How the heck does a typical home transfer switch work?

[Arlen G. Holder]

Correction.

I just put some chalk on the raised letters of my mains circuit breaker which showed the mains breaker to be 200 Amps (not 300 Amps).

There are three separate 100 Amp breakers, each going to a different panel.

So I think, at this point, that the reason for the TWO 100A Generac model

79848A transfer switches is simply that each one handles 100 amps nominally.

Now I just need to figure out how to debug why this two-fisted solenoid isn't switching on automatically - but it does switch on when I flip it manually.

[Arlen G. Holder]

Thanks Clare. That makes sense then as to why the puny generator is only 67 Amps, but since the Mains is 200 Amps, it needs two transfer switches of nominally 100 Amps each.

Thanks for that analysis, which I can't argue with.

Some of these voltages appear to be hard coded, based on this sticker

I'll start looking up where to source spare parts, after calling Generac tomorrow (1-800-GENERAC) to see if they still sell parts for this 79848A.

One problem I realized is that I lost 2 of the Buss fuses, which "may" be why both transfer switches aren't turning on when the power goes out and the generator turns on.

Funny thing is that advertisement for a similar transfer switch seems to have the "green" Buss 600Volt fuses spec'd at 2 Amp based on this picture of the Buss SBS-2 (green color code) for sale

$/Generac-Transfer-Switch-100-Amp-250-VAC-One-_57.jpg>

Notice those are "SBS-2" green 600Volt fuses (not BBS!).

The sticker on the side panel of that transfer switch for sale, and on my side panel both say the same thing, which "implies" 2 amp fuses at 600VAC.

My fuses appear to be red (not green), and they appear to be o BBS-4 (not SBS) o BBS-5 (not SBS)

So what's odd is that mine are higher amperage, but also a different three letter code (mine are BBS while the one for sale is SBS).

I tried to get these fuses at Home Depot, Lowes, and Ace today, but none of them stock these fuse sizes in the 600 VAC rating.

I realized I'm _missing_ two fuses, where, I don't recall, but maybe I removed them to test them and never put them back? It would have been a long time ago (a year or two) so the _first_ thing I'm gonna do is source those Buss fuses after figuring out why some are 4amp and some are 5amp.

I'm not sure _why_ some are the red 4 amp and some are 5 amp though (while the originals seem to be green 2 amp).

Googling, SBS does NOT stand for "slow blow" but for fast-acting!

[Jeff Liebermann]

Let me guess... State Electric Generators formerly in Harvey West Park? They moved to Scotts Valley:

High prices and so-so work. You could do worse. State does much better work than what I saw in your photos which suggests that they were fixing something.

Try this video. Notice that the relays switch based on the condition of one input wire labeled "transfer". "Generac automatic transfer switch explained, demo"

The "transfer" line on the terminal strip comes from the electronics that detects that the utility power has dropped and that the generator has produced stable power for XX number of seconds. When it gets both of those, it grounds the "transfer" wire, which closes the relay, etc. In other words, your problem is not in the relay box, but rather in whatever you're using for electronics to detect utility and generator power (and timers). In the above video, it's the black box with all the terminals and colorful labels. I don't see such a box full of electronics in your photo: Find the "transfer" terminal, disconnect whatever is connected to it, ground it, and see if it acts like the relay in the video.

Incidentally, 200A service should use 2/0 copper (or 4/0 Aluminum or CCA) minimum. In some counties, it's 3/0 copper minimum. That doesn't look like 2/0 in the photo. More like #4. Color me very suspicious.

[Arlen G. Holder]

You are pretty good Jeff, as these are the two stickers on the cover

I generally obfuscate where I live, but suffice to say I can probably see your house from where I am, or close to it. :)

I'm glad the narrator said he couldn't find out how it worked online, which is exactly the type of answer I'm asking about here.

At 34 seconds he explained what that cryptic "194" meant!

