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Electric safe-t-cut (GFI).Any one had device installed in home ?


happy me
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Thank you for a great and detailed information of the GFI. My house is only 7 years old and has single phase 3 wire circuits  so I don't expect any wiring problems (finger crossed). Thank you again for info

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2 hours ago, happy me said:

Thank you for a great and detailed information of the GFI. My house is only 7 years old and has single phase 3 wire circuits  so I don't expect any wiring problems (finger crossed). Thank you again for info

My house is 6 years old and I didn't expect any problems either. Until I found that the electrician saved some wires (money) and combined the neutral wire of several circuits. Not a good idea.

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I had to replace a GFI receptacle in my bathroom the other day - after 34 years of use it was causing me  trouble by tripping off all of the time - but very easy to do. 

When I bought my house - which is an old piece of army barracks re-purposed, not uncommon here back in the day - the whole place was on only two circuit breakers; big old textile-insulated wires in the walls, with twisted and taped connections, simply dreadful. When I got into serious renovations I had an electrician friend come over one weekend and we pried the old tin seal off of the meter, pulled the meter and put a newer panel in and then re-closed the seal again and nobody ever suspected a thing - then I went on to re-wire the whole house myself and had another sparky come over to clean it up a little and it passed inspection easily. You couldn't do this today with the locking meter seals they use now.  

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18 hours ago, happy me said:

Thank you for a great and detailed information of the GFI. My house is only 7 years old and has single phase 3 wire circuits  so I don't expect any wiring problems (finger crossed). Thank you again for info

It's good to give the old brain cells a work-out every now and then.

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15 hours ago, CampariO said:

My house is 6 years old and I didn't expect any problems either. Until I found that the electrician saved some wires (money) and combined the neutral wire of several circuits. Not a good idea.

Unfortunately, this is not unusual in Thailand.

From a contractors point of view, it makes it very difficult to Quote for work ( of any kind ) because until you get into the job, you just don't know what you're going to find / have to fix, in order to get the job done to an acceptable standard.

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On 3/6/2021 at 3:46 PM, CampariO said:

My house is 6 years old and I didn't expect any problems either. Until I found that the electrician saved some wires (money) and combined the neutral wire of several circuits. Not a good idea.

That is no problem, as long as the wires for the load are combined the same way (star network, single wires to a central point in a room and split from there) and the total can't overload the wires (or the protection).

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Dear @Proffesor  - MANY THANKS for the superb and concise information! - if you could help me a little bit...

In  my shop the previous owner had installed showers, without any RCD's (and coming off the same feed as the aircon....)

I changed that by putting a separate 16a fuse switch in the fuse board, and then put an RCD before the shower - is this a correct approach to protect?

Ive not had an earth check done on the building, would you recommend that? (i have a fuse board on each floor)

TIA

 

Peter.

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11 minutes ago, Chappo said:

Dear @Proffesor  - MANY THANKS for the superb and concise information! - if you could help me a little bit...

In  my shop the previous owner had installed showers, without any RCD's (and coming off the same feed as the aircon....)

I changed that by putting a separate 16a fuse switch in the fuse board, and then put an RCD before the shower - is this a correct approach to protect?

Ive not had an earth check done on the building, would you recommend that? (i have a fuse board on each floor)

TIA

 

Peter.

From memory, the shower water heaters I had had a built-in RCD/ELB (with a check operation button for testing).

Similar to this example.

http://www.fec-corp.com/product-detail/wh-x-hot6/4

 

 

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yes - they do all have test / cutoff - but wasnt sure it was good enough - prefer the belt and braces approach, as you do not want a customer electrocuting themselves when having a shower 🙂

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11 hours ago, Chappo said:

Dear @Proffesor  - MANY THANKS for the superb and concise information! - if you could help me a little bit...

In  my shop the previous owner had installed showers, without any RCD's (and coming off the same feed as the aircon....)

I changed that by putting a separate 16a fuse switch in the fuse board, and then put an RCD before the shower - is this a correct approach to protect?

