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TazinCR 01-07-2009 01:36 AM

Electrical connections
 
1 Attachment(s)
Greetings,
Saw this connected yesterday. It is a 220 mini split A/C and they hooked it L1 and L2 to L1 & L2 but hooked the green to ground. Should this not have been hooked to the white neutral? They (neutral & ground) are bonded at the panel but the installer did not know that. The four wires are feeding.

jerryh3 01-07-2009 03:12 AM

If there's four connections at the unit(HHNG, 120/240V) then there should be four wires running to the panel. What's your concern?

TazinCR 01-07-2009 05:59 AM

There are 4 wires feeding and 3 wires to the unit.

jerryh3 01-07-2009 06:07 AM

Quote:

Originally Posted by TazinCR (Post 208483)
There are 4 wires feeding and 3 wires to the unit.

Didn't your picture have 4 wires feeding the unit? If the unit requires a neutral(240/120 circuit), then a neutral should have been ran.

TazinCR 01-07-2009 06:47 AM

1 Attachment(s)
Sorry if I was confusing. In the picture the 4 wires on the right are the feeders from the panel. The three wires on the left are the factory installed feed to the unit. In this situation since the neut. and ground are bonded it gets back to the neutral but if it were a sub-panel with isolated neutral this would not work correct?

CowboyAndy 01-07-2009 06:50 AM

Quote:

Originally Posted by TazinCR (Post 208483)
There are 4 wires feeding and 3 wires to the unit.

If there are only 3 connections on the unit, then it is a straight 240v unit and only requires H-H-G, no neutral.

Based on your posts and diagram, I an umderstanding that the cable feeding it from the panel is a 3 wire + ground cable containing black, red, white and green (or bare) and the unit has black, white and green (or bare)?

If my assumption is correct and there is a white at the unit, then its either a 120v unit OR the white SHOULD be black or red. IF that is the case and it is a 240 v unit, then there is nothing wrong with the way it is wired except that the white should be remarked as a hot.

If my assumption is wrong and it is a 120v unit, then it is wired wrong and the white from the cable should go to the white from the unit.

chris75 01-07-2009 06:53 AM

Quote:

Originally Posted by TazinCR (Post 208494)
In this situation since the neut. and ground are bonded it gets back to the neutral but if it were a sub-panel with isolated neutral this would not work correct?



Yes it would still work, the neutral is isolated at the sub-panel for a reason, but at the main panel its still connected together.

Gigs 01-07-2009 12:59 PM

Even with no neutral or ground at all, it would still work.

Current flows from hot to hot, they are out of phase with each other, 180 degrees. This happens regardless of neutral or ground.

TazinCR 01-07-2009 05:29 PM

The problem I have understanding is that if you read the threads here it is explained that without the grounded neutral the breaker will not work. So if the neutral and ground are separated in a sub-panel and you use the ground how does it work? Here is the thread and pay attention to Stubbies replies. http://www.diychatroom.com/f18/nuetral-feeder-cable-main-panel-question-20753/

chris75 01-07-2009 05:43 PM

2 Attachment(s)
[quote=TazinCR;208907]The problem I have understanding is that if you read the threads here it is explained that without the grounded neutral the breaker will not work. So if the neutral and ground are separated in a sub-panel and you use the ground how does it work? Here is the thread and pay attention to Stubbies replies. http://www.diychatroom.com/showthrea...753[/quote]


Because they get reconnected at the main panel. The reason they are seperated to begin with is to stop objectional current flow.


An example for you.
Attachment 7161
Attachment 7162

Stubbie 01-07-2009 06:47 PM

1 Attachment(s)
Yippie!! I get to post one of my legendary diagrams again.....:thumbup:

Tazin

Along with the diagram posted by Chris I think we can get you straight on this.

First by grounded conductor and the breaker not working...not tripping... I'm talking about the service neutral (service grounded conductor). If you look at the diagram we construct the effective ground fault path as shown with the red dots. At the service equipment the neutrals (grounded legs) and equipment grounds are bonded together at the neutral bar and in turn the service neutral (service grounded leg) is also connected to that neutral bar. Current in a ac system always seeks its source....the transformer. On the grounded side that link to the source is via the service neutral originating at the center tap (Xo) of the transformer.

What makes this key is it is the lowest impedance/resistance path back to the source. Current seeks all paths to the source including earth. But if given a hugely lower impedance path virtually all current will use that path to get to the source. It will not flow to earth with any appreciable amperage provided that low impedance path exists. Earths resistance is much higher than copper or aluminum wire. So if I open that service neutral (disconnect it) I have defeated the low impedance grounded path to the transformer. Now the current looks for another path to take usualy the earth via the grounding conductors to the grounding electrodes thru the earth to the ground rod of the transformer then to Xo (center tap). I think you can trace this on the diagram to see it.

The reason the breaker will not trip during a ground fault is because there is such high resistance, taking the earth path, that there is not enough amperage flowing to trip the breaker. Reconnect that service neutral and massive amperage will flow to the source and the breaker will trip...hope that simplifies that concept.

Now understanding the diagram Chris posted. Look at the sub-panel... the neutral and ground are not electrically connected (bonded). Neutral current can only follow the feeder neutral back to the service equipment where neutral and ground are bonded... then out the service neutral to the transformer center tap. Everything is fine.

Now connect neutral and ground in that sub-panel by visualizing a jumper between the terminal bars. You now have parallel paths that the neutral current will use to return to the source the feeder equipment ground wire and the feeder neutral. Remember current will take all paths provide to it that lead to the souirce. so in effect you have split the neutral current and given it a path on the equipment ground where it is not ever wanted. You only want that equipment ground to facilitate the effective ground fault path in the event of a ground fault...thus allowing fault current to flow to the source under low impedance/resistance so that enough current will flow to cause the breaker to open and clear the fault.

This diagram posted by Chris illustrates what happens if we bond neutral and ground on a 4 wire feeder to a sub panel....note that the service equipment is the first means of disconnect and the panel on the left is a sub-panel. In the image the metal conduit is being used as the equipment ground. Note the parallel paths putting dangerous neutral current on places we don't want it.

http://www.mikeholt.com/onlinetraini...13844669_2.jpg

Stubbie 01-07-2009 07:10 PM

Quote:

Originally Posted by TazinCR (Post 208464)
Greetings,
Saw this connected yesterday. It is a 220 mini split A/C and they hooked it L1 and L2 to L1 & L2 but hooked the green to ground. Should this not have been hooked to the white neutral? They (neutral & ground) are bonded at the panel but the installer did not know that. The four wires are feeding.

In this picture you have no neutral connection. Then neutral from the panel should be capped off not connected to ground. You only have two hots and a ground to the unit. Connecting the neutral to ground in this case really poses no big issue since the unit is strictly 240 volts but it provides no purpose other than giving fault current a second path back to the service equipment and then to the source.

It should be L1 to L1 and L2 to L2 then ground to ground and the neutral (white) capped as it is unnecessary.


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