ECN Forum Forums General Topics of the Trade General Discussion Area 200A Auto-transfer switches

The only difference between an ATS and a MTS is the automatic action; if the ATS trips on overload, the ATS ceases to be automatic and becomes an MTS at that point, doesn't it? I wonder if any AHJs will buy into that explanation?

It's common sense that if you want your generator to be automatic, you ensure it won't overload. If an overload is unlikely but possible and automatic operation is desired but not required- well, you're SOL in 2008...

[This message has been edited by SteveFehr (edited 11-13-2006).]

Lately, we have been specifying a disconnect on the side of the building, due to requirements of 700.12-B-6. We read this to mean that a shutdown switch INSIDE a generator enclosure is not readily accessible, so an additional disconnecting means is required. (I suppose this is so the firemen can disconnect the generator in an emergency). How do you read this, and have you seen this in your area?

IWire, I read the Automatic Transfer Switch - Art 702 link you noted with great interest... thanks. Looks like seems we think alike... wow... if you were a girl I'd marry you, LOL!

It looks like we're fighting a losing battle though; the duties the NEC is charged with is growing increasingly corrupted by manufacturers. Generators are protected and the associated wiring is protected not only by internal electronics (which are very sensitive) but by an OPCD. As was poined out in the thread, if you've got 40 20A breakers, do you need 800A service? And how many times are POCO service feeders sized way to small if they had to follow code? So if there service doesn't have to be upgraded, why should the genset?

Larry Fine makes a good point in that thread of using the aux contacts for load shedding (mine has them) but will that be enough to satisfy an AHJ under the proposed rules?

I do have a problem with the this part of the 702.5 Capacity and Rating for 2008:

(B) System Capacity. The calculations of load on the standby source shall be made in accordance with Article 220 of by another method that is acceptable to the authority having jurisdiction.

It the "another method that is acceptable to the authority having jurisdiction" I have a problem with. I can just see how that will go with the "right" types... though some AHJ's don't seem to give a hoot how or even if a genny is installed. My system passed without the genny in place! AHJ and POCO couldn't care less about what kind of generator I was using... they just wanted to see if the wiring was done to code, no interconnection, proper grounding and bonding, and gas piping was correct and holding 5 PSI when they got there. POCO even said we don't check "appliances". I've seen this on other jobs too - except for some reason when diesel is involved.

It should be pointed out that a genset with a dedicated panel can be overloaded just the same. A 10 Kw genset hooked up to an 8 breaker panel, with 5 15A and 3 20A breakers has a total load potential of 135A. Generator only produces 41.66A so we're in the same boat again. That genset can be overloaded.

As Reno pointed out, it's no good to have a massively oversized genset either. And what about physical space, there might not be enough room for such an oversized unit, not to mention the gas requirements of having such a huge genset. What if the POCO won't upgrade your gas service enough to feed an oversized beast (a 45Kw unit will burn over 500,000 BTU on average), then what happens?

Regarding disconnects really doesn't make a differnce in my opinion... you've got one of the best ones of all - the gas (or fuel) valve - turn it off and the genset stops producing power instantly. Fire department would probably do that anyway in an emergency.

Joe

Rewired, how's the gas pressure, both before and after the regulator? Some genny's require elevated gas pressure, so if you're running NG the typical 3-6" WC probably won't be enough. But there may be ways around that.

I've seen cases where gas pressure too low causes "flooding" since there's not enough pressure to "push" the diaphragm on the regulator and effect proper regulation, and gas pressure too high resulting in "starvation" because there's too much pressure on the diaphragm. Those cheezy regulators are not demand regulators by any means.

The output pressure depends on the spring installed in the regulator. They're usually rated in WC (Water Column) and have limited control range, say 1-3" or 3-6" or 12-15" and so forth. I sometimes pull the adjustment screw and spring out (no, you won't create a gas leak) and use my finger as the "spring" to adjust for the optimum engine performance (and electrical output) under all ranges. When it runs right, I record the output gas pressure and install the appropriate WC range spring, then make the final adjustment.

If you don't have a manometer, you can pretty much "make" one in a pinch if need be.

Many genny's are setup for natural gas, and if you're running propane, you usually have to install an orifice and lean out the carburetor.

Good luck!

Joe

Steve I think that says it all...

