Inverter Air con earthing

[Rimmer]

We just had a new Samsung inverter air con installed, they fitted a 1mm earth cable off the outside unit from a case screw to an earth bolt in the ground.

 

I have previously earthed air cons separately with a cable and an earth rod, but first time we had a close ground lightning strike the induced transients came back up the rod and blew the air con so keeping that in mind I disconnected the small earth wire on the new air con. We have a lot of ground strikes close to us probably from the iron in the soil.

 

Wife now says she can feel a tingle from the outside unit when she wipes it down, maybe its static build up and is normal and maybe I should put the earth bolt and wire back if so would a small bolt still act as an earth rod and shoot any strikes back into the air con?

 

I never knew but apparently the inverter outside unit runs all the time when the air con is on so that might account for a static build up?

 

Advice please as I don't know have not encountered this situation before

 

[BritManToo]

Turn the power to the air-con off at the fuse box before cleaning.

[Rimmer]

5 minutes ago, BritManToo said:

Turn the power to the air-con off at the fuse box before cleaning.

 

That is not the issue, read and try to understand the question again

[Crossy]

If the unit is currently without an earth the tingle will be leakage via the mains filter capacitors, the same mechanism as in a desktop PC that tingles when unearthed.

 

Does your home have earthing installed? If so why is the A/C not connected to that?

 

Multiple independent rods can generate significant voltages between them in the event of local ground strikes (part of the reason the Aussie regs prohibit multiple rods).

 

EDIT It's also worth noting that this earth isn't just a safety earth, it is a "functional earth" which is required in order for the equipment to perform as designed.

 

[Rimmer]

20 minutes ago, Crossy said:

If the unit is currently without an earth the tingle will be leakage via the mains filter capacitors, the same mechanism as in a desktop PC that tingles when unearthed.

 

Does your home have earthing installed? If so why is the A/C not connected to that?

 

Multiple independent rods can generate significant voltages between them in the event of local ground strikes (part of the reason the Aussie regs prohibit multiple rods).

 

 

Thanks for that, yes everything in the house and board is earthed, but for some reason this air con is not and only has L+N cables no earth wire back to the board, impossible to run an earth as house is too big, air con and board over 300mtrs apart.

 

So leave as is or put an earth wire back to the earth ground bolt and if so could a 2 inch long bolt act as a reverse earth rod?

[Crossy]

OK, do you have an earthed power outlet nearby that you could borrow an earth from?

 

If not then:-

 

For now (and I hate to say this) it will probably be safest for the aircon to leave it without a ground.

 

The problem will be if you get a ground strike there could be a large potential between your (grounded at the board) supply neutral and the secondary rod. The A/C will probably not like this much.

 

 

[Rimmer]

4 minutes ago, Crossy said:

OK, do you have an earthed power outlet nearby that you could borrow an earth from?

 

If not then:-

 

For now (and I hate to say this) it will probably be safest for the aircon to leave it without a ground.

 

The problem will be if you get a ground strike there could be a large potential between your (grounded at the board) supply neutral and the secondary rod. The A/C will probably not like this much.

 

 

 

Many thanks for that, I have one outside socket close also one inside in the bedroom, I will see what I can do with those.  

 

The problem will be if you get a ground strike there could be a large potential between your (grounded at the board) supply neutral and the secondary rod. The A/C will probably not like this much.

 

Yep I already learnt that lesson with a brand new air con that I stupidly earthed with an earth rod, whilst not destroying it completely the entire inside of the unit was covered in black soot from the resulting flash which scared the heck out of us, strangely the inside unit was left unscathed.

[Crossy]

Do you have any lightning surge protection?

[Rimmer]

10 minutes ago, Crossy said:

Do you have any lightning surge protection?

 

Yes TP ABB unit connected to the bus bars in the board

[Rimmer]

Had a thought, maybe I could run a single earth wire in the crawl space under the house directly to the terminal on the main earth rod, would that work?

Just entails someone (wife) crawling under there which she hates to do because of the lurking critters that may be down there.

[Crossy]

That would work.

Do you not have a (local) small child you could bribe to pull the cable?

 

With such long cable runs you might want to add more surge suppression near any sensitive kit too.

