Load Management for Generator

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mkgrady

Senior Member
Location
Massachusetts
I need to wire two AC systems so they will not come on when a generator can not handle the load. The Generac ATS has built in contols so you can conveniently interupt the control circuit to the condensing units but I can't get to them. The ATS also has 120 volt outputs meant to control line voltage relays for whatever heavy loads you want to manage while the generator is on. I'm using two pole relays that are sold by Guardian. They have a 120 volt coil and 40 amp two pole contacts. They call it a DLM module.

My question is: is there any reason I have to interupt both legs of the 230 volt circuits to the condensing units? Or can i just control one of the legs? I ask because the relays they offer are in very small enclosures. Running 8-2 NM in and out looks like it would be really difficult.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
I need to wire two AC systems so they will not come on when a generator can not handle the load. The Generac ATS has built in contols so you can conveniently interupt the control circuit to the condensing units but I can't get to them. The ATS also has 120 volt outputs meant to control line voltage relays for whatever heavy loads you want to manage while the generator is on. I'm using two pole relays that are sold by Guardian. They have a 120 volt coil and 40 amp two pole contacts. They call it a DLM module.

My question is: is there any reason I have to interupt both legs of the 230 volt circuits to the condensing units? Or can i just control one of the legs? I ask because the relays they offer are in very small enclosures. Running 8-2 NM in and out looks like it would be really difficult.

Why are you stuck using their relays?
 

kwired

Electron manager
Location
NE Nebraska
Why not interrupt the 24 volt control circuit? Cheaper, smaller conductors, easier to manage, much lower current level being interrupted will greatly lengthen the life of the contacts. Coil probably fails before contacts ever do.
 

mkgrady

Senior Member
Location
Massachusetts
Why not interrupt the 24 volt control circuit? Cheaper, smaller conductors, easier to manage, much lower current level being interrupted will greatly lengthen the life of the contacts. Coil probably fails before contacts ever do.

That is what I do when I can get to the control circuit. In fact I don't even need a relay if I can interupt the condensor control circuit. The contacts are built in to the ATS.

In this case the control circuits are not exposed anywhere that I can get a wire to. The power circuits to the condensors are at the panel next to the ATS so I think interupting the power circuit is all I can do.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
My worry would not be the condenser's compressor, but whatever else may be fed by that circuit

Is there a neutral going to the condensing unit?


Usually whenever I hear someone bought all their own equipment, it becomes a T&M job. Including the time it takes to figure out how to make the poorly chosen components work
 
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mkgrady

Senior Member
Location
Massachusetts
My worry would not be the condenser's compressor, but whatever else may be fed by that circuit

Is there a neutral going to the condensing unit?

Usually whenever I hear someone bought all their own equipment, it becomes a T&M job. Including the time it takes to figure out how to make the poorly chosen components work

Nope no neutral. And the circuit doesn't feed anything but the compressor
 

__dan

Senior Member
My question is: is there any reason I have to interupt both legs of the 230 volt circuits to the condensing units? Or can i just control one of the legs? I ask because the relays they offer are in very small enclosures. Running 8-2 NM in and out looks like it would be really difficult.

If you assume the install will be exposed to the perpetual incompetence of the customer, interrupting both legs may be the only way to stay out of the defendant's chair. Guessing, could be a nominal 6 x 6 j box with a two pole definite purpose contactor (I did not do the math).

Some of those magnetically held contactors are noisy. Alternate is a dedicated small critical load panel after the ATS.
 
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ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
I'm agreeing with _dan and joe.

Since the AC requires a disconnect breaking only one leg would be considered a controller and all that is needed for the load shedding, but I would break both. It's just better, and since the guy is supplying the parts there is a good chance he is going to tinker with it.

And since he is supplying the gear I would do what I needed to do to make it work and charge accordingly. Probably use the supplied relays to control another contacter in a separate box that I can get my wires in.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
If you assume the install will be exposed to the perpetual incompetence of the customer, interrupting both legs may be the only way to stay out of the defendant's chair. Guessing, could be a nominal 6 x 6 j box with a two pole definite purpose contactor (I did not do the math).

Some of those magnetically held contactors are noisy. Alternate is a dedicated small critical load panel after the ATS.


Can you imagine him pulling the wrong disco while on gen power and end up working on something with one hot in it.


Or testing in the unit and assuming everything is de-energized because he found no potential on one leg.

I'm all for the definate purpose contactors, and opening up both legs.

Hey this is all single phase stuff, isn't it?

BTW, arguments could be made as to the advantages and disadvantages of using N/O or N/C contactors, ,,,,,,,,,,,
 

mkgrady

Senior Member
Location
Massachusetts
If you assume the install will be exposed to the perpetual incompetence of the customer, interrupting both legs may be the only way to stay out of the defendant's chair. Guessing, could be a nominal 6 x 6 j box with a two pole definite purpose contactor (I did not do the math).

Some of those magnetically held contactors are noisy. Alternate is a dedicated small critical load panel after the ATS.

The customer is a doctor. The plumber is the gc that I am working for.
 

kwired

Electron manager
Location
NE Nebraska
Is there a code issue with only opening one leg?

For the purpose of control absolutely not.

Can you imagine him pulling the wrong disco while on gen power and end up working on something with one hot in it.


Or testing in the unit and assuming everything is de-energized because he found no potential on one leg.

I'm all for the definate purpose contactors, and opening up both legs.

Pulling wrong disconnect leaves hazard conditions either way.

Improper testing results in not finding one live leg.

A contactor that opens both legs is still not a substitute for a disconnecting means, unexpected energization is a possibility.

You can't idiot proof it, if you do a better idiot eventually comes along.
:happyyes:
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
Why does a doctor get a plummer to buy him a gen-set and then have an electrician install it?

It's like you showing up at the doctors office with a bag of drugs your housekeeper bought at the supermarket and you telling the doctor to use them to fix what ails you.

Yeah, I'll bet he'd go for that.
 

mkgrady

Senior Member
Location
Massachusetts
Can you imagine him pulling the wrong disco while on gen power and end up working on something with one hot in it.


Or testing in the unit and assuming everything is de-energized because he found no potential on one leg.

I'm all for the definate purpose contactors, and opening up both legs.

Hey this is all single phase stuff, isn't it?

BTW, arguments could be made as to the advantages and disadvantages of using N/O or N/C contactors, ,,,,,,,,,,,

Yes it is single phase. I don't even know if the relays are NC or NO. That would depend on how the ATS controls the loads.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Is there a code issue with only opening one leg?

the phrase "open all ungrounded conductors" keeps popping up in my mind, but i'm too
tired to go look and see if i'm right or wrong....

opening one leg would obviously work, but would leave everything hot, in effect, you
would be opening the neutral, as you would be leaving the equipment fully energized,
just as if you opened a neutral on a 120 volt branch circuit.

not safe, in my opinion.
 

kwired

Electron manager
Location
NE Nebraska
A disconnecting means needs to open all ungrounded conductors.

A control only needs to open enough conductors to make the load inoperative.

There are many controls that open only one conductor of a circuit that has two ungrounded conductors.

There are many controls that open only one conductor that is possibly the neutral conductor.

Many air conditioners only have a single pole contactor, water heater thermostats only open one line - the high limit does open both lines, double pole baseboard heaters often only cycle one pole for control and when you turn it to "off" position it opens both poles - this allows it to be considered a disconnect. Single phase motors that have an internal overload device usually only opens one line, electric furnaces usually only open one line with their 'sequencers' as well as high limit devices - and the 240 volt blower is also controlled by opening only one line..
 
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