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

Joe: Very nice install!


I just finished installing a 12 Kw "Briggs and Sratton" unit for a customer, He lives out in the sticks and at the very end of an unreliable primary line. We powered a handful of lights off the generator as well as a sump pump, sewage pump, water pump, furnace, microwave, and the GDO's and garage lights.. No problem whatsoever. Customer insisted his "Dry-O-Tron and pool motor be connected ( you know so the pool room doesn't get humid and the windows fog up, and we had problems. Unit started that mess once and had a hard time doing that, but would not again, it just shut down under the fault "Low Frequency". Guess he will have to deal with foggy windows.

A.D

JJM Nice set up, glad you got it done under the existing rules.

It looks like that will be a violation in 2008 NEC.

For ATS installations the gen set will have to have a rating equal to the calculated load.

Before Y2K,

I spoke with many customers about installing transfer switches and genny's.

9 times out of 10, their original idea was to auto transfer ahead of the mains. However, once they learned of the expense of the the equipment and installation, due to the sizing requirements to handle the supply current, it was usually agreed that the better, and much less expensive option was to install a dedicated panel controlled by a transfer switch.

This dedicated panel only allowed the necessary loads to be operated by the genny, and ensured that the genny wasn't overloaded by accident.

[This message has been edited by ExpressQuote (edited 11-12-2006).]

Thanks guys! Truly an HONOR indeed to get the thumbs from you folks.

Much of the BX in those photos were temp, coming off the gang box (RH top) used to splice from the old panel... all gone now... that 200A panel has a lot more BX in it, almost full.

Rewired, how do you feel about Briggs units? I've only dealt with Onan, Generac and occasionally Kohler. I find Briggs' "Empower" load management interesting... allowing larger loads to be started if the genny has spare power:



Briggs & Stratton Transfer Switches

IWire, that's unreal. Unless the genny was used for life saving equipment, I can't understand why genny sizing would be of any concern for the NEC. As long as all safety aspects of wiring them are met, like cable sizing, grounding, bonding, disconnects, OPCD and so forth are met - and accordingly the installation is safe - what POSSIBLY could be the issue, other than sitting in the dark?

One thing I have found is that gennys are often grossly OVERSIZED - much like what you see with HVAC. It almost breaks my heart when I see a 45Kw genny in some of these McMansions powering only one of two 200A panels, when it's got more than enough juice to power both. I guess it's to be understood, genny dealers don't want to be in the position of not having a system guaranteed to work then have to deal with lawyers.

Two suppliers we buy gennys from told me my 12Kw application would NEVER work. I would need at least a 20Kw to 25Kw unit, and even still I should forget about central air - would have to go even bigger... on my humble little 1,100 SF home. To this day, I never mention anything about my set-up working perfectly. Generac recently started branding their gensets on how large of a central A/C unit they will start. Their 10 kW unit can supposedly "start a 3-ton AC with power to spare". That would be unheard of from a typical genny dealer. Briggs & Stratton is doing this too. Apparently all this fear about central A/C starting was way overblown.

It should also be noted that central A/C systems that normally won't start with a genny can often be "coaxed" into doing so with hard/soft start kits and staggered start-up of the condenser fan (lowering head pressure), compressor, then air handler.

I also wonder if this provision actually will go though with pressure from manufacturers. After all, what's gonna happen with all those larger capacity and likely higher margin ATS units?

Then there's also the practical issue of "calculated load" as a code requirement. That I'm sure is gonna spark fireworks with AHJ's and contractors. Oh, I can just see it know, "Fine, that panel says 200A so I want a 48Kw generator installed, period. Either pull that 30Kw unit out, or put in a dedicated 100A subpanel in or I'm gonna have the whole service red-tagged." Should be interesting...

Not arguing, code will be code I suppose... just venting because it doesn't make sense.

Joe

Joe I could not agree with you more.

I think many have lost sight of what the word optional means.

From what I understand it is the manufactures pushing the change.

If it's a manual transfer switch the rules are unchanged at least for 2008 NEC.

Check this thread out

Automatic Transfer Switch - Art 702

Joe:

I found the Briggs unit not too bad to work with. Actually I found it a lot easier to install than the Generac my boss has at his house.
Only problem I noticed as well with the briggs is when I fired it up for the first time it did not seem to run right, sounded like it had a misfire and the voltage was fluctuating with a very light load. Maybe the mixture is off or something I am not sure but I am going to look into it Tuesday and see if there is a problem.
The unit we have installed does not have that "upgrade" to allow "control" of heavier loads, it just has a set of N.C contacts that will open and lock-out something when the transfer switch is transferred to "GEN".. Might have to use them to lockout the Dry-O-Tron compressor if I can't solve the problem by using a "kickstart" on the Dry-O-Tron.

I too have a back-up gennie, just a lil' "4500W continuous" Kodiak model.. I can run two refers, a freezer, my furnace and central A/C as well as a handful of lights with ease.. I used one of those "kickstart" hard starting devices and that helped bigtime. That and I wired a 2 min time delay into the A/C control, that way it gives the reefers and freezer a chance to start first.

A.D

[This message has been edited by Rewired (edited 11-12-2006).]

I just received an issue of the NFPA's magazine "NEC Digest." This article, IMO, glosses over the most important part of using ANY kind of back-up or supplimental power supply: the transfer switch.

Generator sizing is also a very important matter. This is one situation where 'bigger' is not always better! As a rule of thumb, a generator ought to be run at about 80% of it's capacity .... it's not really good for the genny to be massively oversized.

As for undersizing... well, that's usually something you can deal with- by pulling a few plugs, flipping a few breakers.

Another item often overlooked in genny installs is the regular 'exercising' of the equipment. The genny needs to operate, under load, at least once a month; weekly is better. The genny should operate under load; this can either be with an automatic transfer of power at the transfer switch, or by using a "load bank" to create an artificial load for the genny.

If one is not willing to 'do it right,' then I say they ought to stick to portable units and extension cords.

Reno, load banking would not be an issue with the many NG and Propane units out there now, but definately would for diesel. (Due to wet-stacking of the exaust) Otherwise excersizing is just to keep the battery charged and the oil moving on top of a good waste of fuel.

Bob and Joe, I was looking at that proposal for 2008 I guess... It doesn't sound totaly unreasonable IMO

Sounds more common sense than the current wording to me. Having worked on generators a lot in the past, I'll tell you that many of the safety devices are not immune to failure. And as we all know that breakers are the not the end all beat all of over-current protection. Many generators are equiped with the lowest bidder for breakers if at all, who knows maybe FPE or the like is that low bid? Why not be able to handle the load it is given? 'Cause none of us is going to camp out next to the panel to see what the capacity is for it when it turns on, and I don't think our customers are edjucated enough to do that either if they are even home or awake when it happens. Lets face it, we cant even get them to not over-lamp fixtures when they change bulbs.... Here in CA the black-outs seem to happen in peak use times in the summer, when the AC units are going, and usually at dusk. Several million people going home from work turning on the lights and AC... Then the under-sized neighborhood transformer fails. So in those situations one could easily expect full load when the ATS kicks over. What seems to be an over-sized unit will be getting the locked rotor amperage of at least an AC unit if not two on many of the homes these would be installed in.


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

I don't have much time now but I have to ask this.

If we can not trust breakers to do the job they are designed for we will have to stop installing multi-receptacle circuits.

Also note that that the change will still allow a homeowner to manually overload the circuit.

If it's not safe to let an Auto transfer switch overload the genset than it is not safe to let it be manually overloaded.

I think Joe's installation is perfect example of why we don't need this change.


Gotta go..Bob