El.: 15 Amp Meter, Consumer Unit And Rcbo, 10kw Water Heater

[philo]

Hi.

The water heater gives hot water when the RCD(?) switch is off (red light), but if it is on, opening the hot water shuts down the CU main breaker.

(My wife read 'Consumer Unit and RCBO w(ith) 6/10 Circuit Braker(s)', a white box with a window, main breaker, RCD (RCB?, RCBO?)), 6 breakers from 10 to 63 Amp ?. Latest model Panasonic 10 kW heater for a tub. They hid the earthing while I was away (I am in CM, house in NK). Road meter 15 Amp.)

No electrician to be found. What should I do? I have bought a universal meter, a lead finder screwdriver and a test lamp and some cheap cable.

Also: 220 V and 10kW requieres 45 Amp. Right?

Thanks in advance.

Edited October 29, 2009 by philo

[philo]

I think it is this box (I haven't seen it for 1.5 years). link

The water heater is probably the last picture here. Cannot rember if it has a 6, 7.5, 10 kW switch. Bought early 2008, never used.

Thanks.

[elkangorito]

Pictures would be a great help. Also, since pictures may not show all the information, you must provide details of the size of each circuit breaker.

I'm not a fan of Safe-T-Cut. You may be able to buy a complete CU "on special" but what happens when the RCD unit fails? How much will it cost? I prefer a well known "modular" system...e.g. Square D.

[philo]

Thanks.

I am in Chiang Mai, the house is in Nong Khai and my wife is too lazy to do anything, so no photos. The cables are in the walls (my mistake to want to have the cables hidden). But pictures of the devices are given over.

Is 'size of breaker' amp rating or physical size?

What is a CU "on special"? Are you by "modular" implying that I should use the current CU only for lights and outlets, and buy a separate "box" for the heater (this device fed directly from the blue cable supply)? Something like the picture in post 21 here?. If so, what if that unit fails?

What is "Square D" - a brand? link. Why is it better/special? Will it fit in the CU or can it be placed in a separate housing? There are also references to Square D in the Thai thread.

So - to sum up:

1. Hot water is coming when the RCD in the CU is off. If on, everything is closed down when opening the heater.What can be checked with AVO instrument?

2. Can I keep the CU for light and unearthed outlets?

3. What kind of device for the 10 KW heater and one or two 3.3kW wall showers that is yet to be installed? Brand, stand alone or in CU? One for all heaters, or one for each heater/shower?

4. Can/should I install a new parallell earth cable/rod connected to the earth bar in the CU and/or the new device(s) as long as both rods are hidden (no surface potential difference)?

Hope that you can give advise based on what you would do if you were to do this (se below, copy of an old post) installation from the start or do a repair that will give the same result (money is no conscern here, lack of own knowledge is):

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In layman's terms there are:

1. A 15 Amp meter.

2. The two blue supply cables.

3. A consumer unit with a main breaker, an RCD (or RCB - same thing?) (this is the unit with a test button, red light, 10-30 mAmp - right?), and around 6 brakers from 10 to 63 Amp.

4. Normal ceiling lights.

5. Unearthed outlets in living room and bedrooms.

6. A water heater for a bath tub, brand new 10 kWatt with an ELCB.

7. Cabling for a wall shower unit in the other bath room.

8. Earth rod and earth cable to the consumer unit going further to the two bath rooms.

When the house was finished (joking), all lighting and outlets ok. Turning on the water heater made the main braker close. After 'repair' it gives hot water when the RCB is off. If the RCB is on, opening the hot water triggers the main braker. The 'electrician' is not reachable and I wouldn't trust him anyway.

I want to have the following done:

1. Have one or two wall shower units installed.

2. Check all wiring including earth from the current consumer unit to lights, outlets and water heater/showers.

3. Check the earthing: cable dimension and dig up the soil around the earth rod.

4. May be install a new earth cable if the old cable is too small and/or the rod cannot be located.

5. Maybe have a separate braker/RCB for the water heater and/or the shower unit(s).

6. Ask if this MEN connection should be done.

7. Ask if I need MCB on ordinary outlets for stereo, fridge etc.

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Thanks again.

[philo]

Pictures would be a great help. Also, since pictures may not show all the information, you must provide details of the size of each circuit breaker.

I'm not a fan of Safe-T-Cut. You may be able to buy a complete CU "on special" but what happens when the RCD unit fails? How much will it cost? I prefer a well known "modular" system...e.g. Square D.

Isn't this a Square D CU "on special"? But it is a better brand than what the builder installed in my wife's house? Is that the main point? Should I throw the existing CU in the garbage bin?

Thanks (and sorry for all the questions).

[longball53098]

The water heater is rated at 10kw? If so it draws more current than your system can safely supply. Somewhere around 45A of current at full power of 10Kw. The main supply you say is only rated for 15A.

You need a smaller heater power wise or a much bigger supply.

[philo]

Thanks longball.

I am aware of this (please see my two first posts). The blue supply cables are big enough, but maybe I have to change the meter. Still I get hot water when the RCD (or RCBO) is off.

