Water Heater And Fuse Size

[nong38]

Last year I bought a water heaterfor my bath, I was told I needed 8000amp model by the man who would fit the system for me so thats what I got, for 9 months it worked fine then a couple of months ago no hot water. As it was under guarantee the company sent out an engineer (?) to look at it. He got it working some how but after calling for support earlier he said I needed to replace the 30 amp fuse box with a larger one 40+. Later that night the hot water heater failed again.

Has anybody any thoughts? I am no electrician but if it worked fine for 9 months on a 30 amp fuse I would have thought that was fine and the fault lays elsewhere and am not sure that installing 45 amp fuses is going to change the situation. Thanks for any advice, the engineer (?) comes back on monday.

[ThaidDown]

If you have an 8000 Watt heater then it will be drawing around 35 Amps on full load.

If you have a 30A fuse (as distinct from a circuit breaker) so over time the fuse could well blow as you are overloading it.

Also the cable supplying the heater should be 10mm with 45 amp fuse or 40/50 amp breaker.

[wayned]

The other problem is if it is operating at full load and the input voltage drops, brownout, the current requirement will increase: A = W/V. Of course we never have low power in NS Province, Right!

[nong38]

If you have an 8000 Watt heater then it will be drawing around 35 Amps on full load.

If you have a 30A fuse (as distinct from a circuit breaker) so over time the fuse could well blow as you are overloading it.

Also the cable supplying the heater should be 10mm with 45 amp fuse or 40/50 amp breaker.

I think what I may have is a cicuit breaker, a small switch which says 30A on it. So when the engineer comes on monday I sould let him install a larger circuit breaker and fuse in the fuse box, then hopefully things will be fine. The cable looks fairly thick so I think that is ok.

Thanks for the info.

[nong38]

The other problem is if it is operating at full load and the input voltage drops, brownout, the current requirement will increase: A = W/V. Of course we never have low power in NS Province, Right!

No never, right, only at night when we are all away with the fairies and we know nothing about it!

[Crossy]

The other problem is if it is operating at full load and the input voltage drops, brownout, the current requirement will increase: A = W/V. Of course we never have low power in NS Province, Right!

No never, right, only at night when we are all away with the fairies and we know nothing about it!

A heater is a purely resistive load, if the voltage goes down so do the amps (and the power goes down in an inverse square).

To our OP.

Just sticking a bigger fuse/breaker in is a route to potential disaster, and fitting a bigger incoming breaker without upgrading your supply could get you in hot water with the supply authority.

The cable 'looking fairly thick' is no way a satisfactory test for something that if you get it wrong could burn your house down. Check the cable itself, it will have a size in mm² marked on it, let us know what it says.

An 8kW heater will draw about 36A at 220V so a 40A fuse/breaker is correct, the cable should be a minimum of 6mm² Although you'll be ok on 4mm² with a 30A breaker if you don't take 30 minute showers.

And yes, if it's been working for months on the 30A why should it stop now? Could be an iffy twisted join somewhere fizzing away

EDIT Do you know what is failing? Is it the heater or is the breaker tripping?

[nong38]

The other problem is if it is operating at full load and the input voltage drops, brownout, the current requirement will increase: A = W/V. Of course we never have low power in NS Province, Right!

No never, right, only at night when we are all away with the fairies and we know nothing about it!

A heater is a purely resistive load, if the voltage goes down so do the amps (and the power goes down in an inverse square).

To our OP.

Just sticking a bigger fuse/breaker in is a route to potential disaster, and fitting a bigger incoming breaker without upgrading your supply could get you in hot water with the supply authority.

The cable 'looking fairly thick' is no way a satisfactory test for something that if you get it wrong could burn your house down. Check the cable itself, it will have a size in mm² marked on it, let us know what it says.

An 8kW heater will draw about 36A at 220V so a 40A fuse/breaker is correct, the cable should be a minimum of 6mm² Although you'll be ok on 4mm² with a 30A breaker if you don't take 30 minute showers.

And yes, if it's been working for months on the 30A why should it stop now? Could be an iffy twisted join somewhere fizzing away

EDIT Do you know what is failing? Is it the heater or is the breaker tripping?

The cable looks like 8mm from what I can see, the water heater is for a bath not a shower.

[Crossy]

8mm² is not a standard size, what do the cable markings say? If you're not sure what you are looking at please post a photo.

An 8kW heater is an on-demand heater, does it take 30 mins to fill the bath? If not it will probably be ok on 4mm² with a 30A breaker.

If a 30A breaker is opening then the draw is too large for 4mm² cable.

