from distorted waveforms (produced by computers, Variable Speed Drives etc), choose Type A or Type B.

individual earth leakages devices for all the outlets are to expensive.

I'll need to add one EARTH LEAKAGE PROTECTION DEVICE, 63A, 30 mA or 100mA (will check what they have) or replace the 63A breaker with a combined unit ( EARTH LEAKAGE PROTECTION DEVICE and breaker).

If I add an EARTH LEAKAGE PROTECTION DEVICE, may I put it in front of 63A circuit breaker?

Or should it really be put behind?

In Europe we always put the main circuit breaker first and after that the EARTH LEAKAGE PROTECTION DEVICE.

Is there a problem with turning that around? I guess not?

Just to clarify, an RCD by itself is not capable of opening a circuit because it is not a circuit breaker. An RCD senses "out of balance" current. With the help of electronics etc & if any "out of balance" current is detected, the RCD can then mechanically or electrically operate a circuit breaker. RCD units that can open circuits directly are called Combination RCD's (& other names).

If you install a combination RCD as your Main Switch, you may end up with some problems since the sum of the leakage currents may cause nuisance tripping. This will become particularly apparent as appliances age. To avoid unwanted tripping because of leakage currents and transient disturbances, care should be taken to ensure that the sum of the leakage currents of electrical equipment on the load side of an RCD is significantly less than its rated residual current. RCDs may operate at any value of residual current in excess of 50% of the rated residual current.

It is recommended that the loading of the circuit should be such that the leakage current does not exceed one-third of the tripping current.

To avoid excessive leakage current causing unwanted tripping where power outlets are protected by one RCD having a rated residual current not greater than 30 mA, consideration should be given to the number of power outlets protected and the nature of electrical equipment likely to be connected to these outlets.

It is generally preferred to have any earth leakage detection device as close as possible to the load & also not to have any other protection device (circuit breaker) between it (the RCD) & the load.

Here are your options as I see it;

1] Replace some of your circuit breakers with RCD's as required. Most good quality Combination RCD's are 2 to 2.5 pole spaces wide so this may not be possible without replacing the panel board.

2] Replace your Main Switch with a Combination RCD (as you suggest) & hope that you don't get too much nuisance tripping. You can also split your panel board & simply provide 1 part of it with earth leakage protection. More info on http://www.crossy.co.uk/wiring/Consumer.html

Currently, your main switch is rated at 50kA. This is excessive if you are supplied from a "typical" pole mounted transformer. If you are getting supplied from a "typical" pole mounted transformer, you only need a main switch rated at no more than 10 kA, which should save you a few dollars. All "downsteam" circuit breakers/Combination RCD's can be rated at no more than 6 kA in this situation (Short Circuit Discrimination). All circuit breakers/RCD's/etc in your panel board should be of the same brand. This will ensure correct device discrimination.

Last but not least, Australian Wiring Rules (AS/NZS 3000-2007) says the following;

"The use of fixed setting RCDs with a rated operating residual current not exceeding 30 mA, is recognized as providing additional protection in areas where excessive earth leakage current in the event of failure of other measures of protection or carelessness by users could present a significant risk of electric shock.

NOTE: The use of RCDs is intended only to augment other measures of basic protection.

RCDs do not provide protection against faults between live conductors, nor do they provide protection against voltages imported into the electrical installation earthing system through the supply system neutral conductor. The use of such devices is not recognized as a sole means of protection and does not obviate the need to apply the protective measures specified in Clause 2.4."