Bob on the OCP thing, most of the small sets have CB's that seem to be the cheapest item found, and larger sets will have a rarely used relay to drop out the load contacts. Granted most of the ones I have worked on were older Onan models with a circuit design that probhably hasn't changed since the 60's - but they would often hold all but a direct short, and some held direct shorts.... Anyway, my point was that there are 'certain' cb's we dont trust often - like zinsco, or FPE - why put your electrical design reliablity on a no name hench en mexico breaker? Or a raely used solid state circuits dependant on relays that are often exposed to the elements and harsh vibration? FYI my personal prefferance is a fused disco or fused transfer-switch...

I think Joe's example is not one the average HO should follow... Although Joe may have an average home, as a member of this forum he is not the average HO...
On many gen sets over-load and under freq are optional items...

Maybe the NEC board took an electrically libertarian approach to design for the electricaly libertarian out there with manual transfer. "It's mine, I'll over load it if I want to..."

Joe I have seen AC units that dim the nieghbors lights. Some need all the HP they can muster to start a large motor without bogging down the Hz which is why some seem over-sized - just for FLA and LRA for motor starting. Try your experiment again and start the AC unit last....

But while on the NG subject... There has been an interesting Plumbing code development here. Often people who have been through the quakes here remember being without power for a few weeks - think about getting a generator and the plumber comes by to upgrade the NG main to accomadate the extra pressure and WC needed, and the mandatory (In some cities) siezmic cut-out valve. Most are manual ball/funnel rest type, and make the generator useless after a quake.


[This message has been edited by e57 (edited 11-13-2006).]

E57, regarding the OCPD issue, using my set-up as an example:



What if a 50A main breaker enclosure were installed in between the ATS and the genset disco, similar to the one shown below:



Now the genset and wiring would be covered. I was considering such a configuration at first (you'll note I have room on my board) using a GE 70A enclosure with a 50A 2-pole breaker, but my friend who does lots of genset installs (mainly commercial) said my idea was "retarded" because the genset breaker and electronics provides protection. I could've also used a fused disco, but my supply house didn't have it in stock. Besides, like my friend said, why should I care about protecting less than 10' of cable; if anything, the genset wiring will burn up first long before the #4 in this app.

Funny you should mention disasters... ready for that too: If the natural gas goes out, I've got two 30# LP tanks and an adjustable regulator with a 3/4" connection for just such an emergency. That along with two 20# for the BBQ and I've got 10 hours of fuel minimum at full load (240,000 BTU) if my math is right. Granted, if there were such an emergency, the genset would be operated sporadicaly to conserve fuel.

One of the basic premises behind this discussion is if the genset overloads, and shuts down, the system is not truly automatic, hence not doing what it was designed to do. My question is why does EVERY fault have to result in shutdown and lockout? Why can't the manufacturers modify the firmware to automatically restart the genset say 2-3 times maximum after a brief delay if it's only a simple overload? Of course you'd want the genset to lockout on low oil, temp, or other serious issue... but for a momentary surge the genset? Doesn't make sense.

I think this simple change would go along way with the proposed 702.5, but obviously that won't do much to help the manufacturers bottom line, which I'm beginning to believe is the intent of the proposed changes.

Joe

If I were to get one, and I have been thinking about it.. I'd shoot for diesel for endurance and and the realities of the day I would need it, as it just might be a quake of 6.+ NG would be cut-off in different parts of the city just due to ruptures.

So Joe, you own one, would the breaker in it be one that you stock or would install? I've seen some I would give a second thought about seeing them on landscape lighting. Do you think it will operate in the tested 60hz 120'240 paramiters at ~30hz @ 60 volts? The fact that the safeties that are installed (Over-load, and under-freq) dropped the load before the breaker reaction time to me is pretty telling. Over-load protection circuits are there for protection of the engine, not the wiring or load the gennie is supplying. And some generators offer a by-pass button for that.... Under-freq is kind of a dual protection circuit that protects certain loads and offers some over-load and shortcircuit protection, because in those situations the windings slow down and even stop, but mainly for power quality. Depending on the circuit they may actually be the same 'over-load/under-freq' because the would act the same in effect. A loss in engine RPM.

I used to start 50HP motors with 60Kw generators (not that you would ever do that at home, but as an example) and it would temparalily stall the engine for a moment. From 60 to 10Hz due to in-rush current. The generator would physicaly shutter. This also drops the voltage for anything else on circuit... But do that on a 100Kw set, and you barely notice...