Ive not had an earth check done on the building, would you recommend that? (i have a fuse board on each floor)

TIA

 

Peter.

Good evening, Sir

In my opinion, in an ideal world, every appliance ( A/c, water heater, oven, hob ( + Hood ) ) etc. should have it's own dedicated circuit and breaker. If there is the potential for water and electric to mix - whether it be by design ( a shower heater ) or potential accident ( a hair dryer plugged into a power socket next to the vanity basin in a bathroom ) then that appliance or plug socket circuit should be protected by a GFI / RCH / ELCB ( or whatever ). Plug socket circuits in a kitchen should also have protection ( dishwasher, washing machine, water purifier etc. etc. - all plugged into kitchen wall sockets, all mixing water and electric by design ! )

Yes, a shower / water heater should have its own integrated protection device. Fitting an additional protection device in the supply line isn't going to hurt. I would probably have fitted an additional 16 (? - see below ) amp RCBO at the MDB, instead of the "fuse switch " ( I presume you mean Breaker ) + the RCD - but that's just my approach.

 

Another tip. Shower Water heaters are rated in Kw ( KiloWatts ). 1 Kw = 1,000 watts. There is a formulae that relates Volts, Watts and Amps, which is Watts / Volts= Amps. In Thailand the supply voltage is supposed to be 230 Volts, but with infrastructure overload and poor distribution networks, it is usually less. Let's assume 225. So; a 3.5Kw shower in Thailand draws how many Amps ? 3500 ( Watts ) / 225 ( Volts ) = 15.9 ( Amps ).

If the supply voltage goes down ( as it often does in times of peak demand ) to 200 Volts; then 3500 ( Watts ) / 200 ( Volts ) = 17.5 ( Amps ).  So, your 16 amp fuse / breaker is marginal for a 3.5 Kw shower / water heater - I would use a 20 amp.

 

Rule of thumb - cable sizes.  The rated capacity of a cable differs dependent upon any number of factors, but the rule of thumb that I use for copper cables is :- cable size ( Cross sectional area in Sq.mm )  x 0.66666 = current capacity ( Amps ).

For example :-

0.75 sq.mm = 5 amps

1.0 sq.mm = 6.5 amps

1.5 sq.mm = 10 amps

2.5 sq.mm = 16 amps

4.0 sq.mm = 26 amps

6.0 sq.mm = 40 amps

10 sq.mm = 66 amps

On which basis, using a 2.5sq.mm cable for a 3.5 Kw shower is marginal at best. Possibly O.K. if the cable run is very short. A 4.0 sq.mm cable would be preferable.

 

Sorry - long answer to a short question !

 

Thank-you and Good Night.

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Disclaimer: I am not an electrician or electrical engineer. The following is presented for educational purposes only.

BM @Proffesor presented a “rule of thumb” for sizing electrical cables. IMO the ROT is a bit generous and while there is nothing wrong with over-sizing cables, copper costs money. There is everything wrong with under-sizing a cable.

The following is extracted from a cable manufacturer’s specifications for cables complying with AUS/NZ wiring standards.

image.png

https://www.olex.com.au/eservice/Australia-en_AU/fileLibrary/Download_540225217/Australia/files/OLC15984 Handbook July 2016 FA V3 LR.pdf

 

If we take the third row down, a cable (2 core plus earth) of 2.5mm2 the first column on the left shows a value of 27 amps. The little picture above indicates that’s the value for the cable in free air. The next value to the right shows the current if the cable is fixed to a flat surface, it’s de-rated by 1 amp to 26 amps. Moving from left to right the lowest rating is if the cable is surrounded by thermal insulating material as might happen in a ceiling or roof space with thermal insulation. In that case the cable is de-rated by over half.

Any voltage drop along the cable run manifests itself as heat. The cable in free air, maximum heat dissipation, a cable buried in thermal insulation, minimum heat dissipation. While any heat build-up may not be sufficient to start a fire it may be sufficient to soften the cable insulation allowing the conductors to touch each other either arcing or creating a short circuit. The arcing or short circuit will start the fire.

