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BANGKOK 16 June 2019 14:05
myjawe

Water heater installation, what could go wrong ?

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Posted (edited)
1 hour ago, bankruatsteve said:

By definition the example I gave would be a "borrowed" neutral and you are correct that it is not that case but rather a shared neutral.  In retrospect I should not have mentioned that case as it has no relevance to anything here.  As for US decision to go with split phase I have no idea why.

The split phase was Probably a historical accident.

 

However the neutral in your example is neither a borrowed (you are correct on that) nor yet is it a shared neutral (they are virtually synonymous terms), it is just the neutral for the L1 and L2 phases as they must both be present to give 240V 

 

If you watch the video I posted from about 12:34 John gives a reasonable explanation of 3 phase as 3 phase and 3 phase as 3 separate single phase supplies and the correct neutral configuration. If you ignore the L3 phase you will get the reason why the neutral is just a neutral when a 2 phase system is wired for the double voltage, and why a shared/borrowed neutral can kill you or at least make trouble shooting rather more exciting and frustrating than it needs to be.

 

UK building sites mostly have 2 Phase 110V supplies as there is some theory that a 50V shock is less dangerous (it almost certainly is not) it is the Amps that are usually more dangerous, so a 230V supply with an RCD is safer than an unprotected 110V supply, though if the 110V supply is on an isolation transformer then I don't know enough to comment.

 

 

While talking of the vagaries of the US supply is not completely relevant quite a few people have 3 phase so an understanding of the US/UK building site power is not completely useless.

Edited by sometimewoodworker

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Posted (edited)

This with the wires, borrowed lines, ELCB and whatever seems to be rather complicated. Why not simply use something like this shown here 🙂 Sorry - could not delete the 2nd picture and I tried a lot. Just imagine you need 2 water heaters. 

 

 

 

domestic-wood-fired-water-heater-250x250.jpg

domestic-wood-fired-water-heater-250x250.jpg

Edited by Beggar

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On 5/19/2019 at 6:25 PM, Crossy said:

An RCD or RCBO device will save you from death in the event you touch or otherwise contact a live wire (via a faulty appliance for example). This is particularly important in Thailand where the electrical installations can be somewhat suspect (particularly grounding).

 

 

Thank you. Maybe important but I have never seen it anywhere in a condo or hotel room. So are you sure that it's so essential ? Also never met a Thai who knows what it is.

 

 

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10 minutes ago, myjawe said:

 

Thank you. Maybe important but I have never seen it anywhere in a condo or hotel room. So are you sure that it's so essential ? Also never met a Thai who knows what it is.

 

 

Many Thai "professionals" just copy what they have seen at other Thai "professionals". They copy but don't really understand what they are doing. They did not have any education. Even worse. Some might even get aggressive if you tell them that they do something wrong. 

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10 hours ago, sometimewoodworker said:

The split phase was Probably a historical accident.

 

However the neutral in your example is neither a borrowed (you are correct on that) nor yet is it a shared neutral (they are virtually synonymous terms), it is just the neutral for the L1 and L2 phases as they must both be present to give 240V 

The example I gave was for two 120V circuits sharing a common neutral.  Neutral is not required for a 240V circuit.

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1 hour ago, bankruatsteve said:

The example I gave was for two 120V circuits sharing a common neutral.  Neutral is not required for a 240V circuit.

Now you have me completely confused. I thought you were talking about the US 2 phase supply's?

 

Where you can run circuits L1+N, L2+N and L1+L2+N - 120V, 120V and 240V. None of those configurations have a shared neutral as each could be protected by a single RCD, something that a shared neutral is most likely to trip. 

 

Also as far as I know you do require a neutral for 240V 

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13 hours ago, sometimewoodworker said:

UK building sites mostly have 2 Phase 110V supplies as there is some theory that a 50V shock is less dangerous (it almost certainly is not) it is the Amps that are usually more dangerous, so a 230V supply with an RCD is safer than an unprotected 110V supply, though if the 110V supply is on an isolation transformer then I don't know enough to comment.

The UK isolating transformer used on construction sites is a 240v single phase primary with 110V secondary that has a centre tap connected to ground. The result is a 110V supply for work and two 55v legs out of phase to ground.

 

The 55V legs to ground arrangement will lower risk of lethal electric shock, it is not theory. Voltage and current both determine how lethal a shock can be to the human body shown by ohms law I=V/R and taking in to account that skin resistance is not linear.

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2 hours ago, sometimewoodworker said:

Now you have me completely confused. I thought you were talking about the US 2 phase supply's?

 

Where you can run circuits L1+N, L2+N and L1+L2+N - 120V, 120V and 240V. None of those configurations have a shared neutral as each could be protected by a single RCD, something that a shared neutral is most likely to trip. 

 

Also as far as I know you do require a neutral for 240V 

triplex.jpg.e3fa68c86b2628858e7928349bc398e3.jpg

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2 hours ago, sometimewoodworker said:

Now you have me completely confused. I thought you were talking about the US 2 phase supply's?

 

Where you can run circuits L1+N, L2+N and L1+L2+N - 120V, 120V and 240V. None of those configurations have a shared neutral as each could be protected by a single RCD, something that a shared neutral is most likely to trip. 

