Blowing Fuse

[farmerjo]

Hi,

When i shower(wall mounted unit) usually after 9 at night i tend to blow the 25amp screw in fuse on the main board in the house.

My setup is 15amp meter with 25mm main black cable 600 metres to house.

The main cable has 2 other main lines off it,one to shed with main fork breaker and screw in 25amp fuse which runs one light all night.

The other line goes to outside kitchen(same setup as house and shed).

When i sit outside and the wife showers all the lights go out or very dim.

The problem seems to have esculated since a new pressure pump was installed.

So running at the same time would be 4 lights,2 fans,hot water unit and pressure pump.

Local sparky suggests bigger fuse but i'm reluctant to do that.

It does get a bit scary when you see a long flash out of fuse when it blows.

Any suggestions in laymens terms on how i can fix this problem ie separate fuses,bigger meter,better wiring?

Thanks.

[Forkinhades]

Can you post some pictures, so we can see exactly what you have please.

[IMHO]

Sounds like a classic case of voltage drop. As the voltage goes down, current (amps) goes up - and that's what's taking out your fuse.

If your house has an RCD (Safety Cut), and the water heater is correctly earthed, your sparky is probably giving OK advice.

The correct solution is to fix the voltage drop problem though.

[farmerjo]

Sounds like a classic case of voltage drop. As the voltage goes down, current (amps) goes up - and that's what's taking out your fuse.

If your house has an RCD (Safety Cut), and the water heater is correctly earthed, your sparky is probably giving OK advice.

The correct solution is to fix the voltage drop problem though.

Will take some pics tomorrow

No earth on heater,just 30 amp circuit breaker switch.No rcd just.thefork stlye main breaker..

How would you fix the voltage drop.

I have a little portable transformer i suppose you would call it but thats only hooked in for the bore pump.

When we start the bore pump we turn the dial to say 5 to start then when have water turn back till ringing noise stops.

[bankruatsteve]

Suggest you get your local PEA (or whatever) involved. The grid and the 600m to your CU might be the limiting factors for your voltage problems. IE: no matter what you do, you might need external (PEA) assistance.

[Crossy]

How many Watts is the water heater, the new water pump?

600m of 25mm² copper has an out and back resistance of about 0.8 Ohms.

At 30A you'll be dropping 24V just on the cable resistance which is definitely not helping. Of course the supply at the meter may be low when the shower is operating making matters worse.

You say you have a 15A meter, is that a 5/15 or a 15/45?

Do you have a multimeter (not expensive anyway)?

[farmerjo]

Sorry for the delay,some pics of basic setup.

The cable is not copper,heater 6000w,pump 150w.

Yes i have a multimeter,you would have to tell me what settings,only use to test battery voltage.

Thanks

[Forkinhades]

Quick solution change the heater to one that is 3000W.

[Crossy]

OK, let's do some sums:-

6000W water heater

200W for the pump

200W for everything else

6400W @ 220V that's 29A (wonder why the 25A fuse is unhappy).

That 25mm² aluminium cable is roughly equivalent to 16mm² copper, so you'll be dropping close to 41V on the cable run (could be why the lights get a bit dim).

Can you measure:-

AC volts at the meter (no load) should be around 220V

AC volts at the knife switch (no load)

Same readings with the shower operating.

You should really provide a ground to the shower and install some form of earth leakage protection. Do you want to spend some cash upgrading the system for safety??

The good news is that your meter will be OK with a bigger fuse, but those cables from the knife switch look a bit small.

NOTE - The above calculations are very approximate as the current drawn by your heater will decrease as the voltage decreases (it's a simple resistive load). In fact your 6000W heater will only be providing about 4000W of heating, so Forky's suggestion of a 3500W heater won't actually deliver less hot water.

But do make the above checks.

[farmerjo]

OK, let's do some sums:-

6000W water heater

200W for the pump

200W for everything else

6400W @ 220V that's 29A (wonder why the 25A fuse is unhappy).

That 25mm² aluminium cable is roughly equivalent to 16mm² copper, so you'll be dropping close to 41V on the cable run (could be why the lights get a bit dim).

Can you measure:-

AC volts at the meter (no load) should be around 220V

AC volts at the knife switch (no load)

Same readings with the shower operating.

You should really provide a ground to the shower and install some form of earth leakage protection. Do you want to spend some cash upgrading the system for safety??

The good news is that your meter will be OK with a bigger fuse, but those cables from the knife switch look a bit small.

NOTE - The above calculations are very approximate as the current drawn by your heater will decrease as the voltage decreases (it's a simple resistive load). In fact your 6000W heater will only be providing about 4000W of heating, so Forky's suggestion of a 3500W heater won't actually deliver less hot water.

