ECN Forum Forums General Topics of the Trade General Discussion Area Re: HVAC

Greg and Reno,

I agree with you guys, but this other AHJ says it is not allowed, not me. I don't see anything wrong with it. For all practical purpose, the only person who will use that outlet is the HVAC tech. Plus, when he is using that outlet, the compressor would likely not be on.

I have seen where there are 2 or more compressors at one spot, the EC usually runs a feeder over and puts in a sub panel and a WP GFI outlet.

You can always 90-4 the thing but 210.23(A)(2) would be my sticking point if the FLA was greater than 10a and if the OC device is >20a you are still a no go.

OK, let's cut to the chase. I think we're talking about a specific diconnect: the Square D QO200TR http://www.drillspot.com/products/44409
/Square_D_QO200TR_Air_Conditioner_Disconnect_Switch

This is a nifty little disconnect - you can swap out the 60-amp switch with the QO breaker of your choice. Now one is tempted to ask: what if I tap off one of the legs on the 'in' side, and power my receptacle with that? (Anyone tempted to 'double-lug' here?)

Here are the problems with using the disconnect switch that way: you don't really have room for those splices, there's no place to land your neutral wires, there are not enough ground lugs, and there's a real issue in finding a place to land that third connector.

As an alternative, you could use something like this panel:
http://www.grainger.com/product/SQUARE-D-Load-Center-5B756?s_pp=false

Combine that with a breaker like this one and you're home free: http://www.superbreakers.net/homt20...;utm_medium=ppc&utm_campaign=product

As a caution: Ignore the prices, as they bear little resemblance to what you'll find at the local supply house.

Otherwise, let's imagine a 12/4 cable (2 hots, neutral, and ground) feeding a junction box. From that box it continues direct to a duplex receptacle. Also, from that junction box, you splice off to feed an HVAC disconnect as well. Is this allowed?

Well, let's look at the tap rules. The tap rules all assume that there is overcurrent protection at the tap. So, if there is a breaker or fuse in the disconnect, the disconnect is the 'tap' and you are legal. The problem is that you're now limited to the rating of the receptacle; most HVAC will want more power than 20-amps.

I'm not aware of an easy way to provide the overcurrent protection at the receptacle- unless you want to use another fused HVAC disconnect there. That could work: a gutter for the taps, feeding a row of disconnects.

Greg, I think you're over-thinking the FLA issue. That rule would apply only to the rating of the final overcurrent device- that is, the fuse / breaker in the disconnect. It would not apply to the ampacity of the feeder.

Instead of trying to get tricky -- of which the NEMA crews engineer OUT any such possibilities -- the normal lowest cost, quickest solution is to just run extra conductors.

Out my way HVAC units/ condensers are typically situated less than a dozen feet from the MAINS panel -- on the 'utility' side of the home.

So there is absolutely no point in trying to get tricky. A short run for a GFCI -- trivially short -- is more than sufficient for the Code.

Then the HVAC is run, regular way.

I've never seen a home with the MAINS panel criss-crossed from the HVAC pads... never.

I'll admit, California weather and EUSERC standards make my situation different from many areas of the country.

As for commercial work -- new work -- EVERY contract I've seen in the last fifteen years requires a GFCI at virtually every single RTU/ HVAC condenser -- regardless of the Code.

I will admit that until the Code changed, all of the older work omitted any service power for the HVAC contractors -- who ended up chaining extension cords dang near forever.

Reno, the FLA issue comes up in 210.23(A)(2) in reference to receptacles on branch circuits feeding fixed in place equipment. If you do not have in intervening OC device before you get to the receptacle it is still a branch circuit.

I suppose you might want to start the fight that the disco for the A/C makes that part of the load a feeder but I bet you don't win if the inspector doesn't like this setup.

Your other solution (2/4 box)is a far better idea.

Tesla, I must be the only guy who ever heard of HVAC techs hot wiring their service equipment to the line side of the disco.
My wife was in that business (HVAC sales) before she was a builder and I spent a lot of time talking to the crusty old techs.

Greg, out my way such discos are a little light on neutrals.

But I suppose 230VAC compressors/ freon recovery machines exist.

Out my way commercial RTUs routinely have a GFCI placed directly to the line side of the disco -- itself normally 3-phase -- on its own 120VAC 1phase circuit.

There is a perfectly good ground in there tho and an HVAC tech on a hot roof doesn't know or care that there is a difference.
If one of those phases to ground is 120v, it will run his vac pump and he is outta there. Hot wire in a receptacle on the line side and off you go.
... at least that was what they were joking about.

I always assumed that was why we wanted a real receptacle up there.
210.63 appeared in the code in 87. There are plenty of buildings around here older than that, considering we were 2 cycles behind most of the time.

I guess Tesla has not seen the floor sander guys either!

I came upon an HVAC tech that had a steup with clip-on leads going to a small 480 to 120 transformer so he could have 120 at the unit; that was really a site to see.

For the record...

I've seen floor sanders stick bare, naked, stranded #8 into dryer receptacles to power up their Hummels. (belt style floor sander - Germany)

I had to ask:"Since the 30A 240VAC circuit is used time and again, why aren't you just using a dryer pigtail to Hubbel twist lock pigtail?"

At the most, only two styles would be needed.

...

For your amusement: bowling lanes -- the wood ones -- are sanded by 8 to 15 hp machines. The crews typically clip right on to the 200A 208Y120 bussing -- with battery style jumper clips! That's the NORM for them.

Don't ask how I know.

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