main fuse blowing

fishdog

I wired a large house a few years ago that has recently developed a problem. It keeps blowing main fuses (63A). Because of the size of the house and the type of owner (he does not ever turn anything off!) I applied for and got a 16KVA single phase supply. The fact that he hates to turn things off are shown clearly by his bills, they are in the region of €600 to €700 with a dual tariff meter.

The house with one notable exception has no single large load, no electric shower, cooker is gas, many of the lights are energy efficient etc. The notable exception is he has a geothermal heat pump. This draws about 20 amps when it is up and running. However it appears to have a huge start up current.

I think that this sudden surge of start up current when the rest of the house is drawing 20 amps or so is enough to blow the main fuse. What I want to know is how big is the ESB fuse for a 16KVA supply? I think the standard size is 80A and I am hoping that the 16KVA supply has a larger main fuse so that I can increase the size of the main fuse on my size ensuring that I have the correct discrimination. I was considering installing a unit that contains two main switch fuses, like the type that are used when installing storage heating. One 63A fuse can supply the sub-board that supplies the heat pump, the other supplies everything else. The problem is the ESB supply first goes to a 63A switch fuse and then to a generator change over switch.

RoundyMooney

Should be 100A.

Double check by looking at the side of the fuse carrier at the metering point, it will be either 60/80A, or more likely 100.

cast_iron

fishdog wrote: »

II was considering installing a unit that contains two main switch fuses, like the type that are used when installing storage heating. One 63A fuse can supply the sub-board that supplies the heat pump, the other supplies everything else. The problem is the ESB supply first goes to a 63A switch fuse and then to a generator change over switch.

Is it essential to have the heat pump running on the generator (when the need arises)? If not, your idea could be the way to go. Could the two main fuses not go after the changeover switch?
Is the generator rated for the entire house load and the large start up current together?
Just how large is the start up current?

fishdog

Is it essential to have the heat pump running on the generator

No, it only takes 20A and it is the only large load in the house.

Could the two main fuses not go after the changeover switch?

Yes, but I have a main switch fuse before the change over switch. This is the fuse that keeps blowing.

Is the generator rated for the entire house load and the large start up current together?

The generator is only 10KVA. If the ESB supply is not present it by manually switching the generator change over switch the generator will supply the whole house. Load shedding is necessary. The generator does not "sync" with the ESB network.

When the generator is running the return of the ESB supply will be indicated by a din rail mounted neon indicator light fed from the fuse that is giving me all of this trouble!

Just how large is the start up current?

I dont know! Although the full load current is 20A of the entire geothermal unit I dont know what part of this is the compressor. Typically the start up current of a motor is 6 to 8 times the full load current, but only for a fraction of a second.

Hoagy

I presume you're using a motor rated 63amp fuse?

fishdog

I presume you're using a motor rated 63amp fuse?

No, just the standard type. I did consider this, I was just nervous that the ESB fuse would fail before a 63A motor rated fuse. When I installed the heat pump all was well for about 3 years on the standard 63A switch fuse, so I thought "if it aint broken, dont fix it!".


I did the job a few years ago. Initially there was no heat pump going in at all, there was an oil fired boiler instead. Despite the fact that at the time I was applying for the supply there had no single large load at all I knew that the job would grow and grow, that is why I got a 16KVA supply installed. Just as well!


This problem is only recent. I think it is only a problem now because every few weeks the owner buys another plasma or computer or something and just has it on 24/7!! For example over a period of about 3 years he has gone from 1 fridge to 4! They all add up.

DublinDilbert

fishdog wrote: »

No, just the standard type. I did consider this, I was just nervous that the ESB fuse would fail before a 63A motor rated fuse. When I installed the heat pump all was well for about 3 years on the standard 63A switch fuse, so I thought "if it aint broken, dont fix it!".