Also it is the main 63Amp breaker for the supply that closes, so the cause must be in the house.

Edited October 30, 2009 by philo

[longball53098]

Thanks longball.

I am aware of this (please see my two first posts). The blue supply cables are big enough, but maybe I have to change the meter. Still I get hot water when the RCD (or RCBO) is off.

Also it is the main 63Amp breaker for the supply that closes, so the cause must be in the house.

When you say the 63A breaker closes? Do you mean it cut off power to everything?

Unless you can say what the rated size and spec is for these blue main power cables I would not accept "they are big enough" as a correct answer. To bring in 45Amps safely my calculator says you would need at least 6 mm sq cable size or larger for up to 50 meters from the meter. I would be very nervous about the cable size over the distance from the meter to the house CU. If the main supply is a 15(45) Amp meter this is barely adequate to run this one heater. I would not be connecting other (2 more heaters) heavy appliances to this supply without consulting a person that can do a calculation for max load and sizing the proper cables and CU and breakers.

It sounds like the "electrician" wired the heater directly to the main 63A breaker and when you turn on the heater it trips the main breaker.

Definitely more info and more photos are required to make a more educated reply as to what is going on there.

I hope Crossy or Elk can chime in here with their expertise.

[philo]

1. Yes, of course everything is cut of when the main breaker closes.

2. No, nothing is directly connected to the main breaker. Please read my posts and see the picture of the CU(link in post over).

Things are like this: Supply at pole, meter at pole, blue cables, main 63 Amp breaker, RCOB, bar for MCB's (all in series). Lights, outlets and heater connected to MCB's fed from the bar (all in parallell)

Hot water IS coming when RCOB OFF. When RCBO ON, feedback goes from RCBO detector circuit to main breaker which closes.

[citizen33]

1. Yes, of course everything is cut of when the main breaker closes.

2. No, nothing is directly connected to the main breaker. Please read my posts and see the picture of the CU(link in post over).

Things are like this: Supply at pole, meter at pole, blue cables, main 63 Amp breaker, RCOB, bar for MCB's (all in series). Lights, outlets and heater connected to MCB's fed from the bar (all in parallell)

Hot water IS coming when RCOB OFF. When RCBO ON, feedback goes from RCBO detector circuit to main breaker which closes.

One thing I wasn't sure about in your original post which might help the diagnosis is whether it is the main circuit breaker that trips (i.e.. because of current overload) or if it is the RCD that trips (possibly through earth leakage)? Is it definitely a single integrated box as shown in the link above or do you have separate 63A circuit breaker and RCD devices?

Edited October 30, 2009 by citizen33

[philo]

I do not know, and I cannot find the circuit diagram on the net. Maybe it is integrated and closes because of overload, not earth leakage (the ELCB in the CU is not a clean RCD, but an RCOB). I will have to go to a shop here in CM and see if I can 'inspect' a CU with the cover taken off and also the circuit diagram that is printed inside the case.

Or wait till I go to her house.

I found crossy's page at <URL Automatically Removed> (the pinned link here doesn't work for me). He shows a 'split solution', so that should make it ok for me to separate the water and feed it from a new device.

I think the best thing I can do now is to install one wall 3.3 kW wall shower, disconnect the 10 kW heater and check that everything is ok. If so, take it from there. If not, pay for a real electrician coming from a city. All this stuff and abbrevations are too difficult for me anyway.

PS

I found a post by crossy about the thai and european way concerning where to feed the neutral and this MEN link here. The thai way might be this, I don't know.

Also, I don't understand the implications of this. So I think I give up for now...

[Crossy]

OK as above photos are essential, we can not make sensible suggestions without knowing exactly what you have, 'lectric things are just too dangerous to guess! I for one will not be responsible for you getting hold of a live wire 'coz I told you to in the mistaken belief you had something you don't. I assume you'll be going to visit the installation to act on any advice we give

I worry about you getting hot water when the RCD is off, but it trips the main if you turn on the water with the heater on, something is definately amiss

By the way, a switch or breaker is OPEN when it is OFF and CLOSED when ON, even this seemingly minor thing could lead to death, "I say is it open", you say "yes", I think it's safe where in reality it's live and lethal.

EDIT To our OP, is your '15 Amp' meter a 5/15 or 15/45?

[philo]

Thanks.

I guess I have been to stressed about this because my two children are there. My wife has been told not to touch or activate anything, and being 1000 kms away I just have to trust her. Another thing is that el in the village house, restaurants, wats and outdoor pavement entertainment is typically potentiallly lethal here, but you cannot put your children in a cage 24/7.

I will try to post photos first.

Then I will do like this:

1. Check meter for 5/15 or 15/45 and try to 'read' the blue cables.

2. Check that the main breaker when OPEN cuts both lead and neutral by using the AVO. If not, have a village man disconnect both blue cables at the meter.

3. Disconnect lead and neutral cables for the 10 kW heater in the CU.

4. Reconnect supply and check all lights and outlets.

5. Check RCOB ON and OFF - nothing should happen.

6. Use a test lamp from lead through bulb to earth in the CU to check if the earthing is functioning. I have done it before, the bulb lights up. If RCBO OFF, light will stay on. If RCBO ON, main breaker will disconnect (OPEN).