And he explained what that cryptic "23" meant on my panel! Where: o 23 === ground o 194 === +12VDC So I can now test the two-fisted solenoid by putting 12 VDC across them, which is what the generator should do, which will "transfer" the power from line power to generator power. (This is what I've been doing manually with the mechanical lever.)

The narrator then showed that when the PG&E power is restored, the generator will _remove_ that 12VDC, which flips the two-fisted solenoid back to "line" power.

The one bit of confusion is that he said at 90 seconds that each solenoid is controlling 240 volts, but I think it might only be controlling 120 volts (but I'm not sure if it's controlling 120V or 220V yet).

He then explained the transfer is controlled from the "plastic relay".

I agree his box is different than mine, where mine is just like this one:

Mine and that one for sale are "simpler" looking than his is.

I think it should be easy to put 12VDC onto pins 23 & 194, but I need to get a bunch of those BBS-4 and BBS-5 fuses first.

So my current plan is: a. Source the two missing BBS-4 (or?) BBS-5 fuses. b. Then test with 12VDC to see if the double-fisted solenoid operates

If that makes it work, then my problem is likely the "sensing" circuitry, where this sticker explains all that sensing circuitry is hard coded, I think:

You have a good eye, where all I can say is that I didn't wire it. I did INCORRECTLY say it was 300 Amp mains service, where, when I shined a light on it and put chalk on the mains breaker, it turns out to be 200Amp service.

What's odd is that there are _three_ 100 Amp sub panels!

Which seems kind of strange, but I didn't wire anything and all the permits that were pulled were closed, so, it must make sense (code wise).

Two of those 100 Amp panels are in the house, and one is at the pool.

I need to call Generac (800-GENERAC) where I'm confused about the fuses o Why BBS-4 _and_ BBS-5 fuses?

Once I source those hard-to-get fuses, I will test the 12VDC at cryptic pins 23 & 194.

If the double-fisted solenoid does not trigger...

then we know that the sensing circuit isn't working to put 12VDC across those two pins.

Thanks for that wonderful video.

I'm a bit leery of what I can test with the MAINS connected though, since the power is currently running fine ... so I will need to be careful since it's only once a month that the PG&E power goes out for me to run the full test.

[Arlen G. Holder]

This is closer, but not exactly either, I think:

Apparently, they recommend testing the transfer switch _monthly_

This has a transfer switch testing sequence

I found a paper copy of the 32-page owners manual, part number 98374 which is titled "Generac II Emergency Power Systems Owner's Manual" (revision 0, dated 11/22/1995) and which contains a generic parts list and exploded diagram for both the generator and transfer switch (apparently they come as a matched set).

The four fuses in the exploded diagram just say 2 Amps 600Volts, but I wonder if mine are double that because there are two transfer switches (where on the net, the video Jeff provided _also_ used red 4 amp fuses!).

I found that two outfits will sell generac parts to the public online:

I'll call Generac tomorrow to get more details.

888-GENERAC (888-436-3722) extension 4, extension 2 1-262-544-4811

[Micky-Bob]

+1

[trader_4]

67 amps at 120v, which is equivalent to a 33.5 amp service. But I wouldn't call an 8kw generator tiny either.

so I'm

[trader_4]

Without taking a survey, who knows? It all depends on how large the place they live is and when it was built. 200A service is common in good size single family homes built in the last 30 years or so.

Sounds right and must have significantly increased the cost of the installation. Why you have two panels for the house, instead of one remains a mystery. I've seen new work here that uses two, for 4000 sq ft houses. They run a 300A service, use two panels right next to each other to hold the large number of breakers.

As others have said, since neither one works, it's likely that the Generac generator isn't sending it the signal to switch over. The generator makes that decision. When the line voltage drops, it starts up the generator. Once the generator reaches proper voltage, it sends the cut-over signal. From what I've seen, Generac is crap. I assume that when you say it works when you manually cut it over that means the generator is generating proper voltage. But have you verified it with a meter? If it was putting out 100V or 130V, or 50hz, then the generator logic won't send the cut-over signal. If that's OK, then seems either something is wrong with the generator module/circuitry that controls it or the wiring in between.