I did the job a few years ago. Initially there was no heat pump going in at all, there was an oil fired boiler instead. Despite the fact that at the time I was applying for the supply there had no single large load at all I knew that the job would grow and grow, that is why I got a 16KVA supply installed. Just as well!


This problem is only recent. I think it is only a problem now because every few weeks the owner buys another plasma or computer or something and just has it on 24/7!! For example over a period of about 3 years he has gone from 1 fridge to 4! They all add up.

It sounds like the single phase heat pump motor is probably the main cause of it, as this current will be combined with say the 20A or so the house is drawing anyway. You'd have to wonder how efficient a big single phase motor like that is ( i would guess not very efficient at all)....

Is there anyway you could measure the peak starting current when the heat pump motor is starting up with a clamp meter? this would give you a better idea of what your dealing with.

Is there not some ESB ruling on starting small / medium sized single phase motors?? eg a max size motor? ( from memory i thought there was).

Is there anyway of soft starting this motor, as its a compressor it shouldn't require too much torque on starting.

Hoagy

fishdog wrote: »

No, just the standard type. I did consider this, I was just nervous that the ESB fuse would fail before a 63A motor rated fuse.

Well if it does, it does. It would be one way of getting the Board to put the largest possible fuse into the cutout.

It's not your fault the client has installed a disruptive load.

fishdog

It sounds like the single phase heat pump motor is probably the main cause of it,

I am 100% sure it is

You'd have to wonder how efficient a big single phase motor like that is ( i would guess not very efficient at all)....

Im not sure how efficient the motor is, around 80% I guess. The point is the overall effiency of the geothermal heat pump is over 400%

Is there anyway you could measure the peak starting current when the heat pump motor is starting up with a clamp meter?

I have a "Fluke" grip on ammeter. It is good, but not that good! The start up current only lasts for a fraction of a second. Perhaps there is a fancy bit of kit that can measure this, but I dont have it.

Is there anyway of soft starting this motor, as its a compressor it shouldn't require too much torque on starting

Not without redesigning the whole unit. This is a complicated piece of kit. It is designed and built in Norway. I simply give it a supply and connect sevral auxilleries to make it operate. It is designed for domestic single phase use. I think with any other person it would not be an issue, it is just that this guy has so much other stuff turned on all the time.

RoundyMooney

fishdog wrote: »

No, just the standard type. I did consider this, I was just nervous that the ESB fuse would fail before a 63A motor rated fuse. When I installed the heat pump all was well for about 3 years on the standard 63A switch fuse, so I thought "if it aint broken, dont fix it!".

Even with a 60A main fuse, chances are the Neozed will go first.

fishdog wrote: »

I did the job a few years ago. Initially there was no heat pump going in at all, there was an oil fired boiler instead. Despite the fact that at the time I was applying for the supply there had no single large load at all I knew that the job would grow and grow, that is why I got a 16KVA supply installed. Just as well!

Like I say, you're probably looking at a 100A main fuse so.

fishdog wrote: »

This problem is only recent. I think it is only a problem now because every few weeks the owner buys another plasma or computer or something and just has it on 24/7!! For example over a period of about 3 years he has gone from 1 fridge to 4! They all add up.

Hit him in the pocket, so. It's the only way to counteract such irresponsible behaviour. Have him request an upgrade to a 3 phase supply. New consumer unit etc., might make him think twice about his wasteful attitude.

Hoagy wrote: »

Well if it does, it does. It would be one way of getting the Board to put the largest possible fuse into the cutout.

It's not your fault the client has installed a disruptive load.

It's not the ESB's fault either. Advocating overload to the point where the incoming main fuse goes is not the best way forward. The fact that the clients own main fuse is now blowing repeatedly is enough incentive for him to modify his behaviour or have his supply upgraded again (which depending on his location and his current supply arrangement, could get very expensive very quickly).

fishdog wrote: »

I am 100% sure it is

If he had an electric shower his problem would have manifested long before now

ThOnda

The motors can "ask" more than 2 time higher current at start-up and it gets worse during the time - dust, bearing wear... So the fuse for it should me with characteristics for asynchronous motors "aM". (Yes, characteristic aM MUST be printed in green colour.)

