Jump to content
Thank you for the great forum, Safe Driving over the weekend. Sincerely Jason
Tariq

AC input circuit breaker size

Recommended Posts

Posted (edited)

I have a Kodak vm iii 5 kva, the manufactures suggestion is a 50 amp circuit breaker , I have three phase grid supply and the three phase  breaker( on the dB inside the house ) is rated at 35 amps per phase,. The house is quite old, even though I have a prepaid meter, the old meter box outside the house ( with a spinning meter in series ) has three breakers rated at 50 amps each ( with seals on them , I am assuming it is 50 amps per phase supply from the council )

As I will supply the inverter from one phase, do I change to a 50 amp breaker or stay with the 35 amp supply

Thanks

 

Edited by Tariq
Forgot something

Share this post


Link to post
Share on other sites
Posted (edited)
23 minutes ago, Tariq said:

I have a Kodak vm iii 5 kva, the manufactures suggestion is a 50 amp circuit breaker

 

50 amp circuit breaker for the supply to the inverter?

Sounds like you are talking about the inverter breaker and then about your house/apartment incoming circuit breaker.

23 minutes ago, Tariq said:

I have three phase grid supply and the three phase  breaker( on the dB inside the house ) is rated at 35 amps per phase,. The house is quite old, even though I have a prepaid meter, the old meter box outside the house ( with a spinning meter in series ) has three breakers rated at 50 amps each ( with seals on them , I am assuming it is 50 amps per phase supply from the council )

Quite common in Cape Town & old areas in Jhb.  It is very unlikely you have 50 amps per phase from council.  35 amps x3 = 105 amps btw.

Short story:

You should not in any way mess with incoming circuit breaker.  My apartment building is very old and we have 35 amp 3 phase circuit breakers.  When I went into the metering room, they didn't have circuit breakers down there.  Just a single 90mm x3 wire coming in and being split among the apartments (with no insulation, just open wires).  That means if anyone changes their circuit breakers or touches any of the incoming wire, it'll literally keep going until there is a fire.  In fact a few months ago the wire caught fire and they replaced the wire (but still didn't add any circuit breakers or anything).  In my case the incoming wire into the apartments is 6mm.  35amps for 6mm is actually a bit too high.  And this is in Sea Point.  So don't think because you live in a "nice" area you are safe.  Dodgy wiring from council is how it goes.

/Short story

Council wiring is often very scary, just don't mess with the incoming wire unless you know for sure what is going on and how to size it.  I'm not going to drone on about the insurance, it being a crime, etc. because that rarely keeps people from doing things.  But the fact is to uprate the breaker there are a whole lot of things you need to check first.

23 minutes ago, Tariq said:

As I will supply the inverter from one phase, do I change to a 50 amp breaker or stay with the 35 amp supply

No, circuit breakers are rated for the wire, not the device.  More importantly, that inverter on a good day can supply 22 amps.  A 25 amp circuit breaker is sufficient.  Most circuit breakers have a continuous and instantaneous rating.  A typical circuit breaker has an instantaneous rating roughly 1.5-2x the continuous rating (called the curve of the breaker).

Not sure if I need to say this, but 2.5mm is not sufficient for wire going to the inverter.  I see a lot of people doing that

Edited by Gnome

Share this post


Link to post
Share on other sites
40 minutes ago, Gnome said:

More importantly, that inverter on a good day can supply 22 amps.  A 25 amp circuit breaker is sufficient.

But it could go into bypass mode and pass 40 A from input to output, and be charging the battery from utility at the same time. I'd say that's why a 50 A breaker is recommended (and wiring to suit, of course). My Axpert MKS 5K-48s have a 40 A breaker in them connected to the AC-in active. Kings have that breaker too, but I don't know what rating they have. If it's 40 A, then there's no point using a breaker rated for more than 40 A.

Share this post


Link to post
Share on other sites
Posted (edited)
13 minutes ago, Coulomb said:

But it could go into bypass mode and pass 40 A from input to output, and be charging the battery from utility at the same time

I don't think that makes sense, why would you want to pass 40A through a device that can't possible supply that load?  In bypass it may be able to handle 40A (I'm assuming because I haven't verified this for a fact), but that is non-sensical to me as I would expect you to match your load to your supply.

13 minutes ago, Coulomb said:

I'd say that's why a 50 A breaker is recommended (and wiring to suit, of course). My Axpert MKS 5K-48s have a 40 A breaker in them connected to the AC-in active. Kings have that breaker too, but I don't know what rating they have. If it's 40 A, then there's no point using a breaker rated for more than 40 A.

In South African regulations you would need at least 10mm wire for a 50A breaker.  Possible more depending on the type of wire and the installation method (various kinds detailed in SANS regulations).  Just so we are clear, the regulation require both the wire and regulations are matched.  SANS approved wiring will never be rated for 50Amp+ for anything less than 10mm, but perhaps it isn't clear that both ratings and regulations apply here.

As I've said, I've seen install pictures with people using 2.5mm wire with 25 amp or 32 amp breakers. 4mm with 50amp breakers, etc.  Completely illegal.