[Jeff Liebermann]

Methinks your first problem is finding the box that controls the automagic transfer switch (which contains the sensing, timing, and switching logic). Something like this: "Automatic Transfer Switch Controller Tutorial"

It's probably inside the generator enclosure. Just look for another rats nest of wires. The thresholds, timing, interlock, etc settings are usually adjustable.

I have two guesses:

1. The +12VDC that runs the relay is probably missing because the starter battery in the generator is dead, or the fuse that protects it is blown. That might explain the missing fuses. It might also be that State Electric took one look at the mess and ran away. There might be some lower voltage coming from the charger trying to charge a dead (shorted) cell.

1. Every controller I've seen has a self-test and/or test-run feature. You should be able to test the transfer switch with the test-run button instead of reworking the wiring.

Also, I have some suggestions:

1. Don't play with the transfer switch with the utility AC power applied. The life you save may be your own. The undersized wires feeding the transfer switch should go to a double breaker on the main panel. Flip it open, check that there is now no AC on the contacts or anywhere in the rats nest of wires, and then troubleshoot.

1. Draw as schematic diagram and label everything. If this were my headache, that's the first thing I would do.

2. If you know a local electrician, who won't turn you in to the county, have him look at the wiring and make some recommendations.

[gfretwell]

I would check the easy things first and be sure you don't have a blown fuse.Then test it by tripping the main breaker and see if it doesn't start the generator and flip over. Clare may be right tho. It could be a bad board. I think that board is probably expensive enough that you might want the generac guy to check it out before you start throwing them around. I am not sure what the trouble shooting technique would be. Maybe there is an answer to that on the net.

[gfretwell]

There are literally dozens of varieties of fuses with different ratings of how they blow in that configuration. I would try to find out what Generac specs as the right fuse. For trouble shooting purposes a 2a or 4a in any rating would work based on what you are saying but long term I would get the one they spec. You could go to an electrical supply or order them online. Home Depot is only going to have the most popular sizes and ratings.

[Ralph Mowery]

There is often a big misunderstanding about fuses.

Where I worked 2 men from the Buss fuse comapny gave a talk. At one time they had many fuses with the statement a fuse for every application. But the new selling point was that one fuse could replace many kinds. Mostly all advertising hype. They even handed out a plastic chart about 5x7 inches with all the fuses that could be replaced by their 'newer' fuse.

As long as the fuse fits in the holder and has a high or higher voltage rating, the fast/slow blow, and current ratings are the same it is ok to use most any of the many types in many cases.

[Arlen G. Holder]

Hi Jeff, I agree with you, and I can clearly see that there is a rat's nest inside the generator, which must be doing the initial sensing of the power in the first place, as you mentioned.

I think my task is EASIER than looking at that rat's nest inside the generator though, since all I need are the wires coming OUT of the generator.

I'm not sure yet where to FIND those wires inside the transfer switch, but I think the first (and only?) place I need to look is at what the pins of that "plastic solenoid" do...

since that solenoid seems to send the purple and blue wire 12VDC to the "double-fisted solenoid" to switch power from the mains to the generator.

I understand and appreciate this assessment, where there's LOTS I didn't mention (which is always the case in such things), mainly the fact being I "think" it was me who pulled those fuses long ago and forgot to put them back (I think I was testing them but I don't actually recall).

Also, you're actually correct that the battery in the generator WAS dead, since I had disconnected it to charge it, and then I had left it disconnected where the charge eventually bled off. I actually had to jumpstart the generator when the power last went out, but I have since charged the battery (I'm gonna put quick connect clamps on the battery at some point, which will help in the charging process since I have multiple spare batteries I swap in and out of that generator).

This is good to know, for two reasons:

1. This is dangerous stuff so having safe tests is required, and,
2. Most of what I read suggested testing MONTHLY (which is crazy frequent)

Thanks for that advice, Jeff, as I'm well aware of the power, but I'm not sure yet how to test a transfer switch. It does seem prudent to test the transfer switch ISOLATED from BOTH the mains and the generator.