But do make the above checks.

Put the multi meter into a plug outlet near bathroom,normal load 226 volts.

Turn on water heater and it goes down to 176 volts.

Thats as close as i get to playing with power

Had another look and the shower unit is grounded with a copper rod outside.

Happy to spend the money to make it safer.

So will a 3500w heater still be alright or will have to upgrade other stuff.

Never really had this problem for previous 9 years and the meter was 800 metres away but there's alot more people living in the area now.

Thankyou for all your help so far. .

[Crossy]

Good to hear the heater is grounded

Replacing the heater with a 3500 Watt unit will take your current draw down to 17A. The volt drop would then be about 25V.

If you want to retain the 6000W heater you need to do something with your incoming cable, doubling up on the 25mm² with another 25mm² or 35mm² (or even bigger) cable would be the way to go. Aluminium cable is not expensive, talk to your sparks.

To solve your immediate issue you could replace the fuse with a 30A RCBO like the one in the photo that will solve the fuse issue (and if it does open you just switch it back on), it also adds significant safety to the entire installation by protecting from electric shock (earth leakage breaker).

The photo is a Panasonic unit, Haco do similar, the vital thing to look for is the "Test" button, which is a dead give-away that the unit is an earth leakage breaker, 500 Baht from HomePro last week. Haco unit is SB-E32 on this page http://www.hacothailand.com/product-engshow.php?Page=2&setype=4&setype2=&txtsearch=

EDIT I see a lot of cables vanishing behind that plate with the fuse and knife switch, are they all connected to that one supply?

If they are, scary but a potential easy upgrade to a proper breaker box and an order of magnitude improvement in safety from shock and fire hazards.

[farmerjo]

Thanks Crossy,

For now i will leave cable size until i find out if the pea power will come closer or not in the near future.

So next week i'll get a 3500w heater,a fuse(30) as shown in the photo and could you post a photo of what the box looks like to tidy up all the wires going in.

Regards and many thanks

[KhunBENQ]

Sharp WH 751, 6 kW as already stated.

On full power this could blow the fuse alone.

We have two small 3.5 kW heaters and there are rare "Isan winter" times when the water gets lukewarm only,

Half of the year they are off anyway (water from the plastic tank is warm enough).

The compromise would be a 4.5 kW model, plenty to choose from.

BTW: also invest in modernizing your electricity connection with a magnetic fuse.

As an additional precaution I would replace the circuit breaker for the heater with a RCCB (residual current circuit breaker).

Costs about 400 Baht and gives extra security (not only depending on the "ELB" function of the heater).

See here for a picture (Safe T-Cut brand might be more expensive):

http://www.thaivisa.com/forum/topic/792985-omg-no-earthing/#entry8955903

[Crossy]

Rather than shelling on a new heater, just run the existing one at 1/2 power (turn down the dial)

[IMHO]

Rather than shelling on a new heater, just run the existing one at 1/2 power (turn down the dial)

I was just about to say that

[farmerjo]

Will get a new heater anyway,think 9 odd years out of it is ok.

One thing i did find when testing was the maximun voltage was 176 on full but didn't say that it also fluctuated alot lower on the meter.

Doing the other test into plug outlet voltage maintained consistent,later did a test with the microwave and that also stayed consistant(approx 212 volts).

One more question,when the local fits the new switch breaker to replace the fuse type,does he require any additional wiring?or is it straight swap.

The reason i ask and i ask cause i have no idea is out the back on the wall is a test breaker for the bore pump,but when it is in the on postion running or not thru transformer and i press the red test button,nothing happens,should that not flick it to the off position when pressed?

Thanks for everyone bearing with me.

[Jdietz]

The reason i ask and i ask cause i have no idea is out the back on the wall is a test breaker for the bore pump,but when it is in the on postion running or not thru transformer and i press the red test button,nothing happens,should that not flick it to the off position when pressed?

That's because half the wires are missing. (it needs neutral fed through as well)

[Forkinhades]

New unit is a straight swap

[Crossy]

You can't just swap the fuse for the breaker as noted by Jdietz as the breaker requires a neutral feed so sparky is going to need to do a little re-wiring. That unit on your bore pump is exactly what you need, just wire it correctly and it will work fine.

1. Remove the wires coming out of the knife switch (mark live and neutral)
2. Two wires out of the knife switch into the Line connections of the new breaker.
3. Neutral out of the new breaker to the neutral removed from the knife switch
4. Remove the fuse holder from the board.
5. Lose the wire that used to connect the fuse to the knife
6. The other wire coming from the fuse now goes to the live out of the new breaker

I'll draw a diagram, gimme a few mins.