7. Same procedure as 6. but using long testlamp cable from any lead via bulb to earth in the bathrooms.

7. Disconnect supply.

8. Have the 3.3 kW wall shower installed, watching lead, neutral and earth.

9. Reconnect supply.

10. Put the test lamp between lead and neutral on the shower unit. Nothing should happen - whether RCBO is ON or OFF.

11. Put the test lamp between lead and earth on the shower unit. If RCBO is ON, then it should trip (given that earth is not connected to neutral OR connected to neutral AFTER the RCBO (so that some current will leak to earth in stead of returning to the neutral of the RCBO). Is this CORRECT? (The same argument goes for point 6.)

12. Test the shower with RCBO both ON and OFF. Nothing should happen if it is connected to a 16 or 20 Amp MCB.

13. Check the ELCB manually on the shower unit.

14. Disconnect supply.

15. Check all cables firmly fixed, exposed copper taped up, cables out of use isolated and physically away from everything else, etc (what more?), put on all covers.

16. Reconnect supply.

17. Put RCBO in ON position 30 mA.

18. Test all lights, many outlets used (fridge, TV, el drill) and shower ON at the same time.

19. Tell my wife that there is only hot water in the small bathroom shower unit, the 10 kW heater in the master bathroom is not connected.

Then later on make a 3-pole earthed outlet for a rice cooker.

Then much later start to investigate the 10 kW heater.

Does this make sense, or should I burn down the house?

Thanks again.

[Crossy]

Your tests seem fine.

You should be able to verify that the main switch breaks live (or line) and neutral by visual inspection.

I am assuming when you say 'RCBO off' you bean 'bypass' (i.e. no protection).

Any N-E connection (MEN link) should be on the supply side of your ELCB (Safe-T-Cut), there must be no N-E connection anywhere else.

PLEASE be careful

[philo]

Thanks, crossy

Yes, RCBO off = bypass, on = protection.

I THINK I understand the MEN link now: L and N after the RCD/RCOB must be floating in the sense that the supply and return path of the current must balance.

IF you lose your N connection (but still have earth) after the CU/RCD no current will flow. BUT if there is a faulty appliance, current could flow to ground. If ground has a high resistance there could still be a high potential on ground, and current could flow through a person touching the appliance. The MEN link gives an alternative low resistance return path that hopefully will give a cut off in the RCD and/or MCB.

IF you lose your ground after the ground bar (but still have N), the installation will perform like an unearthed system. Whether there is a MEN link or not doesn't matter.

IF your ground bar lose real ground connection, but you still have your ground cable from appliances to the ground bar, then a MEN link will still give a low resistance return path and hopefully trip the RCD and/or MCB. But if you don't have the MEN link, the system behaves as ungrounded.

IF you lose both N and earth and have a faulty appliance, then you are in deep shit.

Question: Should the MEN link be there even if you do not know whether the closest transformer N is earthed?

PS Before I start I will cut the supply to the heater, measure the supply voltage, turn on the heater, open the supply (connect by closing the MCB OUTSIDE of the bathroom) and measure the voltage drop at the CU. This would give some indication of the (ohmic) impedance of the 90 m blue cables. Correct? If I let the water run for 10 minutes, would I be able to detect heating of the cables?

PS 2 Found this, maybe helpful for others too: link. In the article there is a link called 'The MEN System of Earthing'. I found it useful.

PS 3 This statement: 'Safety isolation indicates a situation where all power frequency voltage from all active conductors, including neutral, is removed from the circuit once the isolation device is tripped or switched to the 'off' position. For RCBOs in which the neutral pole is not switched, the term 'isolation' can only be understood to apply in the strict sense of the word if the RCBO is installed in an electrical circuit in which the neutral can be considered to be reliably maintained at earth potential. While it is not unreasonable to assume such a situation in a residential type installation where the MEN link is made at the main switchboard, it doesn't necessarily follow that this same assumption can be applied to large industrial and mining installations.' should make me check if the RCBO is cutting only L or both N and L?

Thanks again.

Edited October 31, 2009 by philo

[Crossy]

Question: Should the MEN link be there even if you do not know whether the closest transformer N is earthed?

NO!! If you are not certain that you have MEN (the Tx neutral is always earthed, the 'M' is for 'multiple') you should not have a MEN link.

PS Before I start I will cut the supply to the heater, measure the supply voltage, turn on the heater, open the supply (connect by closing the MCB OUTSIDE of the bathroom) and measure the voltage drop at the CU. This would give some indication of the (ohmic) impedance of the 90 m blue cables. Correct? If I let the water run for 10 minutes, would I be able to detect heating of the cables?

On such a long run the volt-drop would be more indicative of undersized cables than a significant temperature rise.

[philo]

Thanks again crossy

I now feel reasonably comfortable having a plan and your information (also the info from the 'Safe - t -Cut' thread made me understand why you don't connect N-E without knowing positively that there is MEN).

philo