Preventing the generator from turning on should be easy as it has a power switch and it requires the battery so it's easy to prevent it from turning on.

I'm not totally sure simply turning OFF the mains will isolate the transfer switch - but that's simply because I'm currently ignorant of the wiring diagram (which is one reason you said to do that first).

If the power goes from the power pole to the utility meter to the main 200 Amp breaker switch, and THEN to the transfer switch, then doing all tests with the main 200Amp circuit breaker off is prudent. (Obviously I'd doublecheck with the Fluke DMM.)

Yup. I agree. I had wanted from this question on Usenet to first get a general idea of how these transfer switches work - which - I think I kind of now have - but the exact wiring of every connection is still needed before I can effectively troubleshoot.

Generac sent me the owners manual for my 09067-9 generator, which contains exploded diagrams, for example, here's the exploded diagram of the 09067-9 Generator Control Panel:

And the wiring diagram for the 09067-9 generator itself:

And here's the exploded view for the 79848A transfer switch:

And the wiring diagram for the 79848A transfer switch:

Once, I called a well pump guy, and told him I had a problem, which he fixed, but I told him before he came out to charge me based on the fact I would be standing there right next to him as he debugged, asking him questions while he did the work in front of me.

It was then that I noticed he simply replaced entire circuit boards, simply by the process of pulling them out, putting the new one in, and finding that it worked, so he was about to take the old circuit board "home" with him, where I said if I'm paying for the new one, I want the old one (I still have it). Some day I'll figure out specifically what's "wrong" with it. :)

A similar thing happened with the heater repairman, who simply replaced the main circuit board, but he insisted that there was a core charge which _he_ wanted back - and that he's have to charge me for that - so he got the core charge, not me.

I learned from that that these guys replace the entire board rather than figure out what's wrong ON the board.

Given that replacing things seems to be what the repair techs do also, in this case, I think I have three options, two of which are what many people use, while the third option is the approach I'm currently trying:

1. Replace everything, one by one, until the damn thing works
2. Pay State Electric or Spiess Electric to fix it (in my presence)
3. Debug the damn thing (after first figuring out how it works)

Personally, I like to debug first, where simply UNDERSTANDING how the circuit works usually causes the offending part to SCREAM OUT that it's broken.

To that end, I'll follow your advice and start marking up the panel with a label of the purpose of each of the myriad connections.

[Arlen G. Holder]

Thanks for that helpful advice where I gave up trying to source at a local hardware store since I had tried three local box stores, none of which sold the Buss BBS-4 or BBS-5 600V fuses o Ace, Home Depot, Lowes

I called Generac today, where I was surprised to find that they don't have an "opening" time - their customer support is open 24/7/365, which is surprising in this day and age, don't you think? o 888-GENERAC (888-436-3722) extension 4, extension 2 (or 262-544-4811)

They confirmed there is no separate manual for the 79848A transfer panels; the transfer panels are covered in the 32-page owners manual (PN 98374) for the Generac 09067-9 8KW propane generator itself (where the manual is mostly about the generator but it does have a few pages about the transfer switch).

There IS a parts diagram though, which gave me the Generac part numbers o PN 63617 Transfer Relay

o PN 73590 BSS-2 Fuse 2A o PN 71340 100Amp 2pole Relay etc.

Generac told me the cheapest place to get the parts is usually o

But they also said there is a good Generac parts lookup engine at o

Where I ran a quick price survey of the three parts above for reference: o PN 63617 Transfer Relay $18 at Jacks, $25 at Tree o PN 73590 BSS-2 Fuse 2A $6 at Jacks, $9 at Tree o PN 71340 100Amp 2pole Relay $243 at Jacks, $287 at Tree etc.