 

Also as far as I know you do require a neutral for 240V 

I was referring to the US "split phase" supply.  A  single phase 240V transformer is bonded at the mid-point to ground/neutral.  It is not 2-phase.  L1 - L2 is 240V - no neutral.  There is no RCD front end protection in the states.  Not even sure that is feasible.  GFCIs are used at point of use locations (bath, outside) for RCD protection.

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Posted (edited)
36 minutes ago, bankruatsteve said:

I was referring to the US "split phase" supply.  A  single phase 240V transformer is bonded at the mid-point to ground/neutral.  It is not 2-phase.  L1 - L2 is 240V - no neutral.  There is no RCD front end protection in the states.  Not even sure that is feasible.  GFCIs are used at point of use locations (bath, outside) for RCD protection.

Certainly an RCD/GFCI/AFCI could be used to cover the 2 110V supplies though it would require rearranging the CU a little and is already used on some 110V/240V circuits 

 

It seems that neutral is usually used in the US 

Quote

Why do some 240 outlets have three prongs, while others have four?

Recently, 240 volt outlets have switched from three prong to four prong. Older, three prong outlets were designed to contain two live wires and one neutral. The additional prong on four prong outlets adds a ground, providing additional safety against electrical shock. Rewiring your appliance with a new, four wire cord (and four prong plug) will solve any compatibility issues.

 

Edited by sometimewoodworker

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5 minutes ago, sometimewoodworker said:

Certainly an RCD/GFCI/AFCI could be used to cover the 2 110V supplies though it would require rearranging the CU a little and is already used on some 110V/240V circuits 

 

It seems that neutral is usually used in the US 

 

I suppose it is possible to have front-end RCD in the states but it would take electronics versus rearrangement.  Whatever, I have never heard of that being done.  

 

It's been over 30 years since i wired a house in the states.  At that time, there was only 2 normal applications for 240V - dryer and range/oven.  To my recall, the dryer used L1, L2, and ground to a special receptacle (no neutral).  The range took all 4 but only because it also used 120V for <whatever>.  i don't recall the receptacle for that - if there was one.

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23 hours ago, Crossy said:

 

It will significantly reduce the danger of your dying from direct (grab a live wire) or indirect (faulty heater with no ground) contact, there are no guarantees in this world.

 

The classic 30-30-30 (30V, 30mA, 30ms) rule means that something like 90% of the population will survive (that's why the 25kV final-anode voltage on a CRT TV is limited to 25mA), the old, young or infirm may have a lower tolerance and die anyway 😞

 

An RCD (GFI, ELCB or whatever you want to call it) is no substitute for a decent earth/ground on an appliance (water heater) that needs it. Together they provide a very reliable safety system, each alone is more of a lottery.

 

 

I agree with you, there are no guarantees.

I read about the earth rod placings and sure wouldnt rely on ground in Thailand. As people think , just put a rod in your soil and its done.

They use inferior cheaper materials (copper plated iron), which will affect the working at one time when salty, sour ingredients in the ground corrodes the rod. They dont measure, so does it work?

The RCD's and others protect then, they also protect when there is no ground socket.

And they are there, a lot.

You can plug in a metal based device, like a metal lamp, on a socket with no ground and then it can go seriously wrong. the RCD devices then could provide your safety.

So yha im a big fan of RCD families.

How many houses are there with no ground sockets or no ground at all in Thailand?

 

Many people dont know what can happen. And then they ask , is it ok when i feel a power tickle. SOme feel them for the last time, as i read a story about Thai father and son working on pump and got electrocuted. Could have been prevented by a RCD.

 

Yes there are no guarantees with the RCD's but would rely more on them, specially in Thailand, then on ground. You can test them, but again no guarantee it will work on the time you need it. Its a mechanical device, but also the fuses.

If you dont have, it can be fatal with your first encounter.

 

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14 minutes ago, xtrnuno41 said:

You can plug in a metal based device, like a metal lamp, on a socket with no ground and then it can go seriously wrong. the RCD devices then could provide your safety.

 

But, if the lamp also had a ground (even a poor one) the RCD would open without you (or a loved one) even getting a shock. Believe me, touch a live wire, even with and RCD in circuit, you get a significant whallop, it just probably won't be for long enough to kill you.

 

Class-1 appliances (most of the metal cased things), need a ground AND an RCD to be completely safe. The two are complementary and safety is additive.

 

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4 minutes ago, Crossy said:

 

But, if the lamp also had a ground (even a poor one) the RCD would open without you (or a loved one) even getting a shock. Believe me, touch a live wire, even with and RCD in circuit, you get a significant whallop, it just probably won't be for long enough to kill you.

 

Class-1 appliances (most of the metal cased things), need a ground AND an RCD to be completely safe.

 

In my younger days i still remember touching without and with RCD.

Not i wanted to test but happened.

There is an absolute super significant difference ! You never forget. I know the difference, 

 

If your ground is that poor (how poor is poor?) and its resistance is that high, your RCD can just stay in and will shut then when you touch the lamp, then you have the lowest resistance to ground and you will feel.

Of course if resistance of ground is low enough to have more then 30mA leakage, it will shut down.  

With metal based devices, as i said, how many people know this? They go to shop , buy and plug in, no ground, it's possible to do. They dont know, layman in electricity. Just plug and play. So, i think, at least every house should have the RCD's or RCBO's or whatever.

 

 

 

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