Higher consumption of electricity is the second factor. The fuse works on thermal basis. The more current goes through fuse, it heats itself more. And if it heats itself above some limit, it'll melt the conductor and break the circuit.

When the average (or maybe stable) consumption was lower, the fuse was cooler and was able to survive overcurrent when the engine started. Now, when the regular consumption is higher, there is not enough space left for the fuse. And it reacts. You can't blame the fuse.

However, you shouldn't use fuse with "aM" characteristics for general protection. And ESB won't allow you to do so.

So first, increasing rated current of the fuse should solve the problem. The second - higher consumption of the electricity has it's limits. Just check if wiring and other means of protection are still suitable for such currents.

fishdog

RoundyMooney

Should be 100A.

Thats what I thought, but how can I check?

ThOnda

The motors can "ask" more than 2 time higher current at start-up and it gets worse during the time - dust, bearing wear

Fair point, I had not thought of that. I think that although this is correct, the bigger problem that I have is that the overall load (not inc. the heat pump)has increased dramatically.

I think that I will have an isolator rated to switch 100A (just to be sure) replacing the 63A switch fuse that I have at present. This will feed the generato change over switch which in turn will feed a double pole 63A switch fuse (like the ones used for storage heating). One 63A fuse will supply the sub board that feeds the heat pump, the other will supply everything else.

ThOnda

check if wiring and other means of protection are still suitable for such currents.

I have a 16 sq. T&E supplying the sub board, and a 10 sq. SWA supplying the heat pump so that end is fine. The large cable sizes are partly to reduce volt drop. The rest of the installation is well within regulations.

Thanks for the help and advice.

RoundyMooney

fishdog wrote: »

RoundyMooney
Thats what I thought, but how can I check?

RoundyMooney wrote: »

Should be 100A.

Double check by looking at the side of the fuse carrier at the metering point, it will be either 60/80A, or more likely 100.

fishdog wrote: »

ThOnda
Fair point, I had not thought of that. I think that although this is correct, the bigger problem that I have is that the overall load (not inc. the heat pump)has increased dramatically.

I think that I will have an isolator rated to switch 100A (just to be sure) replacing the 63A switch fuse that I have at present. This will feed the generato change over switch which in turn will feed a double pole 63A switch fuse (like the ones used for storage heating). One 63A fuse will supply the sub board that feeds the heat pump, the other will supply everything else.

I think your summation is spot on tbh. Any increased consumption due to mechanical deterioration of the pump will be negligible. It is there, but a couple of Nokia chargers left plugged in about the place will have a greater effect

ircoha

great post for a non sparks:)


In my search for these links below I read that the startup can be up to 5 times the normal: not my area but just adding it in.

http://www.ralspeed.com/soft-starter-home.htm might give some ideas

from
http://uk.ask.com/web?q=Soft+Start+Motor+Control&dm=all&qsrc=6&o=312&l=dir&siteid=

I had to install one several years ago as I wanted to use an old Wadkin circular saw with a 3 or 4 horse SP motor which blew the fuse on the ESB pole every time it got switched on.

Hope this helps

RoundyMooney

Who's a non sparks?

Let me know so I can ban them

cast_iron

Considering how this guy consumes power, it might be best to get a dedicated supply for his heat pump.

The OP said the heat pump was rated at 10kVA; a standard supply of 12kVA sounds like it's what was required when the pump was installed. I know the ESB advise a 16kVA supply for a house connection with a heat pump - but that's for the average person - which this guy doesn't appear to be.:)

It's not that unlikely that this guy will continue to add more more and more loads onto the supply in future. Increasing the fuse now may only be a step gap until he reaches that peak.

fishdog

cast_iron

The OP said the heat pump was rated at 10kVA

No, I said:

The generator is only 10KVA

cast_iron

a standard supply of 12kVA

But I have an increased supply, 16kVA.


cast_iron

It's not that unlikely that this guy will continue to add more more and more loads onto the supply in future

That is true, but a poblem for another day and a different sparks!

ircoha

I read that the startup can be up to 5 times the normal

I think it is more like 6-8.

