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Wiring confusion


Mr.A

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Hi All, I recently bought a Mecer 5KV inverter. It states I must use 8 gauge wire for AC IN/OUT. Went to Builders they did know what I was talking about. They gave me stove installation wire. Will this work? Does anyone have gauge conversion to mm used in SA please?   

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That chart is a bit off; maybe it gives the next highest standard metric area for a given AWG. For example, per Wikipedia's American Wire Gauge page, 8 AWG is 8.37 mm², not 10 mm².

6 mm² is sufficient for the AC input of a 5 kVA Axpert; 4 mm² is sufficient for the AC out cable. 5 kVA Axperts have a 40 A circuit breaker inside them (on the AC input side). The reason you need thicker cable on the AC input is that it is possible (even if unlikely) to be utility charging at 3000 W while delivering 5000 VA to the load.

I think the 8 AWG recommendation in the manual comes from the following. They figure they need 6 mm² at least for AC in; that's a nice metric size. But they don't publish it for reasons that are beyond my capacity. They look up the AWG table and see that 10 AWG is a little too small, and odd AWG sizes are rare, so the next biggest cable size is 8 AWG.

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1 hour ago, Mr.A said:

Thanks for the advice but will it cause any harm to the inverter should I use 4mm, which thicker than the 6 I replaced. Dont tell me I will have to do this all over again with 6 mm🤔

It isn't up to the inverter, it is up to what kind of circuit breaker you used.  At 4mm I would stick with 25amp circuit breaker maximum.  That way the worst thing that will happen is a trip or nuisance tripping because you run too close to the limit.  I personally used 25 amp breaker going to the inverter (with 4mm cable) and 20 amp coming from the breaker (with EL integrated) and 4mm wire.  The only reason I used 4mm was at the time it was the recommendation for my previous inverter.  If I redid it, I would have used 6mm.

I've never had a trip but then again the most I put through it is the kettle, some computers and lights.

image.thumb.png.916d670784c793a6124dbf44bbf56654.png

There is more to it than this table.  Voltage drop must be within a permissible range also.  My cable is only 3 meters long and I used installation method 2.  But frankly I plan on worst case (installation method 1)

Edited by Gnome
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Hi Gnome, first of all thank you for the advice. I have since replaced the 6 with 4mm AC input with a 50A breaker. Keep in mind I am not technically experienced. With this in mind will this cause a problem as I would not want to again rewire with 6mm, by the way is 6mm also used to wire a stove connection? I am asking this because this is what Builders gave me when I asked for 8 gauge. 

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15 minutes ago, Mr.A said:

Hi Gnome, first of all thank you for the advice. I have since replaced the 6 with 4mm AC input with a 50A breaker.

50amp breaker is way, way too large for 4mm.  Like I said, aim for 25amp breaker at most.  Also it should be a circuit breaker and not an isolator.  They look very similar.  Also if it is an earth leakage make sure it also has over-current protection (note how similar all these look).  Most earth leakage breakers sold in SA do not feature over current protection and thus cannot be used as circuit breakers.

 

15 minutes ago, Mr.A said:

Keep in mind I am not technically experienced. With this in mind will this cause a problem as I would not want to again rewire with 6mm, by the way is 6mm also used to wire a stove connection? I am asking this because this is what Builders gave me when I asked for 8 gauge. 

Yeah if you aren't technically minded you should probably get someone to do it for you or do a lot of research to ensure you are doing the right things.  Like the circuit breaker above.  That is just not safe at all.

You don't buy wire based on "stove" or "fridge" you buy wire based on how many amps it'll need to supply.

A single phase stove top will typically be supplied by 4mm or 6mm.  Most modern ovens come with a standard house hold plug on the end and would be safe to run on 2.5mm.  But a lot of homes have the stove and oven on the same circuit at which point 6mm really becomes a must.

Three phase is a different story.  In my home the wiring was three phase 2.5mm for the stove (3x2.5mm) which is pretty much overkill.  The oven is then supplied by 2.5mm also which is adequate.

Edited by Gnome
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Thanks, I will replace the circuit breaker. I have a single pole circuit breaker which I will replace with your 25 amp recommendation. For clarity I did not ask for stove wire as I am not busy with a stove but builders people did not know what the SA translation of 8 gauge  was as recommended in the manual was but thanks to Riaanh and The Bulldog I was helped.

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Hi Gnome, in your last reply you stated, " I personally used 25 amp breaker going to the inverter (with4mm cable) and 20 amp coming from the breaker (with EL integrated)." Should it not be 20 amp AC out from inverter?

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3 hours ago, Mr.A said:

Hi Gnome, in your last reply you stated, " I personally used 25 amp breaker going to the inverter (with4mm cable) and 20 amp coming from the breaker (with EL integrated)." Should it not be 20 amp AC out from inverter?

Yeah sorry the inverter out goes to a 20a circuit breaker.  Just because most circuit breaker actually trip slightly above their rating and I couldn't even see myself using 20a constantly (4600 watt @ 230v).  I really wanted it to trip close to the 5kW mark.

Edited by Gnome
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21 hours ago, Mr.A said:

Thanks for the advice but will it cause any harm to the inverter should I use 4mm, which thicker than the 6 I replaced. Dont tell me I will have to do this all over again with 6 mm🤔

I used 8mm for in and out ... had to eventually change over to 6mm as i could not fit more than one wire on the inverter when running in parallel.... Its a different inverter all together, but it is a good indicator on what to expect some times :)

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On 2019/03/26 at 2:29 AM, Mr.A said:

... but will it cause any harm to the inverter should I use 4mm, which thicker than the 6 I replaced. 

Um, I hope you realise that 4 mm² is thinner than 6 mm². Metric cable cross sectional areas are just cross sectional areas; the more the area, the more current it can safely handle.

It's not like American Wire Gauge, where 6 gauge is thinner/lighter/less area/less current than 4 gauge.

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12 hours ago, Coulomb said:

hope you realise that 4 mm² is thinner than 6 mm²

Aaai these metric people. I still like to use km/liter for fuel consumption. But actually, km/liter is a unit of efficiency, it is not a unit of consumption. For consumption, lower is better. For efficiency higher is better. The official unit of consumption is liter/100km.

I assume AWG vs metric has the same issues 🙂

 

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3 hours ago, plonkster said:

I assume AWG vs metric has the same issues 🙂

Not sure what AWG is.  A unit of inches is too complicated so lets use a number that decreases when size increases 🤨

Only an American can come up with something that genius.

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Since the cost difference between thin cable and slightly thicker cable is minimal, I would rather err on the side of caution and put in thicker cables rather. There is no downside in doing that.

In fact since I've been working with low voltage DC, all of these thin ac cables look a bit puny to me...

Edited by DeepBass9
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If you go too thick, like 10mm (or if you can find it, 8mm), it won't fit into the AC terminals...

On the Axpert you can go higher than 70mm on the DC side I'm sure, but frankly it is already pretty tight at 70mm so I didn't risk buying the next size (90mm IIRC).

But otherwise I completely agree with the sentiment.  The cable cost is relatively negligible part of the install if you take labour into account.

Edited by Gnome
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