inverter

[windspeed]

I have read the neutral is bonded on some inverters what does this mean

windspeed

[wpowokal]

Bonded means connected to.

Quality inverters have high isolation between DC side and AC side for safety reasons.

In Australia the neutral is bonded(joined) to earth at the fuse/switch board then tied (bonded) to an adequate ground stake, which is usually remote from batteries to some degree, note: terafirma (the ground) is actually a poor condutor generally.

That will do for now.

allan down under  

[dnix71]

In the US, generators under 5000 watts do not have to be wired like the house.

The neutral can 'float.' That is to say, it is not bonded to ground.

On generators over 5000 wattts, the neutral MUST be bonded so the generator can be hooked up to house mains safely. A floating neutral is safer for portable inverters and generators because you would have to contact two wires to complete a circuit, instead of just touching the hot wire while being grounded.

This means you should not ever hook up a small portable generator (or an inverter) to house wiring without checking first. On common 120 mains outlets, the wide slot on the plug is neutral, the narrow slot on the right is hot. On a floating neutral, neither side is really hot or cold. Unless you have a load connecting both sides, there is no circuit.

On house mains in the US, touching just the right side wire will shock you because that wire is live all the time. The neutral and ground are bonded either at the outlet or back at the power company transformer. 120 volts is made by center tapping the transformer. the center is neutral, either side is 120v, and across the two outside is 240v. The ground wire is really just an extra neutral wire, so if the first neutral fails, there is an easier way for the electricity to go back to the power company than through your body.

Hospitals have separate grounds for each outlet (isolated ground), most homes and businesses have the ground wires bonded to each other. Isolated grounding makes it less likely that an equipment malfunction will damage nearby equipment, but is more costly to do.

With a floating neutral, one side of the inverter or generator outlet goes to the exciter circuit. If you tried to bond that to ground it would probably destroy the inverter or generator.

[Opera House]

Very small inverters, generally under 500W, use the 12V and stack the inverter voltage on top of that to create the 140-160V that the output operates off.  On larger inverters to 4,000W this is independent, but still referenced to ground.  The output current sense can often be between the HV common and the negative 12V.  Regardless, all these inverters use a H bridge output so both the hot and neutral swing from 150V to  zero volts.  Grounding the neutral will put the inverter in current limit at best if not blow out the output fets on the neutral side.

[wpowokal]

Now this post is a good example of a clear question receiving two clear replies, thus being informative not only to the poster but I suspect many others.

allan down under

[rossw]

On house mains in the US, touching just the right side wire will shock you because that wire is live all the time.

Bzzzt!  Touching just ONE conductor won't hurt you under the vast majority of circumstances. You NEED to have a path for current to flow.

If you're standing on a damp floor in bare feet, sure (if the neutral is bonded to earth), you'll get a kick.

The only other condition is if (a) the frequency is high enough, or (b) your surface area and mass is large enough, that there is a capacitive effect, whereby you will pass some current. But at 50/60 Hz, thats going to be pretty small.

[Capt Slog]

Agreed.  I learnt something.

[GlutealCleft]

Yeah, what he said.

Typically, in a home, neutral is bonded (or connected) to ground in the main panel.  In  many inverters, that is not the case - hot and neutral will be 120V (or 240V) from each other, but are "floating", which mean they could be anywhere above or below ground.  In a home setting, that is against electrical code, and for good reason.

The reason that so many inverters don't have a ground is that they are meant to be used in a car, and a car simply doesn't have a true Earth ground to connect to.  It's a bit more common to see inverters which can be grounded, but they're generally the more expensive units, not the $20 specials.

[dnix71]

I have touched enough single conductors in my day to know for sure that just contacting the hot wire on 120 is enough to get a nasty shock. I was never thrown off a ladder, but it never felt good. I wasn't standing in water and I almost always wear rubber sole shoes.

I touched a 240 fault wearing tennis shoes only once and that left my arm numb.

People routinely die from contacting 480. Several people were killed at bus stops down here because some incompetent contractor couldn't properly ground the 480v lighting stepdown transformers (solid coral bedrock underground).

[dnix71]

This

[elt]

I've been confused by this from day one... after you've shut off the mains (or thrown the transfer switch) why can't you connect the hot and neutral to the house circuit and simply leave the inverter's ground disconnected? ... and leave the house ground and neutral bonded?

What shorts or burns up in this case?

I know that the inverter doesn't need it's ground connected because two-pronged devices plugged into the inverter work just fine.

 - Ed.

[americanreman]

Can't help but chime in here, there are many discussions about this and many distorted views.

Touch the black wire and you get a shock...period, any time, any day, of the week whether you are standing in water or standing in the desert.

Break before you make, in other words you should break all 3 conductors on the grid source, then make all 3 conductors on the backup or RE source.

Really that simple, grid ground should never be connected to inverter ground, in fact it will let the smoke out of your inverter sooner or later if you do unless it was intended to operate that way.

[Opera House]

Yes, that will work...........But the inverter and the battery will be at lethal potentials when the inverter is on.  

[dnix71]

And if the neutral floats on the inverter but doesn't in the house wiring you will short out the inverter's exciter circuit when you tie them together.

You will also backfeed the grid unless you have a proper transfer switch. You can't run the grid with any generator or inverter, but you could shock a lineman during a power outage. That's why grid tie inverters only work when the grid does.

[elt]

> And if the neutral floats on the inverter [...]

I don't understand the reference to a floating neutral. (I wonder if it means something other that I think it does.) But how can a two prong table lamp work if the neutral is floating... the 110v (in the US) has to be with respect to something...

- Ed.

[DamonHD]

No more than a rocket ship has to move 'with respect to' the Earth or something else to push against.

A 'floating' power supply has no reference to supply voltages, Earth, etc, and works just fine for the purposes of lighting a lamp.

Time to read up a little General Relativity for your bedtime?  B^>

Rgds

Damon

[elt]

General Relativity didn't seem that hard! To people that know, does the phrase "floating neutral" simply imply that the hot is floating too? Then, okay, I get that the (entire) inverter and battery circuit is floating.

I don't get: if the inverter's ground isn't connected to anything, (and the neutral and hot are floating) how does connecting the neutral to ground, 500v, or any conceivable voltage blow something inside the inverter?

Thanks again,

 - Ed.

[ghurd]

Common language thing? Nomenclature?

Ed elt, avoid connecting ANY plug hole on a common-type inverter to anything else connected to the inverter.  3rd hole. Ground lug. Breaker box. Battery. Ground. Anything.

The out holes can't be connected to each other.

The in holes can't be connected to the out holes.

At all.

(common-type inverters)

Here, US, "floating neutral" can kill, but neutral is often refered to as ground and vice versa.

I have been bit by grounded neutral grid power.  More than once.