RoundyMooney

I think your summation is spot on tbh

I was hoping you would say that.

Thanks guys:D

ircoha

RoundyMooney wrote: »

Who's a non sparks?

Let me know so I can ban them

Okay point taken: you wont see me here again

RoundyMooney

You've lost me now.

(a) I'm not a "non sparks"

(b) I was kidding...

/shrugs

2 stroke

This guy needs to be told that his problems will be solved if he switches items off when he's not using them

RoundyMooney

I think, without second guessing him, that Fishdog has tried such an approach already.

cast_iron

fishdog wrote: »

No, I said:

The generator is only 10KVA

Sorry, I misread.

This one looks like it's sorted then.:)

eoghan.geraghty

Fishdog, could connecting a capacitor parallel to the heat pump reduce the start up current?
It might also improve the efficiency of the pump, particularly if its an older model.
I have something that might suit if its any use.

davelerave

i'd imagine its 100amp esb fuse for the enhanced supply but i never checked .i think the consumers main fuse can go to 80amp
if the tails are suitable.i assume a main switch will do at the consumer unit if the supply is fused at the changeover switch.

fishdog

Quick update.

The engieer that commissions and sells the heat pumps came out do tweak the system.

He connected another capacitor in parallel with the capacitor that the compressor uses and this reduced the full load current by close to 50%
It will have to reduce the start up current also.

This may well solve all my problems! Fingers crossed!

DublinDilbert

fishdog wrote: »

He connected another capacitor in parallel with the capacitor that the compressor uses and this reduced the full load current by close to 50%
It will have to reduce the start up current also.

I know it will solve the problem for now, but in the long term who knows...

If a simple capacitor could 1/2 the power usage by the motor, why would the motor not come with one as standard? Imagine how much energy would be saved in the world if we could 1/2 the current taken by single phase motors. I would guess that its pushed the current out of phase with the voltage, which will not be measured by a standard ESB meter ( ESB meter just measures active power ).

You'd need to put a scope on both the voltage and the current to figure out exactly whats happening. It will also make it slightly harder to blow the fuse as its pushed the current for the motor slightly out of phase with the rest of the house hence the I^2R loss in the fuse is slightly lower, resulting in the fuse not blowing as often.

Michael Collins

DublinDilbert wrote: »

If a simple capacitor could 1/2 the power usage by the motor, why would the motor not come with one as standard? Imagine how much energy would be saved in the world if we could 1/2 the current taken by single phase motors. I would guess that its pushed the current out of phase with the voltage, which will not be measured by a standard ESB meter ( ESB meter just measures active power ).

Exactly, the motor may well have an awful power factor much less than 1, leading to significant reactive power. A capacitor may fix this, thus reducing the peak current through the fuse. It won't save any energy though, as the reactive power is not being consumed by anything in the first place.

fishdog

If a simple capacitor could 1/2 the power usage by the motor, why would the motor not come with one as standard?Imagine how much energy would be saved in the world if we could 1/2 the current taken by single phase motors.

That is a bit like turning off 1/2 the lights in your house, sure you will use less power but there is a trade off. Less light!

I did not suggest that the motor will have the same output as before. This motor is connected to a compressor that increases the pressure of the refrigerant in the heat pump. I am sure we will find that the motor now has to run for longer to get the refrigerant to the required pressure, thus consuming more energy. This is not a problem with this premises, it may be for others. That is why the heat pumps do not all come from the factory like that. Each heat pump is customised on site by the engineer for maximum efficiency. The fact is that the reduced full load current will mean less start up current which will mean that there is less chance of the main fuse blowing now.

