CONNECTING GENERATOR TO MAIN PANEL WITHOUT THE NEED FOR A SUBPANEL

[Maple2]

Hi gurus,

Is there a way to connect a 100A generator via a 200A Manual Transfer Switch (MTS) to a 200A main electrical panel? The Gen is meant to power certain equipment only in the event of power failure. Are there special circuit breaker panels for this kind of purpose?

Normally, I would install a 100A Subpanel for those equipment, connect the subpanel to the 200A main breaker panel via 100A MTS thats also connected to the generator. I like to know if there are other safe options that would not require the use of additional panel. Thanks

 

[itsmoked]

The most economical way is to simply install a 100A breaker in the main panel in one of the two top positions and install an interlock plate. There is no less expensive safe way to do it.

Google Images Interlock Plates

There are hundreds of styles. They cost less than a hundred bucks. Amazon has dozens. You can make your own if you're handy. Do prove whatever you use actually works. There are some labeling requirements in the NEC that usually come with Amazon "Generator Interlock Kits".

If you haven't figured it out, the simple mechanical plate allows both breakers to be turned off AND then only one to be turned on at a time. This COMPLETELY precludes having the generator ever hooked to the utility.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

What is your application? Residence? Work-Shop? Other?
Keith's solution is by far the quickest, easiest and cheapest for a manual installation.
On the other hand, I had a lot of experience hooking smaller generators to larger panels via automatic transfer switches.
The customers soon learned how many air conditioners they could run without tripping the generator breaker.
For the A/C units that started automatically after a power outage, I would install a contactor that would drop out and have to be reset manually.
But, if you are not looking at a lot of air conditioning, residential service panels sized according to the NEC or the CEC tend to be massively oversized.
Example: My fairly large home has a 200 Amp service.
We have:
Sewage pump-out
Deep well pump
Electric clothes drier
Refrigerator and two deep freezers
Microwave
Electric range and oven.
One or two block heaters in the winter
We are on a rural demand limit.
Atco supplies us through a 35 Amp breaker.
We have been here for about 32 months and we have never tripped the 35 Amp breaker.
Did I mention the 1 HP air compressor in the shop and an additional 800 Watts in the winter to keep the stock water running?
You may find that the load never exceeds 100 Amps.
You may be able to disable some loads when on generator power.
I hope that this isn't a Generac package natural gas powered standby.
I am currently redoing one of those that was installed by idiots. (Would you believe? None of the lighting circuits are on the generator panel.)
Are you anywhere near postal code T0C 0R0? Neither am I but I am close to T0C 0R0.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[TugboatEng]

There is an important question, what do you mean by power a few select devices? Do you want your generator to come on and keep them powered or do you expect a person to come out and align the generator to the panel and that same person to select the relevant circuits?

 

[itsmoked]

Wow Bill, 35A! That sucks. Can you get more if you needed it or are the rural lines just way too small. I can't see anyone around here having a permanent residential limit like that. The POCO would see it as 'revenue limiting' and trot out new insulators and transformers jacking up the capacity.

In your situation I'd be seriously considering a big LiFePO4 battery bank. I'd run the whole place as an online UPS. Whatever your peak might ever be would be the sizing. The POCO could then dribble in 24hr/day if needed to meet the 24Hr energy delivery requirement. Then when the POCO takes a dump your lights don't even flicker. You run full battery until it makes sense to crank up the generator which runs full tilt - everything it's got recharging the bank. That way you're generator runs at an efficient point for a short (noisy) period.

But, then I'm sure you know all this. Be fun to setup. Heck, additionally you could use solar or wind to also charge the batteries as convenient. Get Spar to whip up a wind turbine for you.



Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

All good points Keith, but the local economics are crazy.
I have been meaning to call customer service to try to get a tripping curve for the breaker, but the breaker has never tripped. our previous place was similar and the breaker tripped once in about ten years.
I suspect that the breaker will pass more than 35 Amps before tripping.
Billing, revenue, etc.
Why the breaker? We are on a limited demand tariff. We are on a 5 KVA max demand rate. The 35 Amp breaker lets through a little over 8 KVA.
On rural lines, the demand is a big factor.
As for wind and solar, the numbers are pretty bad. With de-regulation and the separation of energy production from energy delivery, we don't pay very much for energy.
Our fixed charges run over $100 per month.
Here is a screen shot of some invoices:

It gets better;
The utility only pays wholesale rates for produced energy.
The wholesale rate is about 25% of the retail rate.
During the day you can replace your consumption with solar, but you must also bank four times the night time energy usage to break even on consumption.
So by a WAG, let's use 50% day time and 50% night time for 171 KWHrs and $10.52 energy charges.
171KWHrs/2 = 85.5 KWHrs of solar will replace daytime usage and save $5.26 per month.
171KWHrs/2 = 85.5 KWHrs x 4 = 342 KWHrs of solar will replace nighttime usage and save $5.26 per month.
Other charges and taxes = ($92.14 + $7.50 + $5.51 = $105.15)
At $5.26 for 85.5 KWHrs that will take an additional 1709 KWHrs.
That's a total of 2136 KWHrs to offset the total charges for 171 KWHrs consumption.
2136 KWHrs per 30 Days = 712 KWHrs per day. Wag 10 hours average solar production per day = 71.2 KW average output.
BUT
There is a 50 KW limit on solar production.
By the way, the government claims to be in favour of alternate energy production.
Looking this over, your questions were really good, Keith. It's the answers that are really cruddy.
Spar may be on a different tariff than I. I never asked him.
I know a man who got into solar early and has a contract at reasonable rates.
His 50 KW installation has paid for itself and is putting money in his bank account every month.
Those contracts are no longer available.
Here are some of our monthly charges. There was a slight rate adjustment on one of the charges so all the entries are doubled, once for the days at each rate. There is an entry for 29 days and an entry for 4 days.

Charges continued:

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[itsmoked]

Gads.. I must mull this foul play

when I have a moment...




Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

With service densities in the cities, the cost of transmission and distribution per user is quite small.
Out here our close neighbours are:
Diagonally one mile west and one mile north.
One mile north of there.
An abandoned farm two miles south.
An abandoned farm one mile west.
A home two miles north.
A farm two miles east and one mile south.
The rest of our neighbours are quite far away.
The biggest cost to the utilities is owning and installing the lines.
Please don't suggest underground. grin
These charges used to be all lumped into the KWHr rate until a politician de-regulated the industry and separated generation, transmission and distribution.
He then sold a lot of the publicly owned power company to his friends and family.
Thankfully it's not yet as bad as Texas.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Maple2]

Hi Gurus,

I would appreciate comments on the attached SLD and layout photos . Instead of having interlock kits install on the 200A distribution Panel, this 'MTS' seem to do the job with its own built-in interlock. From the SLD, it seemed to have power monitoring and 'load sharing Interlock" capabilities. There isnt a dedicated breaker in the panel or subpanel for the gen supply either. It beats me how one could prevent the generator from overloading without manually switching of some circuits in the 200A panel Panel. Which defeats the purpose of an MTS with an interlock in my opinion.

 

[stevenal]

MTS as in manual transfer switch? If someone is present to throw the switch, they should be matching load to generation prior to making the transfer. Same with the main panel interlock proposed above.

The signal relay might be used to control loading, but I fail to see the point with a manual transfer.

 

[JezNZ]

It seems to me your "load sharing interlock" with it's description of "to match loads to supply" is designed to interlock certain loads from operating when on generator supply (actually when NOT utility supply available), whether by dropout contactors or electronic controls. I would have named this "load shedding contact" or the like, but YMMV.