Transformer, wire & Disconnect size?

[muckmail]

How do I calculate Transformer size, wire & Disconnect Size.
to a 24 breaker panel?


1. I have connected five 240VAC line to line circuits on a drawing for a new 24 breaker panel to be installed.

2. The panel has 24 circuits total and the company uses number 10 wire for all circuits. So I figure my panel can have 24 30A circuits max.

3. I have used line to line for 240VAC for my 5 circuits. Other circuits may be connect for 120VAC at 30A.

4. How do I figure the Disconnect, Transformer & wire size for this panel assuming that this is the only panel on the transformer.

Thank you,

 

[augie47]

Excuse my being bold, but the whole approach seems a bit scary to me.
To begin with it looks like "reverse engineering". You appear to be sizing the circuit by the wire size the "company" uses.
There are, to me, three basic steps: Calculate the load (adding for future as desired), determine the conductor size to supply that load, and select the overcurrent device. In your case we would add: selected an appropriately sized transformer and comply with Art 450 and Art 240.
Your post is impossible to answer. You need to know nature of the loads(kw, voltage, phase, motor vs non motor, etc) and the properties of the supply voltage to the transformer,
Once you have worked out all the calculations and determined your wire sizes and overcurrent protection if you will post that I'm sure a number of the members can critique it.

 

[muckmail]

Ok, then hopefully we can discuss the situtation.

I have placed 4 heat trace cirucits on the first 8 circuit breakers with
a load of 3200 watts. Each circuit breaker sized that I used is 30A and
each circuit uses 2 breakers. So I have breakers 9-24 that are spares
at this time.
This is a heat trace panel. So there are 20 breakers that will be used
in the future. So the company needs to estimate the total load for the panel
and remaining breakers?

 

[nakulak]

come up with a list of equipment that will be attached, and the manner in which the equipment will be operated (all at one time, all day long ?), then you can do at least an approximation of a valid load calculation. then you can do the rest. At least then everyone will know what the panel was designed for later on when you run out of power because someone didn't take something into account.

 

[don_resqcapt19]

Ok, then hopefully we can discuss the situtation.

I have placed 4 heat trace cirucits on the first 8 circuit breakers with
a load of 3200 watts. Each circuit breaker sized that I used is 30A and
each circuit uses 2 breakers. So I have breakers 9-24 that are spares
at this time.
This is a heat trace panel. So there are 20 breakers that will be used
in the future. So the company needs to estimate the total load for the panel
and remaining breakers?

The number of spaces has nothing to do with the load on the panel. You need to know what loads will be connected to the spares before you can estimate the total load.
Also the heat trace loads need to be on two pole breakers, not two single pole breakers as your post implies. These breakers also need to provide equipment ground fault protection for the heat trace unless there is another device in the circuit that provides that protection.
What voltage does the heat trace operate at? 30 amp breakers seem excessive for a 3200 watt load that is connected to a two pole breaker.

 

[don_resqcapt19]

What is the amp rating of the panel? I don't think you will find a 24 circuit panel with a 360 amp rating. If you are planning on being able to load the panel to its maximum rating, you would size the transformer and the conductors based on that rating.

 

[muckmail]

I think it is a 70A breaker enclosure