[nong38]

8mm² is not a standard size, what do the cable markings say? If you're not sure what you are looking at please post a photo.

An 8kW heater is an on-demand heater, does it take 30 mins to fill the bath? If not it will probably be ok on 4mm² with a 30A breaker.

If a 30A breaker is opening then the draw is too large for 4mm² cable.

Last night I waslooking with a torch, I have had another loo today with amagnifyling glass, the cleats are not helpful, but I saw 2x2.5 and then what looked like SO.MM 300v.

The circuit breaker has been breaking but not lately, as there has not been any hot water, tomorrow the engineer from the company waits, now I am informed by wife, until the local electrician comes to put in a breaker higher than 30W, I will get the wife to ask him if the cable is up to the job, it looks to be sturdy to my eye.

The company that makes the heater have said that it installing the new circuit breakers, one near the water heater and another in the fuse box from what I can gather, then they will replace the water heater.

[bankruatsteve]

8mm² is not a standard size, what do the cable markings say? If you're not sure what you are looking at please post a photo.

An 8kW heater is an on-demand heater, does it take 30 mins to fill the bath? If not it will probably be ok on 4mm² with a 30A breaker.

If a 30A breaker is opening then the draw is too large for 4mm² cable.

Last night I waslooking with a torch, I have had another loo today with amagnifyling glass, the cleats are not helpful, but I saw 2x2.5 and then what looked like SO.MM 300v.

The circuit breaker has been breaking but not lately, as there has not been any hot water, tomorrow the engineer from the company waits, now I am informed by wife, until the local electrician comes to put in a breaker higher than 30W, I will get the wife to ask him if the cable is up to the job, it looks to be sturdy to my eye.

The company that makes the heater have said that it installing the new circuit breakers, one near the water heater and another in the fuse box from what I can gather, then they will replace the water heater.

Ouch. 2.5mm2 is rated for about 24a so you may have fried it at some point in the run. Possibly not - but you definitely need the larger cable. Crossy will set you straight.

[lopburi3]

As said that is what is normally used for shower on demand heaters which are normally less than half the wattage of your heater. You need a much larger wire as was pointed out earlier. Using for tub is also much longer usage than most people who use showers and turn off flow while washing so can imagine those wires were getting red hot - luckily must not be anything in there path flammable or you could have serious issues.

[nong38]

Ok so tomorrow I need to get the electrician to re wire the whole lot then if I am seeing 2x 2.5mm is correct, I will get him to check it out tomorrow, thanks for your helps chaps, a cold/warm shower today is ok!

[Crossy]

2 Core VAF @ 2.5mm² is rated at 21A in air http://www.bangkokcable.com/catalog/BCC_CATALOG/VAF2EN.HTML 35A continuous is going to make it very hot, I'll bet a crappy taped joint has given up the battle somewhere.

If you are going to have it re-wired the minimum size for an 8kW heater is 6mm² and a 40A breaker (since you're filling a tub I wouldn't skimp and use 4mm² which would be ok for a shower). Make sure your man runs it in one piece from the heater to the board.

The fact that you currently have 2x2.5mm² also suggests that your heater is not grounded, this is a potentially lethal situation. Again if you're re-wiring get the heater properly grounded at the same time.

Do you have any form of earth leakage protection (Safe-T-Cut)? If you don't know please post a photo of your distribution board.

What is the rating of your meter? It will have markings on the faceplate, common ones are 5/15, 15/45, 30/100.

[nong38]

2 Core VAF @ 2.5mm² is rated at 21A in air http://www.bangkokcable.com/catalog/BCC_CATALOG/VAF2EN.HTML 35A continuous is going to make it very hot, I'll bet a crappy taped joint has given up the battle somewhere.

If you are going to have it re-wired the minimum size for an 8kW heater is 6mm² and a 40A breaker (since you're filling a tub I wouldn't skimp and use 4mm² which would be ok for a shower). Make sure your man runs it in one piece from the heater to the board.

The fact that you currently have 2x2.5mm² also suggests that your heater is not grounded, this is a potentially lethal situation. Again if you're re-wiring get the heater properly grounded at the same time.

Do you have any form of earth leakage protection (Safe-T-Cut)? If you don't know please post a photo of your distribution board.

What is the rating of your meter? It will have markings on the faceplate, common ones are 5/15, 15/45, 30/100.

THank you for your comments and I am not being very helpful. I suspect that its not earthed. although there is a green cable coming of the water heater and going around the side of the circuit breaker and continuing on with wiries. The rating of my meter? Sorry I dont understand the meter, I see nothing with 5/15, 15/45, 30/100 I assumed I should look at the box with all the switches in it but there is nothing like what you describing. I can take pictures, I have a camera but have no idea how to post them on TV, I could e mail them to you if you send me a PM with your email address, sorry I am no technical wizard.