You'd need to put a scope on both the voltage and the current to figure out exactly whats happening.

No I think I know what is happening! BTW How will you see the current on the scope?

It will also make it slightly harder to blow the fuse as its pushed the current for the motor slightly out of phase with the rest of the house

Well motors by their nature are inductive. With inductive loads the current laggs the voltage. Connecting another capacitor in to a motor will improve the power factor, bring the current more in phase with the voltage. This will make it more similar to the less inductive loads in the house.

It will also make it slightly harder to blow the fuse

Yes, alot that is what I want. I would expect that my start up current is also halved.

I^2R loss in the fuse is slightly lower, resulting in the fuse not blowing as often.

I dont know what you mean here. Losses in fuses are not normally a concern. The resistance of a fuse is so low under normal conditions that this is a tiny figure.

fishdog

Michael Collins

It won't save any energy though, as the reactive power is not being consumed by anything in the first place.

Where did I say it would save energy!

I just wanted to stop the fuse blowing! I just happened to be lucky that the tweaks that the engineer made to the heat pump solved my problem.:D:D

DublinDilbert

fishdog wrote: »

No I think I know what is happening! BTW How will you see the current on the scope?

You'll need a hall effect current clamp which can connect to a scope. These will give you a true picture of whats happening. Something like a Fluke i410 or something with a smaller current range.

fishdog wrote: »

Well motors by their nature are inductive. With inductive loads the current laggs the voltage. Connecting another capacitor in to a motor will improve the power factor, bring the current more in phase with the voltage. This will make it more similar to the less inductive loads in the house.
Yes, alot that is what I want. I would expect that my start up current is also halved.

I'm trying to think back to my single phase motor classes ( > 12 years ago), there's a few different types of single phase motor.
1) Some are just like a series wound DC motor, from memory these are called a universal motor, in this case the Capacitor would be to limit emissions from the brushes and correct power factor. Armature is in series with the field on these motors, just like a DC series machine.
2) There's a second type of single phase motor which uses straight AC mains on one of the stator windings, and puts a cap in series with the other stator winding which causes its current to lag by 90 degrees. This creates 2 pulsating fields out of phase which induce currents into the rotor and cause it to turn.

fishdog wrote: »

I dont know what you mean here. Losses in fuses are not normally a concern. The resistance of a fuse is so low under normal conditions that this is a tiny figure.

The reason a fuse "blows" is cause it heats up. The reason it heats up is because of power loss, hence I^2R law applies. This is why the fuse curves are shaped the way they are. If you have a small current you get a small I, if I gets very big => I^2 is massive hence the fuse blows really quickly.

fishdog

You'll need a hall effect current clamp which can connect to a scope. These will give you a true picture of whats happening. Something like a Fluke i410 or something with a smaller current range.

Fair point, I have heard of these, but never used one.

I'm trying to think back to my single phase motor classes ( > 12 years ago)

So was I! To be honest I have done nothing on motors since then either!

My main point was that I did not think I had solved the worlds energy problems!:D:D
My aim was to simply reduce the current drawn by the compressor.

The reason a fuse "blows" is cause it heats up.

I remember that much!:D

I just ment that I would not worry about small losses from a fuse blowing.

DublinDilbert

fishdog wrote: »

I dont know what you mean here. Losses in fuses are not normally a concern. The resistance of a fuse is so low under normal conditions that this is a tiny figure.

Oppp sorry, I miss understood....

fishdog wrote: »

Fair point, I have heard of these, but never used one.

They are very handy, get one that can do both AC and DC, and can plug into a multi meter or scope. I got my fluke i410 off ebay for €75, radionics want €210+ vat. I use mine a good bit, also handy for working on the car.

fishdog

I use mine a good bit, also handy for working on the car

Not while driving I hope!:D