220v circuits not connected to service panel ground?

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Old 05-08-19, 09:45 AM
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220v circuits not connected to service panel ground?

I'm having my AC system replaced and checked out the wiring of my existing dedicated 30amp 220v circuit used for the old AC. When I took off the service panel cover, I was surprised to see that the NM cable for this circuit connected to the 2-pole breaker breaker only appears to have 2 conductors.

I understand that it doesn't need a neutral because this is a dedicated 220v with no requirement for 110v, but why isn't there also a ground in order to connect the AC chassis to the service panel ground? Even weirder (to me) is the fact that even though this circuit doesn't appear to have a ground wire (I didn't even know there were NM cables without a bare ground), there IS an outdoor shutoff breaker next to the AC, and the wire from that to the AC DOES have 3 conductors (i.e. black and red hots, and a green which I assume must be ground). Is it possible the outdoor shutoff has a separate ground connected directly to earth? If so, that doesn't seem right because 2 different points connected to the earth can have a small voltage difference?

Also, while I had the cover off, I looked at all of my other 220v circuits (i.e. dryer, stove, well pump), and I don't see a bare ground wire on ANY of them at the service panel.

The house was built in 1979, but I had the electrical service upgraded from 60amp to 200amp when I bought the house is 2009. I did this because the home inspector recommended it (e.g. there were double-tapped breakers and other issues). I didn't ask a lot (or really any) questions at the time when this upgrade was done, but I've been learning since then over the years. For example, I didn't know about backup generators at the time I bought the house, and would have asked the electrician to at least add a transfer switch when he was replacing the entire panel. When I think about this, it bothers me that he didn't even suggest this...
 
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Old 05-08-19, 11:59 AM
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You can add a ground wire. It does not have to follow the same path as the NM-b. Under older code it must come from the main ground within five feet of the panel Newer code allows going from the nearest adequate ground.

Note residential power is 120/240v not 110/220.
 
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Old 05-08-19, 12:28 PM
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So does that mean the the AC can have it's own dedicated ground to earth near the unit (e.g. literally a metal spike in the ground), or does it mean that we need to find another nearby circuit with a ground wire and connect to that? In other words, what is the definition of "adequate"? It sounds like you are saying that the new code is LESS restrictive than the old code. Also, was it EVER code not to have a ground wire for circuits like this? As I said, it's not just my AC circuit, but ALL of my 240v circuits that look like this. I live in MA, if that matters.

Also, I often see 110v/220v, 115v/230v, and 120v/240v used interchangeably. Is the idea that 120v/240v is the intended "target", but the measured value can often be as low as 110v/220v due to losses?
 
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Old 05-08-19, 01:33 PM
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A ground rod to earth is part of a "grounding electrode" system that is typically found connected to the service panel. That is totally different from the "equipment grounding" system that ties to outlets, fixtures, appliances, HVAC, etc. These two different ground systems are tied together in the service panel.
At one point, yes, equipment ground wiring was not required but in 1979 I'm sure it was required at least in localities that followed the NEC. I think Ray is referring to NEC 250.130 (c) where in the 2014 edition they allowed you to access the ground from another branch circuit. Most of the time the code gets more restrictive but not always.
By the way, if you access the ground wiring from another branch circuit, then the size of the ground wire on that other circuit should be at least as large as the minimum ground wire gauge required for the circuit that you are bringing the ground wire to. For example, at least #10 gauge is required for circuits over the range of 30A to 60A. One of the requirements of the equipment ground conductor is that it can reliably conduct the current if there is a short from hot to ground and trip the breaker. A ground rod connection is not a reliable low resistance path for this function.
 
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Old 05-08-19, 01:48 PM
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I often see 110v/220v, 115v/230v, and 120v/240v used interchangeably.
110/220 and 115/are obsolete values. Modern nominal voltages are on single phase residential 120/240 10%. However you may have 208 volts usually in some apartments supplied from 3 phase.

I think Ray is referring to NEC 250.130 (c) where in the 2014 edition they allowed you to access the ground from another branch circuit.
And by adequate I meant in this case a minimum of #10 ground wire or a source connected by continuous metal conduit system to system EGC..
 
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Old 05-08-19, 02:08 PM
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I don't think there are any nearby circuits with #10 gauge wire. Although, the water service is nearby and that might have a jumper to the service panel ground. Or maybe the jumper I'm thinking of just goes between the 2 sides of the water meter...