[bankruatsteve]

If me, I would connect to a nearby outlet.  End result same and sounds much easier.  
It's been said before, but a nearby or direct lightning strike will leave very little electric stuff undamaged and there is nothing can be done to protect.

[Rimmer]

20 minutes ago, Crossy said:

That would work.

Do you not have a (local) small child you could bribe to pull the cable?

 

With such long cable runs you might want to add more surge suppression near any sensitive kit too.

We have no neighbors or children that we know of within half a mile but maybe I can get one of our cats to drag it along if I offer treets at the other end ????

[Yellowtail]

A wife that's wiping down the outside units and is willing to pull-wire through the crawl-space under the house? Dude must be doing something right! 

[Rimmer]

I think I sorted it after discussion with the air con guy.

 

A short length of single 23/0076 with an AMP terminal one end fixed to a case screw, the other end is spread out and just brushes the concrete, when I fixed it as soon as It touched the ground I heard a slight thump from inside the unit as the capacitor discharged.

 

Its not in the ground so no multiple ground rods, just a slight touch now and again as the wind moves it around and it brushes the ground.

 

[Litlos]

A system we used in North West Australia was to insulate the top of the earth rod. Basically get a piece of PVC tube and push it into the ground as far as possible, a couple of metres minimum. Then insert an earth rod through the tube into the soil for a couple of metres. We had dry rocky soil and used to use an airtrac to drill 3metres for the tube and 3 metres for the earth rod. This then puts the earth point below the surface effects of the lightning strike, which diminishes rapidly with depth.

 

Cheers

[Yellowtail]

5 minutes ago, Litlos said:

A system we used in North West Australia was to insulate the top of the earth rod. Basically get a piece of PVC tube and push it into the ground as far as possible, a couple of metres minimum. Then insert an earth rod through the tube into the soil for a couple of metres. We had dry rocky soil and used to use an airtrac to drill 3metres for the tube and 3 metres for the earth rod. This then puts the earth point below the surface effects of the lightning strike, which diminishes rapidly with depth.

 

Cheers

 

Do you mean an additional three meters for the rod, so the OAL of the rad would be 6m?

[Litlos]

Just now, Yellowtail said:

 

Do you mean an additional three meters for the rod, so the OAL of the rad would be 6m?

Yes, the rod needs to extend into the soil past the tube. So if 2metre tube would need about 4 metre rod. They generally sell rod joining clips at the same store.

 

Cheers

 

[Outbackoz]

On 6/18/2021 at 12:23 PM, Rimmer said:

I think I sorted it after discussion with the air con guy.

 

A short length of single 23/0076 with an AMP terminal one end fixed to a case screw, the other end is spread out and just brushes the concrete, when I fixed it as soon as It touched the ground I heard a slight thump from inside the unit as the capacitor discharged.

 

Its not in the ground so no multiple ground rods, just a slight touch now and again as the wind moves it around and it brushes the ground.

 

Depending on how rough the surface is underfloor you may also consider using a small remote controlled dune buggy or similar to take a draw wire through the area 

[Yellowtail]

23 minutes ago, Outbackoz said:

Depending on how rough the surface is underfloor you may also consider using a small remote controlled dune buggy or similar to take a draw wire through the area 

 

Yes, preferably with fiberoptic night vision and servo-controlled release-clips. 

[Rimmer]

42 minutes ago, Outbackoz said:

Depending on how rough the surface is underfloor you may also consider using a small remote controlled dune buggy or similar to take a draw wire through the area 

 

Lots of builders rubble under there, would need a large scale model RC Tiger Tank, that would be able to do the job,  the earth wire could be connected to the end of the gun which would then drive up to the adjacent air brick next to the earth rod and be poked through it for connection to the house earth rod in the car port ????

[Yellowtail]

1 minute ago, Rimmer said:

 

Lots of builders rubble under there, would need a large scale model RC Tiger Tank, that would be able to do the job,  the earth wire could be connected to the end of the gun which would then drive up to the adjacent air brick next to the earth rod and be poked through it for connection to the house earth rod in the car port ????

 

If you can get a cockroach to run all the way, you might be able to get the cat to chase it and pull the wire....