I await the electrician and will get the wife to ask him about Safe-T-Cut, earthing, rewirinf with 6mm abd to use 40A breakers.

The bath is a large one and it does take about 30 ins to fill or more depending on water pressure.

Edited March 18, 2013 by nong38

[bankruatsteve]

The meter is on the electric pole. If you follow the wires from your house to the pole, you should be able to see the meter rating. ie: 5/15 or 15/45

The box with the switches in it is your "distribution board" aka "consumer unit (CU)" aka "switch box". The main breaker is usually the larger one on the far left side or by itself at the top. That is your maximum load. You might reply with the number on that breaker (ie: 30 or 40 or 60 or thereabouts). If you see green wires going into the box or if you take the panel off and see green wires inside, chances are that you have grounding (and possibly even proper). If the green wire from the heater is going somewhere (versus just hanging disconnected), that is a good sign.

Edited March 18, 2013 by bankruatsteve

[nong38]

The meter is on the electric pole. If you follow the wires from your house to the pole, you should be able to see the meter rating. ie: 5/15 or 15/45

The box with the switches in it is your "distribution board" aka "consumer unit (CU)" aka "switch box". The main breaker is usually the larger one on the far left side or by itself at the top. That is your maximum load. You might reply with the number on that breaker (ie: 30 or 40 or 60 or thereabouts). If you see green wires going into the box or if you take the panel off and see green wires inside, chances are that you have grounding (and possibly even proper). If the green wire from the heater is going somewhere (versus just hanging disconnected), that is a good sign.

The meter outside says 15/45. The distribution box, has no figures that give me a clue as to the rating, the switch on the left is a double switch no ratings that look like 30/40/60.

[bankruatsteve]

OK. I think Crossy was just trying to make sure you are good for the 40a breaker and it seems you are. So, get it re-wired with the 6mm2 and you should be good for a hot bath soon after.

[nong38]

OK. I think Crossy was just trying to make sure you are good for the 40a breaker and it seems you are. So, get it re-wired with the 6mm2 and you should be good for a hot bath soon after.

Ok thanks for all the help, still waiting for the electrician

[Crossy]

OK. I think Crossy was just trying to make sure you are good for the 40a breaker and it seems you are. So, get it re-wired with the 6mm2 and you should be good for a hot bath soon after.

Ok thanks for all the help, still waiting for the electrician

Yup, sounds like he's good to go

[nong38]

OK the electrians finally turned up at 1330! I showed them the 2x2.5mm and said I wanted 6mm, I wanted it earthed and a 40 braker. They talked the heater company and decided 4mm would be fine, so I let them get on with it. They have just left, I have hot water and everything seems to be working fine, but then it did the last time for a few hours! So hopefully this time it will be ok, they did another little job for me as well, a team of 3 ( one had the audacity to wear a Chelsea shirt) and the bill was 1600 bts, the labour was 900 as I guess it and dont read Thai.

So, thank you all who have contributed, its at times like this when the value of Thai visa shines, anyone want to pop round for bath let me know!

[Crossy]

Oh well, let's bow to the superior knowledge of a Thai sparks (I hope your fire insurance is paid).

Seriously, 2x4mm² VAF (which is probably what you have) is rated at 29A in air. http://www.bangkokcable.com/catalog/BCC_CATALOG/VAF2EN.HTML

At 36A it's going to get warm (but not as warm as the 2.5mm² did). In reality cables have a pretty conservative rating and can carry a 50% overload for an hour at least, it won't start a fire but you really should not design a system with a 24% overload from the get go.

This assumes that the heater is the only load on that circuit, if you have other loads then all bets are off!

[Sophon]

What would the recommended wire and breaker fuse size be for a 5,100 watt shower water heater?

Sophon

[Crossy]

What would the recommended wire and breaker fuse size be for a 5,100 watt shower water heater?

Sophon

4mm² cable and a 30A breaker.

You could (just) get away with it on a 20A breaker and 2.5mm² cable if it's already installed, heater will pull 23A.

[Sophon]

What would the recommended wire and breaker fuse size be for a 5,100 watt shower water heater?

Sophon

4mm² cable and a 30A breaker.

You could (just) get away with it on a 20A breaker and 2.5mm² cable if it's already installed, heater will pull 23A.

Thanks for the information. No, it's not already installed, just want to make sure that the new house we are building get the correct wiring.

