Please confirm my wiring and ground-bond questions

[ABarbarian]

I am setting up inverter/batteries in UPS/Backup mode in a little house in Thailand.

 

I was hoping the forum could review my wiring, and also answer a couple of questions I have.

 

The house is 220-240V 2-wire single phase

 

Attached is my planned wiring diagram after adding the inverter, anything wrong with this design?

 

Most of the existing loads/outlets connected to the main switchboard do not have ground cables, pretty normal in Thailand and I don't plan to fix this. I am planning to add grounds to the inverter's AC loads.

 

Below is a video for the same switchboard box as used for my main switchboard, at the ~2:30 minute mark it shows how to connect grid wires to the box:

It clearly shows to wire grid neutral to the boxes ground bus, then to main breaker, that seems different to what my existing wiring is (and I understand is correct) to have the grid neutral go to main breaker, then bond the neutral bus to ground bus. Which is correct?

 

Is there any additional bond or grounding needed on the inverter or it's AC Out/inverter switchboard?

 

Is there any problem adding another main breaker (double-pole) in the inverter switchboard?

[Crossy]

What is shown in the Schneider documentation is correct for Thailand's implementation of MEN, you have to wire like that to pass the MEA/PEA inspection. But that only applies for the incoming supply, no N-E links on sub-units.

 

If you bond after the incoming MCB it's electrically similar but if you then replace the incomer with an RCBO for safety it won't stay on!

 

Do you have any earth-leakage protection? If not I would install forthwith.

 

Your inverter wiring looks OK, I would cross-bond the grounds on each side and not rely on the inverter passing the ground reliably.

 

Do you intend including any surge supression on your inverter mains and solar connections (recommended)?

 

You definitely need DC rated fuses/MCBs on your batteries and solar array.

[xtrnuno41]

In the movie, it starts first with a plastic box and then switch to a metal box. They dont show the metal box MUST be grounded.

Thats what ground is about. You can touch a metal frame or any metal piece, which could be by a defect have the phase on the metal.

Do you have a ground rod? Dont see it in your drawing, you should connect it to the ground in the box and ground the box if its metal.

Have you ever tested or have tested the resistance of the ground rod? If it is too high, you dont have protection at all.

You say you have sockets with no ground and you are not going to to add a ground and replace the sockets.  As long as there are no metal parts on electrical devices which you could touch, it is a sort of ok.

If there are you could be electrocuted, as you dont have ground in the sockets. Sockets and the plugs are wrong then.

 

If you have for instance a lamp, metal and only 2 wires and 2 wire plug, It will not save you. Also if there would be a 3 wire plug, with ground, and fit it in 2 wire socket. All though depending what ground plug system then. But people cut the 3 wire plug and add a 2 wire plug, so it fits, but it becomes a danger.

For protection you need RCBO's, at least one in main power or all groups separately.

In having all fuses with a RCBO, just the one with a fault switches off and all others keep on running. You dont put a RCBO then in the main power. It cost some more.

With just one, in the main power, the main power is shut down and nothing is working anymore. But it works for your health.

With a RCBO you protect everybody.

You can connect some earth here and there and some not, but then you have fake protection and it could be the end of a life. NOT with a RCBO.  GET THEM.

And as Crossy said get a fuse for the batteries.

 

The drawing says 200 A, you have the right cables for it? They must be real short, very close to the inverter.

You dont have 200 A, as the inverter is 4000 Watt, 4000 Watt = 4000/48 Volt = 84 A. So this indicates as well, which value the fuse should have. You should go higher as there will be a peak when it comes alive. It is switched? 

You can have multiple cables on it to spread current, power.

If your cables are too light, you could have glow in dark or smoking cables. All depends on how much power you are using.

 

 

 

[ABarbarian]

14 hours ago, Crossy said:

What is shown in the Schneider documentation is correct for Thailand's implementation of MEN, you have to wire like that to pass the MEA/PEA inspection. But that only applies for the incoming supply, no N-E links on sub-units.

 

 

Hi @Crossy thanks for the reply.

 

I get your advice about adding the ground connection that bypasses the inverter, I have updated my diagram (attached).

 

earth-leakage protection: do you mean ground bar? I forgot to add that to the diagram, the main panel's ground bus has a cable to ground bar (currently chopped while gardening, need to fix).

15 hours ago, Crossy said:

Do you intend including any surge supression on your inverter mains and solar connections (recommended)?

Do you mean a breaker on the mains before entering the inverter? I think that is the 50A breaker in the main switchboard?

 

Solar I do not have in this setup, only battery backup.

 

DC: A couple of questions on this, I picked up the attached DC Breaker on Lazada (good feedback), worthwhile  between inverter and batteries and is my wiring OK?

 

I see a lot of people mentioning DC fuses and I see benefit doing this, although understand the inverter already has a fuse. If we added another I guess it would not cause any harm, any advice on a good fuse in my situation? I guess just one on battery> inverter positive wire?