The column at the far right is the voltage drop expressed in millivolts per amp per metre. AUS/NZ wiring rules permit a maximum of 5% voltage drop between the main distribution board and the appliance( when switched on). Unless you want to try and find the Thai wiring regulations it’s probably not a bad value to use.

Motors. While small motors, domestic refrigerator, washing machine etc, generally aren’t a problem large motors, whole of premise airconditioner etc,  can be.  A motor on startup can have an inrush current of 20 times the running current for a split second and perhaps 6-8 times the running current for several seconds. If the voltage drop along the cable during startup is high enough the motor might just stall until either the breaker trips, the motor burns out or the wiring catches fire and the problem is solved. Motor circuits need careful consideration.

Any calculations need to take into consideration the actual premise. Some websites say the nominal voltage in Thailand is 220V others say 230V. I’ll guarantee that very few premises receive either.  When I was living there, a couple of houses further down the soi had an industrial sewing machine and during the early morning they were no doubt knocking out the knockoff handbags they were going to sell that day. During the bursts of sewing activity my UPS kept tripping in at about 180V. First place to start is to know what you supply voltage is like and also the capacity (in amps) of the lead-in cable.

An Android app that works for me is CalcWiz

https://play.google.com/store/apps/details?id=com.don.calcwizlite

Helps design cable runs. Make sure you get the free version. (Ignore the reviews which say the free version is too expensive).

 

Another long answer to the same short question.

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Thanks for your input fygjam.

I'm not going to argue with any information published by a National Institution. In Europe, Electricians follow the IEE ( Institute of Electrical Engineers, I believe ) Regulations, currently Edition 18 is the required standard ( enacted 01/01/2019 ) which, incidentally, requires RCD protection on all plug socket circuits rated at up to 32 Amps.

 

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52 minutes ago, Proffesor said:

Thanks for your input fygjam.

I'm not going to argue with any information published by a National Institution. In Europe, Electricians follow the IEE ( Institute of Electrical Engineers, I believe ) Regulations, currently Edition 18 is the required standard ( enacted 01/01/2019 ) which, incidentally, requires RCD protection on all plug socket circuits rated at up to 32 Amps.

 

Cable sizes, insulation types, length of run, ambient temps, enclosures, bunching, humidity etc all play an important part to what power they are capable of safely carrying.

The important thing is that the safe level is protected properly by the Fuse/trip. Understanding each application can be a nightmare and here in the UK we have a few generic cable sizes for certain situations to make things easier for the trade, EG. house builds.

Given the heat and humidity in Thailand, you are wise to use your rule of thumb and those values look about right to me for a room install, you are unlikely to get an issue with over heating/fire etc as long as the connections are sound.

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1 hour ago, boydeste said:

Cable sizes, insulation types, length of run, ambient temps, enclosures, bunching, humidity etc all play an important part to what power they are capable of safely carrying.

The important thing is that the safe level is protected properly by the Fuse/trip. Understanding each application can be a nightmare and here in the UK we have a few generic cable sizes for certain situations to make things easier for the trade, EG. house builds.

Given the heat and humidity in Thailand, you are wise to use your rule of thumb and those values look about right to me for a room install, you are unlikely to get an issue with over heating/fire etc as long as the connections are sound.

Thanks for the vote of support, Sir

 

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26 minutes ago, Chappo said:

is there a standard in Thailand?

 

I'm sure there is, whether is been translated into English is another matter.

On another forum we had a BM, Australian electrical engineer, who while in Australia designed power systems no doubt to AS/NZS 3008 (the Australian/New Zealand standard for wiring). But during the 1990s he worked in Thailand designing the electrical power systems for AIS cell base stations. He would no doubt know but he didn't come across to this forum.

Meanwhile, here's a link to a cable calculator. Again, it is built around AS/NZS 3008 but it requires a few more parameters than just the required current. Parameters like length of run, maximum permissible voltage drop, cable insulation type, cable mounting, ambient temperature etc.

https://www.jcalc.net/cable-sizing-calculator-as3008

Enjoy.

 

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