I would make your new wires 6mm²

[Forkinhades]

^ sorry did not look properly.

Yes Crossy is correct

[Crossy]

The diagram:-

Easy

[bankruatsteve]

Well, that is the easy way. But you could also get a 4 circuit D-Box CU (for example) with a 40a RCBO main breaker and then split up your loads to 4 circuits (MCB). I think that could be done for B3000 or less. (can't remember) You could then size the circuit breakers to the wires you have in place.

Again, your voltage drop issues might need a session with the PEA to get more grid supply to your area.

[Crossy]

Absolutely Steve ^^^, my current concern was to get him safe and away from constantly blowing fuses at minimum cost / minimum time.

We don't know (but can guess) what's behind that board with the knife and fuse on it, care is required.

[farmerjo]

Thanks again guys for your precious time.

Sort of have been reluctant to approach the pea as basically they told us at the start the run was to long.

They only let us do it cause i put up good quality timber poles(now cement) and they probably thought being farang i needed more space than village life.

As i said in the old days i only needed enough power for a light,fan,tv,fridge,now its sort of tenfold.

I doubt i could do a deal for them to supply their line on my poles and if i was to pay them to extend to my place,for sure i would have about 15 neighbours in 12 months.That i do not wish for.600 metres away is fine.

Back on topic,will look for a compentant local who can read Crossy's drawring

[bankruatsteve]

I encourage you to not be shy with the PEA. I think you mentioned that everything was OK until more people started building in your area. (?) Give them a chance to advise. You might be surprised with the result.

[ksamuiguy]

99% the fuse is in the neutral line. Common older practice here in Thailand and a good way to get a nasty shock.

install a proper breaker in place of the knife switch, get rid of the fuse it is dangerous to have multiple disconnect devices in the same line.

[Crossy]

99% the fuse is in the neutral line. Common older practice here in Thailand and a good way to get a nasty shock.

install a proper breaker in place of the knife switch, get rid of the fuse it is dangerous to have multiple disconnect devices in the same line.

Replacing the fuse with a double pole RCBO as suggested above will mitigate the fused neutral issue

But you need to cite your reasoning behind the statement "it is dangerous to have multiple disconnect devices in the same line". Many codes require a "single point of isolation" which is then followed by the regular consumer unit with a front end breaker and individual MCBs. I make that three disconnect devices in series. Exactly why is that dangerous?

[Gonsalviz]

Suggest you get your local PEA (or whatever) involved. The grid and the 600m to your CU might be the limiting factors for your voltage problems. IE: no matter what you do, you might need external (PEA) assistance.

Good luck with that. The local PEA here will give you advice but it is usually wrong.

A cheap Volt meter will tell you. 190-250 volts will work. If that is ok, I suspect that the fuse is not big enough to handle the pump and the heater but maybe the wiring isn't either so a bigger fuse may not be the answer.

[Gonsalviz]

Rather than shelling on a new heater, just run the existing one at 1/2 power (turn down the dial)

The heater still draws the same current, just not for so long.

It is looking like the MILs house panel. The whole house is run off the same fuse. The knife switch has 2 60 amp fuses inside L & N and puny wires running off of it. Looks like a wiring upgrade is due.

Should not be too difficult unless it is covered.

The aluminum wiring from the meter to the house is normal Thai style. Copper should be inside. As long as the voltage is normal inside the house, the aluminum cable should be ok. Aluminum cable is known to corrode and cause high resistance if it is under heavy loads.

As was mentioned before, the wiring from the knife switch looks a bit thin. PEA bypassed a 100 amp breaker at my house with wiring about that size. Not cool.

If the wiring to the heater or the pump is not getting warm a fuse upgrade maybe needed but a check to see if the wiring is of correct size should still be in order.

[Gonsalviz]

99% the fuse is in the neutral line. Common older practice here in Thailand and a good way to get a nasty shock.

install a proper breaker in place of the knife switch, get rid of the fuse it is dangerous to have multiple disconnect devices in the same line.

Replacing the fuse with a double pole RCBO as suggested above will mitigate the fused neutral issue

But you need to cite your reasoning behind the statement "it is dangerous to have multiple disconnect devices in the same line". Many codes require a "single point of isolation" which is then followed by the regular consumer unit with a front end breaker and individual MCBs. I make that three disconnect devices in series. Exactly why is that dangerous?

Because the entire house is run off of 1 25 amp fuse. This was probably ok with a few lights and a refrigerator but with the addition of a water heater and water pump and who knows what else, it is no longer adequate.

You can't just keep drawing more amperage with out upgrading.