The nice thing about Usenet is that I like to give back to the team, as you're aware (where I respond to all that are helpful at the same time I try to ignore the worthless trolls) - where these two outfits "seem" to be generally useful to source manufacturure parts for MORE than just Generac. o

o

Do folks here know of other outfits useful for sourcing common brand name part numbers for these types of electrical parts (pumps, motors, openers, etc.)?

[Clare Snyder]

They could stop making any fuse rated below 600VDC and nobody would miss them. They could make every fuse "fast quench" too. They'd just be a lot more expensive - but the savings in stocking costs might almost balance it out,

[gfretwell]

There are plenty of engineers who would disagree with you. Fuse science can get pretty complicated and you certainly don't want the same fuse protecting a HVAC compressor (long time delay, dual element) as you would use on an inverter converter power supply (single element, very fast acting). IBM lists over 250 fuses in the handy dandy handbook. That is from tiny fractional amp 3/8" long solder in fuses to bolt in blade fuses the size of a knockwurst at hundreds of amps..

[Jeff Liebermann]

The wiring diagram of the generator shows the (missing) controller, with all the connections to the automatic transfer switch. Pg12 of the manual, lower schematic, shows wires 23 and 194 going to the transfer switch. Since the other end of these wires goes only to the solenoid (relay) coil, I would presume that these should have 0V across them when the transfer switch is on utility power, and 12VDC(?) when it on generator power. Put an LED and resistor across both solenoid coil terminals so you can see what's happening without fumbling with a volts guesser.

Unfortunately, there's no schematic for the controller logic board which runs the show. Near the controller logic board is SW1, which is the "start/stop" switch. That should NOT activate the relay on the transfer switch. This is the generator test switch which I previously indicated was on all such autostart generators.

SW2 is labeled "Set Exercise Switch" which is something like a "test" switch but also is not intended to test the transfer switch. There should be something in the manual on how to use this switch. Here's a video that might offer a clue on what I think is a similar generator: "How To Set Exercise Time on Generac Air Cooled Generator Pre Nexus Controller APSwrap"

There's quite a bit on how a proper test switch should operate:

This is a typical generator test which demonstrates proper operation: "Home Generator Transfer Test"

Also on the schematic is the fuse F1 (15A), which appears to protect the controller 12VDC battery line. Check this fuse if you have a good

12VDC battery, but no controller function. If this 15A fuse is actually blown, you potentially have a high current short somewhere in the generator on the 12VDC line. Be careful tracking this one down.

Remember, you have but one life to give for your backup power system.

[Arlen _G_ Holder]

UPDATE:

Hi Jeff,

As you're aware, PG&E has cut our power here near Santa Cruz and the hills surrounding Silicon Valley, where the fact I'm able to post this means I figured out what the problem was with the power from the generator not getting to the house.

I had _thought_ it was the transfer switch, simply because a couple of those SBS-2 600V 2Amp fast acting ferrule fuses were missing, but it turns out that when I replaced the two missing fuses, nothing changed.

It turns out that half of the part #5 was broken inside (invisibly so)

o Generac Part Number #74969 35Amp Circuit Breaker

I'm not sure if that's the same part as "CB1" in bottom right of this page:

But it's Generac Part Number 74969 35 Amp Circuit Breaker (2 ganged poles), which disconnects 120VAC power based on my measurements on the breaker.

This is what it says on the circuit breaker itself: Carling Switch Inc. AA2.B0.24.635.5D1.C FL AMP 35 MAX VOLTS 227 (? hard to tell) HERTZ 50/60 DELAY 04 (? hard to tell) TRIP AMPS 43 (? hard to tell) Mexico 9513 (probably the 13th week in 1995)

Where the complete circuit diagram is outlined already in this older post:

In summary, there were two problems concurrently:

1. The fuses were missing in the transfer switch
2. Half the circuit breaker was internally broken

The result was that there was no electricity in the house when the PG&E power went out until I replaced the fuses; and there was only electricity to half the house. The 35Amp ganged circuit breaker has two "LINE" and two "LOAD" terminals, where, each circuit breaker innervates half the house.