minimum size loadcenter 20amp 2p demand factor

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wyreman

wyreman

Senior Member
Location
SF CA USA
Occupation
electrical contractor
I have a commercial client just had installed a new FACP 250' from the only distrib.
760.121(B) says I need a dedicated circuit.
The path is 3/4" rigid in concrete slab w [4] #12s. (Phase Phase Grounded Grounding)
The wires move. I think I could pull in a new pair if I have to.

My question:
The PLFA ct has a negligible load.

Can I take the 2p 20 ct that arrives at the FACP and land it in on main lugs of a say
HOM48L125GC
that specs main wire range from
14–2/0

then send the original old1 and old 2 on their ways
and grab a new dedicated ct for facp?

The problem of course looks like I can't limit the open slot from being used :/
I could use it for another dedicated ct to run a service receptacle.

thanks!

sq d epf.jpegScreenshot 2020-04-27 23.35.31.pngsq d epf.jpeg
Screenshot 2020-04-27 23.35.31.png
 
The other old circuit feeds some lights.
I guess the only other objection would be if the two pole sub feed were to trip because of a short in something other than the fire system.
Another word that the fire system sub feed breaker wasn’t dedicated just to fire.
What makes that difficult is that the main distribution as a stinger panel and all the breakers are full
I’d have to create a new panel over there just for this one circuit.

Or rearrange loads at the main to free up a new circuit
Which is what it looks like I’ll do
 
Actually too bad I can’t put the flow switch on the same circuit as the control panel under 760.121(B)
 
Because the flow switch is not power limited it’s 120v 💭 I’ll just ask inspector what he wants 0F955BF4-4D90-4B94-88BF-21739269E89E.jpeg
 
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Admittedly not an expert in 760, could the conduit be used to house a feeder to a subpanel and from that panel a dedicated branch circuit for the FACP?
 
  • Consider two Feeders with the same maximum demand but that occur at different intervals of time. When supplied by the same feeder, the demand on such is less the sum of the two demands. In electrical design, this condition is known as diversity.
  • Diversity factor is an extended version of demand factor. It deals with maximum demand of different units at a time/Maximum demand of the entire system.
  • Greater the diversity factor, lesser is the cost of generation of power.

With the application of demand factors, smaller components can be utilized

That's what I'm wondering: what is the minimum amperage for a loadcenter?
20A 2p is fits the load shape.
Its the demand factor on the four slots in the loadcenter

In this case there is only the FACP, the flow switch and a couple of lights (0.5a)
the problem would be if someone extended the other circuits and tripped the 20a (!)2p main
A 50a subpanel makes that less likely, altho
there is no coordination study here and
any short could also bring down a 30m or 50a 2p just as well

Cant really repurpose the wires at the main because I need 3 cts at point of use:
  1. FACP
  2. Flow $
  3. General Light (I could fuse this circuit at 15a to protect the subfeed breaker)
💭If I could change the flow switch to pick with the FACP voltage it could be on the same ct.

With the application of demand factors, smaller components can be utilized
in the electrical system and greater savings can be passed on to the consumer.
Due to the high cost of wiring, look for designers to utilize these techniques more than ever before.


Just charge them to pull new wire and build another panel! or repipe a$ needed.

sq d 20a2p (text).jpeg
 
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"A 50a subpanel makes that less likely, altho
there is no coordination study here and
any short could also bring down a 30m or 50a 2p just as well"

even if the 20a 2p tripped, there is an amber trouble +buzzer +comms that would disclose from facp battery system
 
here in sf i will just have to ask inspector

He may be, but neither the NEC nor NFPA 72 explicitly says this. It would be based on a local requirement. The general requirement is for a "dedicated" circuit. It could be argued that a sub panel does not meet that requirement because the breaker feeding the sub panel is feeding more than one load, whether the breaker is at the sub panel or back at the main panel.
 
The sprinkler bell is not supervised or powered by the fire alarm control panel. I'm away from the office and don't have the 2008 edition of the NEC, but there is a section on dedicated power for fire alarm panels. My opinion would be that it's not the same as feeding NAC power extenders and you would need a separate circuit.
Click to expand...
I'm sure that is technically correct, specifically why would you want it to be separate?

It's unsupervised. Seems like supervision is desirable, and there would be many other methods to accomplish that. Sharing the circuit would be the simplest, and they generally draw 200- 300mA at 120vac.


 
So I can ask Fire Alarm guy to move the flow switch relay to his power limited system.
Then the FACP can move to the old Flow Switch ct

then the old rub could be that the general lighting ct shares a conduit w the facp, but that should be fine
 
"Can you guys supervise the 120v flow switch relay component of the fire system by moving it to your Power Limited system?
I'll repipe the flow switch for you to wire."

Its a 120v bell now, I'm sure his PLFA panel must have a 120v picked output for that purpose, wouldn't you think?
 
total crock!
i just talked to the fa dude and there is no problem here to parallel the FACP w the bell.
It was just a game of telephone.
he just couldn't find the breaker


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