Ground wire for a/c disconnects

[Ross Neag]

I have asked a local sparky about my calling out central a/c units with no ground wire at disconnect lug. He said not required but is best practice to include. I stated the potential of a vibrating appliance to lose metallic bond, hence ground, is too high not to call out. Do you call them out?

[Jim Port]

Is this run in metallic conduit or some other means?

[Ross Neag]

Chicago almost exclusively uses liquid-tight flexible metal conduit. Otherwise 1/2" metal EMT. NEC gives a threshold of 6' and 60 amps excluding a/c and motor appliances for flex. I'm just trying to make sure my clients are safe without being alarmist.

Did I just answer my own question?

[Michael Thomas]

IMO, you concerns are justified. I've always reported their absence, my notes indicate that NEC 250-188(7)(e) requires a separate grounding conductor in flex to condenser units, and gives Hanson's "Electrical Inspection of Existing Dwellings, 5-7" as the reference. I'll be back from vacation today, and I'll check further then.

[Ross Neag]

Thanks Michael. Makes me feel better. See you soon...

[Michael Thomas]

Well, going over my notes, it looks like metalic sealtite has a 6' maximum if used as an equipment grounding conductor, and the correct (grounding) connectors are required at both ends.

If you are using nonmetallic sealtite, a EGC is always needed.

I'm taking a full day HVAC class the first week in June, and if nobody chimes in with better information before then, I'll ask.

At least in my area loose and/or incorrect connectors are common, I always pull out the Tic Tracer before touching an exterior AC unit, and if there is no requirement for a EGC within flex, there ought to be - a good example of the reason for my concern is this electrocution:

Boy is electrocuted during rush home - Chicago Tribune (http://articles.chicagotribune.com/2007-08-04/news/0708030828_1_conditioning-air-conditioning-boy) ,

I'm not able to determine from the pictures what likely happened, but if there was any overcurrnet protection at all on the condenser, and a decent ground path back to it, it should not have remained energized while this kid hung on the fence.

And then, there's the stuff just done by clowns...

[Corey Friedman]

Hi Guys,

A couple of comments.

Ross, I agree with your perspective that liquidtight whips to the a/c should have a grounding conductor. We have all observed loose liquidtight connectors. I saw one today that was brand spankin’ new and was loose. Keep calling them out. There is no doubt they are safer with the grounding conductor.

Article 350 covers liquidtight flex metal conduit. Although I don’t recall the exact number, within this article it talks about grounding and in that section it indicates that an EGC is required (probably uses the word “shall”) when flexibility is needed (or something to that effect). In my opinion, flexibility is needed and therefore ends any question whether or not an EGC is needed. That said, this is based on the current NEC and I don’t recall what was on the books 20 years ago. Maybe it was the same, maybe not. If you disagree that flexibility is needed, the comments by your electrician are accurate but based on length and amperage rating you indicated.

One of the reasons these connectors probably work themselves loose is because they are never secured. Trade practice is to have the whip unsecured at the disconnect and condensing unit, even though 350 indicates that it should be secured within 12" of a box (or similar).

The bottom line for me is simple. If you think your client is better served by informing them about a lack of an EGC and your concerns associated with that issue, tell them.

Mike, I’m not sure what 250-188 has to do with this and I have no idea what 5-7” means. I assume these are typo’s?

Thanks for posting the electrocution story from the Trib (I can’t believe it’s three years ago already), it’s a good reminder.

Best wishes to all.

Sincerely,

Corey Friedman

[Jerry Peck]

Chicago almost exclusively uses liquid-tight flexible metal conduit. Otherwise 1/2" metal EMT. NEC gives a threshold of 6' and 60 amps excluding a/c and motor appliances for flex.


Article 350 covers liquidtight flex metal conduit.

To clarify: (underlining is mine)

- 350.60 Grounding and Bonding.
- - Where used to connect equipment where flexibility is required after installation, an equipment grounding conductor shall be installed.
- - Where flexibility is not required after installation, LFMC shall be permitted to be used as an equipment grounding conductor when installed in accordance with 250.118(6).
- - Where required or installed, equipment grounding conductors shall be installed in accordance with 250.134(B).
- - Where required or installed, equipment bonding jumpers shall be installed in accordance with 250.102.
- - - FPN: See 501.30(B), 502.30(B), 503.30(B), 505.25(B), and 506.25(B) for types of equipment grounding conductors.

- 250.118 Types of Equipment Grounding Conductors.
- - (6) Listed liquidtight flexible metal conduit meeting all the following conditions:
- - - a. The conduit is terminated in listed fittings.
- - - b. For metric designators 12 through 16 (trade sizes through ½), the circuit conductors contained in the conduit are protected by overcurrent devices rated at 20 amperes or less.
- - - c. For metric designators 21 through 35 (trade sizes ¾ through 1¼), the circuit conductors contained in the conduit are protected by overcurrent devices rated not more than 60 amperes and there is no flexible metal conduit, flexible metallic tubing, or liquidtight flexible metal conduit in trade sizes metric designators 12 through 16 (trade sizes through ½) in the grounding path.
- - - d. The combined length of flexible metal conduit and flexible metallic tubing and liquidtight flexible metal conduit in the same ground return path does not exceed 1.8 m (6 ft).
- - - e. Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed.

[Ross Neag]

Great, thanks Corey, MT and ECJ. I think this covers it. Be safe...

[Michael Thomas]

Sorry, the "250.188" was a typo, should have been (as in Jerry's reference) "250.118".

The "5-7" reference is to the chapter and page in "Electrical Inspection of Existing Dwellings" (see attached).

Per Hanson the AC condenser (compressor) unit is motorized equipment and the flex is "installed for vibration" and must meet 250.118 (6) (e) " Where used to connect equipment where flexibility is necessary after installation, an equipment grounding conductor shall be installed."

This is the source I've been referencing in reports, and I've not received any flack from electricians.

Still open IMO is the question of whether there is a specific code requirement for a separate EGC in rigid conduit in Chicago ( or any nearby communities) in this application, I've heard from time to time that it is, but I've not been able to verify this one way or the other.

[Jim Port]

IIRC this was a change in the 08 NEC to require the EGC in the metallic flex.

[Michael Thomas]

I also have seen the Liquidtight FMC installed without the grounding ferrule, and the jacket just sort of stuffed into the fitting.

[Jim Port]

MT, on those the steel grounding ferrule screws into the metallic flex and continues the ground path.

[Michael Thomas]

Well, that was sort of my point: missing ferrule, potential open/high resistance equipment ground.

I don't yank on FMC, but I do give a gentle pull, and I've had the FMC pull right out of the fitting due to a missing ferrule, and the fitting pull out the box or condenser housing because of a loose/missing lock ring, etc. Real good argument to me for a separate EGC.

[Jim Port]

Sorry, read right past the part where you said the ferrule was missing. I just wanted to explain the operation during a correct install.