 

 

[ABarbarian]

1 hour ago, xtrnuno41 said:

If there are you could be electrocuted, as you dont have ground in the sockets.

Seems pretty common here to not have grounding. This house is temporary for us and re-wiring would be a nightmare so will take the risk..

 

I just updated the diagram with the grounding rod, it does have it at the main panel, although by my studies it is not so important, especially with no RCBOs, the ground>neutral bond is more important to ensure enough current is pulled during a short to trigger the breakers..?

 

could I change the breaker between mains and the inverter to an RCBO, because I will ground everything after that point? But leave the main switchboard's main breaker as not being an RCBO, because so many of the old mains wiring is not grounded. At least then the inverter part of the system is protected.

 

Maybe the 200A DC breaker I bought is over-spec, still worth adding?

 

I have 35mm wire between batteries and inverter, not long, <1 meter. 10mm connecting switchboards and inverter.

 

1 hour ago, xtrnuno41 said:

It is switched? 

Not sure what you mean, maybe about the inverter being able to switch between grid and battery? Yes it can, that is it's planned function, to be a UPS backup when grid fails.

[xtrnuno41]

The 35 mm2 cables should be protected by a 125 A fuse and the wiring can handle 94 A.

Your 200 A doesnt work for the safety and protecting your cables, it will only be an on/off switch. So where you want to go? 

 

Yes you can replace main fuse C50, with a C50 fuse included with a RCBO. Note the RCBO function must be 30 mA ! RCBO means, if there is a difference between L and N of 30 mA, it shuts off. It is totally different the a fuse.

A fuse combined with earth leakage (RCBO) has a test knob for. That is the easiest way to see. Also you can see on device , it will say C16 30mA or C16 I∆N= 0.03 or 30 Ma

All the other groups are also protected by this, by putting it in the main.

 

However if you are running on the batteries, it means you dont have power to the mainbox, there is no connection to that one from the output of the inverter.

Only to inverter switch box, which isnt protected then. You should replace the C63 as well, a fuse with combined RCBO.

Beside as the inverter is 4000 W, the value of that one is way too big.

4000 W, comes to 18 A. The C63 A will probably never work for protection off your box, cables. Again it is then only a switch.

You could lower it in value when replacing to 20 A.

If you do replace them, then look at fuses with a B-caracteristic, those switch on 1-5 x the value of the fuse. So more sensitive then the C, which switches on 5-10 X the value..

Meaning if you have a fuse of 16 A, it will switch B 80 A, C 160 A, quite a difference.

 

 

the ground>neutral bond is more important to ensure enough current is pulled during a short to trigger the breakers..?

 

NO, the meaning of grounding is, electricity (phase) is led away from metal parts, you can touch when there is a failure in the device. That is why all, devices, cables should have that ground connected. Otherwise it is worthless.

If not then ground fails and you become the ground and will be electrocuted.

The fuses will never break until it reaches up to 5-10 x (C-caracteristic) the value of the fuse. If the ground works properly, meaning ground must have very low resistance, you are some "safe". If not, then you still can be electrocuted and die. Electricity takes always the lowest resistance route. 

It is however never meant to draw big currents to trip the fuse.

 

If you are going to replace fuses , like the main fuse, be aware the power is off.

I think fuses with RCBO are a big improvement to safety, to prevent electrocution.

You dont see electricity, but sure can feel it and it ....kills in a jiffy time..

 

 

   

 

[bluejets]

On 5/1/2022 at 12:17 AM, xtrnuno41 said:

It is however never meant to draw big currents to trip the fuse.

Actually, it is.

The impedence of this earth return to the MEN under earth fault conditions, commonly known as earth loop impedence, is what determines the trip levels of circuit breakers etc.

Circuit breakers are commonly chosen to match these known levels, i.e. a lower current protection device is necessary as the impedence levels rise.

[tjo o tjim]

On 4/30/2022 at 4:17 AM, xtrnuno41 said:

However if you are running on the batteries, it means you dont have power to the mainbox, there is no connection to that one from the output of the inverter.

You still have a neutral on battery until you open your RCBO; the inverter should bridge the house neutral to the critical load neutral.

 

@Crossy is there any way to deal with this other than to tie the inverter in ahead of the RCBO?  Add a grounding transformer?

[Crossy]

I would be wary of actually grounding the inverter output neutral unless the manufacturer says it's OK. Waving random earths around transformerless inverters can be hazardous to their health.

 

Time to talk to Support, you may be lucky.

 

To ground the N or not is the subject of many debates on inverters/gensets. Generally for low-power stuff people tend not to bother despite it being against the regs in many locations.

 

If you ground nothing other than the metalwork you have an IT system which is actually "2 faults to danger", adding an RCD/RCBO to your second box would detect the second fault (the inverter may even detect the first fault). This is what I would do and is how we are set up.

