I am trying to size a 120 VAC UPS. Typically, all of my devices are 120V and I know either the VA or Watts so I would convert Watts to VA and add all of the VA's together to size the UPS. This time some of my devices are 24 VAC, which I will have a 120/24 VAC transformer for.

I am getting stuck with trying to calculate the total VA for the devices that are 24 VAC. The data sheet for these devices state 72 VA at 24 VAC. How can I find the VA for these devices @ 120VAC?

This is what I have calculated, but I need someone to please tell me where I am going wrong here.

24V - 72VA

1. Find current 72VA / 24V = 3.125A

2. Find resistance of device 24V / 3.125A = 7.68 Ohms

3. Find current @ 120VAC with resistance being constant 120V / 7.68 = 15.625A

* I think this is not correct..shouldn't the current be lower with a higher voltage??

4. Calculate VA @ 120V 120V * 15.625A = 1875VA

Thanks for your help,

Saint Germain ]]>

2. # 10 Wire at 90C degree 40 amp

3. 1 Inch Emt.

4. Breaker 20 amp

5. Wire Thhn/thwn Solid

How many circuits can be in conduit

Derate

4-6 wires 80%

7-9 wire 70%

10-20 Wires 50%

I always have my neutral counted as current carrying.

How many? Breaker terminal confuses this. How does it affect. ? ]]>

Heat tracing branch circuit is from the circuit breaker in the panel to the power box. Than the "consumer" or utilization equipment starts after the power box with heat tracing "heater cable".

The length we are using to determine the branch circuit voltage drop is from the breaker to the power box, not the heat tracing wire itself. Is this correct? ]]>

One of the things I did not like was the VFD controlling a vacum pump motor. Noticable variation in rpm ever second or two. In the hundreds.

This may or may not have influence on PQ, but how tough is this on the motor? ]]>

generation of electrical energy.

thermal energy from fuels.

nuclear energy to electrical energy. ]]>

Below is the only source I've been able to find. It seems to suggest ignoring the smaller transformer of the two and looking at it as a single phase situation. Does anyone have any other links, references, books, etc they could suggest to backup either approach? Thanks.

http://light.dakotaelectric.com/Hand...%20Values.aspx

**V-Phase (Open Wye-Open Delta) services**have maximum fault currents equal to or less than single-phase services with the same transformer size and voltage. Use the single-phase table and the larger of the two transformers to identify the maximum secondary fault current.

* have the breaker tested and then not worry about it, buy a

* refurbished breaker already tested (do they exist)

* Call for a new breaker designed to retrofit into this board (do these exist)

Any input you might have would be appreciated,

Mike ]]>

I know we have some Cali wizards on this site and I'm about as far from there as you can get.

A big box wants to carry our product and I need to let them know what listings, certifications, etc. we have.

Instead of hitting you with a bunch of questions, is this 2012 form still accurate?

http://www.energy.ca.gov/appliances/...structions.pdf

It looks like we make "appliances" that do not need laboratory testing in order to be Title 24 compliant. It also appears we can do self-certification by sending in some "stuff". Our product is a lighting control.

Thanks! ]]>

I ran across this panel schedule, and something seemed wrong to me. First off, I'm not used to seeing schedules where they just use L1 and L2. Most panel schedules I have used break up L1 & L2 into 2 columns each so you can

see the exact load being contributed at each circuit breaker.

When I look at this schedule, it seems to me that the BTS pulls 19,000 W and the surge would be pulling 0. Anyhow...

I can't figure out where the engineer got their "25% of Largest Continuous Load (LCL)" from. I tried working backwards from the total load amps, but I'm not getting figures that even make sense to me if they're rounded.

Is anybody up to the challenge on a Monday to give me some clue what's going on?

Thanks!

Are they saying double the size of the larger dryer? Or something else? Sorry, it might be obvious, I just can't quite put it together. ]]>

for example:

what's the allowable ampacitie of 9 #12 THHN current carrying conductors in a 1/2 EMT?

1/2 EMT - 9 #12 THHN

7-9 Adj. 70%

#12 THHN 90°c - 30 amps

30 x .70% = 21 amps

so good for a 20 amp breaker ?

although the ** by #12 sends you to 240.4(D)

that's only referring to max ocpd

so you still derate at 30 amps correct ?

9 wires in 1/2 allowed 20 amps.

i don't know anybody who would do that..

help ?

thank you ]]>