240V Panel

[Reesh14]

I am having trouble understanding a situation I saw in field with a 240V Panelboard. A 100A,120/208v. 3phase panel has a 90A/3P circuit breaker labeled "240V panel transformer". A 1" conduit from the bottom of this panel feeds a Square D load center panel through two-2kva, single phase ACME transformers. There is another 3/4" conduit from the top of the 120/208V panel also going into the load center panel.

The load center currently feeds a hot water heater with a 30A/2P breaker, a sewage sump pump with a 20A/2P breaker, and two 20A/2P breakers serving 220V Receptacles (which will be taken out).

I am not sure why there are two feeders going to the "240V panel" and if it even really is 240V. I am not sure if the panel is 2 wire or 3 wire or even the phase.

I am supposed to replace the wire and conduit between the 120/208V panel and the "240V panel", but I do not know what the existing wire sizes are so I am not sure how to size the new wires and conduit.

The two feeds, the 90A/3P feed breaker, the two transformers , and the whole situation just does not make sense to me. Could the feed with the two transformers only be feeding some of the breakers in the panel?

Any help/advise would be appreciated. Thanks!

 

[davidbeach]

You need to open the panels and take a look.

 

[waross]

240 volt equipment is typically used on 208 volt circuits. However heating equipment such as hot water tanks will be derated and may not be able to keep up with the demand for hot water. Small dry type transformers may be used in an open delta, autotransformer configuration to boost the voltage.
At times a 208:240 volt transformer may be used to supply single phase power at 240 volts.
When using auto transformer connections to boost the voltage the following relationships apply.
Transformers rated at 120:12 volts will boost the 208 volts to 229 volts.
Transformers rated at 120:18 volts will boost the 208 volts to 239 volts.
Transformers rated at 120:24 volts will boost the 208 volts to 249 volts.
The transformer secondarys must be rated for the load current.
Some information on the transformer ratings will be helpful.
respectfully