Regardless of the choices made, I would definitely size the breaker for the wire.

As for uprating a council breaker, you need the council to approve that, your wiring needs to be adequate or uprated and your short circuit impedance needs to be tested again to ensure your breaking capacity is sufficient for the incoming supply.  It is a very technical process, 100% would not recommend a DIYer do it.

Edited by Gnome

Share this post


Link to post
Share on other sites

1) The 50 amp circuit breaker is recommended on the inverter input, also the manual says to use 6 mm wire on the input and output .

2) I live in Pinelands, Cape  Town, so you probably are right about the 35 amps per phase supply.

3) looks like best/safest to stay with the 35 amp breaker, and if the load goes to high, the external main breaker will trip

 

Share this post


Link to post
Share on other sites
Posted (edited)
18 minutes ago, Tariq said:

1) The 50 amp circuit breaker is recommended on the inverter input, also the manual says to use 6 mm wire on the input and output 

6mm wire is not adequate for 50amps.  And you can put whatever circuit breaker you want on there.  It'll just trip if it goes over.  I have 25amp breaker and I've never, ever had it trip.  I would personally not go over 30 amps for Axpert inverter.

amp_ratings.thumb.png.59831a17a9fc40daf092cc9a37d19f79.png

SANS regulation, in South Africa, supersedes what the device specifies.  Also notice that the current carrying regulation depends on the installation method.

Edited by Gnome

Share this post


Link to post
Share on other sites
Posted (edited)
12 minutes ago, Tariq said:

Looks like best to stay with the 35 amp breaker and 10 mm wire, thanks for you help Gnome

Still, consider using a 30 amp breaker for your inverter (and 6mm wire).  Worst case it'll trip (Which I can almost guarantee you now it will not).  Doesn't make sense to install a 50 amp breaker if your supply is less than 50 amps.

Typical 30 amp breakers will allow 7kW to pass through continuously before tripping.  That is an enormous amount of power.

Edited by Gnome

Share this post


Link to post
Share on other sites
Posted (edited)

Hi Gnome,

        What is the maximum load that can be hooked up to each phase , is it 230 volts x 35 amps = 8050 watts or is it a higher wattage as you don’t use all appliance/load all the time

Edited by Tariq

Share this post


Link to post
Share on other sites
Posted (edited)
4 hours ago, Gnome said:

I don't think that makes sense, why would you want to pass 40A through a device that can't possible supply that load?

In bypass mode, it literally connects AC-in to AC-out via some relays. The relays are rated at 40 A, and presumably the internal wiring is stout enough to handle it, at least for short periods of time (say 30 minutes). You wouldn't do this regularly, but it can happen that someone turns on a moderate load not realising that there is already the washing machine and a hair dryer running. Rather than dropping out and possibly blacking out the house, the inverter switches to bypass mode, assuming AC-in is present of course. If not, it has no choice but to stop with an overload fault code. I believe I'm correct in assuming that the King models, despite their dual conversion design, retain this behaviour in the case of an overload.

The fact that the inverter proper can't provide more than 21.7 A (5000 VA / 230 V) has nothing to do with how much current and therefore power the machine can pass through in bypass mode.

Edited by Coulomb

Share this post


Link to post
Share on other sites
Posted (edited)
48 minutes ago, Tariq said:

Hi Gnome,

        What is the maximum load that can be hooked up to each phase , is it 230 volts x 35 amps = 8050 watts or is it a higher wattage as you don’t use all appliance/load all the time

35 amps per phase, so 8050 watts per phase.  Also note that your incoming breaker doesn't trip immediately as soon as you hit 35 amps. For example:

image.thumb.png.a9bf73a2c405376c29b40024c4b736d8.png

This is the data sheet for the common CBI breaker feature in 90% of homes.  Notice that at 250% it takes 1 second to trip (87.5 amps for 1 second).  At 100% it takes almost a full minute to trip. etc.

34 minutes ago, Coulomb said:

In bypass mode, it literally connects AC-in to AC-out via some relays. The relays are rated at 40 A, and presumably the internal wiring is stout enough to handle it, at least for short periods of time (say 30 minutes). You wouldn't do this regularly, but it can happen that someone turns on a moderate load not realising that there is already the washing machine and a hair dryer running. Rather than dropping out and possibly blacking out the house, the inverter switches to bypass mode, assuming AC-in is present of course. If not, it has no choice but to stop with an overload fault code. I believe I'm correct in assuming that the King models, despite their dual conversion design, retain this behaviour in the case of an overload.

The fact that the inverter proper can't provide more than 21.7 A (5000 VA / 230 V) has nothing to do with how much current and therefore power the machine can pass through in bypass mode.

Ah I always disabled that option.  Also, I find it scary that it is using that kind of relay to switch such high currents.  I take it the AC3 rating is laughable low which is why I'm scared of relying on that kind of feature.

Edited by Gnome

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


Topics

Contact Us - Power Forum South Africa

×
×
  • Create New...