Control Transformer in ATS

[Open Neutral]

So in a large residence, there's a backup generator and an ATS.

1. PoCo fails
2. 1 2 3 potato
3. generator cranks
4. It comes up to speed for say 30 seconds
5. ATS switches.

We want some tiny amount (a few watts...) of 24VAC during 4, and before 5. (It's doing things to reduce the startup load at 5....)
I recall the control transformers in motor starters had a fuse in their primary. What swamp of regulatory compliance would we step in to add such to the pre-ATS generator output inside/adjacent, to the ATS? I assume there's no panelboard on the generator itself, or is there?

 

[Ingenieur]

Are you trying to stage loads?
there are simpler methods
for example put an on delay relay on the hvac unit thermostat signal
power comes on via xfer switch
t-stat is calling for htg or clg
10 sec later unit starts up

 

[Open Neutral]

This is more complex than that.

 

[Daniel malack]

So in a large residence, there's a backup generator and an ATS.

1. PoCo fails
2. 1 2 3 potato
3. generator cranks
4. It comes up to speed for say 30 seconds
5. ATS switches.

We want some tiny amount (a few watts...) of 24VAC during 4, and before 5. (It's doing things to reduce the startup load at 5....)
I recall the control transformers in motor starters had a fuse in their primary. What swamp of regulatory compliance would we step in to add such to the pre-ATS generator output inside/adjacent, to the ATS? I assume there's no panelboard on the generator itself, or is there?

What do you need the tiny amount of 24v for?

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[Open Neutral]

What do you need the tiny amount of 24v for?

To run some relays. I prefer to use AC relays vs. DC since they are being driven by actual contacts vs. semiconductors; and there's that nasty inductive spike to tolerate.

 

[Ingenieur]

This is more complex than that.

an explanation/sequence of operation might help
some on this forum understand much more complex things, me excepted lol

There is a reason no one does what you propose

if they don't add/sequence loads AFTER xfer
they use batteries
or delay xfer once the genset is ready to accept load and use the genset to set-up the loads, then xfer

 

[Ingenieur]

To run some relays. I prefer to use AC relays vs. DC since they are being driven by actual contacts vs. semiconductors; and there's that nasty inductive spike to tolerate.

potter-brumfield and others make solenoid type dc relays
not solid state

 

[gar]

170820-1323 EDT

open neutral:

What "nasty inductive spike to tolerate" with a DC relay? A simple diode eliminates any inductive voltage greater than the forward diode drop, but does somewhat increase dropout time.

I don't think your question is really about the whether a DC or AC or solid-state relay is used.

.

 

[bsmith8691]

Most generator manufacturers make a load shedding control that will bring in the load after transfer when the genset is capable of handling it. I have built controls separate of the generator equipment that allowed the owner to switch certain loads onto The genset after it was up to speed. I don't think either of these are options that you are seeking.

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[Open Neutral]

170820-1323 EDT

I don't think your question is really about the whether a DC or AC or solid-state relay is used.

Quite correct, it is not. It is about a 24VAC transformer on the generator side of a ATS. It's part of a project that might be a product. Hence my unwillingness to spill all my candy in the lobby.

SSR's are quite impractical in this application. Even if they came Form C, 1.6V_fd * 40A * 2 poles * say 24 circuits adds up to a few watts.

These relays will enable/disable loads during generator startup. I'd rather have the loads off during ATS transfer & after {for some interval}. But to ensure that, the relay power supply must be available pre-ATS. Hence my query as to the legality [well, code-compliance] of a control transformer with fuse.

 

[gar]

170820-2942 EDT

An on delay relay for each load could accomplish what you want. Select different times for each relay to distribute turn on loading.

.

 

[Daniel malack]

Still wondering why you need to control something before transfer to stand by?

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[Daniel malack]

So in a large residence, there's a backup generator and an ATS.

1. PoCo fails
2. 1 2 3 potato
3. generator cranks
4. It comes up to speed for say 30 seconds
5. ATS switches.

We want some tiny amount (a few watts...) of 24VAC during 4, and before 5. (It's doing things to reduce the startup load at 5....)
I recall the control transformers in motor starters had a fuse in their primary. What swamp of regulatory compliance would we step in to add such to the pre-ATS generator output inside/adjacent, to the ATS? I assume there's no panelboard on the generator itself, or is there?