That proposed 702.5, for ATS would allow 2 options, full load, or load managment. Load management can be done in a number of ways, and still not exclude you from running the whole house as a connected load - just a managed load... A home like yours (Which has about 3X the load of mine at 1300sq') is a much smaller load than what I see install a 1/2 mile away from me in richer areas of town. Where as you could max yours out at 100+% and have to try to do it. Some of the homes I wire would stall a generator of that size - easy. Like dropping the clutch in your truck. But the diffence if that it doesn't just damage the engine, it creates other voltage and current problems on all the circuits connected to it. (Depending on the winding and regulator design.) A frequency controlled design would then just pump more fuel to compansate the loss in RPM/Hz - if it can... The reason they often wont auto-by-pass or reconnect is because this can be a dangerous electrical fault, and the idea not to self-destruct of cause damage. Would you connect to an under-voltage, 35Hz source? Or purposely over-load a transformer, or phase convertor? A generator is no different - IMO it has nothing to do with manufactures or thier bottom line. A generator is nothing more than a rotating transformer - in your case, a 12Kw transformer with an engine primary.

Really these types of residential units are kind of new in the grand sceme. I think the code is just playing catch up to the consumer protections and Darwin Award winning homeowners, but left some leeway for those facilities that still have qualified humans to operate these machines in reasonable methods, as opposed to the auto-connecting switch....

Thermal overload isn't going to do a very good job of preventing generator overload- the trip curves on those breakers are just far too lenient; I wouldn't expect a 12kW to put out 24kW long enough to trip! In cases like this, the generator really aught to have an electronic relay designed to trip before the engine stalls. Or maybe it's just not a big deal on engines this small, and at least saves on fuel if the engine just dies vice running unloaded...

I might be unique here in that I've only ever worked with the BIG gensets, 200kW, 400kW, 3MW etc, and we always have current transformers, PLC logic and servo-breakers with the luxury of sophisticated programming of the switchboards to do whatever we want. When you're talking about emergency power, sizing to avoid overload isn't just good practice, it's absolutely essential. What sort of brains do these small ATSs have? Is it just an atmel chip, a few lines of code on an EEPROM and a 2P contactor? That doesn't generally allow for reactive droop and closed transition back to utility power, does it?

On the big gennies, they're always rated for overload, and include internal protections to shut down if things are too out of whack for the engine to maintain proper rpm. I can go up to the panel on any of these and set what frequencies are acceptable, maximum current levels, etc, and adjust the trip settings on my breakers to match it. In-rush on startup is usually the worst; if the breakers can be timed to come back on one at a time, or not come back on at all if the generator is overloaded, it can allow a marginally sized generator to power a load it might otherwise stall or trip on. I can see how that might be cost probititive to a homeowner...

I'll just stick with my little manual-start 3.6kW that I bought a few years ago but have thankfully never had to use It'll keep the fridge, TVs and lights on, and even run the A/C if I'm expedient with my load-shedding. As this forum shows up in a google search that laymen might find, I won't mention how I plug it in...



[This message has been edited by SteveFehr (edited 11-14-2006).]

On a side note, I have been following the latest craze in management circles.

When confronted by a crisis, such as a power failure, you should pause, take a deep breath, and ask:

"How would the ancient Egyptians solve this?"

E57, I hear you on CB quality on some gensets. I don't like pointing fingers, but a lot of the switchgear on Generac units in general leaves something to be desired. And the larger they seem to be, the worse they seem to get.

But in answer to your question about the CB in my particular unit, aside being from a French company (with the unoffical boycott and all) I'd use it... SquareD two pole, common trip... I believe QO series, not HomeLine if I remember right. That's why I like Onan. They're more expensive, but the quality seems to be much better.

If you're in CA I don't blame you for wanting to go diesel because of earthquake considerations (not to mention reliability and torque) but in NY that really isn't a major concern (although it's said we're due for one, but that's another issue). Cold weather is an issue though, diesels aren't too happy about being awoken in the cold.

Wow Steve... a 3Mw genset, now that must be fun! I don't think I've ever run into anything bigger than 200Kw, and that was for a large restaurant. And yes Steve, we know what a bad boy you are hooking up your own portable genny but considering the monsters you work with, I think we can make an exception.

Joe