120V Panel off 240V Delta (ungrounded)
- Thread starter Cletis
- Start date
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
First see whether you have the needed ground detector. If it is required, adding your transformer will not change that.
Second, you can add a transformer with a 220V primary and either a 120V secondary or a 240V center tapped secondary.
In either case it will be wired as an SDS.
You will ground one conductor of the secondary.
The placement and size of primary and secondary OCPD is something I will leave for later.
Ok, thanks I'll look into all that. Wouldn't this create a "virtual" ground ? I heard they don't work good with VFD's and other things ??
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
It creates a real grounded conductor, just like the one from a typical service. Fault current will go back to the transformer over a solid ECG, and the GES connection and bonding must meet the size requirements for an SDS. Not virtual at all.
under8ed
Senior Member
- Location
- Charleston, SC., USA
I suppose a single phase sub panel will keep the cost down; but I would consider the versatility of a 3 phase panel. You mentioned VFD's, which suggests more 3 phase capability could be useful. A 120/208 volt panel can provide for future 3 phase loads as well as convenience outlet circuits. A 3 phase Delta/Wye transformer feeding a 3 phase panel may make sense.
- Occupation
- Licensed Electrician
While not disagreeing with the notion that a three phase panel can be more useful than a single phase, in this case the OP stated the existing service is 240V Delta.
There is probably plenty of three phase available at 240V. Getting 208V gains nothing other than the need to identify another voltage system. What's likely needed is some breaker spaces for circuits that use 120V to ground.
Actually, there are 4 services around this building. But, they are all getting tapped out. There is an area where they want to add a bunch of additional 120V loads near the 240V delta service which would be easier if possible and practical. The 480/277V 4 wire 600 amp service is almost tapped out currently and physically far away. I was just brainstorming some ideas so when this happens i have a plan..I have a feeling the cheapest most practical way may be upgrade the 600 to a 1000 or 1200 and just run a new 1000ft feeder over to that area and set a new transformer for a 120/208V panel.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
Is the 204V delta service currently under heavy use?
Could you have the power company reconnect their transformers to provide a 120/240 single phase or a 208/120 three phase service?
-Jon
Could you have the power company reconnect their transformers to provide a 120/240 single phase or a 208/120 three phase service?
-Jon
208/120V 3? 4W or 240/120V 3? 4W would likely require POCO to run a neutral and EC to continue through service equipment.
120/240V 1? 3W would likely require changing out the service equipment entirely.
With 4 different services to the premises currently, changing may not be permitted if it duplicates an existing config'.
under8ed
Senior Member
- Location
- Charleston, SC., USA
If you went with the 120/208 panel, I don't see why you would need to run 1000 ft. to the 480 service. If the ampacity is there at 240 delta, that delta/wye transformer is not uncommon. You may not even need the capacity of a standard, full size panel.
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