 

[Muhendis]

Please note that under normal operating conditions the inverter output maximum current is about 18 Amps. I would suggest reflecting this limitation in the selection of circuit protection downstream from the inverter.

[Crossy]

1 hour ago, Muhendis said:

Please note that under normal operating conditions the inverter output maximum current is about 18 Amps. I would suggest reflecting this limitation in the selection of circuit protection downstream from the inverter.

 

Yeah, whilst the inverter is unlikely to actually be able to trip an MCB it will protect itself electronically (hopefully), I'd replace that front MCB with a 20A/30mA RCBO.

[BritManToo]

On 4/29/2022 at 8:11 PM, ABarbarian said:

I see a lot of people mentioning DC fuses and I see benefit doing this, although understand the inverter already has a fuse. If we added another I guess it would not cause any harm, any advice on a good fuse in my situation? I guess just one on battery> inverter positive wire?

I'm not convinced this is the right kind of DC breaker for a battery or the right value.

For a 4kW inverter 4000W/48V = 83A ..... so that's the approximate value of the breaker you need.

100A MCB is what I use it cost 156bht delivered ........ but for some reason they want 350bht now.

https://www.lazada.co.th/products/dc-air-breaker-electric-car-miniature-circuit-breaker-dc-12v-to-125v-150a-200a-250a-mini-mcb-1pole-single-phase-mcb-i2867374375-s10463770613.html?.

[BritManToo]

On 4/30/2022 at 9:17 PM, xtrnuno41 said:

Beside as the inverter is 4000 W, the value of that one is way too big.

4000 W, comes to 18 A. The C63 A will probably never work for protection off your box, cables. Again it is then only a switch.

Most inverters will switch to bypass when overloaded (mine does).

So there is a valid reason to use a larger AC breaker on the output than the inverter max load.

[BritManToo]

1 hour ago, Muhendis said:

Please note that under normal operating conditions the inverter output maximum current is about 18 Amps. I would suggest reflecting this limitation in the selection of circuit protection downstream from the inverter.

Disagree for reason in previous post.

[BritManToo]

20 hours ago, Crossy said:

I would be wary of actually grounding the inverter output neutral unless the manufacturer says it's OK. Waving random earths around transformerless inverters can be hazardous to their health.

Agree,

Use the same earth bar for everything that has an earth.

Keep Inverter neutral on it's own bar, do not connect to earth at all.

 

I split my fuse box so all the house wiring goes through it.

Added in a second Neutral bar and MCB for the inverter output.

Made the existing wiring long enough to reach without extending.

 

 

Sadly I couldn't make it neat with the inverter MCB, to the right of the inverter fuses as the idiot wiring my house ran the incoming grid through the middle of the fuse box (behind that middle white plastic bar).

 

Separate fuse box for the inverter, couldn't fit the battery breaker in it as it would make the battery wires 0.5m longer than I wanted.

 

[Muhendis]

1 hour ago, BritManToo said:

Most inverters will switch to bypass when overloaded (mine does).

So there is a valid reason to use a larger AC breaker on the output than the inverter max load.

 

1 hour ago, BritManToo said:

Disagree for reason in previous post.

My thoughts are that, since the inverter is to be used as a UPS, the maximum circuit power would need to be limited to the maximum available source which in this case is the inverter. The problem of the utility supply taking up the slack so to speak is that, if there is no utility supply available at the time of overload then the only protection for the inverter is within the inverter itself. The right size MCB is a bit less expensive than a failed inverter so I would fit suitable circuit protection rather than rely solely on the inverter's internal protection.

[BritManToo]

5 minutes ago, Muhendis said:

 

My thoughts are that, since the inverter is to be used as a UPS, the maximum circuit power would need to be limited to the maximum available source which in this case is the inverter. The problem of the utility supply taking up the slack so to speak is that, if there is no utility supply available at the time of overload then the only protection for the inverter is within the inverter itself. The right size MCB is a bit less expensive than a failed inverter so I would fit suitable circuit protection rather than rely solely on the inverter's internal protection.

My inverter (really cheap) switches to bypass with no damage, as my woman has tested twice by accident so far. I have no worries.

 

Maybe if I spent as much as you on an inverter I'd be more concerned.

(Which is pushing the logic of paying  more for quality a little)

[Muhendis]

5 hours ago, Muhendis said:

 

My thoughts are that, since the inverter is to be used as a UPS, the maximum circuit power would need to be limited to the maximum minimum available source which in this case is the inverter. The problem of the utility supply taking up the slack so to speak is that, if there is no utility supply available at the time of overload then the only protection for the inverter is within the inverter itself. The right size MCB is a bit less expensive than a failed inverter so I would fit suitable circuit protection rather than rely solely on the inverter's internal protection.

Ooops correction. maximum should read minim