Sophon

[bankruatsteve]

OK the electrians finally turned up at 1330! I showed them the 2x2.5mm and said I wanted 6mm, I wanted it earthed and a 40 braker. They talked the heater company and decided 4mm would be fine, so I let them get on with it. They have just left, I have hot water and everything seems to be working fine, but then it did the last time for a few hours! So hopefully this time it will be ok, they did another little job for me as well, a team of 3 ( one had the audacity to wear a Chelsea shirt) and the bill was 1600 bts, the labour was 900 as I guess it and dont read Thai.

So, thank you all who have contributed, its at times like this when the value of Thai visa shines, anyone want to pop round for bath let me know!

Just wondering if they pulled the 2.5 cable and see any damage? The issues you had with the water heater now OK? Who did the initial install? Just some things somebody reading this might help.

[wayned]

OK the electrians finally turned up at 1330! I showed them the 2x2.5mm and said I wanted 6mm, I wanted it earthed and a 40 braker. They talked the heater company and decided 4mm would be fine, so I let them get on with it. They have just left, I have hot water and everything seems to be working fine, but then it did the last time for a few hours! So hopefully this time it will be ok, they did another little job for me as well, a team of 3 ( one had the audacity to wear a Chelsea shirt) and the bill was 1600 bts, the labour was 900 as I guess it and dont read Thai.

So, thank you all who have contributed, its at times like this when the value of Thai visa shines, anyone want to pop round for bath let me know!

For that price it sounds like he just installed a normal 40 amp breaker. Does the heater have a safety cutout on it? If the heater does not have one built in I think that you should replace the normal breaker with an RCBO.

[nong38]

OK the electrians finally turned up at 1330! I showed them the 2x2.5mm and said I wanted 6mm, I wanted it earthed and a 40 braker. They talked the heater company and decided 4mm would be fine, so I let them get on with it. They have just left, I have hot water and everything seems to be working fine, but then it did the last time for a few hours! So hopefully this time it will be ok, they did another little job for me as well, a team of 3 ( one had the audacity to wear a Chelsea shirt) and the bill was 1600 bts, the labour was 900 as I guess it and dont read Thai.

So, thank you all who have contributed, its at times like this when the value of Thai visa shines, anyone want to pop round for bath let me know!

For that price it sounds like he just installed a normal 40 amp breaker. Does the heater have a safety cutout on it? If the heater does not have one built in I think that you should replace the normal breaker with an RCBO.

The initial installation was by a "friend" it worked fine for about 9 months, 3 of which I was in the UK. I understand the water heater unit has safety cut out. The bath seems to be working ok, so far. I cant argue very well with Thais, it may be that they will have to come back for another job and up rate the cabling but I am thinking I will not be having really hot baths so I think it will be ok and yes the house is insured!

[Ticketmaster]

OK the electrians finally turned up at 1330! I showed them the 2x2.5mm and said I wanted 6mm, I wanted it earthed and a 40 braker. They talked the heater company and decided 4mm would be fine, so I let them get on with it. They have just left, I have hot water and everything seems to be working fine, but then it did the last time for a few hours! So hopefully this time it will be ok, they did another little job for me as well, a team of 3 ( one had the audacity to wear a Chelsea shirt) and the bill was 1600 bts, the labour was 900 as I guess it and dont read Thai.

So, thank you all who have contributed, its at times like this when the value of Thai visa shines, anyone want to pop round for bath let me know!

Why is it that a customer tells a Thai "electrician" what he wants, then the electrician just ignores the customer and goes his own way? This happens all the time to a friend of mine who is remodeling. I am building a house and I DO NOT tolerate such nonsense. I mean, if the customer asks for and is willing to pay for 6mm, <deleted> is it with the Thai "electrician" insisting on using something smaller? Is it harder to bend? Is the Thai "electrician" simply too lazy to work with stiffer wire? Is that it?

Buy the way, Nong38, if you come back here, I'm just curious, when they pulled the 2.5mm wire out, was it fried anywhere?

Edited July 8, 2013 by Ticketmaster

[doglover]

Why is it that a customer tells a Thai "electrician" what he wants, then the electrician just ignores the customer and goes his own way?

Because he believes that he really is an electrician and that his knowledge is superior to that of his customer. Frustrating indeed.

If it wasn't so hot up in the attic I'd climb up there and do it myself.

[212traders]

Just few days ago, I have the similar problem. The water heater suddenly stopped working. My water heater is Stiebel Eltron AQ 35E. It's rated 230V at 3.5kW. The electrical cable is 4mm. I opened the heater and measured the power. It has power all the way into the heater. But the heater just won't turn on.

Any ideas?