If the generator has a receptacle on it run 120v to transformer and get your 24 volts. If no receptacle you could still tap off of the Generator breaker and step down to your 24 volts. If you need the 24 volts when in utility also just add a contactor.

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[Ingenieur]

Quite correct, it is not. It is about a 24VAC transformer on the generator side of a ATS. It's part of a project that might be a product. Hence my unwillingness to spill all my candy in the lobby.

SSR's are quite impractical in this application. Even if they came Form C, 1.6V_fd * 40A * 2 poles * say 24 circuits adds up to a few watts.

These relays will enable/disable loads during generator startup. I'd rather have the loads off during ATS transfer & after {for some interval}. But to ensure that, the relay power supply must be available pre-ATS. Hence my query as to the legality [well, code-compliance] of a control transformer with fuse.

that is already done
mfgs sell packages with the gensets/xfer switch
it is very common to power everything down and sequence loads on

 

[gar]

170821-1109 EDT

open neutral:

These relays will enable/disable loads during generator startup. I'd rather have the loads off during ATS transfer & after {for some interval}. But to ensure that, the relay power supply must be available pre-ATS. Hence my query as to the legality [well, code-compliance] of a control transformer with fuse.

Why must? "the relay power supply must be available pre-ATS"

A simple time delay relay's output is off before power is applied, remains off for some time after power is applied, after the delay turns on, and when power is removed immeadiately turns off.

.

 

[Open Neutral]

170821-1109 EDT

open neutral:
Why must? "the relay power supply must be available pre-ATS"
.

This product requires it; it does several things. That's all I'm prepared to say in public for now.

My question for the froup is code-focused.

Can we add a control transformer to an ATS without a complete breaker panel to protect it? Is a sole fuseholder allowed if inside the ATS or adjacent box holding the xfmr?

BTW, the generator is distant from the ATS, so a generator outlet is far less convenient. But we might end up with such.

 

[Ingenieur]

This product requires it; it does several things. That's all I'm prepared to say in public for now.

My question for the froup is code-focused.

Can we add a control transformer to an ATS without a complete breaker panel to protect it? Is a sole fuseholder allowed if inside the ATS or adjacent box holding the xfmr?

BTW, the generator is distant from the ATS, so a generator outlet is far less convenient. But we might end up with such.

No
no internal modifications to a listed device

you don't want to add it to the xfer sw output
you want to add it to the generator side
just use an external terminal box and tap off with a fused disconnect

again
it's all been done before

most ats have a set of contacts that indicate when the gen is ready to accept load
prior to a delayed cut over
it is used to shed load prior to excercising or when utility power is available and you still want to use gen power

read the features https://www.vertivco.com/globalasse...es-300-ats-brochure-pub-1195-r17_135499_0.pdf
pre-transfer signal
24 vac control power
option small ups card for control power

• ● Selective load disconnect, double-throw contact to operateat an adjustable 0 to 20 second adjustable time delay priorto transfer and reset 0 to 20 seconds after transfer.
  

 

[Jraef]

Quite correct, it is not. It is about a 24VAC transformer on the generator side of a ATS. It's part of a project that might be a product. Hence my unwillingness to spill all my candy in the lobby.

SSR's are quite impractical in this application. Even if they came Form C, 1.6V_fd * 40A * 2 poles * say 24 circuits adds up to a few watts.

These relays will enable/disable loads during generator startup. I'd rather have the loads off during ATS transfer & after {for some interval}. But to ensure that, the relay power supply must be available pre-ATS. Hence my query as to the legality [well, code-compliance] of a control transformer with fuse.

I'm not following you here. Are you thinking that the inclusion of a fuse on a control transformer somehow allows you to power something on the generator side before the generator powers up?

 

[Open Neutral]

just use an external terminal box and tap off with a fused disconnect

Thank you. Would that require the terminal box sized for the full current of the ATS?
Or can it just tap off one side/phase of the generator input and feed over to the disconnect?

I'm off to try to find a small fused disconnect. The simplest ones I can think of are those pullblock HVAC disconnects.

 

[hbiss]

Just put a suitable enclosure for the transformer and a 15A fuseblock next to the ATS connected with a nipple. You can use 14ga wire to the generator side. You're going to have to figure out how to connect the #14 to the lugs since they aren't listed for both wires.

Geeze engineers. :happysad:

-Hal