This particular circuit was probably installed sometime in the 1980's when the original AC was put in (i.e. not original to the house). Was it code to NOT have a ground for 240V appliances back then?

So, since we are changing the AC outdoor unit, does it need to be connected to the service panel ground, or can it be grandfathered? Does it void the warranty of the unit if not grounded? What about all of my other appliances that appear to be on circuits wired with un-grounded NM cable? The stove and dryer were replaced around 2005 by the previous owner. The dryer has a 3-prong receptacle, and I don't know what kind of receptacle the stove uses (could it be hardwired?).

Also, is the ground wire in NM cable always the same gauge as the other insulated conductors, or is it thicker? I don't see why it would be thicker...
 
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Old 05-08-19, 02:10 PM
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Since the 1960's residential NM has had a grounding conductor. Since your house was built in 1979 it is more likely the wire was just cut off at the end. Take a close look. Also most cables have printing on them that have the date and other info.
 
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Old 05-08-19, 02:32 PM
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Why would someone cut off the ground wire at the end instead of connecting it to the panel?
 
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Old 05-08-19, 05:02 PM
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Well, on at least 1 of the 240v circuits, the jacket on the NM cable says 14/2WG. So that means they cut off the ground. WTF?
 
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Old 05-08-19, 07:46 PM
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It used to be standard practice back in the day to cut off the grounds. Only had two prong receptacles so installers didn't think it was needed and it was faster/easier. Then they kept up the practice way too long refusing to learn how to do it right.

So what you can do is cut the cable back on both ends and you should have a workable ground. You probably would have to find some slack or mount a junction box a foot away to splice a new NM cable to the ends.
 
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Old 05-09-19, 09:28 AM
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Since the 1960's residential NM has had a grounding conductor.
Not quite. In the late '70s and early '80s NM cable was available with no grounding conductor. I have seen 14-2, 12-2, 14-3, 12-3 plain cables at supply houses and used in branch circuits with no ground although in most municipalities it would not have passed inspection. 10-3, 8-3 and 6-3 plain NM cable was widely used across the country for electric dryers and ranges as the grounding was done through the neutral conductor.

My best guess is that the OP's house built in 1979 was built in an area that at that time had no codes or inspections and the cheapest materials available were used.
 
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Old 05-09-19, 10:10 PM
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Before my time so you saw that it took close to 20 years for some areas to follow the grounding rules? Also, I wasn't thinking about dryer/range receptacles as the NEC 4 wire requirement is only from the 90's.

Even the braided NM that I see usually has a ground but smaller. Seeing the 16 (?) gauge is weird. Older than that is usually AC (rarely with the bonding strip).


Found this on mikeholt.com but not sure of its accuracy:

History of Grounding

I am working on a brief history of significant changes to grounding
Here is what I have so far
1923 NEC - First mention of driven rod or pipe electrodes
1925 NEC - Driven rod electrodes now called �artificial�, 8 ft long, 1/2� rod or �� pipe
If resistance >25 ohms, requires 2 electrodes spaced 6 feet apart
1951 NEC - Ten feet of less of metal water pipe must be supplemented with additional electrode
1947 - Grounding receptacles required for laundry
1956 - Grounding receptacles required for garages, basements, outdoors
1962 - All branch circuits must include a grounding conductor
16 AWG for 12 and 14 gage circuits, 14 AWG for 10 gage circuits

1963 - Research paper presented by H.G. Ufer at IEEE Conference
1969 - Full size ground required for circuits
1971 - Water pipe electrode must be supplemented with additional electrode
1971 - Ufer ground must be used �If Available�
1974 - NFPA TIA �if available� does not mean it has to be used.
1999 - Additional electrode must have resistance of 25 ohms or less, or be supplemented with additional electrode
1993 - Interior metal water piping more than 5 ft from point of entrance can not be used as part of the grounding electrode system
1999? - No longer allowed to use use neutral for frames of ranges, etc
2002 - Can't reground neutral if creates a parallel path to separate buildings
2005 - Ufer ground must be used when present
2005 - Bonding added to title
2008 � Supplementary ground rod changed to auxiliary ground rod
2008 - Ground is now the earth
2008 - Can not reground the neutral at separate buildings
 
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Old 05-10-19, 07:09 PM
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1999? - No longer allowed to use use neutral for frames of ranges, etc

That would be 1996 and affects the wiring of electric dryers and electric ranges in a typical dwelling.
 
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